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14

Metal formed into round or rectangular

bar is subsequently transformed into

a number of products through a variety

of manufacturing processes. Bar is

often machined and converted into other

forms to meet industry requirements

and end product applications. The

nature of the end product application -

from bridge components to steering

columns - requires high strength, elastic

metal that bends when a load is applied

but does not break. Mechanical

properties such as strength, ductility,

hardness, and fatigue are important

measures of bar and its suitability for a

particular application.

Tension

The Challenge

Tensile testing provides a relatively easy and

inexpensive technique for developing or

evaluating mechanical properties, and

provides basic information concerning theresponse of metals and alloys to mechanical

loading. In some cases, manufacturers can

test specimens that closely resemble the

final product. In other instances, a specimen

must be cut or turned down from the original

material. Both types of testing are valuable

in comparing materials, checking quality

control, and developing alloys. There are a

number of important factors to consider when

conducting tensile tests on bar samples,

including frame stiffness, proper gripping,

specimen alignment, extensometry, machine

control, data collection, and result reporting.

Frame stiffness and grip selection are

particularly important when testing heavy bar

stock that is subject to extreme mechanical

loading conditions.

Our Solution

To meet these challenges, Instron offers rigid

load frames for breaking specimens at

capacities up to 3,500 kN (800,000 lbf)

which can accommodate bar specimens upto 120 mm (4.75 in) in diameter and flat

specimens up to 150 mm (6 in) thick.

For larger specimens or unique testing

considerations, Instron has designed tensile

testing systems with capacities up to 10 MN

(2,000,000 lbf).

To meet the gripping challenges of testing

bar stock, Instron offers a wide range of

in-crosshead, mechanical, pneumatic, and

hydraulic wedge grips with a vast array offlat, V-cut, or special coated jaw faces. Most

wedge-action grips feature an open front

design, which facilitates easy-loading of large

specimens. Specially-suited for industrial

environments where dust and metal chips may

be present, these grips contain protective dust

covers that fit easily over the faces to shield the

moving surfaces. Additionally, Instron offers

shoulder-end and threaded-end specimen

holders for testing machined samples. The

split-sleeve design of the shoulder-end holders

expedites production floor testing.

d

1500 kN (337,500 lbf) hydraulic wedge-action grips

and M300 automatic extensometer for testing

high capacity bar samples.

dModel 300DX with shoulder-end specimen holders

for testing machined samples.

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15

Hardness

The Challenge

The most common type of hardness testing

for bars is a Rockwell test. Benchtop testing

of very long or heavy bar specimens requires aspecial fixture to support the sample while it

is being tested. Another common type of

hardness test performed on smaller, round bar

is a Jominy end-quench test used to determine

the hardenability of steel.

A hardness test is typically required as part

of the incoming inspection process for raw

or unfinished stock. In the case of extremely

large stock, the test equipment must be

brought to the part as opposed to bench or

lab-type testing.

The Challenge

A bend test provides important information on

a material's ductility and toughness. The

range of requirements, from I-beams inbridges to common stair railings, dictates the

need for a bend test to prove a material's

suitability for the task at hand. The infinite

variety of materials, specimens, and

applications together with the continual

advance of materials science puts an even

greater demand on the need to develop

specialized test fixtures.

Our Solution

For testing elongated parts in a hardness

tester, a Vari-Rest or Jack-Rest test fixture is

the most likely choice for providing thenecessary support. Wilson Instruments'

Equitron fixture is recommended for the

Jominy end-quench test. The Equitron fixture

supports the specimen and ensures accurate

positioning of the sample for successive

Rockwell hardness testing at 1.6 mm

(1/16 in) intervals.

Our Solution

Instron bend fixtures come in a wide variety

of configurations designed for three or four-

point bend testing on specimens of differentspans, capable of testing round steel bars up

to a full 180 bend. The span for a given

diameter is determined based on specimen

diameter and bending pin diameter according

to various ASTM specifications including

ASTM A 615, ASTM A 616, and ASTM A 617.

Instron bend fixtures feature an adjustable

support span and interchangeable nose pins

to accommodate a wide range of bar sizes

with one fixture.

Portable hardness testers are ideal when

the size of the test specimen prohibits

moving the sample to the tester. WilsonInstruments mobile hardness testers are

lightweight, easy-to-operate, and highly

accurate. A variety of models have been

developed to provide a convenient means

for determining Rockwell hardness readings

in situations that do not lend themselves to

bench testing. A clamping mechanism holds

the tester to the workpiece. Calibrated,

preloaded spring mechanisms apply minor

and major loads, and results are read on a

dial gauge.

d

C-clamp type mobile tester model M-2

performing Rockwell test on bar.

d

Four-point bend test fixture and deflectometer.

Bend/ Flex

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Shear

The Challenge

Many applications and product designs use

bars that are subjected to shear stresses. These

applications vary from simple pin and clevisadapters to shear pins that function as

mechanical fuses to protect expensive

machinery. In such cases, it is imperative to

understand how the bar will perform under

in-service shear conditions.

Our Solution

Instron provides both single and double-

shear test fixtures to meet these challenges.

For a full explanation of fixtures for sheartesting please refer to the Fastener section

on page 22.

1 616

d

Double-shear test on a bar sample.

d

Dynatup pipe and bar support fixture.

Impact

The Challenge

From handrails to high-speed train rails,

many products made from bar material are

subjected to impact. Thus, impact testing is

necessary to understand how bar products

will perform under live conditions. Impact

testing is commonly used to determine

material properties such as yield strength.

These properties can be used to discover

unforeseen changes that may take place

during manufacturing.

Our Solution

Instron provides both pendulums and drop

towers to simulate any number of real-life

impact conditions that bar products may see.

Instron pendulums are designed for testing

Charpy bars, while Instron drop towers can

accommodate a completely finished product.

Instron can also develop strikers of any

geometry to impact the finished product to

duplicate its real-life impact scenario.

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1 7

Torsion

The Challenge

Torsion or twist testing can characterize

material properties such as shear modulus,

ultimate shear strength, modulus of rupture inshear, and ductility. To determine these

properties, accurate measurement of torque

and angle of twist over a fixed gauge is

required. Although seemingly

straightforward, torsion testing can be

difficult because bar stock is often difficult to

grip, and measuring the angle of twist is

challenging. Specimens often need to be

machined with a reduced area in the middle

and double, triple, or hex flats at the grip ends.

Our Solution

Maintaining proper alignment of the

specimen in the grips is critical to obtaining

accurate test results. Round specimens canbe difficult to grip without slippage during

testing. In response, Instron provides

chuck-style torsion grips that can

accommodate round, hex, or triangular

specimens up to 9.5 mm (0.375 in) in

diameter. Keyless operation allows rapid

gripping and release of specimens. Instron

also provides tight-fitting plugs to prevent

tubular specimens from being deformed

deformation in the grips.

For accurate torque and angle measurements

on stiff specimens, Instron provides a twist

gauge (sometimes called a troptometer ortorsional extensometer) to measure the

relative difference in twist over a defined

length of the specimen. When attachment of

the troptometer to the specimen is not feasible,

the angle of position can be determined from

the rotation of the grips, and captured by the

software and electronics.

17

FatigueBar manufacturers or end-user companies

often need to know how their products will

perform when subjected to conditions such as

in-service loading, high and low-cycle

fatigue, fracture mechanics, high strain rate,

and thermo-mechanic fatigue. These tests are

typically ASTM E 647 for fatigue crack growth

and ASTM 1820 for fracture toughness. For

more information on Instron's fatigue testing

solutions see page 41.

Creep andStress-RuptureOccasionally, bar manufacturers or end-user

companies need to determine how their

products will perform when subjected to

constant loads at both ambient and elevated

temperatures. These tests are typically

conducted for an extended time in accordance

with standards such as A STM E 139 and

ASTM E 292. For more information on

Instron's creep and stress-rupture testing

solutions see page 41.

d

Model 55MT10 with bar grips and troptometer for

measuring torsional rotation.

d

Three-face collet design securely clamps bar for

torsional testing while troptometer measures

angular rotation.

d

Split tube furnace with optional side entry

extensometer port (M3-SF16, W-8711B).

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For information on Instron products and services call your local worldwide sales, service and technical support offices:

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All of the specifications shown in this brochure are subject to change without notice. WB1212

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