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Materials Equations > Fracture Questions > Flashcards

Fracture Questions Flashcards

1
Q

What is the stress concentration at the elliptical crack ?

A
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2
Q

What is the stress concentration at a blunt crack ?

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3
Q

What does Griffiths energy releases rate state?

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4
Q

What does the strain energy release rate, G equal?

A
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5
Q

What is Gc?

A
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6
Q

What is the fracture toughness, Kc? How is it relate me to the critical energy release rate?

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7
Q

What is the stress intensity factor, K?

A
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8
Q

What value does the stress intensity factor equal for failure to occur?

A
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9
Q

What is the size of the plastic zone around the crack, ry?

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10
Q

At what stress will fracture occur?

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11
Q

At what stress will plastic failure occur?

A
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12
Q

How can we combine the 2 equations for failure stress to obtain ac, the transition flow size?

A
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13
Q

If a < ac, what is the failure governed by?

A
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14
Q

If a > ac, what is the failure governed by?

A
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15
Q

If a > ac, what is the failure governed by?

A
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16
Q

If a > ac, what is the failure governed by?

A
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17
Q

Why is the fracture an unfavourable mechanism?

A

It can be catastrophic

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18
Q

Why does fracture failing occur?

A

Due to pre existing cracks

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19
Q

What is the fracture strength of most brittle materials in terms of E?

A

E/15

20
Q

What is fracture?

A

The splitting of a body into 2 or more pieces under stress

21
Q

What is brittle fracture?

A

When there is little plastic deformation before it / little energy absorption

22
Q

What materials undergo brittle fracture?

A

Glass, ceramics

23
Q

What is ductile fracture?

A

When extensive plastic deformation occurd before fracture, meaning a lot of energy is absorbed

24
Q

What are the 4 main factors for fracture?

A

Stress concentration, speed of loading, temperature, thermal shock

25
Q

If we load a stress containing a hole, what happens?

A

Stress conentrates around the hole, = 3 x stress

26
Q

For a fracture which is infinitely small, what theory do we use?

A

Griffith’s release energy rate

27
Q

What is Gc?

A

The fracture energy / critical strain energy release

28
Q

What is toughness?

A

The energy absorbed per unit area of crack

29
Q

What does Griffith’s theory state?

A

That failure occurs if G > Gc

30
Q

When will a fracture propagate?

A

If the bonds between the atoms break

31
Q

What is G ? equation also

A

G is the strain energy release rate = stress^2 / E x pi x area

32
Q

What is Kc?

A

The stress intensity factor = root (Gc x E)`

33
Q

When does fracture occur in terms of stress intensity factor#?

A

If the stress intensity factor > fracture tougness

34
Q

What will materials with higher fracture toughness values (Kc and Gc) do?

A

Reisist fracture more

35
Q

What does the size of the plastic zone determine?

A

Whether we will have ductile tearing or cleavage

36
Q

What does a ductile crack do?

A

Absorbs a lot of energy. meaning that there is a large plastic zone

37
Q

What do ductile metals have?

A

Localised plastic deformation ahead of advancing crack, around impurtities, cavities form from crack growth, and as crack advances, these cavities line up

38
Q

Why do metals undergo ductile fracture?

A

High fracture strength, meaning they have small inclusions. Under stress, these inclusions cause gaps until they merge, causing the crack to propagate slowly

39
Q

What happens to fibre-reinforced composites under stress?

A

Fibres are embedded, work is done to debond the fibre from the matrix at the interface

40
Q

What is cleavage?

A

Brittle fracture

41
Q

When does brittle fracture occur?

A

When bonds between the atoms are broken

42
Q

At low temperatures, why are metals less ductile?

A

Dislocations move less, meaning higher yield strength and the plastic zone reduces

43
Q

In tension, what happens to concrete?

A

Perpendicular cracks grow unstably, resulting in fast fracture at low tensile stress

44
Q

What happens to perpendicular cracks in concrete under compression?

A

Perpendicular cracks close

45
Q

What does the fracture process zone of cocnrete include?

A

Many microcracks, the max stress for fracturing opening is the finite tensile strength

46
Q

What is the Charpy Impact?

A

A high strain rate that is used to measure the amount of energy absorbed during fracture

47
Q
A

Materials Equations (11 decks)

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