Chapter 6

Question 1

What material is this chapter about?

Answer 1

metals

Question 2

When can you use a strain test?

Answer 2

If a load is static or changes relatively slowly with time and is applied uniformly over a cross section or surface of a member

Question 3

When are strain tests most commonly conducted?

Answer 3

Metals at room temperature

Question 4

What are the three principal ways in which a load may be applied?

Answer 4

Tension, compression, and shear

Question 5

What is the principal way that strain tests are performed?

Answer 5

Tension

Question 6

Why was the “dogbone” specimen configuration chosen?

Answer 6

So deformation is confined to the narrow center region and to reduce the likelihood of fracture at the ends of the specimen

Question 7

What is the tensile testing machine designed to do?

Answer 7

Elongate the specimen at a constant rate and measure the applied load

Question 8

In order to minimize the geometrical factors in tensile testing (such as area of a specimen) what parameters did they create?

Answer 8

Engineering stress and engineering strain

Question 9

What is engineering stress’ relationship?

Answer 9

Force/cross-sectional area

Question 10

What engineering strain’s relationship?

Answer 10

deformation elongation/ original length

Question 11

In what direction does the specimen contract in a compression test?

Answer 11

Along the direction of the stress

Question 12

Are compressive strains positive or negative?

Answer 12

Negative

Question 13

When are compressive tests used?

Answer 13

When a material’s behavior under large and permanent strains is desired or when the material is brittle in tension

Question 14

What is torsion?

Answer 14

A variation of pure shear in which a structural member is twisted and the torsional forces produce a rotational motion about the longitudinal axis of one end of the member relative to the other end

Question 15

What are three examples of torsion?

Answer 15

Machine axles, drive shafts, twist drills

Question 16

Through what relationship are stress and strain proportional?

Answer 16

Hooke’s law

stress= E (strain)

Question 17

What is an elastic deformation?

Answer 17

A deformation in which stress and strain are proportional

Question 18

What does the slope of a linear stress v. strain plot correspond to?

Answer 18

The modulus of elasticity

Question 19

What can you think of the modulus of elasticity as?

Answer 19

Stiffness/ a material’s resistance to elastic deformation/ the resistance of separation of adjacent atoms

• the greater the modulus, the stiffer the material

Question 20

Is elastic deformation permanent?

Answer 20

No

Question 21

On an atomic scale, what does macroscopic elastic strain look like?

Answer 21

Small changes in the interatomic spacing and the stretching to interatomic bonds

Question 22

How does the modulus of elasticity relate between ceramics, metals, and polymers?

Answer 22

Ceramics and metals are about the same and polymers are lower

Question 23

What is anelasticity?

Answer 23

The time-dependent elastic behavior (time it takes for the material to actually return to normal after deformed)

Question 24

What is the anelastic component like in metals?

Answer 24

Small and often neglected

Question 25

What is the anelastic component like in polymers?

Answer 25

In some the magnitude is significantly

Question 26

Theoretically, what should Poisson's ration be for isotropic materials?

Answer 26

1/4

Question 27

What does elastically anisotropic mean?

Answer 27

The elastic behavior varies with crystallographic direction

Question 28

Is plastic deformation permanent?

Answer 28

yes

Question 29

From an atomic perspective, what does plastic deformation correspond to?

Answer 29

The breaking of bonds with original atom neighbors and then re-forming of bonds with new neighbors as large numbers of atoms

Question 30

What is a slip?

Answer 30

The process through which deformation is accomplished for crystalline solids

Question 31

How does plastic deformation in noncrystalline occur?

Answer 31

viscous flow mechanism

Question 32

How can you identify where plastic deformation begins on a stress strain curve? What is this point called?

Answer 32

When the line stops being linear The proportional limit P

Question 33

What is the magnitude of the yield strength for a metal a measure of?

Answer 33

it's resistance to plastic deformation

Question 34

What does the M point in a stress strain graph correspond to?

Answer 34

the maximum stress that can be sustained by a structure in tension

Question 35

At maximum stress, where is the deformation? What is the called?

Answer 35

deformation is confined at the neck. This is called necking.

Question 36

What is ductility?

Answer 36

A measure of the degree of plastic deformation that has been sustained at fracture

Question 37

What is the opposite of ductile?

Answer 37

Brittle

Question 38

What are the two ways you can numerically express ductility?

Answer 38

Percent elongation Percent reduction in area

Question 39

What is fracture strain of a brittle material?

Answer 39

Less than 5%

Question 40

Do the magnitudes of yield and tensile strengths decline or increase with increasing temperature?

Answer 40

decline with increasing temperature

Question 41

What is the yield point phenomenon?

Answer 41

When the elastic-plastic transition is very well defined and occurs abruptly

Question 42

What occurs at the upper yield point?

Answer 42

Plastic deformation is initiated with an apparent decrease in engineering stress

Question 43

What is the lower yield point?

Answer 43

Where continued deformation fluctuates slightly about some constant stress value

Question 44

What is the magnitude of the yield strength of a metal a measure of?

Answer 44

It's resistance to plastic deformation

Question 45

What is resilience?

Answer 45

the capacity of a material to absorb energy when it is deformed elastically and then to have this energy recovered

Question 46

What is the modulus of resilience?

Answer 46

Ur, the strain energy per unit volume required to stress a material from an unloaded state up to the point of yielding

Question 47

What are two characteristics of resilient materials?

Answer 47

high yield strength and low modulus of elasticity

Question 48

What is fracture toughness?

Answer 48

a property that is indicative of a material's resistance to fracture when a crack is present

Question 49

What is notch toughness?

Answer 49

The ability of a material to absorb energy and plastically deform before fracturing.

Question 50

For a metal to be tough, what two characteristics must it display?

Answer 50

Ductile and strength

Question 51

Does the decline in the stress necessary to continue deformation past the maximum point M indicate that a metal is becoming weaker?

Answer 51

no. It is increasing in strength. the cross-sectional area is decreasing rapidly within the neck region.

Question 52

Where is the region of the true stress-strain curve?

Answer 52

From the onset of plastic deformation M to the point of necking

Question 53

Does necking occur in compression?

Answer 53

No

Question 54

What is hardness?

Answer 54

a measure of a material's resistance to localized plastic deformation

Question 55

What is the most often performed mechanical test? Why?

Answer 55

Hardness 1. Simple and inexpensive 2. Test is nondestructive 3. Tensile strength can be estimated from hardness data

Question 56

What are the four hardness tests?

Answer 56

Rockwell Hardness Brinell Hardness Knoop Vickers

Question 57

What are both tensile strength and hardness indicators of?

Answer 57

A metal's resistance to plastic deformation

Question 58

What are the two symbols for hardnes?

Answer 58

HB and HRC

Question 59

How do you calculate the modulus of resiliene?

Answer 59

The area under the elastic portion of the engineering stress-strain curve

Question 60

What are five factors that can lead to scatter in measured material properties?

Answer 60

1. test method 2. variations in specimen fabrication procedure 3. operator bias 4. apparatus calibration

Question 61

Do materials with large or small elastic moduli deform less?

Answer 61

Large

Question 62

What does the elastic modulus depend on?

Answer 62

Interatomic bonding forces

Question 63

What is Poisson's ratio for metals, ceramics, and polymers?

Answer 63

Vmetals= 0.33 Vceramics= 0.25 Vpolymers = 0.40

Question 64

What are the 4 elastic constants?

Answer 64

1. Young's Modulus (E) 2. Shear Modulus (G) 3. Bulk Modulus (K) 4. Modulus of Resilience (Ur)

Question 65

What kind of deformations are in the plastic region?

Answer 65

elastic and plastic

Question 66

What is the fracture strength?

Answer 66

Strength that the material breaks

Question 67

Visually, when does the maximum on the stress-strain curve appear for metals?

Answer 67

When it starts necking

Question 68

What is the toughness for metals, ceramics, and polymers?

Answer 68

Metals- large ceramics/polymers- small

Question 69

Is there a lower or higher yield strength for the second deformation?

Answer 69

Higher

Question 70

What are the two things that a large hardness means?

Answer 70

1. High resistance to deformation from compressive loads 2. Better wear properties

Question 71

What is the hardness range for each scale? The useful range?

Answer 71

range: 0-130 useful: 20-100