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Construction > Mechanical tests > Flashcards

Mechanical tests Flashcards

1
Q

What are some mechanical properties?

A
  1. Strength
  2. Hardness
  3. Ductility
  4. Brittleness
  5. Toughness
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2
Q

What are some mechanical tests?

A
  1. Tensile tests
  2. Compressive
  3. Hardness
  4. Impact
  5. Fatigue
  6. Creep
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3
Q

What is the size effect?

A
  1. Bigger volume in a material
  2. Higher chance of having flaws in material
  3. Lower strength for same cross-sectional area when you have a bigger volume
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4
Q

What is the tensile test?

A
  1. Test that measures the amount of strain acquired depending on the amount of stress applied to a specimen when elongated
  2. A stress-strain graph is plotted from the test
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5
Q

What is Young’s modulus?

A
  1. The slope of the linear region of a stress-strain curve
  2. Acquired by the ratio of stress / strain
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6
Q

What is Hooke’s Law?

A

Uses Young’s modulus * strain = stress

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7
Q

What is elastic behaviour?

A
  1. Behaviour of a material to return to its original size when load is applied and removed
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8
Q

What is the difference between linear elastic behaviour and nonlinear elastic behaviour?

A
  1. Linear follows the same path when load is applied and removed and returns to its original form
  2. Nonlinear does not follow the same path when load is applied and removed but still returns to its original form
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9
Q

How do you increase the strength of a material?

A
  1. Increase stress above yielding stress
  2. Remove stress to 0
  3. Material has strain-hardened and its strength has been increased
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10
Q

How do you obtain yield stress (yield strength) for a nonlinear elastic material?

A
  1. Start from 0.2% offset of strain (0.002)
  2. Draw a line tangent to curve at 0
  3. Find point where your tangent line touches the stress-strain curve
  4. Find your yield strength
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11
Q

What are some examples of linear elastic materials?

A
  1. Steel
  2. Brittle materials (cast iron, concrete)
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12
Q

What are the strengths and weaknesses of brittle materials?

A
  1. They resist poorly to tensile stress
  2. They have high compressive strength
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13
Q

What are the 3 service conditions affecting behaviour of a failure mode?

A
  1. Temperature
  2. Strain rate
  3. Degree of triaxiality
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14
Q

How do the 3 service conditions affect a failure mode?

A
  1. High temperature = more ductile
  2. High strain rate = more brittle
  3. High degree of triaxiality = more brittle
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15
Q

What is necking?

A

Reduction of a cross-sectional area of a ductile material when subjected to tension

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16
Q

What is the failure mode of a ductile material under tension?

A
  1. 45 degrees to the axis of tensile stress
  2. Necking occurs before failure
17
Q

What is the failure mode of brittle materials?

A
  1. Failure due to crack propagation perpendicular to axis of tensile stress
  2. No necking because brittle materials are not ductile
18
Q

What are the 3 tension tests for concrete?

A
  1. Direct tension test
  2. Splitting tension test
  3. Pressure tension test
19
Q

What is the barrel effect in a compression test?

A
  1. Concrete tries to expand perpendicularly to the compressive stress (Poisson effect)
  2. Friction forces between the concrete and the steel plates stops concrete expansion
  3. Concrete is in a barrel shape
20
Q

What is 3-point bending in flexural testing?

A
  1. Bending of a material at 1 point of loading
  2. Maximum stress at that 1 point
21
Q

What is 4-point bending in flexural testing?

A
  1. Bending of a material at 2 points of loading
  2. Maximum stress is in between these 2 points
22
Q

What is the difference between 3-point bending and 4-point bending?

A
  1. Maximum stress of 3-point is higher than maximum stress of 4-point
  2. Only 1 point is under max stress whereas the whole section between the 2 points is under max stress
  3. Higher probability for failure at 1 point which means strength has to be higher
  4. 3-point bending better for steel whereas 4-point bending better for concrete since shear stress is negated in 4-point bending
23
Q

What is hardness?

A

Ability of a material to resist damage at the surface level

24
Q

What is the hardness test?

A

Testing a material’s resistance to an indenter or a cutting tool

25
Q

What are the types of hardness tests?

A
  1. Superficial Rockwell (30kg)
  2. Common Rockwell (150kg)
  3. Brinell (10 mm ball at 3000kg)
  4. Knoop test
  5. Vickers diamond pyramid
  6. Nano-hardness
26
Q

What is an impact test?

A

Testing a materials resistance to an impact

27
Q

What is the impact test called and what does it do?

A

1.Charpy test
2. Indent the material with a v-notch in the middle
3. Use a pendulum at a specific weight and a specific height to hit the material in the middle
4. Material is more ductile when there is a bigger shear plane (black region)

28
Q

What is fatigue?

A

Deformation caused by long term repeated stresses on a material

29
Q

What are the stages of fatigue?

A
  1. Crack initiation
  2. Crack propagation
30
Q

How does a crack initiate?

A
  1. Starts from a flaw in the material
  2. Starts from a discontinuity on the surface (anything that deviates from a flat surface)
31
Q

What is the mechanical test for fatigue and what does it give?

A
  1. Fatigue test : material undergoes repeated cycles of compression and tension
  2. Graphs a stress-cycle graph (S-N diagram) that shows how much stress is loaded depending on how many cycles
32
Q

What is the fatigue limit?

A

1.Maximum amount of stress without permanently damaging a material at a given number of cycles

33
Q

What is creep?

A

Deformation caused by extremely long-term sustained stress on a material

34
Q

What is a creep curve?

A

Graph of the tensile elongation of a material under constant load

35
Q

What conditions affect creep?

A
  1. Higher temperatures = more creep
  2. Higher loads = more creep

Construction (16 decks)

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