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2015
Conference Paper
Titel
Hypervelocity impact simulation on hard ballistic composites
Abstract
Over the last years an increasing amount of polymer-matrix composites have been used in ballistic armor systems, for example in flak jackets or vehicle protection. This class of materials is characterized by an excellent weight specific stiffness and ballistic performance. Typical armor systems include Aramid fibers (Twaron®, Kevlar®), PP-fibers (Tegris®, Curv®) or ultra-high molecular weight polyethylene (UHMWPE) fibers (Dyneema®, Spectra®). In particular, systems based on UHMWPE fibers have gained a lot of interest due to their extraordinary ballistic performance. Experimental testing at high and hypervelocity impact conditions is a very difficult and financially expensive task. The design process of multi-material armor systems therefore requires predictive numerical models for describing the response of UHMWPE composites under shock loading. In this paper a modeling approach for UHMWPE composites is presented allowing the simulation of ballistic impact onto plat panels. The stress tensor is decomposed into a hydrostatic and a deviatoric stress tensor. For low pressure, the material response is dominated by the deviatoric component of the stress tensor. The deviatoric stress tensor is described by the linear-elastic orthotropic properties as well as potential plastic flow and strain hardening. For high pressure, the stress tensor is dominated by the hydrostatic stress component. The hydrostatic stress component can be described by the shock equation of state. The model is then calibrated for a selected hard ballistic composite (DYNEEMA® HB26) using an available extensive experimental data base allowing accurate description of the linear-elastic, plastic, and shock response for this particular composite material. Hypervelocity impact experiments were performed on DYNEEMA® HB26 panels for impact velocities ranging from 2000 m/s up to 6600 m/s. Impact velocities and residual velocities were measured. The tests were modeled using the commercial FE package ANSYS AUTODYN. The numerical predictions capture the main mechanisms observed during hypervelocity impact testing. Also, the predicted residual velocities behind the target are in good agreement with the experimental evidence.