Chapter 6 Numerical and Experimental Investigation of Density Graded Foams Subjected to Impact Loading Vijendra Gupta, Dennis Miller, and Addis Kidane Abstract Cellular materials offer many advantages due to their higher energy absorption capacity and strength for a given weight. The energy absorption performance is dependent on material density. Different density foams can be tailored and graded in a structure so that the merits of both low density and high density foams can be exploited. In this work, density graded polymeric foams with different configurations are examined, and their response to impact loading is studied both numerically and experimentally. Two-dimensional cell-based finite element model is developed for modeling the dynamic response of foams with different density gradation in Abaqus, a commercial finite element software. Three different types of foam structures are studied. Each of the foam structures is made up of three different density layers. The experimental investigation is also carried out on a gas gun setup incorporating high-speed imaging and is used to verify the numerical results. The stress-strain curves and the energy absorption characteristics of different graded foam structures are evaluated. It is found that the graded foam structure with higher density layer on the impact side absorbs more energy than the uniform foam structure at lower strains. Keywords Graded foam · Impact loading · Energy absorption · Voronoi model · Digital image correlation Introduction Cellular foams are known to have excellent energy absorption ability and find applications wherever the effect of impact loading is desired to be mitigated [1]. The response of the solid foams depends mainly on the density. Lower density foams absorb more energy at lower stress levels, and higher density foams absorb more energy at higher stress levels. A superior energy absorption performance can be obtained if layers of different densities are united together. There have been several numerical and experimental works on analysis of the mechanical response of solid foams. The effect of various microstructure irregularities in two-dimensional (2-D) foams has been studied at the quasi-static loading rate [2]. Wang et al. [3] investigated three-dimensional (3-D) foam subjected to high-velocity dynamic loading using a finite element model. Ajdari et al. [4] examined 2-D graded foam structure subjected to high rate dynamic loading. The quasi-static response of foam made up of discrete layers has been experimentally investigated [5]. In the present work, the response of the graded foam is studied under high impact velocity loading and compared to the foam having uniform density keeping the overall density same. The energy absorption performance of the foams is studied through both numerical models and experimental investigation. The numerical model is developed using cell-based finite element models in Abaqus. The model is generated by random 2-D Voronoi tessellation. 3-D models are closer to the real foams but are complex and computationally time intensive. Even though 2-D models do not capture the porosity of real foams in the third dimension, they are more straightforward and computationally more efficient. Thus, 2-D models were used for studying the dynamic behavior of foams. The foam structure is divided into discrete layers with different densities and its response is analyzed when subjected to dynamic loading. The numerical results are supported by the experimental investigation which is implemented using digital image correlation (DIC) along with high-speed imaging. The deformation of layered rigid polyurethane foam samples is analyzed under high-velocity impact loading. V. Gupta ( ) · D. Miller · A. Kidane Department of Mechanical Engineering, University of South Carolina, Columbia, SC, USA e-mail: vijendra@email.sc.edu © Society for Experimental Mechanics, Inc. 2020 L. E. Lamberson (ed.), Dynamic Behavior of Materials, Volume 1, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-30021-0_6 31
RkJQdWJsaXNoZXIy MTMzNzEzMQ==