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Pressure dependent behaviour

I have come across a material which has a higher failure stress in compression than in tension. The elastic limit is the same in tension as well as in compression.Both the tensile and compression tests (experimental tests I mean)  have been carried out at the same strain rate –please correct me if I’m wrong, I presume such a behaviour is termed as "pressure" dependent behaviour.

I'm not sure why this is termed as "pressure" dependent.I have 2 questions:

 

1) Can anyone please explain what is this ebhaviour termed as-if it is "pressure" dependent- what is exactly "pressure" dependency? I do not follow.

2) Can anyone please explain sucha  behaviour and advise what material model (in ANSYS, LS DYNA,etc.) is available that would capture such an efefct?

 

With regards,

Kajal

 

Pressure dependent materials are those which their yield criteria contains the effect of the mean hydrostatic stress, like the first stress invariant. For example the Von-Mises yield criteria is suitable only for pressure-independent materials like steel, because in its formulation we don’t see the effect of the hydrostatic stress : F = √(J2) - K=0  . For this reason the shape of this model in the σ1- σ2-σ3 space is a cylinder.  But pressure-dependent materials are those which show different behaviors under different mean hydrostatic pressures. For example soil’s stress-strain curve is different for different confining pressures. For this reason we have to choose a model which includes the effect of the hydrostatic stress. For example the Drucker-Prager model which has a cone like shape in the  σ1- σ23 space includes this effect : F = αI1+√(J2 ) - K=0 . 

For more information refer to “plasticity for structural engineers” by professor W.F Chen. 

 

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