Impact Mechanics of Composite Materials for Aerospace Application

Abstract

Next-generation aircraft engines made of lighter and stronger fiber-reinforced polymer composites are envisioned to replace the conventional metal ones. To certify these engines, ballistic impact tests and related computational analyses should be performed to simulate a “blade-out” event in a catastrophic engine failure. To meet this objective, several papers on extensive numerical computational models derived from basic constitutive relations to failure analyses and experimental evaluation of strain-rate-dependent behavior of resin matrix are presented in the first series in this two-series July and October 2008 special issue on Impact Mechanics and High-Energy Absorption Materials. Goldberg and his coworkers conducted a combined experimental and analytical study to evaluate the loading and unloading behavior of polymers. In particular, the effects of strain rate and hydrostatic stress on the nonlinear regions of the deformation response were characterized. The load and unload tests of polymers under tension, compression, and shear at several strain rates were performed, and a modified constitutive law based on the state variable originally developed for metals was considered to model the nonlinear unloading behavior. A good correlation between the experimental results and analytical constitutive modeling was observed in their study. Zhu, Chattopadhyay, and Goldberg presented a modified Hashin failure model to characterize different failure modes related to high-velocity impact of composite laminates, and their computational study showed that the model is capable of simulating shear failure, delamination, and tearing failure of composite laminates under high-velocity impact. Zheng and Binienda incorporated the rate dependence of elastic modulus of the polymer matrix constituent in an existing constitutive model originally developed for metal and analyzed the nonlinear, strain-rate-dependent deformation behavior of polymer matrix composites. The state variable-based viscoplastic equations were modified to account for the effects of hydrostatic stresses in the polymer matrix, and they were implemented within a strength-of-materials-based micromechanics method to predict the nonlinear, strain-rate-dependent deformation of the polymer matrix composites. The proposed models were then input in LS-DYNA as user-defined materials UMATs to simulate the deformation behaviors of polymers and polymer matrix composites for a wide range of strain rates. Cheng and Binienda developed a simplified methodology to model 2D triaxially braided composite plates under impact of a soft projectile using an explicit nonlinear finite-element