Chapter 3

Question 1

What is the dilemma between design and manufacturing in terms of mechanical properties

Answer 1

A design should have strong material, but in order to manufacture it, said material should not be strong

Question 2

What are the three types of static stresses

Answer 2

Shear, tensile, and compression

Question 3

State Hooke’s law

Answer 3

Hooke’s Law defines the stress-strain relationship for an elastic material: σ = Eε, where E = the modulus of elasticity.

Question 4

What is the difference between engineering stress and true stran

Answer 4

Engineering stress divides the load on the test specimen by the original area, while true stress idvides the load by the instantaneous area

Question 5

Define tensile stress of a material

Answer 5

Maximum load experienced during the tensile test divided by the original area

Question 6

Define yield strength of a mateila

Answer 6

Stress at which the material begins to plastically deform.

Question 7

Why can’t a direct conversion be made between the ductility measure of elongation and reduction in area using the assumption of constant volume

Answer 7

Because of necking

Question 8

What is work hardening (strain hardening)

Answer 8

Increase in strength that occurs when metals are strained

Question 9

In what case does strength coefficient have the same value as the yield strength

Answer 9

When the material is perfectly plastic and does not strain harden

Question 10

how does the change in cross-sectional area of a test specimen in compression test differ from its counterpart in a tensile test specimen?

Answer 10

In compression, the cross-sectional area increases while in the tenisle test, the cross-sectional area decreases

Question 11

What is the complicating factor that occurs in a compression test

Answer 11

Tha barreling (diameter go big) of the test specimen, causes more friction between the machine and the material, meaning that it requires extra force to compress

Question 12

Tensile testing ins not appropriate for hard brittle materials such as ceramics. What is the test commonly used oto determine the strength properties of such materials

Answer 12

A three point bending test is commonly used to test the strength og brittle materials. The test provides a measure called the transverse rupture strength for these materiañsH

Question 13

How is the shear modulus of elasticity G related to the tensile modulus of elasticoty E on average

Answer 13

G = 0.4E, on average

Question 14

How is shear strength S related to tensile strenght TS, on average

Answer 14

S = 0.7 TS, on average

Question 15

What is hardness and how is it generally testedh

Answer 15

Hardness is defined as teh resisitance to indentation of a material. It is tested by pressing hard objects into the test and measuring the size (deph, area) of the indentation

Question 16

Why are different hardness tests and scales required?

Answer 16

Because different material possess widely differing hardnesses A test whose measuring range is suited for very hard materials is not good for testing bery soft material

Question 17

Define the rectystallization temperature for a metal

Answer 17

The recrystallization temperature is the temperature at whcih a metal recrystallizes rather than work hardens when deformed

Question 18

Define viscocity of a fluiD

Answer 18

Vsicocity is the resistance to flow of a fluid of a nateral. The thicker teh fluid teh grater the material

Question 19

What is the definind characteer of a newtonian fluid

Answer 19

One for which viscocity is constant at a fiven temperature

Question 20

Strain hardening?

Answer 20

since the lattice structure starts ahanging after entering the plastic region, the defects start moving, when they meet, they can no longer go forward, so they make the material harder

Question 21

Types of materials that are perfectly elastic

Answer 21

brittle (ceramics works)

Question 22

Materials that are elastic and perfectly plastic

Answer 22

Melted metals. When they yield, but don’t break

Question 23

Materials taht are elastic and strain hardening

Answer 23

Ductile metals

Question 24

Can compresison tenst be used in brittle materials

Answer 24

No, they go boom.

Question 25

When does strain hardening not occur

Answer 25

hot

Question 26

Recrystalization of a meral

Answer 26

half its melting point (aprox)

Question 27

What is viscoelasticity as a materia property?

Answer 27

Refers to the property of plymers that defines the strain of the martial as a function of stress and temperature over time. viscosity + elasticity.

Question 28

Which of the follwing are three basic types of static stresses? a) compression, (b) hardness, (c) reduction in area, (d) shear, (e) tensile, (f)
true stress, and (f) yield?

Answer 28

a, d, e

Question 29

Which one of the following is the correct definition of ultimate tensile strength, as derived from the
results of a tensile test on a metal specimen: (a) the stress encountered when the stress-strain curve
transforms from elastic to plastic behavior, (b) the maximum load divided by the final area of the
specimen, (c) the maximum load divided by the original area of the specimen, or (d) the stress
observed when the specimen finally fails?

Answer 29

c

Question 30

If stress values were measured during a tensile test, which of the following would have the higher
value: (a) engineering stress or (b) true stress?

Answer 30

b

Question 31

If strain measurements were made during a tensile test, which of the following would have the higher
value: (a) engineering strain, or (b) true strain?

Answer 31

a

Question 32

The plastic region of the stress-strain curve for a metal is characterized by a proportional relationship
between stress and strain: (a) true or (b) false?

Answer 32

b The plastic region is characterized by a power function of stress and strain

Question 33

Which one of the following types of stress strain relationship best describes the behavior of brittle
materials such as ceramics and thermosetting plastics: (a) elastic and perfectly plastic, (b) elastic and
strain hardening, (c) perfectly elastic, or (d) none of the above?

Answer 33

c

Question 34

Which one of the following types of stress strain relationship best describes the behavior of most
metals at room temperature: (a) elastic and perfectly plastic, (b) elastic and strain hardening, (c)
perfectly elastic, or (d) none of the above?

Answer 34

b

Question 35

Which one of the following types of stress strain relationship best describes the behavior of metals at
temperatures above their respective recrystallization points: (a) elastic and perfectly plastic, (b) elastic
and strain hardening, (c) perfectly elastic, or (d) none of the above?

Answer 35

a

Question 36

Which one of the following materials has the highest modulus of elasticity: (a) aluminum, (b)
diamond, (c) steel, (d) titanium, or (e) tungsten?

Answer 36

b

Question 37

The shear strength of a metal is usually (a) greater than or (b) less than its tensile strength?

Answer 37

b

Question 38

Most hardness tests involve pressing a hard object into the surface of a test specimen and measuring
the indentation (or its effect) that results: (a) true or (b) false?

Answer 38

a

Question 39

Which one of the following materials has the highest hardness: (a) alumina ceramic, (b) gray cast
iron, (c) hardened tool steel, (d) high carbon steel, or (e) polystyrene?

Answer 39

a

Question 40

Viscosity can be defined as the ease with which a fluid flows: (a) true or (b) false?

Answer 40

b: it is the resistance to flow