Inelastic Transversely Isotropic Constitutive Model for High Performance Polymer Fibers

High performance polymer fibers such as Kevlar, Spectra and Dyneema are widely used in ballistic impact applications. Under transverse compression at finite strains these fibers exhibit nonlinear inelastic behavior. The role of transverse compression during ballistic impact is not very well understood. In this work we implement a transversely isotropic inelastic constitutive model as a user defined material model (UMAT) in LS-DYNA®. A plasticity approach is used to model the material nonlinearity and a pseudo-elastic approach for the large residual strains in the transverse fiber plane. Based on the experimental results, the material nonlinearity and inelasticity are decoupled from the fiber direction. The UMAT predictions for a single Kevlar KM2 fiber under transverse compression are compared to the experimental load deflection under monotonic and cyclic loading.