Biomaterials I: Chapter 7

Front 1

What is Engineering Stress?

Back 1

The instantaneously load applied to a specimen divided by its cross-sectional area before any deformation.

Front 2

What is Engineering Strain?

Back 2

The change in gauge length of a specimen (in the direction of applied stress) divided by its original gauge length.

Front 3

What is the formula for engineering strain?

Back 3

Instantaneous length - original length over original length

Front 4

What is Elastic Deformation?

Back 4

Deformation that is nonpermanent - that is, totally recovered upon release of an applied stress.

Front 5

What is G?

Back 5

shear modulus - the slope of the linear elastic region of the shear stress-strain curve.

Front 6

What is Poisson's Ratio?

Back 6

For elastic deformation, the negative ratio of lateral and axial strains that result from an applied axial stress.

Front 7

What is the general elastic modulus for metals?

Back 7

45 - 407 GPa

Front 8

What is the general elastic modulus for ceramics?

Back 8

70 - 500 GPa

Front 9

What is the general elastic modulus for polymers?

Back 9

0.007 - 4 GPa

Front 10

At low elastic modulus levels, stress and strain is proportional to what?

Back 10

Elastic deformation!

Front 11

What is Anelasticity?

Back 11

Time dependent elastic deformation

Front 12

For isotropic materials, shear and elastic moduli are related to each other and to Poisson's ratio according to what formula?

Back 12

E = 2G(1 + v)

Front 13

If stress is uniaxial and the material is isotropic, the strain in the x direction is equal to what?

Back 13

The strain in the y direction!

Front 14

What is Plastic Deformation?

Back 14

Deformation that is permanent or nonrecoverable after release of the applied load.

Front 15

Plastic Deformation is accompanied by what?

Back 15

Permanent atomic displacements!

Front 16

What is Slip?

Back 16

The motion of dislocations that causes permanent deformations in metals or the shear displacement of two adjacent planes of atoms

Front 17

What is Yielding?

Back 17

The onset of plastic deformation

Front 18

What is Proportional Limit?

Back 18

The point on a stress-strain cure at which the straight-line proportionality between stress and strain STOPS.

Front 19

What is Yield Strength?

Back 19

The stress required to produce a very slight yet specified amount of plastic strain.

Front 20

What is the offset used to find yield strength?

Back 20

A STRAIN offset of 0.002

Front 21

What is Tensile Strength?

Back 21

The maximum engineering stress, in tension, that may be sustained without fraction.

Front 22

What is another term for Tensile Strength?

Back 22

Ultimate Strength

Front 23

What is Ductility?

Back 23

It is a measure of the degree of plastic deformation that hasa been sustained at fracture.

Front 24

Ductility may be expressed quantitatively as what two values?

Back 24

Percent elongation and percent reduction in area

Front 25

What is Resilience?

Back 25

The capacity of a material to absorb energy when it is deformed elastically and then upon unloading, to have this energy recovered.

Front 26

Assuming a linear elastic region, what is the modulus of resilience?

Back 26

(0.5)(yield stress)(strain at yielding)

Front 27

What is Toughness?

Back 27

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

Front 28

What is True Stress?

Back 28

The instantaneous applied load divided by the instantaneous cross-sectional area of a specimen.

Front 29

What is Flexural Strength?

Back 29

Stress at fracture from a bend

Front 30

What are the terms b and d in the flexural strength equation for a rectangular cross section?

Back 30

Width and height

Front 31

Porosity is deleterious to the flexural strength for what 2 reasons?

Back 31

1. Pores reduce the cross-sectional area across which a load is applied
2. pores act as stress concentrators

Front 32

What is an elastomer?

Back 32

A polymeric material that may experience large and reversible elastic deformations.

Front 33

What is Viscoelasticity?

Back 33

A type of deformation exhibiting the mechanical characteristics of viscous flow and elastic deformation.

Front 34

What is Hardness?

Back 34

The measure of a material's resistance to deformation by surface indentation or by abrasion.

Front 35

What are 3 reasons why hardness tests are performed more frequently

Back 35

1. Simple + inexpensive
2. Nondestructive
3. Other properties can be estimated from it

Front 36

What is Viscoelastic Creep?

Back 36

Time-dependent deformation when stress is maintained as constant

Front 37

When can viscoelastic creep occur?

Back 37

Can occur at room temperature and below yield stress.

Front 38

If susceptibility to creep decreases, what happens to crystallinity?

Back 38

It increases!

Front 39

What is Safe Stress also called?

Back 39

Working Stress!

Front 40

What is Safe Stress?

Back 40

A stress used for design purposes: for ductile metals

Front 41

What is the formula for Safe (Working) Stress?

Back 41

For ductile metals, it is the yield strength divided by the safety factor

Front 42

What happens if N (Factor of Safety) is too large?

Back 42

Component overdesign will result: too much material or alloy having a higher-than-necessary strength will be used.

Front 43

Normal factor of safety values span what range?

Back 43

1.2 to 4

Front 44

What are the 3 factors that should be considered in designing laboratory tests to assess the mechanical characteristics of materials?

Back 44

1. applied load
2. load duration
3. environmental conditions

Front 45

Regarding hardness, for some metals, a plot of hardness versus what is linear?

Back 45

Tensile strength!

Front 46

What are the hardest known materials?

Back 46

Ceramics

Front 47

Why is the hardness of ceramic materials difficult to measure?

Back 47

Because of their brittleness and susceptibility to cracking when indented!