Special Section on Advances in Ballistic Impact and Crashworthiness Response of Aerospace Structures

Understanding the response of aerospace structures under ballistic impact and crash conditions is becoming increasingly important in the design and analysis of aerospace structures. Specific applications where understanding the impact response of the structure is important include fan containment systems for aircraft engines, crash dynamics of rotorcraft structures, and landing systems for the new Orion manned space capsule. To further explore the state-of-the-art technologies in this subject area, a symposium on Advances in Ballistic Impact and Crashworthiness Response of Aerospace Structures was organized as part of the ASCE 2012 Earth and Space Conference, which was held on April 16–18, 2012, in Pasadena, California. In this special section, papers based on a selection of the presentations given in the symposium are presented. Specifically, papers related to impact testing and analysis of aerospace structures, impact analysis of textile materials, and the analysis of the mechanical and impact response of braided composites are presented.

In “Simulating the Response of a Composite Honeycomb Energy Absorber. I: Dynamic Crushing of Components and Multiterrain Impacts,” Jackson et al. describe an externally deployable composite honeycomb that is designed to absorb energy during the crash of a rotorcraft structure. The characterization and use of a composite impact damage model available within the commercial transient dynamic finite-element code LS-DYNA to simulate the impact response of the energy absorber is described. To validate the material model, small-scale crush tests of the composite honeycomb structure were conducted experimentally and simulated analytically. Large-scale tests and simulations of the crash response of full rotorcraft structures outfitted with the composite honeycomb system onto a variety of impact surfaces were also conducted.

In “Simulating the Response of a Composite Honeycomb Energy Absorber. II: Full-Scale Impact Testing,” Fasanella et al. describe, in a more detailed discussion, the large-scale tests and simulations of the composite honeycomb energy absorber structure described in the previous paper. In addition, further discussions of the adjustment of the parameters in the material model used to simulate the crash response of the composite based on the results of the large-scale crash tests are presented.

In “Sand Impact Tests of a Half-Scale Crew Module Test Article,” Vassilakos and Hardy present tests that describe the impact of the proposed Orion manned space capsule onto various types of sand. The goals of this work were to study the impact response of the Orion capsule in the event that a landing on solid ground, as opposed to the designed water landing, would be required. Analytical simulations of the sand impact landings were also conducted using LS-DYNA. To properly carry out the simulations, small-scale experiments and analytical methods needed to be used to determine the correct material properties for the sand. In addition, studies were conducted to determine the best methods of simulating the boundary conditions present in the test.

In “Ballistic Impact Testing of Aluminum 2024 and Titanium 6Al-4V for Material Model Development,” Pereira et al. present a set of ballistic tests on aluminum and titanium flat panel specimens. The goal of the experimental program was to develop a set of high-quality impact data suitable for use in impact simulations conducted using these materials. The ballistic limit and residual projectile velocity after impact were determined for each of the specimens. Cylindrical projectiles were used for the smaller specimens, whereas projectiles meant to simulate the features of an actual engine fan blade were used for the larger specimens. The effects of parameters such as friction and projectile hardness on the impact response of the panels were also determined.

In “Macromechanical Approach to Modeling Barely Visible Damage in Braided Composites,” Blinzler and Binienda describe a computationally efficient methodology developed to analyze the architecturally dependent impact damage in braided polymer composites. The braided composite is simulated as a series of parallel laminated composites. In the presented paper, the application of the method to model barely visible damage under impact conditions is presented. Specifically, the application of cohesive elements between layers of the braid to simulate the damage before penetration in the braided composites is presented.

In “Analytical Model and Numerical Analysis of the Elastic Behavior of Triaxial Braided Composites,” Zhang et al. describe the development of a detailed mesomechanical finite-element model of a triaxially braided polymer matrix composite. The procedures used to determine the detailed geometry of the finite-element model based on detailed examination and measurements of micrographs of the actual composites are presented. Methods to determine the effective elastic properties of the impregnated fiber tows, including the effects of fiber undulation, are described. The effective elastic properties of the braided composite are presented. The effects of factors such as edge effects and fiber tow undulation on the overall elastic response of the braided composites are discussed.

In “Enhancements to Modeling Dry Fabrics for Impact Analysis,” Deivanayagam et al. present methods to model aircraft engine fan containment systems composed of dry Kevlar fabric. A constitutive model is described, and the coupon level tests required to characterize the constitutive model are discussed. Furthermore, the simulation of large-scale ballistic impact tests of structures composed of the Kevlar fabric are presented, and comparisons between the experimental results and the analytical simulations are presented.