Lecture 12/13 Flashcards

1
Q

What is Kr?

A

Kelastic/Kelasticplastic

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2
Q

What is Lr

A

Load/Plastic collapse load

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3
Q

What does a steep load line on a Kr-Lr curve show?

A

The structure will undergo brittle failure

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4
Q

What does a shallow load line on a Kr-Lr curve show?

A

The structure will undergo plastic collapse

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5
Q

What does an average gradient load line on a Kr-Lr curve show?

A

The structure will undergo ductile failure

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6
Q

What is wrong with the BS 7910 envelope?

A

Too conservative

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7
Q

Why can generalised curves be problematic?

A

They can be too liberal and therefore parts may fail before they’re predicted to

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8
Q

What does Kr = 1 mean?

A

Kelastic = Kelasticplastic

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9
Q

What is proof stress?

A

An estimation of yield stress, found by drawing a line parallel to the linear stress/strain line from a strain of 0.2%

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10
Q

What is analysis based on initiation?

A

Assessment undertaken for initiation of cracking as defined by initiation fracture toughness

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11
Q

What is initiation-based analysis suitable for?

A

Brittle mechanisms with no tearing

Ductile mechanisms with no benefit taken from the increase in toughness due to tearing (Kmat = K0.2)

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12
Q

What is analysis based on enhanced toughness after a limited amount of ductile tearing?

A

Based on toughness enhanced by a small amount of tearing
Kmat = Kdeltaa
Yes that says delta a

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13
Q

What is analysis based on enhanced toughness after a given amount of ductile tearing?

A

Assessment undertaken by reference to a detailed tearing resistance curve

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14
Q

How is Kmat defined for brittle fracture?

A

Kmat = K

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15
Q

How is Kmat defined for brittle fracture toughness measured from a test?

A

Kmat = KC

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16
Q

How is Kmat defined for initiation toughness for ductile material behaviour

A

Kmat = K0.2

17
Q

How is Kmat defined for enhanced toughness after some amount of tearing?

A

Kmat = Kdeltaa

18
Q

What is the equation for total Kr?

A

Kr = Kr^p + Kr^s

Primary stresses + secondary stresses

19
Q

What is the problem with secondary stresses?

A

They’re mostly estimates, eg for welding, bolting

20
Q

What is F^L and what is it a measurement of?

A

The load factor/safety factor on load

It is a measure of the margin of load available before failure occurs

21
Q

How can F^L be found?

A

OB/OA
O is origin
A is structural assessment point
B is the point where the assessment line meets the curve

22
Q

How does residual stress affect the location of the structural assessment point?

A

It moves upwards (initial Kr is higher)

23
Q

What effect does heat treatment have on secondary stresses?

A

Heat treated: 2ndary approx 10% of yield

Non-heat treated: 2ndary approx 60-100% of yield

24
Q

Where does the structural assessment point move to with an increase in yield stress?

A

Left, directly (closer to axis)

25
Where does the structural assessment point move to with an increase in material fracture toughness?
Down, directly (closer to axis)
26
Where does the structural assessment point move to with an increase in crack length?
Up and right, proportionally to sqrt(a)
27
Where does the cut-off point move with an increase of flow stress?
To the right