ENGR 271

Materials Science Laboratory

Spring 2015

LAB 2 TENSILE TEST

ENGR 271

2

Stress-Strain Testing

Typical tensile test machine

Adapted from Fig. 6.3, Callister & Rethwisch 8e. (Fig. 6.3 is taken from H.W. Hayden, W.G.

Moffatt, and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, p.

2, John Wiley and Sons, New York, 1965.)

specimenextensometer

Typical tensile specimen

Adapted from Fig. 6.2, Callister & Rethwisch 8e. .

gaugelength

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ENGR 271

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Linear Elastic Properties

Modulus of Elasticity, E:

(also known as Young's modulus)

Hooke's Law:

s = E e s

Linear-

elastic

E

e

F

Fsimpletensiontest

Units:

E: [GPa] or [psi]

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Stress at which noticeable plastic deformation has occurred.

when ep = 0.002

Yield Strength, sy by 0.2% offset method

sy = yield strength

Note: for 2 inch sample

e = 0.002 = z/z

z = 0.004 in

Adapted from Fig. 6.10 (a), Callister & Rethwisch 8e. .

tensile stress, s

engineering strain, e

sy

ep = 0.002

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Plastic tensile strain at failure:

Adapted from Fig. 6.13, Callister & Rethwisch 8e. .

Ductility

Another ductility measure: 100xA

AARA%

o

fo-

=

x 100L

LLEl%

o

of-

=

Engineering tensile strain, e

Engineering

tensile

stress, s

smaller %El (Brittle)

larger %El (Ductile)Lf

AoAfLo

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Tensile Strength, TS

Adapted from Fig. 6.11, Callister & Rethwisch 8e. .

sy

strain

Typical response of a metal

F = fracture or

ultimate

strength

Neck acts

as stress

concentrator

engin

eeri

ng

stre

ss

engineering strain

Maximum stress on engineering stress-strain curve.

TS = Tensile

Strength

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Why Use True Stress & Strain

Adapted from Fig. 6.11, Callister & Rethwisch 8e.

Specimen area is decreasing

Stress calculated on instantaneous area

is increasing

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True Stress & Strain True Stress

True Strain

iT AF=s

oiT ln=e ee

ess

=

=

1ln

1

T

T

Adapted from Fig. 6.16, Callister & Rethwisch 8e.

Valid up to

point M

ENGR 271

LAB 2 TENSILE TEST REQUIREMENTS

Fill out the table, show

all calculations, graphsExperimental Theoretical % Error

Modulus of Elasticity

Yield Strength

Tensile Strength

Fracture Strength

Ductility

Toughness

ENGR 271

LAB 2 TENSILE TEST REQUIREMENTS

Plot the Engineering vs. True Stress and Strain Diagram.

Comment on your results and include the discussion points

below to your report.

Why does it not make much sense to calculate true stress and true strain using the equations given in the

lab notes after the maximum load is reached?

In general, A36 can be categorized as a ductile material, and cast iron as a brittle material. Based on the results of

the tensile tests, discuss the differences between the

ductile and brittle materials in terms of the overall

deformation and fracture behavior.