The success of any progressive failure analysis of composite structures is influenced by the failure criteria and the associated material property degradation models. The failure criteria are the conditions for the prediction of the occurrence of material damage. The degradation models are mathematical representations of the residual properties for each material damage state predicted by the failure criteria. A brief summary of the major classes of failure criteria pertaining to the degradation models is followed by a review of degradation models that have been developed for unidirectional polymer matrix composite laminates. The review is organized around the relationships of the various models to associated failure criteria as well as the various constitutive frameworks for finite element implementation. Models that invoke residual properties as a one-time sudden degradation of the original properties are described followed by models where the mathematical representation of at least one property invokes gradual property degradation as a function of some other evolving field variable.

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Composite materials are often utilized in weight-critical applications, owing to their higher specific strength\stiffness characteristics. In addition, composite materials also possess qualities such as better corrosion resistance, lower coefficient of thermal expansion, etc., which makes them a potential material choice for riser systems in high pressure and high temperature environments. However, design certification of risers using the finite element method requires modeling and analysis techniques, centric to the multi-layered nature of composite structures. Riser systems, owing to their high aspect ratios, have traditionally been modeled with beam elements. The methodology for extracting the stress results and certifying a metallic riser is well established in the Oil and Gas industry. However, for analyzing a composite riser, three-dimensional shell or hexahedral elements are generally required to capture the through-the-thickness (or pipe cross-sectional) variation of structural response, especially in critical regions such as touchdown point, pipe-intersection zones, etc. In this paper, a method for analyzing a detailed local model (discretized with shell\hexahedral elements) driven by results from a global model (meshed with beam elements) is presented. The global model captures the structural response whereas the local model provides cross-sectional stress\strain information for individual layers. Although the method is illustrated for a composite riser, it is also applicable to metallic structures.

The layered architecture of composite material allows for designing light-weight structural components. However, one of the challenges associated with composite structures is design and analysis considering impact damage. Although the damage associated with high-velocity impact events is often readily observed in a structure, by loss of material, for example, low-velocity impact damage is not always visible. However, low-velocity impact damage can undermine the strength capacity of a composite component. To ensure the structural integrity of components, predicting the residual strength after impact damage is critical. In this paper, a methodology for analysis of low-velocity impact on a curved composite panel is discussed. First, impact analysis of the panel utilizing Abaqus\Explicit is presented. A metallic projectile is utilized to simulate a tool drop event. Thereafter, a simulation technique for predicting the residual strength of the panel is discussed. The residual strength is measured in terms of collapse load when the panel is subjected to axial compression. Finally, parameter sensitivity analysis is performed to understand the influence of the various design parameters on the residual strength of the component after impact. This procedure requires automating the entire simulation workflow. The results of the simulation are presented along with the important observations.