Lab 2 Tensile Test

ENGR 271 Materials Science Laboratory

Spring 2015

LAB 2 – TENSILE TEST

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Stress-Strain Testing Typical tensile test machine

extensometer

Typical tensile specimen

specimen

gauge length

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

2

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Linear Elastic Properties • Modulus of Elasticity, E: (also known as Young's modulus)

Units: E: [GPa] or [psi]

• Hooke's Law:

s=Ee

s

F E

e Linearelastic

F simple tension test

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Yield Strength, sy by 0.2% offset method • Stress at which noticeable plastic deformation has occurred. tensile stress, s

when ep = 0.002

sy

sy = yield strength Note: for 2 inch sample

e = 0.002 = z/z  z = 0.004 in engineering strain, e

ep = 0.002 Adapted from Fig. 6.10 (a), Callister & Rethwisch 8e. .

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Ductility Lf - Lo x 100 %El = Lo

• Plastic tensile strain at failure: smaller %El (Brittle) Engineering tensile stress, s

larger %El (Ductile)

Engineering tensile strain,

• Another ductility measure: Adapted from Fig. 6.13, Callister & Rethwisch 8e. .

Lo

Ao

Af

e

Ao - Af %RA = x 100 Ao

Lf

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Tensile Strength, TS • Maximum stress on engineering stress-strain curve.

TS = Tensile Strength

F = fracture or ultimate strength

engineering stress

sy

Typical response of a metal

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

Neck – acts as stress concentrator

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Why Use True Stress & Strain

Specimen area is decreasing Stress calculated on instantaneous area is increasing Adapted from Fig. 6.11, Callister & Rethwisch 8e.

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True Stress & Strain • True Stress s T = F Ai • True Strain e T = ln i  o 

s T = s 1  e  e T = ln1  e  Valid up to point M

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

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LAB 2 – TENSILE TEST REQUIREMENTS Fill out the table, show all calculations, graphs Modulus of Elasticity Yield Strength Tensile Strength Fracture Strength Ductility Toughness

Experimental

Theoretical

% Error

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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.