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Mechanical Properties Flashcards

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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
what is on the x axis of a stress stain curve?
strain
26
what does tensile stress result in?
elongation
27
what does compressive stress result in?
shortening
28
what is cross-sectional area?
the area of a shape that you get if you make a cut that is perpendicular to an applied force
29
what is engineering strain?
the change in dimension as a result of an applied stress
30
what is change in length also known as?
displacement
31
what is the initial linear region of a stress strain curve called?
the elastic region
32
what type of deformation does the elastic region undergo?
elastic deformation
33
in the elastic region, what will happen when the force is removed?
the material will regain it's original shape
34
what is the end of the linear/elastic region marked by?
the yield point
35
any stress larger than the yield stress will cause what?
permanent deformation
36
what is another name for permanent deformation?
plastic deformation
37
What is the UTS of a material?
the most stress it can handle without fracturing
38
After UTS, why is less stress needed to cause further deformation?
because the cross-sectional area of the material begins to thin in a process called necking.
39
What is Young's modulus?
a value that measures a materials resistance to being deformed elastically.
40
how can Young's modulus be found?
by finding the gradient of the elastic (linear) region of the stress strain curve
41
what does a steeper elastic/linear region mean?
that the material is stiffer
42
what can Youngs modulus be used to predict?
deflection
43
What does Yield Strength or UTS divided by the safety factor give?
max allowable load/stress
44
What is load?
the amount of force applied to an object
45
Engineers aim to keep the max possible stress below what?
the max allowable stress (failure)
46
what does tough mean?
that the material can absorb a lot of energy without breaking
47
what does ductile mean?
that the material deforms under pressure
48
Springs need to:
absorb and release energy without permanently deforming
49
what does brittle mean?
that a material breaks with very little deformation
50
you can tell if a material is brittle or ductile by examining what?
the fracture surface
51
what does the fracture surface of a ductile material look like?
a characteristic cup and cone
52
what does the fracture surface of a brittle material look like?
granular and flat
53
some materials can go from ductile to brittle when:
their temperature is lowered
54
what is hardness?
a measure of how resistant solid matter is to various kinds of permanent shape change when a compressive force is applied
55
what is hardness directly related to?
the stiffness and yield strength of a material
56
young's modulus gives what?
stiffness/elasticity
57
what is the yield stress?
the minimum stress required to cause permanent deformation
58
what is the ultimate tensile stress?
the maximum stress a material can withstand
59
what is a force?
an influence that can change the motion (velocity) of matter (an object)
60
what is a pivot?
a point or axis from which an object is rotated (or provided a force aiming to rotate)
61
what does a lever consist of?
a simple machine consisting of a beam or rigid rrd pivoted at a fixed hinge or fulcrum.
62
what is a lever?
A lever is a rigid body capable of rotating on a point on itself
63
what is the definition of strain?
a dimensionless quantity that depends on the length of the material and how much it is deformed (compressed or stretched)
64
a less massive object can still have a greater moment provided that:
it has a greater distance (leverage)
65
what is stress relaxation?
the observed decrease in stress in response to strain
66
what variables can impact stress relaxation?
magnitude of load, the speed of loading and temperature
67
What is stress relaxation due to?
keeping the structure in strained conditions (hence causing some plastic strain)
68
what is creep?
the tendency of a solid material to move slowly or deform permanently under the influence of persistent mechanical stresses.
69
What can creep be due to?
long-term exposure to high levels of stress that are still below the yield strength of the material
70
What are two similarities of creep and stress relaxation?
both are time dependent both are properties of viscoelastic materials
71
what does annular mean?
ring shaped
72
what is it called when stress + strain change if you repeat the stress many times?
fatigue
73
what factors can affect elastic modulus?
change of length elongation temperature impurities

Materials Science (1 decks)

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