Dear all,
I'm carrying out a Stress analysis for pressure induced by external blast where I can go up to an allowable of 0.8 of tensile strength. Now I have a question of can I make use of the linear stress strain curve or Non linear stress strain curve to perform the analysis. Since the external blast is going o be extremely impulsive should i carry out the linear Stress strain function.
or
Can i make use of the linear stress strain curve to qualify the stresses and make use of Non linear stress strain (True curve) to design the bottom structures.
Any sort of help is of great use for me to proceed further.
Thanks in advance!!
If it is normal plastic behaviour, carry out an elastic calculation and check whether the von Mises stress exceeds the yield stress at any point.
If not, the assumption of elasticity is justified. (Finite element programs do the same thing, actually.)
@ Martin Baeker
Vielen Dank für Ihre schnelle Antwort
Exactly! in FEM we define the non linearity by specifying the tangent modulus beyond yield.
But my doubt is will the material behave (Stress strain relationship) in the same way for sudden impulsive loading ie Blast induced pressure is the source of load ?
Can a Non linear behavior be used to evaluate stresses for sudden loading ?
I think you should look up strain rate sensitivity. I wrote down some papers I've cited which might help. The basic equation is 𝜎=𝑘(d𝜀/dt)^𝑚 where sigma is the flow stress, epsilon dot the strain rate, and m the strain rate sensitivity. Sorry if the eq is ugly.
The flow stress of a material is a function of strain rate. The higher the strain rate, the higher the yield stress. If you do not know the exact relationship of your material, it should be sufficient to know that it will probably yield above it's normal yield point due to the blast. So, you can do what the above review suggested to determine if it is in the elastic range; just know this is now a conservative estimate.
If you want to go further into this, the sensitivity parameter is not simply related to the strain rate or the strain. I believe Picu talks about this.
Y. Chen et al
Stress–strain behaviour of aluminium alloys at a wide range of strain rates
International Journal of Solids and Structures 46 (2009) 3825–3835
R.C. Picu et al
Strain rate sensitivity of the commercial aluminum alloy AA5182-O
Materials Science and Engineering A 390 (2005) 334–343
@Everett M. Criss
Thanks a lot for your quick reply.
You really opened a new dimension for me.
To my understanding you are suggesting to approach the problem in linear material behavior considering it to be conservative?
If yes can i continue the linear relationship till 0.8 of tensile strength or can i be sure that the shift in yielding will not go to that extend
PS : The duration of blast is for 60ms approx
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