Development of a Continuum Damage Mechanics Material Model of a Graphite- Kevlar Hybrid Fabric for Simulating the Impact Response of Energy Absorbing Subfloor Concepts

This paper describes the development of input properties for a continuum damage mechanics based material model, Mat 58, within LS-DYNA® to simulate the response of a graphite-Kevlar® hybrid plain weave fabric. A limited set of material characterization tests were performed on the hybrid graphite-Kevlar® fabric. Simple finite element models were executed in LS-DYNA® to simulate the material characterization tests and to verify the Mat 58 material model. Once verified, the Mat 58 model was used in finite element models of two composite energy absorbers: a conical-shaped design, designated the "conusoid," fabricated of four layers of hybrid graphite-Kevlar® fabric; and, a sinusoidal-shaped foam sandwich design, designated the "sinusoid," fabricated of the same hybrid fabric face sheets with a foam core. Dynamic crush tests were performed on components of the two energy absorbers, which were designed to limit average vertical accelerations to 25- to 40-g, to minimize peak crush loads, and to generate relatively long crush stroke values under dynamic loading conditions. Finite element models of the two energy absorbers utilized the Mat 58 model that had been verified through material characterization testing. Excellent predictions of the dynamic crushing response were obtained.