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Engineering Materials > Mechanical Failure > Flashcards

Mechanical Failure Flashcards

1
Q

Define stress.

A

A loading force applied to a cross sectional area (F/A).

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2
Q

Define strain.

A

A material’s response to stress and is the deformation in the direction of the stress.

(Extension / Length)

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3
Q

Define YM.

A

The measure of the stiffness of a material.
The ratio of stress to strain in a given direction.

Stress / Strain
FL / Ax

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4
Q

Define yield strength.

A

The pressure at which the materials begins to deform permanently or plastically.

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5
Q

Define tensile strength.

A

Maximum pressure a material can take before it fails.

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6
Q

Define ductility.

A

A material’s ability to deform under tensile stress.

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7
Q

Define malleability.

A

A material’s ability to deform under compressive stress.

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8
Q

Define brittle.

A

Materials that experience little deformation when stressed and fail without plastic deformation.

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9
Q

Define hardness / stiffness and give the unit.

A

The ability of a material to resist permanent deformation.

Determined by a standard test where the surface resistance to indentation / penetration is measured.

Pa

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10
Q

How is hardness determined?

A

A standard test where the surface resistance to indentation or penetration is measured.

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11
Q

What does the area under a stress-strain graph represent?

A

Toughness

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12
Q

What does a steep stress-strain line represent?

A

High YM –> Stiff

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13
Q

What does a gentle stress-strain line represent?

A

Low YM –> Elastic

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14
Q

What does the Charpy Test measure?

A

Indicates the energy a material absorbs during fracture.

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15
Q

Describe the Charpy test.

A

Specimen is hit by a swinging arm

Sample is fractured by impact. Impact energy indicates toughness.

Height of swinging arm indicates energy absorbed during fracture.

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16
Q

What does the Vickers’ Hardness Test observe?

A

A material’s ability to resist plastic deformation.

17
Q

Describe the Vickers’ Hardness test.

A

Square based pyramidal indenter makes an indentation in the sample material.

Hardness number = Load / surface area of the indentation

18
Q

How do materials fail?

A

Materials contain inclusions (material trapped inside minerals).

When load is applied onto material, inclusions act as stress concentrations.

Inclusions separate from matrix, causing voids to grow and then fracture.

19
Q

What is the equation for the stress concentration factor?

A

K SC = maximum local stress / nominal load

20
Q

What is fatigue?

A

Material fails due to cyclic loads below the material’s yield strength.

21
Q

What is creep?

A

Slow, continuous deformation of a material at high temperatures, ending in fracture.

22
Q

Describe the two stages of creep.

A

Steady-state: deformation over a long period of time.

Tertiary: Massive increase in strain over a small time before fracture.

23
Q

How does temperature affect mechanical properties of a material?

A

At low temperatures, some materials can experience ductile to brittle transitions.

24
Q

Define wear.

A

The removal of solid from a material due to impact from another material.

25
Q

Define erosion.

A

Removal of solid from a material due to contact with fluid containing hard particles.

26
Q

In industry, what fails due to wear?

A

Pumps and valves

27
Q

In industry, what causes erosion in pipes?

A

Solids in flow
Oil and gas
Waste

28
Q

Name two types of wear.

A

Adhesive
Abrasive

29
Q

Describe adhesive wear.

A

Hard surfaces wear down when surfaces slide.

30
Q

Describe abrasive wear.

A

Hard material wears away soft material when surfaces slide past.

31
Q

What does a low Archard wear rate represent?

A

Less wear for a material.

32
Q

Name five factors erosion depends on.

A

Impingement angle (α)
Particle velocity
Particle size
Particle shape
Hardness of both materials

33
Q

Name two ways a liquid can cause erosion.

A

Impingement
Cavitation

34
Q

Describe impingement.

A

High pressure fluid on surface.

35
Q

Describe cavitation.

A

The bursting of bubbles at the surface of a material, resulting in water jets that removes materials.

36
Q

Where is the tensile strength of a material on a graph?

A

The highest peak

37
Q

Which material properties are most important when considering wear and erosion?

A

Mechanical properties such as hardness and fracture toughness.

Properties of solids in fluids like shape, size, mechanical properties and temperature.

38
Q

Give two examples of wear in chemical engineering.

A

Pulleys
Pumps

39
Q

Give two examples of corrosion in chemical engineering.

A

Sand in oil and gas.
Rocks and minerals in mining.
Stones and rocks in fruit picking.

Engineering Materials (8 decks)

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