Chapter 6

Question 1

Engineering Stress and Strain

Answer 1

stress = Force / Original Area
Strain = change in length / original length

Easy to compute, accurate interpretations of what the material actually experiences only for small deformations

Question 2

True Stress and Strain

Answer 2

stress = Force / area at time force is applied
strain = natural log( current length / original length)

Accurately represents what the material experiences at all deformation levels but are difficult to compute.

Question 3

Tensile Strength

Answer 3

Most Important Material test

Gives accurate values for a wide variety of material properties which are valuable in engineering calculations

Question 4

Tensile Test

Elastic Modulus

Answer 4

Slope of the linear, elastic first portion of the curve

Question 5

Tensile Test

Yield STrength

Answer 5

Point from which elastic unloading would result in a 0.2% (0.002) permanent strain

Question 6

Tensile Test

Ultimate Tensile Strength

Answer 6

Maximum value of the engineering stress on the curve

Question 7

Tensile Test

Modulus of Resilience

Answer 7

Area under the elastic portion of the curve

Represents energy/volume that can be stored in the material before it yields

Question 8

Tensile Test

Modulus of Toughness

Answer 8

Area under entire curve

Represents energy/volume that must be expended to break the material

Question 9

Tensile Test

% Elongation to failure

Answer 9

(final length - original length) / original length *100%
fracture strain * 100%

Overall measure of ductility

Question 10

Tensile Test

Poisson’s Ratio

Answer 10

Ratio of lateral contraction strain to longitudinal extension strain

Question 11

Tensile Test

% Redunction in Area

Answer 11

(original area - final area)/original area * 100%

local measure of ductility at the point of fracture in the neck

Question 12

Hardness Test

Answer 12

Measure of resistance to indentation/scratching and qualitative measure of strength of the material

Found by pressing a spherical, conical, or pyramidal indenter into the material and measuring either the size of the indentation or the depth of penetration

Rockwell, Vickers, Brinnel, Knoop, Mohs

Question 13

Hardness Test Advantages

Answer 13

Easy

Cheap

Portable

Nondestructive to the material

Question 14

Rockwell Hardness Test

Answer 14

Measures the depth of penetration

Question 15

Impact Test

Answer 15

Direct measure of energy to fracture a specimen

Useful as a pass/fail test for whether a material is tough enough, but does not give nearly as many high quality material properties as tension test

Question 16

Bending Test

Answer 16

Measure properties of materials that will be used in bending mode and brittle materials which are amenable to tension testing

Can get both strength and stiffness data from a bending test, but results are much harder to interpret than tension testing because the stresses in a bending specimen are non-uniform both axially and through thickness

Question 17

Torsion Test

Answer 17

If done on a thin-walled tubular specimen this is almost as useful as the tension test

Harder to perform, harder to interpret, and much less commonly performed than the tension test