The Low Velocity Dynamic Energy Absorption of Composite-Lattice Sandwich Structures

Abstract

Recent advances in additive manufacturing have allowed the investigation of the static and dynamic performance of 3-dimensional cellular structures for the application of absorbing mechanical energy. The inclusion of lattice structures in energy absorbers allows lighter weight design that can sustain large elastic deformation. Structures that perform well under static loading may not perform well under dynamic loads due to kinetic energy and wave propagation effects. Thus, the complexity of the design process increases when designing energy absorbing structures through a range of strain rates and impacting inertias. In this study we investigate the dynamic performance of existing and novel lattice structures sandwiched between carbon fiber composites and Kevlar fabrics for the application of lighter weight, better protecting armor and helmets. The results of this novel sandwich design are directly compared to the performance of the material layers used in United States Army’s standard issue Advanced Combat Helmet (ACH). Dynamic low velocity impact experiments are conducted using a drop tower system. The energy absorbed by the sandwich structure is recorded based on the difference in acceleration from the top impacted surface and the base of the structure. A base-level study of the existing lattice structure energy absorption is conducted prior to the testing of composite sandwich structures. The existing structures tested include body center cubic (BCC), face center cubic (FCC), kelvin truss (KT), and diamond cubic (DC). Across all tests the BCC reduced the most acceleration followed by the DC, FCC, and KT lattice. It is observed for all tests that at constant impacting mass and strain a lower relative density allows more deformation of the lattice resulting in a higher acceleration reduction. The lower relative density structures undergo compression for a longer period yielding higher impulse or momentum change. This study provides insights into how the use of cellular materials, carbon fiber composite sheets, and Kevlar fabrics may provide enhanced energy absorption at a lighter weight compared to existing helmet material and structural systems.