## Chapter 1: Composite Material Modeling Introduction

The Autodyn hydrocode has extensive capabilities for the modeling of composite materials subjected to a range of loading conditions. A simple linear-elastic orthotropic constitutive model, inherent in which is a linear equation of state, suitable for modeling applications subjected to structural (rather than shock) type loading can be used. Or, for applications such as hypervelocity impacts where the shock effects are obviously important, the orthotropic model can be coupled with nonlinear equations of state. Damage/Failure can be treated as brittle via directional failure models like Material Stress and/or Strain Failure (see Brittle Damage Model). It can also be treated by a specific Orthotropic Damage model (see Orthotropic Damage Model), which takes into account the softening behavior that can sometimes be observed when failure occurs in composites.

This document provides a single point of reference for using these models and describes all of the above options. Often the greatest difficulty in using such models is a lack of available material data or not knowing how to properly characterize the material should experimental facilities be available. Therefore this document also provides a description of material characterization experiments that may be performed in order to calculate the required material input parameters.

ANSYS Autodyn is an integrated analysis program designed for nonlinear dynamics problems. There is at times a need to consider the treatment of materials where the properties of materials are not identical in all directions (for example, composite laminates, fiber reinforced materials). Material models suitable for such anisotropic material behavior have been developed in Autodyn. These models have differing levels of complexity and require differing amounts of material data as input.

The purpose of this document is to fully describe the composite material modelling capabilities of Autodyn. Further guidance is offered to help the user select the most appropriate models for a specific application and to obtain the relevant material data.

After describing the definition of the principal directions in Autodyn in Principal Directions in Autodyn, the material models are presented for both the constitutive behavior and for predicting failure/damage in Orthotropic Constitutive Models and Orthotropic Material Failure Models respectively. The most common problems in using such models are the lack of material data and the difficulty in obtaining the measurements. In Material Characterization Tests a series of experimental tests are presented which have been used in projects at ANSYS to successfully characterize various composite materials. Derivation of the model parameters from the experiments is not always straightforward. Derivation of Material Properties outlines the required steps in extracting the parameters from experiment into a form suitable for input into Autodyn.

Example applications are presented in Example Applications and recommendations on how to perform a typical composite analysis are discussed in Recommendations.

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