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This paper details a numerical modeling and experimental test program focused on high energy ballistic impacts on composite rib-stiffened structures. The numerical model used in this paper is designated as the Multiconstituent Composite Model (MCM), which is implemented within the CTH shock physics code for simulation of ballistic impact damage on composite structures. The presented work utilized a building block approach, where component level flat panels were studied first, followed by sub-structure level T-joint specimens, both fabricated from a carbon/epoxy composite material. All numerical studies and experimental tests utilized the military grade 0.50 caliber M2 Ball round as a projectile. Following testing, each panel was inspected both visually and using Ultrasonic C-Scan techniques to determine the extent of damage sustained upon impact. Finally, comparisons of the experimental data with the numerical predictions are presented and discussed. Both the flat panel and T-joint damage predictions were in good agreement with the experimental data.

Failure of composite materials often results from damage accumulation in the individual constituents (fiber and matrix) of the composite. At times, damage may even be limited to a single constituent. The ability to accurately predict not only ultimate strength values but also intermediate constituent level failures is crucial to the success of introducing composite materials into demanding structural applications. In this paper, we develop two progressive failure models for the analysis of a plain weave composite material. The formulations are based on treating the weave as consisting of separate but linked continua representing the warp fiber bundles, fill fiber bundles, and pure matrix pockets. Retaining constituent identities allows one to access constituent (phase averaged) stress fields that are used in conjunction with both a stress based and damage based failure criterion to construct a nonlinear progressive failure algorithm for the woven fabric composite material. The MCT decomposition and the nonlinear progressive failure algorithm are incorporated within the framework of a traditional finite element analysis. The constituent based progressive failure algorithm combined with both the stress based and damage based failure criteria are compared against experimental data for a plain weave, woven fabric composite under various loading conditions. The analytical results from the damage based approach show a marked improvement over the stress based predictions and are in excellent agreement with the experimental data.

The inability to accurately predict the onset of failure in modern fabric-reinforced composite materials has hindered the implementation of these materials into the mainstream applications. Excessive qualification and structural testing must be performed on composite members as a result of uncertainty in the performance of the material, resulting in significantly higher expenses associated with these materials. This situation can only be improved through the rigorous development of both improved failure and material response prediction capabilities and improved experimental verification. The current study addresses these issues, as well as explores recent developments in numerical predictions and experimental techniques. A combined numerical investigation of damage initiation mechanics and experimental verification of predicted results for a woven glass–vinyl ester composite material is performed. More specifically, 18-oz biased (5 warp/4 fill rovings) plain weave E-glass–vinyl ester laminate with warp rovings oriented in [0/90]s and [0/90/±45]s configurations are investigated. Experimental data for the E-glass–vinyl ester [0/90]s laminate is summarized in a two-dimensional biaxial failure envelope. The feasibility of using thickness-tapered cruciform specimens for generating the experimental biaxial test data is also addressed. Finally, numerical predictions of failure of the fabric-reinforced laminate are developed and compared against the experimental failure envelope for the cross-ply laminate.

An ongoing challenge within the structural analysis community is to accurately predict damage and progressive failure in large-scale structural components composed of composite materials. Multicontinuum technology (MCT) provides a means to produce constituent (fiber and matrix) level stress and strain information within the framework of commercial finite element analysis. Constituent level stress/strain information forms the basis for a progressive failure algorithm that has successfully been used to predict coupon failure in a wide range of composite materials and laminate configurations. In this paper, MCT is used to analyze the failure of rib-stiffened panels associated with advanced composite grid-stiffened structure (AGS) designs. More specifically, MCT is used to predict and analyze the separation of the rib to skin interface for comparison with tee pulloff and tee bend test data. Predictions for the initial and final separation of the rib to skin interfaces are shown to be in good agreement with experimental test data. The results also lend insight into design and manufacturing considerations that are key to the strength and performance of the rib to panel interface.

Marine composite materials typically exhibit significant rate dependent response characteristics when subjected to extreme dynamic loading conditions. In this work, a strain-rate dependent continuum damage model is incorporated with multicontinuum technology (MCT) to predict damage and failure progression for composite material structures. MCT treats the constituents of a woven fabric composite as separate but linked continua, thereby allowing a designer to extract constituent stress/strain information in a structural analysis. The MCT algorithm and material damage model are numerically implemented with the explicit finite element code LS-DYNA3D via a user-defined material model (umat). The effects of the strain-rate hardening model are demonstrated through both simple single element analyses for woven fabric composites and also structural level impact simulations of a composite panel subjected to various impact conditions. Progressive damage at the constituent level is monitored throughout the loading. The results qualitatively illustrate the value of rate dependent material models for marine composite materials under extreme dynamic loading conditions.

The rapidly growing acceptance of Elastic Memory Composite (EMC) materials for deployable space structures illustrates the fact that EMC materials offer substantial performance improvements over existing spaceflight-qualified materials. This growing acceptance has, however, revealed a pressing need for further advancement of models to accurately predict key, non-classical, aspects of the material’s behavior. A critical deformation mechanism dominating the bending response of EMC materials at elevated temperatures is fiber microbuckling occurring within the softened resin. This paper will focus on analysis efforts aimed at predicting the geometric nonlinear response of EMC materials loaded in bending including fiber microbuckling. The analysis is based on a finite strain (Lagrangian) micromechanics analysis of a lamina in bending with an initial fiber waviness. Comparison of analytical predictions to experimental results for structural applications are provided.

This study details and demonstrates a strain-based criterion for the prediction of polymer matrix composite material damage and failure under shock loading conditions. Shock loading conditions are characterized by high-speed impacts or explosive events that result in very high pressures in the materials involved. These material pressures can reach hundreds of kbar and often exceed the material strengths by several orders of magnitude. Researchers have shown that under these high pressures, composites exhibit significant increases in stiffness and strength. In this work we summarize modifications to a previous stress based interactive failure criterion based on the model initially proposed by Hashin, to include strain dependence. The failure criterion is combined with the multi-constituent composite constitutive model (MCM) within a shock physics hydrocode. The constitutive model allows for decomposition of the composite stress and strain fields into the individual phase averaged constituent level stress and strain fields, which are then applied to the failure criterion. Numerical simulations of a metallic sphere impacting carbon/epoxy composite plates at velocities up to 1000 m/s are performed using both the stress and strain based criterion. These simulation results are compared to experimental tests to illustrate the advantages of a strain-based criterion in the shock environment.

The inability to accurately predict the onset of failure in modern fabric reinforced composite materials has hindered the implementation of these materials into mainstream applications. Excessive qualification and structural testing must be performed on composite members as a result of uncertainty in the performance of the material, resulting in significantly higher expenses associated with these materials. This situation will only be improved through the rigorous development of both improved failure and material response prediction capabilities and improved experimental verification. The current study addresses these issues, as well as explores recent developments in numerical predictions and experimental techniques. A combined numerical investigation of damage initiation mechanics and experimental verification of predicted results for a woven glass/vinyl ester composite material was performed. More specifically, 18-oz biased (5 warp/4 fill rovings) plain weave E-glass/vinyl ester laminate with warp rovings oriented in [0/90] s and [0/90/±45]s configurations were investigated. Experimental data for the E-glass/vinyl ester [0/90] s laminate is summarized in a two-dimensional biaxial failure envelope. The feasibility of using thicknesstapered cruciform specimens is also addressed. Numerical predictions of failure of the fabric reinforced laminate are developed and compared against the experimental failure envelope for the cross-ply laminate.