Material strength and fracture

Von Mises strength

A Von Mises material yields when the second invariant of deviatoric stress \(J_{2}\) reaches a critical value (input parameter ys=yield stress=\(\sigma_{vm}\)). Under uniaxial stress, the material yields when the principal stress exceeds the yield stress, \(\sigma_1 > \sigma_{vm}\). Planar shock waves are uniaxial strain, and the Hugoniot Elastic Limit \(\sigma_{HEL} = (1-\nu) \sigma_{vm} / (1-2\nu)\).

Von Mises strength requires two material parameters: the shear modulus (gmod) and the yield stress (ys).

Example configuration file entry (mks):

mat1:
    str:
        type   : 'VM'
        gmod   : 47.7E9
        ys     : 0.12E9

Steinberg-Guinan strength model

A very beta version of the Steinberg-Guinan strength model is in v0.6.1x-dev based on Wilkins book. It needs to be debugged. See Test15 notebook.

Example configuration file entry (mks):

mat1:
    str:
        name   : 'Al-Wilkins-SG'
        type   : 'SG'
        Y0     : 0.29E9
        Ymax   : 0.68E9
        beta   : 125.0
        n      : 0.1
        b      : 8.0
        h      : 6.2E-4
        Tm0    : 1220.0
        mu0    : 27.6E9

Hydrodynamic material

A hydrodynamic material (shear modulus \(G=0\)) is indicated with this configuration file entry:

mat1:
    str:
        type   : 'HYDRO'

Fracture and void space

Dynamic fracture is implemented as an optional feature. Fracture needs development to be more stable or ignored under extreme conditions.

Fracture requires an EOS with a tension region.

The fracture algorithm is not used if the frac input block is not included. Comment out or remove to prevent facture.

Input parameters: pfrac is the fracture stress. nrhomin is the maximum distension (rhomin/rhoref). The default value for nrhomin is 0.8.

Example configuration file entry (mks):

mat1:
    frac:
        pfrac   : 1.0E9
        nrhomin : 0.8

The code has the ability to close void spaces when surfaces come into contact. The current implementation of void closure uses a simplified calculation compared to Wilkins book for the time step for contact. The full convergence loop for contact time should be implemented in the future.