[MBDyn-users] Understanding prestrain and prestress in cont laws

Richard Crozier r.crozier at ed.ac.uk
Fri Sep 14 18:03:53 CEST 2018


Hello,

I'm trying to understand something, which I haven't yet found explained 
in the manual. For constitutive laws one can apply a prestrain and 
prestress. Is the following correct?

prestrain: this value will be subtracted from the geometrical strain

prestress: this value will be added to the calculated force

I have taken these guesses at the meaning from the documentation for the 
rod element which is the only place they are discussed.

Just to be clear, if I have two nodes in the exact same location 
(resulting in a geometrical strain of zero), and added a deformable 
displacement joint with a linear elastic isotropic constitutive law 
between them with a prestrain, does this mean there will be an initial 
force pushing them apart with an absolute value of k*prestrain? I'm 
curious what direction the force would take in this case.

Thanks,

Richard

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