Implementation of Constitutive Equations for Viscoplasticity with Damage and Thermal Softening into the LS-DYNA Finite Element Code, with Application to Dynamic Fracture of Ring- Stiffened Welded Structures

Constitutive equations for a viscoplastic model with damage and thermal softening are implemented in the Finite Element (FE) code LS-DYNA using a User Defined Subroutine UMAT. A modified Johnson-Cook constitutive model, UMAT 15, which accounts for strain rate viscoplastic effects, is used. The Continuum Damage Mechanics (CDM) is based on Bonora formulation (Bonora, 1997). The combined material model, named UMAT 41, is added to the program static library using Digital Visual Fortran (FORTRAN 90). A brief procedure on how to implement a UMAT is also briefly discussed in this work. Using the User Defined Material, the solution of an explosive charge applied to a ring-stiffened welded structure is analyzed. This type of structure is widely used in ships and aircraft, which are subject to explosive or projectile attack. Results obtained using models with and without damage softening agree very well with previously published data with respect to crack paths. However, the time histories and thresholds are sensitive to the model used.