Investigation and Analysis of Field Hockey Masks

Andrew Charter, 20617004, Design and Analysis of Hockey Face Masks

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Investigation, Design and Comparative

Analysis of Field Hockey Face Masks.

Andrew L. Charter

20617004

School of Mechanical Engineering

University of Western Australia

Supervisor: Jeremy Leggoe

Associate Professor

School of Mechanical and Chemical Engineering


Final Year Project Thesis

School of Mechanical and Chemical Engineering


Submitted: June 30th

, 2013


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Project Summary:

Field Hockey is one of the most popular sports on the planet and played across the

globe. One particular phase of play known as a Penalty Corner is especially

dangerous. In this play, players are expected, at the international level, to stand on the

goal line and attempt to save a ball travelling at approximately 120 km/hr.

For this passage of play, players are able to wear protective facemasks although with no

official standards in place by the sports governing body the FIH (International Hockey

Federation) it was the authors suspicion that masks currently on the market did not

provide adequate protection.

Current off-the-shelf masks were tested by simulating a high-velocity impact using a

ball machine and viewed using a high-speed camera (1000 fps). The forces calculated

were then compared to an adjusted risk function based on previous medical studies to

provide a likelihood of facial fracture.

The results found that the current off-the-shelf masks are grossly inadequate and would

result in fracture of all major facial bones except the frontal bone. Leading to the second

phase of the project which aimed to develop a new and innovative design based on the

needs of international level players which was tested under the same regime.

While the final prototype design did prevent the ball from impacting the face it was

found to be impractical due to the thicknesses required and cost of production.

A range of recommendations have also been prepared for presentation to the sports

governing body regarding the implementation of standards and policy around protecting

the players.


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Letter of Transmittal

Andrew L. Charter

38 Salisbury Street

Saint James, WA, 6102

30th

June, 2013

Winthrop Professor John Dell

Dean

Faculty of Engineering, Computing and Mathematics


35 Stirling Highway

Crawley, WA, 6009

Dear Professor Dell

I am pleased to submit this thesis, entitled Investigation, Design and comparative

analysis of protection provided by Field Hockey face masks as part of the requirement

for the degree of Bachelor of Engineering.

Yours Sincerely

Andrew L. Charter

20617004


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Acknowledgements:

The author would like to take this chance to acknowledge the support provided by a

large number of key parties in the creation and review of this thesis.

Firstly to my supervisor Jeremy Leggoe for his enthusiastic assistance over the 12

months that we have been working together. His help allowed me to stay on track and

achieve the results I have presented in this paper so coherently.

Secondly to Simon Barnett from OBO hockey, his insight and previous dealings with

FIH gave me unfathomable insight into the approval system used. The company also

provided me with multiple masks for testing which otherwise would have been even

more limited due to budget constraints.

Next to Select Sports who also provided me with the Mazon face masks and the use of

their Bola hockey ball machine for the experimentation phase.

Last but not least Ridley Williams of Slow Motion Cameras Australia for being so

understanding of the limited budget of this thesis project, the camera used for analysis

was provided free of charge for a number of weeks. Without this support analysis of the

impacts would have been almost impossible.

Again thanks to everyone involved, I believe this project was an outstanding success

and it would not have been possible without the support of all parties noted above.


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Table of Contents

1. Introduction: .............................................................................................................. 7

1.1. Penalty Corner Phase .......................................................................................... 8

1.2. Facial Structure:................................................................................................ 11

1.3. Bone Tolerance to Fracture: ............................................................................. 12

1.4. Permanent Damage from Fracture: .................................................................. 12

1.5. FIH Equipment Standards: ............................................................................... 13

2. Literature Review: ................................................................................................... 17

2.1. State of the Art: ................................................................................................ 17

2.2. Standards System ............................................................................................. 21

2.3. Parallel Technologies ....................................................................................... 23

2.4. Conclusions to be made .................................................................................... 31

3. Force Approximation: .............................................................................................. 32

4. Risk Function Creation ............................................................................................ 34

4.1. Male Risk Function Criteria ............................................................................. 34

4.2. Risk Function Plot ............................................................................................ 36

5. Test Rig Design and Construction: .......................................................................... 37

6. Ballistic Testing (Experimental Chapter) ................................................................ 41

6.1. Method .............................................................................................................. 41

6.2. Materials ........................................................................................................... 42

7. Results and Analysis ................................................................................................ 44

7.1. Results .............................................................................................................. 46

7.2. Analysis/Discussion ......................................................................................... 48

7.3. Metal Cage Comparison ................................................................................... 49

8. Mask Design: ........................................................................................................... 50

8.1. Conceptual Design ........................................................................................... 50

8.2. Preliminary Design/Shell Profile ...................................................................... 53

8.3. Detail Design and Development ....................................................................... 54


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8.4. Redesign and Prototyping................................................................................. 54

8.5. Prototype analysis ............................................................................................. 56

9. Conclusion and Recommendations .......................................................................... 59

10. Further Work ........................................................................................................ 61

11. Appendix 1 Image Sequences ........................................................................... 66

11.1. OBO FaceOff V1 .......................................................................................... 66

11.2. OBO FaceOff V2 (Banned) .......................................................................... 67

11.3. Mazon V1 ..................................................................................................... 68

11.4. Mazon V2 ..................................................................................................... 69

11.5. OBO FaceOff V2 Run 2 ............................................................................... 70

11.6. Prototype 1 Layer ......................................................................................... 71

11.7. Prototype 3 Layer ......................................................................................... 72

11.8. Prototype 3 Layer No Deflection .................................................................. 73

11.9. Prototype 4 Layer Filmed ............................................................................. 74


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1. Introduction:

Field Hockey is one of the most popular sports on the planet and played across the

globe. Though it is an inherently dangerous sport with 0.16 Kilogram balls travelling at

speeds of near 140 kilometres an hour. One particular phase of play known as a

Penalty Corner is remarkably dangerous. In this play, players are expected, at the

international level, to stand on the goal line and attempt to make a save. This places

them in an extremely vulnerable position with the chance of severe facial trauma

possible.

Before a penalty corner players are allowed to don protective equipment, including

gloves and a facemask, in an attempt to lower the chance of injury. At this point in time,

the sports governing body FIH (International Hockey Federation) have not

implemented a standards system that protective equipment must adhere to. This

ultimately allows manufacturers to place any mask on the market, with no legal

responsibility to ensure that it protects the players from severe impacts. OBO Hockey

undertook their own research into the protection provided by current facemasks by

simply filming the impacts, these videos have been released online

(http://www.faceofftruestory.com/#/home). These showed the severity of impacts and in

some cases the catastrophic failure of existing masks, suggesting that the current

products are inadequate. This information was presented to FIH who still believed that

the safety of the player in line of the ball was secondary to a low speed player on player

collision thus requiring no action to be taken (Barnett, 2010).

This project sought to test and evaluate a range of off-the-shelf masks through a series

of ballistic tests simulated through the use of a cricket bowling machine and a custom

fabricated test rig. It then relates the approximated forces to historical medical data of

facial bone tolerances to calculate a percentage chance of fracture based on a normal

distribution.

The project also resulted in the initial design exploration, and construction of a

prototype face mask implementing some key principles in force mitigation

technologies;


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The use of a hard strike face

Energy dissipation zone

Angular profile.

These increase the materials strength, stiffness and resistance to ballistic impact. These

masks will also be placed under the same ballistic impact tests as the off-the-shelf

models.

From the ballistic testing analysis a range of recommendations are prepared with a view

to their future presentation to FIH to engage some key policy changes to protect the

players of the games.

1.1. Penalty Corner Phase

A penalty corner is a unique piece of play in field hockey it is a set piece with a

conversion rate of approximately 33% and accounts for a significant percentage of goals

within the game.

A penalty corner consists of 4 defenders and 1 goalkeeper starting behind the baseline,

the figure below shows the general set up of a penalty corner;

FIGURE 1 - PENALTY CORNER STARTING POSITION(EVANS, 2007)

Once the player has moved the ball from the starting position the defending team can

move (International Hockey Federation, 2010a). The most basic and most widely used

defence has the defending team finishing in a structure shown below;


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FIGURE 2 - PENALTY CORNER STRUCTURE(EVANS, 2007)

There are a number of dangerous situations for players in penalty corner defence; the

player running to the top of the circle is expected to run down the line of the shot

protecting the left side of the goal using his body. This is dangerous as attackers try to

flick through this line leading to a high chance of being hit in the legs or higher.

Secondly, and arguably the most dangerous, is the player standing on the left post. It is

expected throughout the world that this player stand inside the goal and attempt to save

a ball that misses the runner. This is extremely difficult for a number of reasons:

1. The running player obstructs the players view.

2. The player is only allowed to play the ball with their stick.

3. It is against natural reactions to stand in the line of a ball rather than attempt to

evade.

Just prior to the submission of this paper on July 22nd

2013 a player (Paul Nicholls) in

Perths premier Hockey Competition the Melville Toyota League was hit by a drag flick

from Adrian Lockley while standing on the post. The ball deflected off his stick

impacting the TK mask he was wearing resulting in right zygomatic fracture at the time

of submission he was due to consult a surgeon.

Lastly, the player on the right is also in a dangerous position. The natural flicking

action requires converting anti-clockwise rotational velocity into tangential velocity.

There are situations where the player gets the ball stuck in the hook of their stick and

the ball is released late causing the player to pull the ball towards the right of the goal

(from defenders perspective), Kris Glass, a close friend of the author, was hit in this

position. He was not wearing a facemask, resulting in a broken mandible which

required surgery to correct.


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Knowing the danger presented to the defending team the sports governing body (FIH)

introduced rules allowing players to wear protective equipment for these situations

including and limited to;

1. Gloves for protection which do not increase the natural size of the hands

significantly (International Hockey Federation, 2010b)

2. A smooth preferably transparent or white but otherwise single coloured

facemask which closely fits the face when defending a penalty corner

(International Hockey Federation, 2010b)

3. Shin guards and a groin protector as standard hockey protective equipment.

The point of concern is that there is no implemented national or international standard

for the protection that masks need to provide. Other similar sports such as Ice Hockey

have certification processes implemented by respective councils like the HECC

(Hockey Equipment Certification Council) where they ensure all products approved are

in accordance with government standards for example; Headgear used by goal tenders

only is evaluated to ASTM F1587 standard Specification for Head and Face Protection

for Ice Hockey Goaltenders this standard simulates a number of dangerous scenarios

including stick penetration and ballistic impact testing at variety of angles to ensure

there is no cage breakages etc. (The Hockey Equipment Certification Council Inc,

2013). To simulate these scenarios pucks are aimed and fired at 80 mph (~128 kph) at

various locations, the centre of the eyes and mouth and below the eyes on each side to

check for breakages or facial impact. Impact absorption properties are also tested

through the dropping of the mask from a specified height onto a flat surface with forces

measured from head form instrumentation. (ASTM International, 2012b). A similar

process is undertaken for the certification of Full Face protectors in accordance to

ASTM F513 with them requiring to prevent facial impact at puck speeds of 63 mph

(~101 kph) (ASTM International, 2012a).

This lack of certification process in field hockey has possibly leaded to an influx of

masks being approved for use in the sport by the governing body. That may provide

inadequate protection leading to significant chance of fractures of the facial structure

with the possibility of death. There is also a chance of catastrophic failure that they may

increase damage through fragmentation and piercing of the ocular regions.


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1.2. Facial Structure:

As the masks primary role is to prevent fracture of the facial structure in the event of a

ballistic impact a significant background of the bone structure is required.

The human face is a complicated skeletal structure with a number of key bones that can

cause permanent injury if damaged. For this report we will mainly concentrate on the

major forward facing bones due to their likelihood of impact.

FIGURE 3 - MAJOR FACIAL BONES(NUCLEUS MEDICAL MEDIA, 2009)

The above figure shows the skeletal structure of a fully grown adult, as previously

stated this paper is looking primarily into the main frontal facing bones including the

Zygoma (Cheek bone), Zygomatic Arch, Nasal, Mandible and the Frontal (Skull Cap)

bones.

It is also worthwhile investigating the Temporal bone commonly referred to as the

temple. Not all players are fearless; some shy away or turn, in the saving motion

leading them to expose the side of the head to potential damage. The temple or

temporal bone contains a number of vital structures including the facial nerve, jugular

vein, carotid artery and more (March, 2013). Severe blunt force damage to this area can


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result in severe injury such as facial nerve paralysis, hearing loss, cereberospinal fluid

otorrhea and a range of others (March, 2013).

1.3. Bone Tolerance to Fracture:

To quantitatively assess the damage to the facial structure under ballistic impact it is

necessary to know the force tolerances for all bones in question.

A number of previous studies have attempted to compile these but due to the range of

variations across the population (Age, Health, Gender and physical structure) it is

difficult to gain a clearly defined boundary. Though Table 1 lists the range of tolerances

compiled from previous studies by Hampson (1995).

TABLE 1 - REVIEW OF BONE TOLERANCES (HAMPSON, 1995)

1.4. Permanent Damage from Fracture:

The advancement of maxillofacial surgery has improved substantially over the last

decade but there still exists the possibility of severe long-term complications post-

surgery. These complications can severely affect the individual involved by damaging

their way of life and impacting on their ability to return to work after severe trauma.

Superficial damage including cuts and lacerations can generally be repaired through

stitches and plastic surgery if required. In the case of a facial fracture it generally


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requires serious and invasive surgery to correct without guarantee that it will be

successful.

1.5. FIH Equipment Standards:

In relation to the introduction of masks in hockey the sports governing body employed

a third party company to design a set of criteria which masks are required to conform to

before being approved for play at international competition. This document was referred

to as the Draft Criteria. (The International Hockey Federation, 2012) Although it has

not been released publicly, it is being used to ban masks from use in international

competition.

On review of the Draft Criteria it is the Authors opinion that there are a number of

areas for concern that need to be identified and addressed by FIH to create an effective

means of assessing and evaluating the merits of a mask for use within the sport.

The primary objective of the criteria is to approve masks that not only properly protect

the wearer as intended, but that should be of such design that it presents no potential

danger to unprotected players in the event of collision. (The International Hockey

Federation, 2012)

But the criteria are flawed in rule 3.2.3 the hockey ball. Can reach velocities up to

and including 70 Km/h (Approximately 19.5 m/s) which are not representative of

speeds being reached in current international level hockey, which as Tables 2 & 3 later

in the paper show are at times in excess of 140 km/h or 38 m/s. These velocities were

recorded at an Australian Hockey Team training session. This makes the draft criteria

immediately redundant and fundamentally flawed as this basis is used in the later

mentioned Potential Surface Compression test.

The true velocities in the sport approximately double the criterias specifications. This

may have led to an influx of masks into the market that do not protect against the high

velocity ballistic impacts that will be experienced. This places a large number of

individuals in potentially mortal danger with a false expectation their mask will protect

them; since it is approved for use in the sport it also places the governing body a legally

vulnerable position.


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D r a f t C r i t e r i a - R a t i n g S y s t e m

The draft criteria relies on a rating system for three key criteria Material Hardness,

Shape and Potential Surface Compression (Impact) with the score in each representing

either a mark of 1,2,3 or 7 with any facemasks/guards that have a combined rating of

seven or more will not be acceptable(The International Hockey Federation, 2012).

There are a number of issues with this rating system that are outlined below.

Firstly, there are inconsistencies in the Shape and Material Hardness rules. The shape

section states all edges and protrusions of forward facing components or those that

have the potential to be (The International Hockey Federation, 2012) should be

considered under the rules. Where Material Hardness section states the material

hardness rating for all components of the facemask/guard will be determined by taking

the highest value(The International Hockey Federation, 2012). The rating criteria are

shown below;

FIGURE 4 - MATERIAL HARDNESS RATING(THE INTERNATIONAL HOCKEY FEDERATION,

2012)

FIGURE 5 - SHAPE RATING(THE INTERNATIONAL HOCKEY FEDERATION, 2012)

It is logical to only consider components that are forward facing or likely to be involved

in an on field collision rather than any component in the mask. FIH recognise this in the

Shape section but is then disregarded in the Material Hardness section. It is irrational for


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a mask to be denied approval based on a hard component that in no likely collision

poses a threat to either player.

There is also a third area for rating known as Potential Surface Compression this is

the process of testing aimed to measure the danger a face mask presents to a player in a

collision. This involves the dropping of a ball at various heights (1.9m 1.0m and 0.25m

to represent 70, 50 and 25 kph) (The International Hockey Federation, 2012) into air

dried clay and comparing the indentation to a mask fitted to a standard head form and

dropped from 110 mm. This is flawed as a ball dropped from 1.9m will not achieve a

speed of 70kph as suggested and also basic oversights such as clay hardness that will

affect this test.

FIGURE 6 - POTENTIAL SURFACE COMPRESSION

Lastly, the additions of ratings seem unsound. While items A, B and C may exhibit a

risk on their own, ratings should only be added if they directly impact each other. This

is not the case for the draft criteria. For example consider 2 masks;

Mask A: Has a front face constructed of a hard material that scores a rating of three with

a small edge radius of 4mm also scoring a rating of 3. This results in a mask with a total

rating of 6 which will be approved for use.

However;

Mask B: Has a greater edge radius scoring a rating of 2 but has a hard flat fastener in an

unlikely impact zone scoring a rating of 7. Resulting in a score of 9 and in turn being

banned from competition.


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Here mask A intuitively presents more of a danger to players on the field due to the

small impact edge and high hardness yet mask B under the criteria will be banned solely

due to the use of a hard flat fastener. This is evidence that the rating system is vitally

flawed and needs to be improved.

It is therefore recommended to find an improved way of rating the masks by for

example breaking it into elements (Cage, strapping system, fasteners) as opposed to the

facemask as a whole.


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2. Literature Review:

2.1. State of the Art:

Over the years masks have been designed and constructed for a number of sports

including, but not limited to, cricket, baseball and hockey. Below is a brief overview of

the ones that have recently been used in hockey, or designed specifically for hockey use.

K P R F a c e P r o t e c t o r C a g e s t y l e ( B a n n e d ) :

The KPR face protector was originally designed for use in cricket for wicket keepers.

The basis of the design was to prevent keepers having to wear batsman helmets. While

it hasnt been used extensively in cricket it found an unlikely market in hockey. The

Australian Mens Hockey Team used these masks in international tournaments prior to

2011 at which time FIH banned their use stating they are a danger if players collide.

Figure 7 - KPR Face Protector(Cricket, 2012)

However there is anecdotal evidence that these masks provide a significant level of

protection. Ex-Australian player, Luke Doerner, was hit during the Dutch domestic

competition, by an international level flicker, while wearing one of these (Doerner,

2010). He received no injury and was able to keep playing on immediately after the

impact. While the speed of the impact wasnt recorded it is approximated at 105 km/hr

knowing the flicker was the Netherlands Roderick Weustoff who has been previously

scouted by the Australian National Team.


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Even though banned, this mask is included in the state of the art as it demonstrates a

couple of key concepts in ballistic protection. One, the wire cage prevents the projectile

from entering the mask and hitting the wearer and two, the deformation/travel in the

wire and foam on the frontal bone and mandible increase the impact time thus

decreasing peak force and thirdly, the large contact area on the face and mainly the

frontal bone. The frontal bone is significantly stronger than any other frontal facing

bone and the large surface area means the force is distributed over a large region also

limiting the chance of lacerations and fracture.

It was found to be in breach of the Draft criteria for the approval of hockey field

players facemasks (The International Hockey Federation, 2012) under rule 3.2.2

Shape which states Facemasks/guards should have no protrusions or bars which was

introduced after the mask was banned.

P l a t e S t y l e M a s k :

FIGURE 8 - PLATE FACEMASK(JUST HOCKEY, 2013A)

The Plate style mask shown above in Figure 8 is one of the most widely used

particularly in domestic competition due to its cheap cost and is released under a

number of various brands. There is video evidence that these masks may shatter on an

impact exceeding 70 miles per an hour or 116 kilometres per an hour (OBO Hockey,


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2010). This is cause for concern as speeds in penalty corner situations reach, or exceed,

these velocities. It may actually present a more dangerous situation than no mask due to

penetrating damage to the ocular regions by plastic fragments on fracture. These videos

have been released on OBO Hockeys FaceOff True Story website

(http://www.faceofftruestory.com/#/home).

O B O F a c e o f f V 1 :

FIGURE 9 - OBO FACEOFF V1 MASK (JUST HOCKEY, 2013B)

The mask featured above is arguably the most widely used mask on the international

stage at the moment. This mask was released a number of years ago and is widely used

because players believe it is the safest currently available and provides good vision.

Made from polyurethane plastic it fulfils all the regulations outlined in the Draft

Criteria. Although it has some design problems, for example, the eyeholes or goggles

as OBO term it sit substantially off the face. This enables the mask to clear the nose but

means when the player looks down their vision is obstructed. Also depending on the

individuals facial structure there may be limited distance between the mask and nose

allowing for very little travel or deformation of the mask before facial impact.


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O B O F a c e O f f V 2 :

FIGURE 10 - FACEOFF V2(OBO HOCKEY, 2011)

Lastly, the mask in Figure 10 is the OBO Faceoff V2. This mask was released 2 years

ago and gained rapid popularity within the hockey community. In the design process

OBO put this mask through 70 mph impact tests and the mask did not fracture and

stayed securely fastened to the head form. Shortly after the release FIH informed all

national associations that the mask was banned as these masks do not closely fit the

face and is not smooth and was to be dangerous to other players (England Hockey,

2011). It was not allowed to be used in any domestic or international competition as of

the 7th

of March 2011 (England Hockey, 2011). It was banned under the draft criteria

rule 3.2.2 where any forward facing part must have an external radius not less than

3mm.(The International Hockey Federation, 2012). The ridge in question is

highlighted in the above figure.

This mask was then redesigned by OBO to fulfil the requirements of rule 3.2.2. OBO

changed the ridges radius to 4mm - just greater than the minimum stated by the draft

criteria.

This adjusted design was again presented to the FIH for approval but was again rejected

on the opinion of the FIH medical committee stating the overall profile of the mask in

question is not smooth. The various ridges (especially at the brow and even with a

larger radius) are considered potentially dangerous (Webb, 2011).


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2.2. Standards System

The problems with the design and manufacture of the OBO FaceOff V2 exemplified the

issues associated with the sports current design criteria and processes. Manufacturers

have rough guidelines to design within but can still be banned on individual merit by the

sports governing body and its associated medical committee. This has led to companies

stopping product research and development due to concerns that any product developed

may be banned (Barnett, 2010) even after fulfilling all design criteria.

These reasons alongside the need for player confidence in the masks they are wearing

create a need for the implementation of a standards system. If the governing body is

unable to implement a standards system due to prohibitive costs or time constraints it is

suggested to piggyback onto the HECC or CSA (Canadian Standards Association)

standards in Ice Hockey, which test in accordance to ASTM F513-12. This allows for a

clear and definitive standards system and all costs of certification are solely the

responsibility of the manufacturers.

The most applicable existing standard is the previously mentioned ASTM F513-12

Standard Specification for Eye and Face Protective Equipment for Hockey Players. This

standard addresses a number of key criteria that would also be applicable in Field

Hockey including the testing of Peripheral Fields of Vision, Optical Quality Field of

Vision, Load Bearing area, Contact and Toughness (ASTM International, 2012a).

Peripheral Fields of Vision are measured using a photosensors in the head form, at each

40 degree step in the horizontal direction the mask is moved between the range of 35

degrees downward and 60 degrees upward. If the photosensor reads below a specified

threshold it will register a blind spot which can be analysed at the conclusion of the

testing.(ASTM International, 2012a)


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Next is the Load bearing area for the mask is the area that the face protector will rest on

the face that is not part of the existing helmet. The specifications are shown in Figure

11.

FIGURE 11 - LOAD BEARING AREA(ASTM INTERNATIONAL, 2012A)

Though most importantly is the Contact and Toughness testing of the masks. Each

model must undergo 6 tests (3 Contact and 3 toughness) using a different sample for

each test. A puck is fired at 101 kph at the centre of eye, centre of mouth and side

(defined as halfway between the mouth and eye level 25 degrees to the median plane)

though for ease of the reader it is approximately the cheek bone.

To pass the contact test a pressure sensitive paste is applied to the head form and after

each test checked for coloration. If there is no change in colour of the paste impact did

not occur and the mask passes the test.

To pass the toughness test after each impact there must be no breakage of structural

components, joints of attachment or chipping of surface coatings (ASTM International,

2012a).

These Standards have been used for a number of years and are extensively researched

and backed by the HECC and CSA proving the confidence of the Ice Hockey Industry

in their use.


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With the velocities in Ice Hockey exceeding those of Field Hockey and the puck weight

of 6oz. (MonsterPuck, 2013) approximately 175 grams comparable to 160 grams in

field hockey. These specifications ensure that a mask that is suitable for use in Ice

hockey is also safe for use in field hockey.

2.3. Parallel Technologies

While the area of Field hockey facemasks has not been thoroughly investigated, its key

concepts parallel a number of existing technologies in the field of force mitigation and

ballistic protection, including but not limited to, Transparent Military Ballistic Armour,

Crash Limitation Technology (SAFER Barrier) and Ice Hockey Visors.

T r a n s p a r e n t B a l l i s t i c A r m o u r

The world is a hostile place with a large number of Australian and American troops

deployed in countries such as Afghanistan and Egypt (Royal Australian Army, 2013b)

and the need for ballistic armour for the protection of soldiers and vehicles is as

necessary as ever. Exemplified by projects such as the Australian Defence Forces

Diggerworks to design a Soldier Combat Ensemble which includes items such as

body armour (Royal Australian Army, 2013a).

Of particular notice is Transparent Armour Systems for vehicles. A number of the key

design criteria outlined by (Grujicic et al., 2011) are similar to that required in the

design of an effective facemask;

Distortion-free and durable surfaces for optical clarity/transparency.

High single- and multi-hit ballistic resistance

High-wear/low-velocity impact-scratch/damage resistance

High performance to cost ratio

Transparent Armour Systems for military uses originally consisted of a number of glass

plates laminated and backed with a polycarbonate. With the improvement of rounds

(Bullets) and an increase in requirements for multi hit protection these panels became

prohibitively big leading to large increases in vehicle weight, reduction in cabin space

and loss of optical clarity (Grujicic et al., 2011).


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So a new approach was needed and typically consists of 3 distinct layers each with a

specific purpose.

FIGURE 12 - TRANSPARENT ARMOR SYSTEM

The outer most layer consists of a projectile-blunting/eroding/fragmenting hard strike

face (Grujicic et al., 2011). This layer attempts to dissipate the energy of the round

either by, blunting it so it minimises penetration or fragmenting the round into smaller

pieces, each carrying less force then the original round.

The middle layer is a energy absorbing, crack arresting, thermal-expansion-mismatch

intermediate layer (Grujicic et al., 2011). This layer attempts to stop the fracture of the

outer layer by providing crack arresting properties on impact, and also to absorb the

energy of the now blunted or fragmented round. Depending on the level of protection

required the projectile blunting and crack arresting layers are repeated.

And the last layer is debris containment spall-liner/backing this layer simply stops any

fragmentation or remaining projectile from penetrating into the vehicles cabin.

The hard strike face and crack arresting layers are of particular importance in the design

of a field hockey facemask. The outer most layer must resist fracture and deformation

on impact attempting to deflect the projectile while the crack arresting layer will

increase the stiffness of the outer layer, provide crack arresting properties and prevent

fragmentation if catastrophic failure does occur.

C r a s h L i m i t a t i o n T e c h n o l o g y ( S A F E R B a r r i e r ) :

Motor racing is a worldwide sport with international competition in the form of Formula

1 and various national competitions such as Americas NASCAR. With the

advancement of motor vehicle technology the speeds achieved during races has risen


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substantially resulting in more severe accidents leading to a call for greater safety

requirements to the drivers and spectators (Ried et al., 2002).

This resulted in the improvement of chassis design for example the carbon monocoques

used within Formula One, the implementation of the HANS (Head and Neck Support)

device, designed to prevent basilar skull fracture, and the improvement of safety

barriers, most notably the SAFER Barrier that was first introduced in 2002 for an Indy

500 race.

The major issue of non-deformable barriers is as the angle of impact increases with

reference to the wall the deceleration of the vehicle and the driver becomes increasingly

severe. This is due to the relatively fast (short) impact time in the collision due to the

barriers rigidity. If this can be increased it leads to notable decreases in deceleration of

the vehicle and occupants and significantly lower forces.

The creators of the SAFER barrier noted that serious injuries and fatalities could be

mitigated through the use of a deformable modular barrier opposed to the non-

deformable concrete barriers that were commonly used. While the SAFER barrier was

designed with oblique angled impacts in mind (more parallel then perpendicular with

reference to wall orientation) the general concepts involved are the same.

The investigation and design of the SAFER barrier concentrated on two materials

HDPE (High Density Polyethylene) plates and crushable foam (Ried et al., 2002). These

two materials were chosen due to their high-energy absorption potential the HDPE

plates though buckling and bending and the crushable foams uniform deformation on

impact.

The use of these energy-absorbing deformable materials leads to a longer impact time

like stated earlier leading to a slower deceleration of the vehicle. This is shown in the

Figure 13


26

FIGURE 13 SAFER BARRIER VS CONCRETE WALL(RIED ET AL., 2002)

As it can be seen in Figure 13 the SAFER barrier by McGehee lowers the impact

accelerations by around 60%. While the final design varied significantly from the

original concept it still maintains its key principles.

During the initial design stage these materials were used almost exclusively on their

own as shown in Figure 14.

FIGURE 14 - PROPOSED SAFER BARRIER DESIGN(RIED ET AL., 2002)


27

a) Shows the HDPE panel design tensioned by steel cables and b) shows the crushable

foam construction. Both of these designed proved problematic lacking in a number of

key criteria(Ried et al., 2002).

Low friction: If the friction between the vehicle is too high it may cause the

vehicle to grip and spin or cause more severe decelerations.

Puncture and bending strength: If the vehicle penetrates the barrier and impacts

the wall the problem of extreme decelerations still exists.

Ability to transfer load to large number of cartridges.

While two out of the three criteria arent applicable to hockey facemasks, the puncture

and bending strength is crucial. If the projectile penetrates or deforms the mask

substantially this will lead to injury as the ball will directly impact the face negating any

other protection methods in place.

The SAFER barrier was ultimately refined to Figure 15.

FIGURE 15 - IMPLEMENTED SAFER BARRIER(RIED ET AL., 2002)

It consists of three layers. The front surface is steel tubing, this is to prevent penetration

into the foam system and lower the friction between the vehicles and surface. The

second layer is the energy-absorbing foam, allowing for deformation and lowering of

accelerations. The third is the existing concrete barrier. This generally exists at tracks

and is mainly there to mount the SAFER system and prevent the vehicle entering the

spectator zone.


28

So, the key principles to be gained from the design of the SAFER barrier are the need

for an energy-absorbing medium to lower the peak forces transferred to the individual,

the bending strength requirement to prevent penetration of the impact face to ensure

energy absorbing medium is 100% utilised.

To achieve this, these principles need to be the key focus when designing the mask

seats. That is the areas where the mask is in contact to the face prior to impact. These

are the locations that forces will be transferred to the face through the mask succeeds in

preventing facial impact.

I c e H o c k e y P r o t e c t i o n V i s o r :

Ice Hockey is a professional sport and has gained worldwide popularity due to its fast

pace. In recent times it has received criticism for safety standards, most notably the lack

of facial protection, namely eye protection for players (Petchesky, 2013).

In response, the American Hockey League (AHL) committee came to the decision to

mandate eye protection to protect up and coming players from career and life impacting

injuries. While the National Hockey League (NHL) hasnt followed suit more and more

players are beginning to wear eye and face protection (Petchesky, 2013). This could be

attributed to the influx of players from the AHL ranks (Wilder, 2013), or the increasing

media exposure (Petchesky, 2013), and impact that career ending eye injuries are having

on raising concern of the existing playing group.

Initially eye and face protection was provided through the use of a Cage system

shown in Figure 16.

FIGURE 16 - HELMET WITH CAGE(MONKEY SPORTS INC, 2012)


29

While these masks provide significant protection for the individual they also bring rise

to a number of problems. The number one concern being vision, the bars obstruct the

players view of the puck and can be distracting (ChrisK, 2013). Full cages in the NHL

have also been banned under rule 9.6 Dangerous Equipment requiring players to have

approval by the NHL to wear full them due to the danger they present in a collision.

Ultimately these were superseded by the half visor shown below in Figure 17.

FIGURE 17 - OAKLEY HALF VISOR(OAKLEY INC, 2012B)

These initially had problems with fogging, reducing player vision, and was/is regularly

used as defence against the mandating of facial protection. With the improvement in

lens technology and coatings, low optical clarity and fogging are non-existing problems.

These visors are approved under ANSI Z87.1 for impact resistance and optical clarity.

While these have been approved to the ANSI Z87.1 standard there has already been

direct evidence in the sport supporting the case for mandatory protection. Francois

Beauchemin was hit by a shot that was close to 90 mile per an hour (Oakley Inc, 2011).

The visor remained in one piece, and he only received stitches to his eyebrow. In his

opinion, he couldve lost his eye or broken the bone (Oakley Inc, 2011). Drew Doughty

is another player who has been hit by a stray puck. While wearing a visor, with Gord

Miller saying, Well never know for sure, but after watching a shot hit Drew Doughty

in the visor, its quite likely that the shield saved Doughtys eye, (Oakley Inc, 2012a).

This technology shows that the use of plastics in facial protection may be possible with

effective design.


30

I c e H o c k e y G o a l T e n d e r M a s k

Goal Tender masks are arguably the most important piece of the protective equipment

used by an Ice Hockey Goal Tender with this in mind they have evolved over the years

to what they are today. Figure 18 shows the Bauer Concept 2 helmet released in 2013.

FIGURE 18 - BAUER CONCEPT C2 (GREAT SKATE HOCKEY SUPPLY CO, 2012)

These masks are constructed from an extremely resilient and light weight carbon fibre

shell to provide optimal strength. It also utilises a steel flat wire system for the cage, this

minimises the profile of the wires to the wearer and increases the effective thickness to

increase bending strength on impact opposed to the standard round wires. The angular

profile of the mask also encourages the ball to deflect upon impact this minimises the

force transferred to the wire or shell. Lastly the inner foam layers are a purpose built

impact absorbing foam known under its trade name as PORON XRD. This foam is

comfortable during general use but when impact occurs it hardens up to distribute the

force over a greater area (Rogers Corporation, 2013) .

Every one of these properties could be used in the design of new field hockey face mask

if the governing body allowed the use of metal cages in their construction.


31

2.4. Conclusions to be made

As stated previously, while no real investigation has been made into field hockey

facemasks there are a number of key points to be gained from the analysis of existing

parallel technologies. The SAFER barrier and transparent armour systems both followed

the same basic principles to dissipate force.

Hard Strike faces: Prevent the projectile from entering the energy dissipation

zone, or at least fragment it.

Energy dissipation zone: This is where the energy of the projectile is lowered

through the use of deformable foam creating a more gradual deceleration

creating less impulse in the impact in the example of the SAFER barrier. The

use of a polymer layer in transparent ballistic armour was used to provide crack

arresting properties and can be implemented in prototype design.

A spall backing or lining to prevent any remaining fragments from entering the

vehicle or crowd in these examples.

These fundamental principles may be implemented in the design of a new and

innovative face mask to provide effective protection for players. The outmost layer is

the strike face needs to be strong and durable; due to the proximity to the face any

fracture may cause severe injury.

An elastomer could also be incorporated in the visor design to provide crack arresting

properties. It will also keep the mask in a single piece when catastrophic failure does

occur to prevent fragments from separating from the bulk.

The effectiveness of polycarbonates in the construction of Ice Hockey Half Visors to

reach ANSI Z87.1 specifications and to be proven on field, particularly in the cases of

Francois Beauchemin and Drew Dougherty, demonstrates that there are materials on the

market that are easily constructed, that can withstand high energy collisions without

fracture. These represent a promising lead for the design and construction of an

effective facemask.


32

3. Force Approximation:

Next it was required to gain an approximate value of the forces involved through a basic

theoretical calculation using the following equation;

To use this equation an estimate for the impact time was made. It was envisaged this

study will be for the benefit and application at the elite level meaning that players will

have very small amounts of facial fats and assuming a rigid position with no extension

through the neck during impact (Worst Case Scenario) an extremely small impact time

of 0.001 seconds was chosen.

The second assumption made was a purely elastic collision while this is not true in the

real world it again simulates the worst-case scenario.

The other two variables are velocity and mass, velocities were measured at an

Australian Mens Hockey Team training session through the use of a Prospeed CR-1K

radar gun by Decatur Electronics. Four flickers and hitters were selected with 5 shots

each the Mean and 95% confidence interval were then calculated using the following

equation and tabulated in Tables 2 and 3.

Where;


33

Flicker Mean

(Km/hr)

Lower

Bound

(Km/hr)

Upper

Bound

(Km/hr)

A 115.8 112.26 119.3

B 104.3 90.5 118

C 112.3 108.3 116.2

D 105 102.3 107.7

TABLE 2 - FLICKING VELOCITIES (95% CONFIDENCE INTERVAL)

Hitter Mean

Km/hr

Lower

Bound

Km/hr

Upper

Bound

Km/hr

A 120.25 117.3 123.2

B 135.5 128.6 142.4

C 118.3 111.5 125

D 138.7 134.1 143.4

TABLE 3 - HITTING VELOCITIES (95% CONFIDENCE INTERVAL)

From the above data it was found that the maximum velocity of a flick was around 120

Kilometres per an hour (33.3 m/s) and maximum velocity of a hit was about 142

kilometres per an hour (39.44 m/s). It is worth noting that this is in severe disagreement

with the speeds stated in the draft criteria (The International Hockey Federation, 2012)

of 70 km/h (19.6 m/s). Unfortunately due to the limits of the radar it cannot be attained

at what point during the balls travel this is measuring.

The last variable is the mass of a field hockey ball, rule 3.1.c (International Hockey

Federation, 2010a) states the ball weighs between 156 and 163 grams therefore the

approximate force of impact can be found as;


34

4. Risk Function Creation

A risk function was modelled based on a previous study (Cormier et al., 2006) creating

an approximating function for the percentage failure of bones across the entire

population.

The objective of this project is to find if the amount of protection that field hockey

masks provide is adequate. While the force of the impact will most likely be measured

in Newtons (N) this is not intuitively linked to the severity of injury caused.

Therefore a risk function was developed that predicts the percentage of the population

that will fracture under a specified range of forces. A review of facial injuries

(Hampson, 1995) compiled the table of bone tolerances provided earlier at Table1.

These ranges are representative of the entire population and needed to be adjusted to

simulate the hockey playing population generally 20-30 year old male and females. It

has been found previously that 70-80 year olds have a 20-30% decrease in bone strength

when compared to the target population (Yamada and Evans, 1970). It has also been

found that females have a considerably lower tolerance for bone fracture than males

(Gadd et al., 1968) and has been advised that it play a crucial part in the practical

application of bone tolerances for design (Hampson, 1995).

Unfortunately due to constraints placed on the project only young fit male bone

tolerances will be investigated. A female design criterion is an avenue for future work.

4.1. Male Risk Function Criteria

As stated previously (Yamada and Evans, 1970) found that 70-80 year olds have 20-

30% less bone strength when compared to 20-30 year old. This implies that the upper

thresholds in Table 1 are correct for the 20-30 year old demographic while the minimum

need adjusting, this was done through a simple calculation shown below.


35

Where;

X = Population Minimum

Y = Adjusted minimum (20 to 30 year old demographic)

Giving the following bone tolerances for the 20-30 year old males;

Bone Maximum (N) Minimum (N)

Adjusted

Minimum (N)

Frontal 6494 1000 1250

Nose 450 342 427.5

Maxilla 1801 668 835

Mandible 1779 685 856.25

Zygomatic Arch 1779 890 1112.5

Zygoma 2401 489 611.25

TABLE 4 - MALE ADJUSTED CRITERIA

Once the data range had been found a normal distribution is applied to it using

Microsoft Excel using the inbuilt function NORMDIST based on the following formula.

( )

(( )

)

Where;

Using the calculated mean;

And Standard deviation approximation;


36

This gives the final criteria of the male risk function in Table 5;

Bone

Maximum

(N)

Adjusted

Minimum

(N) Mean (N)

Standard

deviation

(N)

Frontal 6494 1250 3872 874

Nose 450 427 438 3.75

Maxilla 1801 835 1318 161

Mandible 1779 856 1317 153

Zygomatic

Arch 1779 1112 1445 111.

Zygoma 2401 611 1506 298

TABLE 5 - MALE RISK FUNCTION CRITERIA

4.2. Risk Function Plot

With a normal distribution applied to the ranges and standard deviations outlined in

Table 5 a cumulative probability function can then be calculated by simply integrating

the area between 0 and force x of the previous function.

Excel calculated this simply by the adding of magnitudes from 0 through to the upper

threshold of each bone giving the risk function in Figure 19.


37

FIGURE 19 - RISK (BONE FRACTURE VS FORCE)

To use this function when a force has been calculated the intercept between this value

and the corresponding bone gives the percentage chance of fracture on the Y-axis. With

the means of assessing the performance of masks created the experimental process is

outlined next.

5. Test Rig Design and Construction:

As stated previously to realistically simulate a ballistic impact similar to that in hockey

it was required to design a test rig that effectively models the impact dynamics that

would be experienced. Key elements of the design include the shape and weight of the

head form used this will be in line with ASTM F429 10(ASTM International, 2010)

which specifies the use of a standard head form with a combined mass of 5.5 Kg

500g, it is also desirable for a neck system that provides realistic motion.

Due to the large number of variables involved in the real life neck system, for example

the individuals musculoskeletal state, their awareness and bravery all of which may

lead to an increase or decrease in stiffness at the time of impact. Therefore it is

impossible to create a perfect system to test the impacts and compromises were made.

Three test rig designs were considered;


38

Rigid

Spring Tension System

Rubber Tendon

R i g i d :

The completely rigid test rig was a simple design it simply consisted of a standard head

form rigidly mounted to an immoveable surface. The main advantage of the rigid

system is the ease of construction as there is minimal work required and the rig would

be extremely robust.

The main problem with this design was its unrealistic impact dynamics. There is no

flexion/extension through what should be the neck, creating an almost elastic collision

where the forces experienced are likely to be substantially higher than actually

experienced.

S p r i n g T e n s i o n S y s t e m :

Unlike the rigid system the spring tension system allows for neck movement throughout

the impact. It was realised that to simulate a realistic impact it was required that the

head-form move during the impact and the resistance to this movement to be

representative of the resistance provided by the musculo-skeletal system of a 20-30 year

old hockey player.

A spring tension system allows for an easily adjustable resistance to flexion/extension.

This is achieved through a number of springs being mounted to the base of the head

form and to the ground through bolts, as the bolts are tightened the springs extended

increasing the resistance. This allows for precise tensioning of the system to a defined

resistance but was envisaged to be extremely difficult to manufacture, costly and

definitive data for resistance required was impossible to locate.


39

R u b b e r T e n d o n :

The tendon system uses a flexible rubber tendon shown in Figure 20 to mount the head

form to a rigid surface. The universal joint allows for motion through the neck to

approximately simulate the impact. The advantage of this system is its relative ease of

manufacture while also providing somewhat realistic motion through the neck.

FIGURE 20 - CHINHOOK RUBBER TENDON(CHINHOOK, 2013)

W e i g h t e d a n a l y s i s o f t e s t r i g s :

A weighted analysis of the proposed test rigs was undertaken with each of 3 key criteria

(Ease of Manufacture, Realism and Cost) being given a weighting. Each rig was given a

score between 1 and 5 with 1 being the best in each category this was then multiplied

the criterias weighting (bracketed value) and summed. The lowest score of the test rigs

provided the most effective solution.

Rig Type Ease of

Manufacture

(5)

Realism

(3)

Cost

(4)

Total

Spring Tension 5 1 5 48

Tendon 2 2 2 24

Rigid 1 5 1 24

TABLE 6 - RIG COMPARATIVE ANALYSIS


40

As it can be seen both the Tendon and Rigid systems achieved a score of 24, the tendon

system was ultimately chosen due to its more realistic impact dynamics.

The constructed Tendon test rig is shown below; it was housed in a polycarbonate

enclosure to limit the chance of damage or injury to any nearby individuals.

FIGURE 21 - TEST RIG

H e a d C r e a t i o n :

Due to limited budget the head form had to be created in-house rather than purchasing a

purpose built and designed one. A fibreglass mannequin head was purchased and

modified to fulfil this need.

The head of the mannequin purchased was too narrow requiring widening to allow the

masks to fit correctly. Bulk was added to the mannequin through the addition of

Septone Car Filler. This was applied in layers to key areas of the head (Jaw, Cheeks and

forehead) to reach a thickness and cranial shape similar to that of fully-grown hockey

player. Once general bulk was achieved it was sanded down to a smooth surface to

allow for easy fixing of force measuring devices in the testing stage. Before and after

images are shown below.


41

FIGURE 22- MANNEQUIN

6. Ballistic Testing (Experimental Chapter)

6.1. Method

Ballistic testing of each off-the-shelf mask was undertaken using the following

procedure;

An international level Kookaburra hockey ball was fired from a Bola ball machine at

maximum velocity from a range of 1 metre at the test rig. The impact was viewed using

a high speed camera at right angle from the impact vector at a distance of 4 metres.

Pressurex-micro film was placed on mask contact zones to approximate force

distribution if registered. A ruler with 10cm markings was placed slightly in the

foreground to provide a measurement reference when analysing the results. The

experimental schematic is shown in Figure 23.


42

FIGURE 23 - EXPERIMENTAL SCHEMATIC

Velocities both pre and during impact can be measured through analysis using the

cameras AOS Imaging Studio V3. These numbers formed the basis of analysis and

relation to the risk function described earlier in Chapter 4.

6.2. Materials

H i g h - S p e e d C a m e r a

The high-speed camera used in the experiment was an AOS Technologies S-MIZE with

a 75 mm C-mount Lens installed to limit geometric distortion. Capturing images at a

rate of 1000 fps (Frames per second) with a shutter speed of 100s (0.0001 seconds).

This camera is shown below;

FIGURE 24 - S-MIZE CAMERA(AOS TECHNOLOGIES AG, 2012)


43

B a l l M a c h i n e

The ball machine used was a BOLA Hockey ball machine this uses two spinning

drive wheels to propel international level hockey balls at speeds of up to 100 km/h with

reasonable accuracy.

FIGURE 25 - BOLA HOCKEY BALL MACHINE(SELECT SPORTS, 2013)

P r e s s u r e S e n s i t i v e F i l m

The pressure sensitive film used was Pressurex-micro Green 3 (50-450 PSI). This was

applied to the dummy under all areas where the mask rested on the face prior to impact.


44

7. Results and Analysis

Using the imaging suite provided with the AOS camera it was possible to analyse the

impact frame by frame using the programs Point and click measurement tool. This

allowed velocity to be calculated by measuring the distance travelled between

consecutive frames.

Impact velocities when the ball strikes the face are approximated by measuring the

distance in the pre-impact frames (2 frames directly prior to impact). For example in the

Figure 26, impact velocity was found by measuring the distance between frames A and

B not B and C. While this will overestimate the velocity, as the ball will continue

decelerating between B and C, there is no feasible way to measure it more accurately

without a higher performance camera.


45

FIGURE 26- IMPACT VELOCITY MEASUREMENT (ENLARGE)


46

Impact times were measured by counting the number of frames from impact to the point

where the ball ceases forward movement. This is shown in Figure 27, it can be seen that

the ball/mask impacts the face in frame C and comes off the face in frame D leading to

an impact time of ~0.001 seconds based on the camera frame rate.

FIGURE 27 - IMPACT TIME EXAMPLE

Unfortunately due to the majority of masks failing to keep the ball from impacting the

face very little force as transferred to the contact zones therefore the pressure films

recorded little in terms of results.

7.1. Results

Image sequences for all runs can be found in Appendix 1 from these velocities and

impact times were found and forces calculated based on the simple formula.

( ) ( ) (

)

( )

Results are shown on the following page in Table 7 with peak forces calculated from the

above equation in the right most columns.


47

TABLE 7 - BALLISTIC RESULTS

Mask

Frame Displacement

(cm) Velocity (Km/hr) Velocity (m/s)

Frame Distance

directly prior to face

impact (cm)

Velocity

before Facial

contact (m/s)

Impact

Period (sec)

Peak

Force (N)

OBO V1 2.4 86.4 24 1.86 18.6 0.001 2976

OBO V2* 2.38 85.68 23.8 N/A N/A 0.003 1269

Mazon V1 2.41 86.76 24.1 1.95 19.5 0.001 3120

Mazon V2 2.61 93.96 26.1 1.42 14.2 0.001 2272

OBO V2 Run 2 2.62 94.32 26.2 1.74 17.4 0.001 2784

* No impact with head forms face hence

N/A values


48

7.2. Analysis/Discussion

Table 7 comprehensively shows the impact forces experienced by each of the off-the-

shelf masks tested in this paper. It can be seen that no mask prevented direct impact to

the face except for the OBO FaceOff V2 on one of the two occasions tested.

Unfortunately due to the limited resources only a single test was possible with each

mask.

Due to the limits of testing available due to resources and accuracy of ball machine it

was not possible to test impacts to each particular part of the face this is an area for

future work. So for the purpose of analysis against the risk function described in section

4.2, it will be assumed the forces approximated are independent of impact location.

The risk function has been included in Figure 28, the vertical lines representing the

forces experienced by each mask and the intersections with the risk functions

representing the chance of fracture on the Y-axis.

FIGURE 28 - RISK FUNCTION INTERCEPTS

Due to printing most likely being in greyscale the intersections have been provided in

the following table.


49

OBO V1

Mazon

V1

Mazon

V2

OBO V2

Run 2

Nose 0.99 0.99 0.99 0.99

Zygoma 0.99 0.99 0.98 0.99

Zygomatic Arch 0.99 0.99 0.99 0.99

Mandible 0.99 0.99 0.99 0.99

Maxilla 0.99 0.99 0.99 0.99

Frontal 0.2 0.25 0.05 0.15

TABLE 8- LIKELYHOOD OF FRACTURE

It can be seen that the current off-the-shelf masks based on the testing and assumptions

made in this experiment are providing little or no protection to any type of facial

fracture of the major bones except the frontal. Nevertheless there is still a substantial

chance of fracture of the frontal bone which is unacceptable due to the severity of injury

this may result in (Brain damage). This shows the need for further investigation into the

design of these masks to provide adequate protection.

7.3. Metal Cage Comparison

For the purpose of comparison, testing was also done using a metal Bauer Cat-Eye

cage under the same analysis process. While this is currently banned it provides useful

means for comparison between polymer and metal cage protection. The impact

sequence is shown below in Figure 29.


50

FIGURE 29 - BAUER CAT-EYE CAGE IMPACT

This impact was at 93 kilometres per an hour and can be seen that there is little or no

deformation to the cage and the impact lasts for approximately 1 frame (0.001 seconds).

Though this means that the peak force is extremely high (4160 N) it is distributed across

the entire frontal bone and mandible through the chin cup. With smart material selection

like the use of energy absorbing foam similar to the SAFER barrier, the transfer of this

force to the skull can be lowered by lengthening the impulse time allowing for a lower

peak force.

8. Mask Design:

As the results in chapter 7 convey the current state of the art is grossly inadequate for

use in the sport. This chapter outlines the design process of a new and innovative

approach to field hockey protection drawing on existing parallel technologies. Due to

manufacturing and budget restraints it was required to create simple designs that were

easily produced and tested. This was done using a 4 stage process; Conceptual Design,

Preliminary Design and Detailed design and development and lastly Redesign and

prototyping.

8.1. Conceptual Design

A survey of existing Australian National squad members was undertaken to gain an

understanding of the primary concerns of players. They were asked to rank a number of


51

criteria from most to least important this enabled the design process to have clearly

defined primary objectives.

P l a y e r N e e d s :

The ranking of the surveys are shown below and were close to unanimous, with each

criterion having a brief outline.

Rank Criteria

1 Protection/Impact Resistance

2 Forward Vision

3 Peripheral Vision

4 Ease of Use

5 Comfort

6 Aesthetics

TABLE 9 - DESIGN CRITERIA

Protection/Impact Resistance: Listed as the main concern of the players is protection

for the face. It is required that the mask have a high impact resistance to prevent serious

injury to the player, ideally preventing lacerations and bone fractures particular through

the major bones such as mandible, zygoma and frontal.

Direct Vision: Direct vision was defined as the visibility provided by the mask when

the player is looking directly forward. As their position requires them to see and play at

a ball moving at significantly high velocities a clear line of sight is highly desirable if

not essential.

Peripheral Vision: Peripheral vision was defined as any sightlines that arent directly

forward of the skull; for example if the ball drops to the ground it may be difficult for a

player to locate the ball at his feet or nearby if these sight lines are obstructed.

Obstructions could include the mask sitting too far from the face and the distortion

created by refraction through a transparent material.

Ease of Use: Includes the ease that the mask can be put on or removed; umpires may

send a player off if they take too long to put on his equipment. Also at the end of the


52

play the mask must be removed before the player can participate further meaning that

removal must be quick and easy to ensure minimal delay in them returning to play.

Comfort: While ranked low the comfort of the mask is important; if it is irritating to the

player it may take their mind of the task at hand. But is probably more important from a

commercial view, if a mask is comfortable the buy will be more inclined to purchase it.

Aesthetics: Is simply the look of the mask this is included for commercial reasons and

also the vanity of players. It may also make the regulatory committee more inclined to

approve the mask if it looks clean and not dangerous.

P o s s i b l e D e s i g n s :

The above findings lead to the identification of the 2 key design criteria, as expected the

need for protection rated as the most important to the players. This is achieved through

smart design choices using the same principles as the SAFER barrier. A hard strike face

to prevent the projectile making direct contact on the face and to dissipate force over a

large area this backed by an energy dissipating elastomer that provides crack arresting

properties. Contact zones on the face should be through an energy absorbing foam to

increase the impact time and decrease peak forces experienced.

The second key point is the need for clear vision both forward and on the periphery. To

create a clear unobstructed view for the player two methods were possible.

1. The first being vision modelling. This process involves modelling the edges of a

players vision and then designing the mask so the materials dont intrude into

these areas. This was found to be problematic, as the mask needs to sit

substantially away from the face to prevent it from deforming and impacting the

nose or other major facial bones. The impact of this clearance meant that

extremely large openings were required which would not prevent the ball

impacting the face.

2. The second option is the use of a transparent material in the construction of the

mask for example a high quality polycarbonate. This has been previously

employed in Ice Hockey in the design of the Half Visor and also in field


53

hockey masks shown in Mazon mask and the OBO Faceoff. The field hockey

masks have only implemented the concept in the periphery but with limited

success due to the large curves leading to significant refraction.

A design combining the two was selected, in line with the key design criteria, it was

decided to have no material directly in front of the players eyes leading to a clear

unobstructed view forward with no refraction. Below the eye line transparent

polycarbonate half Visor will be used to enable some peripheral vision while still

being distorted. Though the use of advanced manufacturing techniques may allow for

minimal distortion this is work for future investigation. Using the same concept as the

OBO V2 Faceoff the gap in material at eye line will be substantially less than diameter

of a hockey ball meaning without catastrophic failure or significant deformation the ball

shall not impact the face directly.

The remaining criterion, ease of use, comfort and aesthetics are all able to be designed

based on the masks overall structural shape.

8.2. Preliminary Design/Shell Profile

In-house design of an entirely new and purpose built field hockey mask would be ideal,

unfortunately due to budget and manufacturing limitations it is required to use existing

technology for the shell design. It was decided to modify existing goalkeeper helmets to

allow for an easier and safer product. The helmet modified in this design was a Bauer

Profile 1400 shown in Figure 30.

FIGURE 30 - BAUER PROFILE 1400(GOALIESTORE, 2012)


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The Bauer mask was modified by the removal of the back plate, as players are unlikely

to get hit here. It also makes the mask more difficult to wear and remove, which was

one of the key criteria identified by the playing group.

As stated in the section 8.1 the final design calls upon the idea used in the OBO V2

Faceoff. This will be achieved by the construction of a polycarbonate Visor that will

create a half cage allowing for a gap between the top of it and the bottom of the shell

substantially smaller than the balls diameter. This gives the wearer an unobstructed

view in the forward and lateral directions and the use of the clear polycarbonate allows

some peripheral vision to the wearer when looking down.

8.3. Detail Design and Development

As discussed in the previous section the mask design is going to consist of a

polycarbonate half cage mounted on an existing Bauer profile 1400 mask.

The creation of the visor due to limited manufacturing ability was done by the

thermoforming 3mm Bayer Makrolon polycarbonate coated in 3M ULTRA 400 safety

film. The safety film was applied as the Energy Dissipation zone discussed earlier. It

provides energy dissipation though stretching providing strain energy relief and

preventing fragmentation in the event of catastrophic failure.

A sharp profile was designed to induce deflection rather than direct impact. This limits

the forces experienced by the material and therefore transferred to the face through the

mask.

8.4. Redesign and Prototyping

On initial testing of the 3mm visor, it was found that substantial deformation was

occurring rather than deflection upon impact leading to large forces being transferred

directly to the face. This was attributed to two key points; one the visors bending

strength and stiffness are not high enough to induce deflection (this requirement was

outlined in the SAFER barrier) and secondly highlighted in Figure 31;


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FIGURE 31 - KEY DESIGN FAULT

The visor was mounted by a single fastener on the bottom edge this significantly

impacts the top edges bending strength meaning a substantially lower stiffness.

After initial testing the visor was redesigned to have 2 fasteners, one on both the top and

bottom edges along with 2 alternate designs in regards to thickness and shape were

applied.

1. Sharp profile 4 layers of polycarbonate film interlaid with 3M ULTRA 400

security film.

2. A slightly more gradual profile 3 layer with no 3M film.

The two mounted visors are shown in the Figure below, 4 layers filmed on the left and

the slightly more elliptical 3 layer on the right.

FIGURE 32 - REDESIGNED VISORS


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Both these designs performed well in ballistic testing and are discussed further on in the

paper.

8.5. Prototype analysis

Analysis of the prototyped designs was undertaken using the exact same process as the

off-the-shelf testing. It can be seen from the image sequences below that both the 3 and

4 layer designs prevented facial impact. The increase in stiffness of the impact face

induced deflection theoretically minimising forces transferred through the shell.

FIGURE 33- 3 LAYER PROTOTYPE


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FIGURE 34 - 4 LAYER FILMED


58

Mask Frame Displacement

(cm) Velocity (Km/hr)

Velocity (m/s)

Frame Distance

directly prior to

face impact (cm)

Velocity before Facial

contact (km/hr)

Impact Period (sec) Peak Force (N)

Prototype 1 Layer 2.45 88.2 24.5 2.1 75.6 0.001 3360

Prototype 3 Layer 2.64 95.04 26.4 N/A N/A 0.002 2112*

Prototype 3 Layer No deflection 2.27 81.72 22.7 N/A N/A 0.003 1211*

Prototype 4 Layer Filmed 2.48 89.28 24.8 N/A N/A 0.003 1323*

* Due to deflection these forces are an overestimation N/A cells mean that the ball did not make contact with the headform

TABLE 10 PROTOTYPE FORCES


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Its worthwhile noting that for one particular impact on the 3-layer gradual curve

deflection was not induced. Rather the point of the visor was hit directly front on and all

forces were transferred to the mask contact zones on the frontal bone. This impact is

shown in Appendix 1 section 11.8. Though it did prevent impact to the face peak forces

would have been higher than a deflected impact experienced by the angular profile. This

demonstrates the worst-case impact scenario possible for this visor with the full force

being transferred to the material.

9. Conclusion and Recommendations

As shown in the previous chapters the results for the experiment are extremely

concerning and support the authors view that the current state of the art is not

acceptable for domestic let alone international hockey. The velocities of impacts in this

experimental setup were approximately 20% lower than the standard international level

flicker. Yet still the likelihoods in Table 8 categorically show that the use of any of the

current off-the-shelf masks would likely result in severe facial fractures and possible

lifelong injuries.

The design of the prototype mask and visor was in 1 view a success. The

implementation of the hard strike face (Polycarbonate) and energy dissipation zone (3M

Film) when applied in a layer system resulted in reduced deformation and forced the

ball to deflect rather than impacting the face when compared to the single layer design

and current masks. Though this does ultimately protect the player it raises further

issues; such a thick polycarbonate is expensive to purchase and manufacture in the

desired shape, it also results in substantial refraction impacting on the peripheral vision

requirement outlined by the playing group. It is the authors view that the use

polycarbonate in protective masks is unfeasible due to the above-mentioned reasons and

due to the unpredictable nature of polymers which fail statistically rather than the

predictable nature of metals.

It is worth noting that the banned Cat-Eye cage shown in Figure 29 performed

extremely well under the same ballistic conditions and resulted in little to no

deformation. This predictable behaviour allows for the implementation of smart design

principals like the use of energy absorbing foams to dissipate the force when it is


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transferred to the contact zones. The behaviour of metals is also more predictable than

plastics and can continue to be used when no plastic deformation has occurred. The key

difference being the failure mechanisms, metals undergo a ductile failure process

absorbing energy through the plastic deformation while rigid plastics suffer brittle

fracture when the materials threshold has been exceeded.

While this paper shows that the use of plastics in the design of facial protection for

ballistic impact in hockey is possible. It is not a truly viable or safe option, the

thicknesses required to prevent direct facial impact are substantial (~10mm), costly to

manufacture and have substantial impact on player sight.

While the Author understands the governings body view on protecting players in a

player on player collision. Anecdotal eviden

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Investigation and Analysis of Field Hockey Masks

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