# Effective plastic strain

Home » Knowledge Base » General » Effective plastic strain

Effective plastic strain is a monotonically increasing scalar value which is calculated incrementally as a function of  (Dp)ij, the plastic component of the rate of deformation tensor. In tensorial notation, this is expressed as…

epspl=integral over time of (depspl)=integral[sqrt(2/3(Dp)ij*(Dp)ij)]*dt

Effective plastic strain grows whenever the material is actively yielding, i.e., whenever the state of stress is on the yield surface.

In contrast, the tensorial strain values, written by LS-DYNA when STRFLG is set to 1 in *DATABASE_EXTENT_BINARY, are not necessarily monotonically increasing as they reflect the current, total (elastic+plastic) state of deformation. To fringe the tensorial strains in LS-PrePost, click Fcomp > Strain.

Effective strain, expressed in tensorial notation, is sqrt(2/3(eps)ij*(eps)ij); (See p. 461 of LS-DYNA Theory Manual 2006). This is NOT the same thing as effective plastic strain.

Other measures of strain can be fringed in LS-PrePost but these are calculated by LS-PrePost from nodal displacements, e.g.,
FCOMP > Infin ; (infinitesimal or engineering strain)
FCOMP > Green
FCOMP > Almansi

Effective stress, also known as von Mises stress, is defined as follows:

sigvm=1/sqrt(2)*sqrt[(sigx-sigy)^2+(sigy-sigz)^2+(sigz-sigx)^2+6*sigxy^2+6*sigyz^2+6*sigzx^2]