failure criteria for brittle materials

huangyhg

failure criteria for brittle materials
hi to everybody,
i have to develop a fem structural analysis of a part made of a plastic substance. this substance has a different behaviour between traction and compression (the ultimate traction strength is about 1/3 of the ultimate compression strength). i think that the mohr-coulomb failure criteria is appropriate, but someone has a better idea?
do you mean tension by the wording "traction"??
if so:
brittle materials exhibit little yielding and fracture close to when the elastic behaviour ceases. if as your material exhibits, agreatly higher compressive allowable against tension, then when loaded in pure tension it will fail in tension, but when loaded in pure compression it will fail in shear.
coulomb-mohr theory is based on either considering friction along slip planes, or observing the largest of mohr's circles in 3 dimensions.
depending upon your loading, then you could consider other options.
tension loading will give similar results for using max principal, whilst compression loading will give similar results for tresca.
personally , i would check my part using max and min-principal for brittle materials; and von-mises and min-principle for ductile materials.
yes i mean tension strength, thks!