Dynamic Response of Glass-Fiber Reinforced Polymer Composites Under Shock Wave Loading

Synthetic heterogeneous material systems, for example, layered composite materials with organic matrices reinforced by glass fiber reinforces polymers (GRPs), are attractive for a variety of lightweight structural applications. This chapter deals with the dynamic response of layered heterogeneous material systems, such as the GRPs, under shock wave loading conditions. To understand material and geometric dispersion of stress waves in the GRPs, these are modeled as elastic–elastic and/or elastic–viscoelastic bilaminates. The analysis makes use of the Laplace transform and Floquet theory for Ordinary Differential Equations (ODEs) with periodic coefficients. Both wave front and late-time solutions for step-pulse loading on a layered half-space are analyzed. The results of the analytical study show that the structure of acceleration waves is strongly influenced by impedance mismatch of the layers constituting the laminates, density of interfaces, distance of wave propagation, and the material inelasticity. Next, series of plate impact experiments are conducted on two different architectures of GRP composites – S2-glass woven roving in CYCOM 4102 polyester resin matrix and a balanced 5-harness satin weave E-glass in a Ciba epoxy (LY564) matrix. The experiments are conducted using an 82.5 mm bore single-stage gas-gun at CWRU. In all experiments, the history of the shock-induced free-surface particle velocity profiles at the rear surface of the target plate are monitored using a multibeam VALYNTM VISAR. In the first series of experiments, the structure of the shock waves in the S2-glass GRP is investigated as a function of shock-induced compression and the distance of shock wave propagation. The results of the experiments show the absence of an elastic precursor. The critical shock stress amplitude at which a clear shock front is seen to develop in the GRP was determined to be between 1.5 and 2.0 GPa. Combining the results of the present experiments with data from Dandekar et al. (1998, 2003a), the equation of state (EOS) of the S2-glass GRP was determined in the stress range of 0.04–20 GPa. Besides the EOS, the Hugoniot curve (Hugoniot stress vs Hugoniot strain) was calculated using the Rankine–Hugoniot relationships; the Hugoniot elastic limit (HEL) of the S2-glass GRP was estimated to be about 1.6 GPa. In the second series experiments, the postshock spall strengths of the S2-glass and E-glass GRP composites were investigated by subjecting the specimens to shock compression and combined shock compression and shear loadings. The spall strengths of the two GRP composites were observed to decrease with increasing levels of shock compression. Moreover, superposition of shear–strain on the normal shock compression was found to be highly detrimental to the spall strengths. The E-glass GRP composite was found to have a much higher level of spall strength under both normal-compression and combined compression-and-shear loading conditions in comparison to the S2-glass composite. The maximum spall strength of the E-glass GRP was 119.5 MPa, while the maximum spall strength for the S2-glass GRP was only 53.7 MPa. In the third series of experiments, plate impact shock–reshock and shock release experiments were conducted to study the residual shear strength of the S2-glass GRP under various levels of shock compression (0.8–1.8 GPa). To conduct these experiments, a dual flyer plate assembly was used. Using the self-consistent procedure outlined in Asay and Chhabildas (1981), the critical shear strength following shock-induced compression (in the range 0.8–1.8 GPa) was determined. The results indicate that the critical shear strength of the GRP increases from 0.108 to 0.682 GPa when the shock compression level is increased from 0.8 to 1.8 GPa. This increase in critical shear strength may be attributed to the rate-dependence and/or pressure-dependent yield behavior of the GRP composites.