Mechanics of Materials 99 (2016) 37–52 Contents lists available at ScienceDirect Mechanics of Materials journal homepage: www.elsevier.com/locate/mechmat Research paper Micromechanical modeling and characterization of damage evolution in glass fiber epoxy matrix composites Zhiye Li a , Somnath Ghosh b,∗ , Nebiyou Getinet c , Daniel J. O’Brien c a Department of Civil Engineering, Johns Hopkins University, Baltimore, MD 21218, United States b Department of Civil, Mechanical and Materials Science & Engineering, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, United States c Composite and Hybrid Materials Branch, U.S. Army Research Laboratory, Aberdeen, MD 21001, United States a r t i c l e i n f o Article history: Received 6 March 2016 Revised 8 May 2016 Available online 20 May 2016 Keywords: Glass fiber Epoxy matrix Non-local continuum damage mechanics Strain-rate dependent Cohesive zone models RVE a b s t r a c t This paper develops an experimentally calibrated and validated 3D finite element model for simulating strain-rate dependent deformation and damage behavior in representative volume elements of S-glass fiber reinforced epoxy-matrix composites. The fiber and matrix phases in the model are assumed to be elastic with their interfaces represented by potential-based and non-potential, rate-dependent cohesive zone models. Damage, leading to failure, in the fiber and matrix phases is modeled by a rate-dependent non-local scalar CDM model. The interface and damage models are calibrated using experimental results available in the literature, as well as from those conducted in this work. A limited number of tests are conducted with a cruciform specimen that is fabricated to characterize interfacial damage behavior. Val- idation studies are subsequently conducted by comparing results of FEM simulations with cruciform and from micro-droplet experiments. Sensitivity analyses are conducted to investigate the effect of mesh, ma- terial parameters and strain rate on the evolution of damage. Furthermore, their effect on partitions of the overall energy are also explored. Finally the paper examines the effect of microstructural morphology on the evolution of damage and its path. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction The utilization of glass-fiber epoxy-matrix based composites in a variety military and commercial applications, e.g. rotor-craft yokes and prop-rotor blades, is substantial. Noteworthy among these are the S-glass fiber reinforced composites, containing mag- nesium alumino-silicate or borosilicate fibers, that are known for their high stiffness and strength to weight ratio, impact resistance, and durability under extreme temperature or corrosive environ- ments. Design of these materials for various structural applications, subject to dynamic loading conditions require considerations of a complex mix of properties contributing to weight, performance and reliability. Robust modeling, accounting for microstructural de- tails, as well as material and interfacial properties, is an indispens- able ingredient of the material design process. These models are crucial in unraveling the underpinnings of microstructure-property relationships. The mechanical and damage response of fiber-reinforced poly- meric composites depend on the microstructural morphology, as ∗ Corresponding author. Fax: +1 410 516 7473. E-mail address: sghosh20@jhu.edu (S. Ghosh). well the material and interfacial properties. Damage mechanisms are particularly sensitive to the local morphology, e.g. spatial dis- tribution, size and interfacial strength. For dynamic conditions, strain-rate dependent material properties govern both the mechan- ical and damage behavior. While rate-dependent material prop- erties have been extensively investigated for metals over a wide range of strain-rates, there is a paucity of information on experi- mentally observed strain-rate effects on mechanical and failure be- havior of reinforced composites. For glass-fiber epoxy matrix com- posites, studies at a range of strain-rates have been conducted (e,g, in Davies and Magee, 1975; Lifshitz, 1976; Okoli and Smith, 2000; Staab and Gilat, 1995; Shokrieh and Omidi, 2009). Some of these studies demonstrated that while the elastic stiffness and failure strain are less sensitive to the strain rate, the dynamic failure stress could be 20 − 30% higher than the static failure stress. Also, larger damaged regions have been observed with increasing strain-rates. A variety of micro-mechanical computational models, using e.g., the finite element method, have been developed to predict de- formation and failure in composite micro-structures. A number of these models define representative volume elements (RVEs) or sta- tistically equivalent RVEs (SERVEs) of the microstructure as com- putationally tractable reductions of the actual microstructure. A majority of damage studies in composite materials use unit cell http://dx.doi.org/10.1016/j.mechmat.2016.05.006 0167-6636/© 2016 Elsevier Ltd. All rights reserved.