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Engineering Science > Mechanics Of Deformable Bodies > Flashcards

Mechanics Of Deformable Bodies Flashcards

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1
Q

A force perpendicular to the section is…

A

Axial

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2
Q

A force parallel to the section is…

A

Shear

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3
Q

Moment parallel to the cross section…

A

Bending

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4
Q

Moment perpendicular to the cross section…

A

Torsion

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5
Q

External forces cause…

A

Change in the state of motion of a body

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6
Q

An external force is…

A

A force that develops at the surfaces of contact between bodies

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7
Q

Internal forces cause…

A

Deformation

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8
Q

What is failure (the engineering kind of failure)?

A

When an object no longer functions as intended

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9
Q

Failure is dependent on what 2 things?

A

Applied force and cross sectional area

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10
Q

What is the formula for stress?

A

Stress = force / area

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11
Q

Definition of stress…

A

Force acting per unit area.

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12
Q

A material is continuous if…

A

Uniform distribution of matter; no voids

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13
Q

The material is cohesive if…

A

All portions are connected together; No breaks, cracks or separations

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14
Q

A homogeneous material has…

A

Same physical and mechanical properties all throughout

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15
Q

And isotropic material has…

A

Same properties in all directions

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16
Q

A prismatic object has..

A

Constant cross-sectional area

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17
Q

Average normal stress is… And it is represented by the Greek letter…

A

Average normal stress is when the force is acting perpendicular to the cross section. Represented by sigma ( looks like o ).

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18
Q

If the force is parallel to the object the stress is called… And it is represented by the Greek letter…

A

Average sheer stress… Tau (looks like T)

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19
Q

The unit of stress is called the…

A

Pascal 1 N/m^2

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20
Q

What are the three design considerations?

A

Strength, serviceability, economy

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21
Q

What is strength?

A

The actual load a structure can carry

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22
Q

What is serviceability?

A

Resistance to vibrations, deformations, deflections, cracks. Overall functionality.

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23
Q

What is economy?

A

Most efficient and cost-effective design

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24
Q

What Greek letter represents deformation?

A

Delta (looks like d)

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25
Q

What causes deformation?

A

When forces are applied or temperature is changed

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26
Q

Define strain.

A

Normal strain is the change in length. Shear strain is the angular change between two perpendicular segments.

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27
Q

Normal stresses lead to…

A

Normal strain

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28
Q

Strain is represented by the Greek letter…

A

Epsilon (looks like a reversed 3)

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29
Q

Normal strain is calculated with the formula…

A

Strain = deformation/original length (E=d/L)

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30
Q

Is the object gets longer the normal strain is…

A

Positive

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31
Q

What is shear strain?

A

Angular change between 2 perpendicular segments. A change in shape.

32
Q

What is the formula for shear strain?

A

Gamma= pi/2 - theta

33
Q

A … is used to measure elongation…

A

Extensometer

34
Q

What does a universal testing machine do?

A

Measures stress and strain

35
Q

What are the two types of stress strain diagrams and what’s the difference between them?

A

There’s conventional and true. A conventional diagram uses the original dimensions while a true diagram uses the actual dimensions of the material the moment the load is applied.

36
Q

What are the four ways steel behaves?

A

Elastic behavior, Yielding, Strain hardening, necking

37
Q

What is elastic behavior?

A

When you remove the load it will returns to its original shape

38
Q

The upper stress limit is called…

A

Proportional limit

39
Q

The elastic limit is…

A

The point past the proportional limit where the material could still respond elastically

40
Q

What is yielding?

A

The specimen will continue to deform without load increase.

41
Q

Plastic deformation is…

A

Permanent deformation

42
Q

Stress that causes yielding is called…

A

Yield stress or yield point

43
Q

The maximum stress is called…

A

Ultimate stress or ultimate strength

44
Q

What happens during necking (the engineering kind)?

A

The cross sectional area decreases causing the load carrying capacity of the object to decrease.

45
Q

The specimen breaks at the…

A

Fracture stress

46
Q

Who formalized the concept of stress and strain?

A

Thomas Young

47
Q

Young’s modulus or the modulus of elasticity is given by…

A

Stress / strain ( gives the slope of the elastic region)

48
Q

The modulus of rigidity or the shear modulus is given by…

A

G = shear stress /shear strain (g=T/y)

49
Q

The modulus of resilience is…

A

The amount of energy a material can take before experiencing permanent deformation. In the graph it is the area where stress is proportional to strain.

50
Q

The modulus of toughness is…

A

The amount of energy an object can take before it breaks. It is the entire area of the graph.

51
Q

Poisson’s ratio is…

A

Ratio between lateral strain and longitudinal strain. Represented by V

52
Q

An object is ductile if…

A

Can undergo large deformations before failing.

53
Q

An object is brittle if…

A

It experiences little or no yielding before failing.

54
Q

What are the types of failure?

A

Elastic (excessive elastic def.), Slip (excessive plastic def. due to slip), Creep (excessive plastic def. over a long period of time under constant stress), fracture (complete separation)

55
Q

The engineering equivalent of wiggle room or allowance is called…

A

The factor of safety or ignorance

56
Q

What is the formula for factor of safety?

A

Ultimate stress/working stress

57
Q

Factor of safety is always …

A

> 1

58
Q

What is Torque?

A

A twisting couple

59
Q

Angle of twist is proportional to…

A

Applied torque and length of shaft

60
Q

In a circle, after torque is applied every plane remains…

A

Plane and undistorted because a circle is axisymmetric.

61
Q

What happens when non-axisymmetric shafts are subjected to torsion?

A

The cross sections become distorted.

62
Q

Shear strain is proportional to…

A

Twist and radius

63
Q

Shear strain is proportional to…

A

The distance from the center.

64
Q

Maximum shear strain in circular shafts occurs…

A

At the outermost points

65
Q

What is the polar moment of inertia?

A

Ability of geom to resist twisting

66
Q

What is the formula for angle of twist?

A

Phi = TL / JG where T is torque, L is length of shaft, G is the modulus of rigidity, J is the polar moment of inertia

67
Q

What is the formula for polar moment of inertia?

A

Pi/2 * r^4

68
Q

When subjected to torsion a ductile material breaks along

A

The plane of maximum shear (perpendicular to shaft axis)

69
Q

When subjected to torsion a brittle material breaks at an angle of…

A

45 degrees along the shaft axis

70
Q

What re the principal considerations in designing transmission shafts?

A

Power and speed

71
Q

In designing transmission shafts one should choose materials without exceeding…

A

Maximum angle of twist and maximum torsional shearing stress

72
Q

How do you calculate torque giving speed and power?

A

Power = torque x angular velocity

73
Q

What is a column?

A

Straight structural members subjected to compressive axial loads

74
Q

What are the types of columns and the failure that governs them?

A

Short-crushing, Long-buckling

75
Q

What is buckling?

A

When a structure subjected to compression undergoes visibly large displacements transverse to the load.

76
Q

What is the formula for the critical load for buckling?

A

P = pi^2EI/KL^2 ; E is Young’s modulus,I is the moment of inertia of the weaker axis; K is the effective length factor; L is the length of the column

Engineering Science (3 decks)

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