Impact Mechanics of Composite Materials for Aerospace Application

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 impactof a soft projectile using an explicit nonlinear finite-element analysis code, LS-DYNA. An arbitrary Lagrangian-Eulerian formulation was used to resolve numerical problems caused by the large deformation of the projectile, and the developed numerical model was capable of simulating the ballistic impact of a triaxially braided composite with a reasonable level of computational efficiency.

Littell and his coworkers conducted an experimental investigation using optical measurement techniques to obtain the stress versus strain curves in tension, compression, and shear for Epon E862 epoxy resin under a wide range of strain rates. The epoxy specimens were tested in tension, compression, and torsional loadings under various strain rates ranging from ${10}^{-5}$ to ${10}^{-1}{\mathrm{s}}^{-1}$ and temperatures ranging from room temperature to $80°\mathrm{C}$ . A commercially available software package, ARAMIS, was used to convert the recorded displacements to full-field strain measurements, and clear strain-rate and temperature dependencies in the material response were observed for the epoxy resins characterized.

Teng and Wierzbicki presented a numerical study of the failure response of an aircraft engine containment panel obliquely impacted by a titanium turbine fragment. Extensive finite-element simulations of the impact test using ABAQUS and LS-DYNA were conducted, and numerical results successfully revealed the formation of an indentation/gouging channel on the proximal surface of the panel and the growth of a crack on the distal surface. Based on the numerical analyses, their study concluded that both the residual thickness and mass loss of the panel are sensitive to the magnitude of the pitch angle of the projectile, and a large difference between ABAQUS and LS-DYNA exists in the calculated energy dissipation.

Xu, Askari, Weckner, and Silling adopted peridynamics to analyze impact damage in composite laminates. In particular, the delamination and matrix damage impact process in composite laminates under low-velocity impact were investigated, and their simulation results compared very well with the available experimental data.

We, on behalf of the Journal of Aerospace Engineering and ASCE, want to acknowledge the following reviewers for their effort and constructive comments that make this double-series special issue, “Impact Mechanics and High-Energy Absorption Materials” (the July and October Issues of 2008) a success.