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Failure Analysis of Brittle and Ductile Materials:
Raising the Surface Energy
Failure Analysis of Brittle and Ductile Materials:
Raising the Surface Energy
2007 North Carolina State Science Fair______ Middle School
6th Grade Entry
by
_____Deleted for privacy purposes_____
Science Instructor: Ms. __________
February 13, 2007
Table of ContentsTable of Contents
• Background
• Motivation
• Problem
• Hypothesis
• Material Lists
• Experimental Procedures and Variables
• Results
• Observations and Data Analysis
• Conclusions
• Acknowledgements
BackgroundBackground
• Structure is a long molecular chain
• Actually a type of plastic although clear like glass
• Material is light but very durable
• Can be laminated to make “bullet resistant glass”
• Crystal structure of silica or quartz or “glass”
• Hard, but easily broken due to symmetry of crystal and microscopic defects
• Most common particle found in sand
BackgroundBackground
• Many ductile materials are metals that have an FCC crystal structure including Aluminum and Copper
• Brass is a substitutional alloy of copper and zinc
MotivationMotivation
Failure Analysis Can . . . .
• Improve human safety– Prevent plane crashes – Bullet resistant shielding
• Improve engineering design– Cars (safety features)– Trains– Sky Scrapers
• Help criminal investigations– Forced entry
• Improve environmental protection – Prevent oil tanker spills
Video deleted for privacy purposes
Figure containing sensitive (military) information not shown
Problem and HypothesisProblem and Hypothesis
• Problem: – How and which materials fail under the conditions of
impact force and/or tensile loading and how is energy transferred to these materials under these conditions?
• Hypothesis: – Under impact testing (window glass, tile, acrylic glass,
polycarbonate), all the brittle materials will shatter or break into fragments. The window glass will break into the most fragments.
– Under ductile testing (Aluminum, Brass, Copper) the
metal sheets will bend and the aluminum foil will probably tear completely. The most ductile metal will be the copper.
Impact Testing MaterialsImpact Testing Materials
• Brittle Targets:– Window glass– Acrylic glass– Bathroom tile– Polycarbonate
• Impact Forces:– Large chrome
doorknob – Brass Caster
• Support Materials:– Large cardboard box– Large wooden box– Large foam pillow
• Tape measurer or ruler• Glass cutting kit• Saftey goggles• Leather gloves• 5lb Postal scale• Ziplock plastic bags• Optional: Digital camera
Impact Testing ProcedureImpact Testing Procedure
1) Put on saftey goggles and leather gloves
2) Cut pieces of target material to be 11 X 11cm except for polycarbonate or acrylic glass, for these mark an area of the same dimensions on the material with a marker
3) Place target material on support material and setup testing area to prevent injury.
4) Weigh each impact force material with the postal scale
5) Drop impact force material onto the target from exactly 3 ft by using the tape measure
6) Optional: Before touching anything take a picture of broken pieces or damages from targets using the ruler or tape measure as a scale in the picture
7) Carefully count the number of pieces and record the data before storing them in the Ziplock bags.
8) Impact Energy Effects: Repeat procedure using the brass caster or another spherical-like object of different weight. Using the weight value to calculate the potential energy or impact energy.
9) Support Material Effects: Repeat procedure using the different support materials
Impact TestingImpact Testing
Tension Testing MaterialsTension Testing Materials
• Tensile Specimen– Aluminum foil – Copper flashing– Brass sheet
• Scissors• Two C-clamps• 1 gallon jug• 10lb postal scale• Safety goggles and leather gloves• Level or large ruler• Caliper
Tension Testing ProcedureTension Testing Procedure
1) Cut out ~0.1 mm thick, 16X6 inch metal strips from the tension specimen using scissors. Measure thickness with Caliper. Five sheets of standard Al foil pressed together should equal a 0.1mm thickness.
2) Find two flat parallel bars suspended in air or line up two table overhangs of equal height separated by a known distance. Use these surfaces to firmly clamp down the metal strips on both ends with the length of the strip suspended in air between the two clamps
3) Mark the center of the metal strip (half the length) with a line at one of the edges to indicate the measuring point.
4) Weigh the jug on the postal scale
5) Measure the height of the metal strip with the level/ruler from the measuring point to the floor.
6) Place the empty jug in the center of the metal strip and measure the height again at the measuring point.
7) Effect of Loading: Take off the jug and repeat steps 4), 5), and 6) but while increasing the weight of jug by filling with various levels of water (make sure to close the jug tightly).
8) Calculations: Use the change in height plus some geometry to find the change in length of the tension specimen. The length during the load minus the length after load is the change in the elastic deformation length. The length after load minus the length before the load is the change in the plastic deformation length.
Tension TestingTension Testing
Impact Testing Results Impact Testing Results
Effect of Impact Energy for Impact Testing on a Cardboard Surface
0
10
20
30
40
50
60
tile window glass acrylic glass polycarbonate
# o
f F
rag
men
ts o
r C
rack
s
chrome (1.25 kg, Impact E = 11.2 J)
brass (0.30 kg,Impact E = 2.7 J)
The Effect of the Support Material on Impact Testing
0
10
20
30
40
50
60
tile window glass acrylic glass polycarbonate
# o
f c
rac
ks
an
d f
rag
me
nts
Cardboard
Wood
Foam
CracksFragments CracksFragments
•
Impact Testing Observations / Data Analysis
Impact Testing Observations / Data Analysis
• More Brittle = More Fragments
• Window glass is very brittle
• Both Impact Energies not enough to break
• Acrylic glass or polycarbonate
• Polycarbonate so ductile it doesn’t crack!!
• Foam support adsorbs a lot of impact energy (Foam support actually broke) so there is less energy to directly break the target, however the time of impact is longer.
• Wood adsorbed the least impact energy so the time of impact was shorter. Impact of tile on wood support caused many small pieces in specific area because of nail underneath, caused error in data
• Cardboard adsorbs a little less energy than foam and allows for an impact time longer than that for wood. This caused a larger # of fragments for the window glass
Forms of Energy during Impact Testing
Forms of Energy during Impact Testing
Forms of Energy during Impact Testing of Very Brittle Materials (Window glass and Tile)
0
2
4
6
8
10
12
14
Potential Energy Kinetic Energy Adsorbed StrainEnergy
New Surface Energy
Arb
itra
ry U
nit
s o
f E
ne
rgy
Before drop
During drop
Just before contact
After contact
Forms of Energy during Impact Testing on Non-Brittle Materials
0
2
4
6
8
10
12
14
Potential Energy Kinetic Energy Adsorbed StrainEnergy
New Surface Energy
Arb
itra
ry U
nit
s o
f E
ne
rgy
Before drop
During drop
Just before contact
After contact
Forms of Energy during Impact Testing of Somewhat Brittle Materials (Acrylic Glass)
0
2
4
6
8
10
12
14
Potential Energy Kinetic Energy Adsorbed StrainEnergy
New Surface Energy
Arb
itra
ry U
nit
s o
f E
ner
gy
Before drop
During drop
Just before contact
After contact
• Before dropping, impact force there is a certain potential energy.
• During drop, potential energy changes into kinetic energy
• After impact, energy is either adsorbed as strain energy or released as new surface energy
• More surface energy = more surface area = more pieces
Tension Test ResultsTension Test ResultsElastic Deformation by Tensile Load Testing of Thin Metal Sheets
0
0.2
0.4
0.6
0.8
1
1.2
0 5 10 15 20 25 30 35 40
Load Weight or Force (N)
To
tal
Ela
sti
c D
efo
rma
tio
n L
en
gth
(m
m))
Brass
Aluminum
Cardboard backed Copper
Plastic Deformation by Tensile Load Testing of Thin Metal Sheets
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 5 10 15 20 25 30 35 40
Load Weight or Force (N)
To
tal
Pla
sti
c D
efo
rma
tio
n L
en
gth
(m
m)
Brass
Aluminum
Cardboard backed Copper
Total Deformation by Tensile Load Testing of Thin Metal Sheets
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0 5 10 15 20 25 30 35 40
Load Weight or Force (N)
To
tal
De
form
ati
on
Le
ng
th (
mm
)
Brass
Aluminum
Cardboard backed Copper
Stress Strain Behaviour of Thin Metal Sheets
y = 0.1848x + 1E-04
R2 = 0.9731
y = 0.3779x + 0.0002
R2 = 0.9718
y = 0.5126x + 0.0001
R2 = 0.9793
0
0.0005
0.001
0.0015
0.002
0.0025
0.003
0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016
Strain (unitless or m/m)
Str
es
s (
MP
a)
Brass
Aluminum
Copper
Linear (Aluminum)
Linear (Brass)
Linear (Copper)
Tension Testing Observations / Data Analysis
Tension Testing Observations / Data Analysis
• Copper had cardboard backing which may have introduced some errors in our results, esp. for the elastic deformation b/c the cardboard seemed to make it more elastic
• General trend – Aluminum is the most ductile, then Brass, then Copper
– consistent with published results
Table 1: Comparison of Elastic Moduli for Selected Thin Metal Sheets with Published Values found for Thicker Metal Specimens
Thin metal sheet (thickness ~ 0.1 mm)
Elastic or Young’s Modulus Experimental (MPa)
Elastic or Young’s Modulus Published Value (GPa)
Aluminum 0.185 69 Brass 0.380 97 Copper 0.513 110
Conclusions Conclusions
• Impact Testing Conclusions:– More surface energy = more surface area = more fragments.
– Window glass and tile are the most brittle since they adsorb less impact energy but instead release surface energy so more fragments are created under impact forces.
– Polycarbonate is the least brittle (actually ductile) as it adsorbed more impact energy without releasing surface energy so it didn’t even have cracks.
• Tensile Testing Conclusions:– Copper was not the most ductile but was actually the most stiff as it had
highest elastic modulus, so my hypothesis was wrong.
– Alloying copper and zinc (brass) allows it to become more ductile than either copper or zinc.
– Aluminum is most ductile since it had the lowest elastic modulus and did not tear under the applied load.
– Energy from tensile load is adsorbed by ductile materials and stretches elastically or plastically instead of rapidly breaking it into pieces.
AcknowledgmentsAcknowledgments
• I want to thank . . . .
Deleted for privacy purposes