Lecture 12/13 Flashcards
What is Kr?
Kelastic/Kelasticplastic
What is Lr
Load/Plastic collapse load
What does a steep load line on a Kr-Lr curve show?
The structure will undergo brittle failure
What does a shallow load line on a Kr-Lr curve show?
The structure will undergo plastic collapse
What does an average gradient load line on a Kr-Lr curve show?
The structure will undergo ductile failure
What is wrong with the BS 7910 envelope?
Too conservative
Why can generalised curves be problematic?
They can be too liberal and therefore parts may fail before they’re predicted to
What does Kr = 1 mean?
Kelastic = Kelasticplastic
What is proof stress?
An estimation of yield stress, found by drawing a line parallel to the linear stress/strain line from a strain of 0.2%
What is analysis based on initiation?
Assessment undertaken for initiation of cracking as defined by initiation fracture toughness
What is initiation-based analysis suitable for?
Brittle mechanisms with no tearing
Ductile mechanisms with no benefit taken from the increase in toughness due to tearing (Kmat = K0.2)
What is analysis based on enhanced toughness after a limited amount of ductile tearing?
Based on toughness enhanced by a small amount of tearing
Kmat = Kdeltaa
Yes that says delta a
What is analysis based on enhanced toughness after a given amount of ductile tearing?
Assessment undertaken by reference to a detailed tearing resistance curve
How is Kmat defined for brittle fracture?
Kmat = K
How is Kmat defined for brittle fracture toughness measured from a test?
Kmat = KC
How is Kmat defined for initiation toughness for ductile material behaviour
Kmat = K0.2
How is Kmat defined for enhanced toughness after some amount of tearing?
Kmat = Kdeltaa
What is the equation for total Kr?
Kr = Kr^p + Kr^s
Primary stresses + secondary stresses
What is the problem with secondary stresses?
They’re mostly estimates, eg for welding, bolting
What is F^L and what is it a measurement of?
The load factor/safety factor on load
It is a measure of the margin of load available before failure occurs
How can F^L be found?
OB/OA
O is origin
A is structural assessment point
B is the point where the assessment line meets the curve
How does residual stress affect the location of the structural assessment point?
It moves upwards (initial Kr is higher)
What effect does heat treatment have on secondary stresses?
Heat treated: 2ndary approx 10% of yield
Non-heat treated: 2ndary approx 60-100% of yield
Where does the structural assessment point move to with an increase in yield stress?
Left, directly (closer to axis)
Where does the structural assessment point move to with an increase in material fracture toughness?
Down, directly (closer to axis)
Where does the structural assessment point move to with an increase in crack length?
Up and right, proportionally to sqrt(a)
Where does the cut-off point move with an increase of flow stress?
To the right
