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A high fidelity assessment of accumulative damage of woven fabric composite structures subjected to aggressive loadings is strongly reliant on the accurate characterization of the inherent multi-scale microstructures and the underlying deformation phenomena. Damage in composite sandwich and joint structures is characterized by the coexistence of discrete (delamination) and continuum damage (matrix cracking and intralaminar damage). A purely fracture mechanics-based or a purely continuum damage mechanics-based tool alone cannot effectively characterize the interaction between the discrete and continuum damage and their compounding effect that leads to the final rupture. In this paper, a hybrid discrete and continuum damage model is developed and numerically implemented within the LS-DYNA environment via a user-defined material model. The continuum damage progression and its associated stiffness degradation are predicted based on the constituent stress/strain and their associated failure criteria while the discrete delamination damage is captured via a cohesive interface model. A multi-scale computational framework is established to bridge the response and failure predictions at constituent, ply, and laminated composite level. The calculated constituent stress and strain are used in a mechanism-driven failure criterion to predict the failure mode, failure sequence, and the synergistic interaction that leads to global stiffness degradation and the final rupture. The use of the cohesive interface model can capture the complicated delamination zone without posing the self-similar crack growth condition. The unified depiction of the continuum and discrete damage via the damage mechanics theory provides a rational way to study the coupling effects between the in-plane and the out-of-plane failure modes. The applicability and accuracy of the damage models used in the hybrid dynamic failure prediction tool are demonstrated via its application to a circular plate and a composite hat stiffener subjected to shock and low velocity impact loading. The synergistic interaction between the continuum and discrete damage is explored via its application to a sandwich beam subjected to a low velocity impact. [ABSTRACT FROM AUTHOR]

The intent of this paper is to investigate the mechanics of delamination growth in an isotropic, ideally-brittle layered material under an impact load and to present guidelines for the design of more energy absorbent structures. Using a finite element model, both two- and three-layered configurations are considered. Prompted by the results from this model, closed-form solutions for the interlaminar shear strength and the interfacial fracture toughness corresponding to maximum energy absorption are derived for the two-layered laminate. These solutions were used to develop guidelines for the optimal design of two- and three-layered laminates. [ABSTRACT FROM AUTHOR]

A simplified method for determining the individual mode components of the strain energy release rate of free-edge delaminations in composite laminates is proposed. Interlaminar stresses are evaluated as an interface moment and interface shear forces obtained from equilibrium equations of stress resultants at the interface between the adjacent layers. The deformation of edge-delaminated laminate is calculated by using a generalized quasi-three dimensional classical laminated plate theory developed by the authors. The analysis provides closed-form expressions for the Mode-I, Mode-II and Mode-III component of the strain energy release rate by combining the deformation of the edge-delaminated laminate with the interface moment and the interface shear forces. The presented method is compared with existing method suggested by Li for the asymmetry laminate. Comparison of the results with a finite element analysis using the virtual crack closure technique shows good agreement. [ABSTRACT FROM AUTHOR]