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Materials Science > Mechanical Properties > Flashcards

Mechanical Properties Flashcards

1
Q

what are mechanical properties?

A

properties that involve a reaction to an applied load

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2
Q

what do mechanical properties do?

A

determine the range of usefulness of a material
establish the service life that can be expected from a material

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3
Q

List 6 mechanical properties

A

strength
ductility/malleability
hardness
elasticity
impact resistance
toughness

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4
Q

what is tension?

A

two pulling forces directly opposing each other that stretch out an object and try to pull it apart/elongate it.

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5
Q

what happens to molecules under tensile stress?

A

the molecules pull back, trying to stay together and keep from being ripped away

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6
Q

what is compression?

A

two pushing forces directly opposing each other which squeeze an object, trying to squash/compress it.

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7
Q

what happens to molecules under compressive stress?

A

the molecules push back, trying to stay apart and not get crushed

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8
Q

what is shear?

A

two misaligned pushing or pulling forces that are close together but do not directly oppose each other.

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9
Q

what happens to molecules under shear?

A

the molecules hold onto each other to resist being slid apart

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10
Q

what is bending?

A

when a moment or ‘turning force’ is applied to a structural member, making it deflect (sag or arch) by bending from its original position

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11
Q

what happens to molecules under bending?

A

the top shelf of molecules is in compression; therefore, the molecules get squeezed together, therefore the molecules push back trying to stay apart.
the bottom of the shelf is in tension; therefore, it gets stretched apart, therefore the molecules pull back trying to stay together.

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12
Q

when a beam is bending, what is it said to do?

A

‘smile’

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13
Q

what is a moment?

A

a ‘turning force’ caused by a force acting on an object at some distance from a fixed point

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14
Q

what is torsion?

A

created when a moment (turning force) is applied to a structural member or piece of material, making it deflect by rotating (twist)

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15
Q

what is a moment which causes twisting called?

A

a twisting/torsional moment

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16
Q

what is the moment of a force?

A

a measure of its tendency to cause a body to rotate about a specific point or axis

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17
Q

how can the magnitude of a moment be increased?

A

by increasing the force
by increasing the distance from the pivot point

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18
Q

what do levers use moments as?

A

‘force multipliers’

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19
Q

what are examples of levers?

A

spanner
tap head
door handle
wheelbarrow
claw hammer
shovel

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20
Q

what is a tensile test?

A

a fundamental test in materials mechanics
it is performed by pulling a sample of material apart until failure, while measuring the force and displacement

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21
Q

what are pascals?

A

the metric unit for pressure

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22
Q

what does strain describe?

A

how much deformation has occurred with an applied force

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23
Q

what does engineering stress describe?

A

the amount of force per unit area

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24
Q

what is on the y axis of a stress stain curve?

A

stress

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25
Q

what is on the x axis of a stress stain curve?

A

strain

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26
Q

what does tensile stress result in?

A

elongation

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27
Q

what does compressive stress result in?

A

shortening

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28
Q

what is cross-sectional area?

A

the area of a shape that you get if you make a cut that is perpendicular to an applied force

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29
Q

what is engineering strain?

A

the change in dimension as a result of an applied stress

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30
Q

what is change in length also known as?

A

displacement

31
Q

what is the initial linear region of a stress strain curve called?

A

the elastic region

32
Q

what type of deformation does the elastic region undergo?

A

elastic deformation

33
Q

in the elastic region, what will happen when the force is removed?

A

the material will regain it’s original shape

34
Q

what is the end of the linear/elastic region marked by?

A

the yield point

35
Q

any stress larger than the yield stress will cause what?

A

permanent deformation

36
Q

what is another name for permanent deformation?

A

plastic deformation

37
Q

What is the UTS of a material?

A

the most stress it can handle without fracturing

38
Q

After UTS, why is less stress needed to cause further deformation?

A

because the cross-sectional area of the material begins to thin in a process called necking.

39
Q

What is Young’s modulus?

A

a value that measures a materials resistance to being deformed elastically.

40
Q

how can Young’s modulus be found?

A

by finding the gradient of the elastic (linear) region of the stress strain curve

41
Q

what does a steeper elastic/linear region mean?

A

that the material is stiffer

42
Q

what can Youngs modulus be used to predict?

A

deflection

43
Q

What does Yield Strength or UTS divided by the safety factor give?

A

max allowable load/stress

44
Q

What is load?

A

the amount of force applied to an object

45
Q

Engineers aim to keep the max possible stress below what?

A

the max allowable stress (failure)

46
Q

what does tough mean?

A

that the material can absorb a lot of energy without breaking

47
Q

what does ductile mean?

A

that the material deforms under pressure

48
Q

Springs need to:

A

absorb and release energy without permanently deforming

49
Q

what does brittle mean?

A

that a material breaks with very little deformation

50
Q

you can tell if a material is brittle or ductile by examining what?

A

the fracture surface

51
Q

what does the fracture surface of a ductile material look like?

A

a characteristic cup and cone

52
Q

what does the fracture surface of a brittle material look like?

A

granular and flat

53
Q

some materials can go from ductile to brittle when:

A

their temperature is lowered

54
Q

what is hardness?

A

a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied

55
Q

what is hardness directly related to?

A

the stiffness and yield strength of a material

56
Q

young’s modulus gives what?

A

stiffness/elasticity

57
Q

what is the yield stress?

A

the minimum stress required to cause permanent deformation

58
Q

what is the ultimate tensile stress?

A

the maximum stress a material can withstand

59
Q

what is a force?

A

an influence that can change the motion (velocity) of matter (an object)

60
Q

what is a pivot?

A

a point or axis from which an object is rotated (or provided a force aiming to rotate)

61
Q

what does a lever consist of?

A

a simple machine consisting of a beam or rigid rrd pivoted at a fixed hinge or fulcrum.

62
Q

what is a lever?

A

A lever is a rigid body capable of rotating on a point on itself

63
Q

what is the definition of strain?

A

a dimensionless quantity that depends on the length of the material and how much it is deformed (compressed or stretched)

64
Q

a less massive object can still have a greater moment provided that:

A

it has a greater distance (leverage)

65
Q

what is stress relaxation?

A

the observed decrease in stress in response to strain

66
Q

what variables can impact stress relaxation?

A

magnitude of load, the speed of loading and temperature

67
Q

What is stress relaxation due to?

A

keeping the structure in strained conditions (hence causing some plastic strain)

68
Q

what is creep?

A

the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses.

69
Q

What can creep be due to?

A

long-term exposure to high levels of stress that are still below the yield strength of the material

70
Q

What are two similarities of creep and stress relaxation?

A

both are time dependent
both are properties of viscoelastic materials

71
Q

what does annular mean?

A

ring shaped

72
Q

what is it called when stress + strain change if you repeat the stress many times?

A

fatigue

73
Q

what factors can affect elastic modulus?

A

change of length
elongation
temperature
impurities

Materials Science (1 decks)

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