Lecture 12/13

Question 1

What is Kr?

Answer 1

Kelastic/Kelasticplastic

Question 2

What is Lr

Answer 2

Load/Plastic collapse load

Question 3

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

Answer 3

The structure will undergo brittle failure

Question 4

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

Answer 4

The structure will undergo plastic collapse

Question 5

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

Answer 5

The structure will undergo ductile failure

Question 6

What is wrong with the BS 7910 envelope?

Answer 6

Too conservative

Question 7

Why can generalised curves be problematic?

Answer 7

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

Question 8

What does Kr = 1 mean?

Answer 8

Kelastic = Kelasticplastic

Question 9

What is proof stress?

Answer 9

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

Question 10

What is analysis based on initiation?

Answer 10

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

Question 11

What is initiation-based analysis suitable for?

Answer 11

Brittle mechanisms with no tearing

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

Assessment undertaken by reference to a detailed tearing resistance curve

Question 14

How is Kmat defined for brittle fracture?

Answer 14

Kmat = K

Question 15

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

Answer 15

Kmat = KC

Question 16

How is Kmat defined for initiation toughness for ductile material behaviour

Answer 16

Kmat = K0.2

Question 17

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

Answer 17

Kmat = Kdeltaa

Question 18

What is the equation for total Kr?

Answer 18

Kr = Kr^p + Kr^s

Primary stresses + secondary stresses

Question 19

What is the problem with secondary stresses?

Answer 19

They’re mostly estimates, eg for welding, bolting

Question 20

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

Answer 20

The load factor/safety factor on load

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

Question 21

How can F^L be found?

Answer 21

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

Question 22

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

Answer 22

It moves upwards (initial Kr is higher)

Question 23

What effect does heat treatment have on secondary stresses?

Answer 23

Heat treated: 2ndary approx 10% of yield

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

Question 24

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

Answer 24

Left, directly (closer to axis)

Question 25

Where does the structural assessment point move to with an increase in material fracture toughness?

Answer 25

Down, directly (closer to axis)

Question 26

Where does the structural assessment point move to with an increase in crack length?

Answer 26

Up and right, proportionally to sqrt(a)

Question 27

Where does the cut-off point move with an increase of flow stress?

Answer 27

To the right