Chapter 3

Question 1

Define: Engineering Stress

Answer 1

F/A ; the applied force divided by the original area of the object.

Question 2

Define: Engineering Strain

Answer 2

Change in L / Original L (L = length)

Question 3

Define: Modulus of Elasticity

Answer 3

Or Young’s Modulus; measure of the inherit stiffness of a material

Question 4

Define: Yield Point

Answer 4

Change in slope at the end of a linear region on the stress-strain diagram .

Question 5

Define: Yield Strength

Answer 5

Or yield stress; property of a material that indicates the stress associated with the yield point

Question 6

Define: Ultimate Strength

Answer 6

Property of a material when the applied load reaches a maximum value of engineering stress; known as tensile strength or ultimate strength.

Question 7

Define: Necking

Answer 7

After reaching the tensile strength, the object begins a process of localized elongation b
Which becomes concentrated in one small section of the specimen.

Question 8

Define: Fracture Stress

Answer 8

The stress calculated just prior to failure (breaking)

Question 9

Define: Ductility

Answer 9

Amount of strain a material can endure before failure; measured as elongation (EL) or area reduction (AR)

Question 10

Define: Elongation

Answer 10

Measure of ductility; change in Length / original length

Question 11

Define: Area Reduction

Answer 11

Measure of ductility; change in Area / original Area

Question 12

Define: True Stress

Answer 12

Instantaneous stress found by dividing the applied load by the instantaneous value of area

Question 13

Define: True Strain

Answer 13

Instantaneous strain found be dividing “instantaneous” elongation per unit length of the material

Question 14

Define: Work Hardening

Answer 14

or Strain hardening; using strain to make a metal stronger.

Question 15

Define: Flow Curve

Answer 15

Stress = (K) e^n ; approximation of the behavior of metals in the plastic region, including their capacity for strain hardening

Question 16

Define: Strength Coefficient

Answer 16

“K” ; units of MPa; equals the value of true stress at a true strain value of 1.

Question 17

Define: Strain Hardening Exponent

Answer 17

“n” = slope of the stress vs. strain graph

Question 18

Define: Elastic Behavior

Answer 18

Behavior of material completely defined by its stiffness. Fractures rather than yielding to plastic flow.

Question 19

Define: Perfectly Plastic Behavior

Answer 19

Once yield strength is reached, material plastically forms at constant stress level (Y=K) and n=0.

Question 20

Define: Strain Hardening Behavior

Answer 20

Material obey’s Hooke’s law int heat after the yield strength, deformation requires ever-increasing stress so that K>Y and n>0.

Question 21

Define: Barreling

Answer 21

Consequence of friction between surfaces in that middle of the specimen is permitted to increase in area much more than that at the ends. (compression test)

Question 22

Define: Flexure Test

Answer 22

or Bending Test; where beam is supported by two supports and load is applied at its center. Measures bend.

Question 23

Define: Torsion Test

Answer 23

Measures shear stress and strain by torquing a tube via twisting

Question 24

Define: Hardness (Brinell, Rockwell)

Answer 24

Brinell - Mostly for nonmetals and metals of low to medium hardness; conducted with steel ball placing pressure on a specimen

Rockwell - More versatile and done with a cone-shaped indentor

Question 25

Define: Viscoelasticity

Answer 25

Property of polymers that determines the strain a material will experience when subjected to combinations of stress and temperature over time.