JOURNAL OF COMPOSITE MATERIALS Article Damage characterization of composites to support an orthotropic plasticity material model Bilal Khaled 1 , Loukham Shyamsunder 1 , Canio Hoffarth 1 , Subramaniam D Rajan 1 , Robert K Goldberg 2 , Kelly S Carney 3 , Paul DuBois 3 and Gunther Blankenhorn 4 Abstract The focus of this paper is the development of test procedures to characterize the damage-related behavior of a unidir- ectional composite at room temperature and quasi-static loading conditions and use the resulting data in the damage sub-model of a newly developed material model for orthotropic composites. This material model has three distinct sub-models to handle elastic and inelastic deformations, damage, and failure. A unidirectional composite—T800/F3900 that was the focus of our previous work, is used to illustrate how the deformation and damage-related experimental procedures are developed and used. The implementation of the damage sub-model into LS-DYNA is verified using single- element tests and validated using impact tests. Results show that the implementation yields reasonably accurate predictions of impact behavior involving deformation and damage in structural composites. Keywords Orthotropic composite, damage characterization tests, stress–strain curves, impact simulation Introduction Composite materials are increasingly becoming ubiqui- tous in the design of structural systems used in aero- space, automotive, and other industries. These structural systems are often subjected to a variety of environmental and loading conditions. Impact events are among the most critical of loading conditions. Predicting the behavior of the system requires powerful numerical tools. Under impact loads, composite struc- tures experience deformation, damage, and failure at both the micro and macro scales. All three components influence the future response of the composite. Damage typically effects the residual stiffness of the composite. Though damage is an important factor when attempt- ing to predict the response of composites under impact, there is often a lack of available damage-related experi- mental data for a given composite and analysts rely on empirical damage evolution models to predict the response. Damage in fiber-reinforced polymer matrix compos- ites (FRP) is typically a phenomenon observed at the microscale, which manifests itself as a degradation of macroscopic properties. Typically, damage does not result in a complete loss of load carrying capacity in the composite. Rather, it results in a reduction of load- carrying properties as the effective load transfer mech- anisms are altered. Damage can be realized in various ways in composite materials including fiber fracture, matrix cracking, and fiber–matrix debonding. 1 Damage is often quantified as a reduction of apparent elastic stiffness of the material. This phenomenon is especially important when simulating impact events as parts of the structure may undergo loading, unloading, and reloading. Extensive research has been performed 1 School of Sustainable Engineering and the Built Environment, Arizona State University, USA 3 Research Scientist, George Mason University, USA 4 Software Engineer, Livermore Software Technology Corp., USA Corresponding author: Subramaniam D Rajan, School of Sustainable Engineering and the Built Environment, Arizona State University, Tempe, AZ 85287, USA. Email: s.rajan@asu.edu Journal of Composite Materials 0(0) 1–27 ! The Author(s) 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0021998318793506 journals.sagepub.com/home/jcm