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A method is developed to predict numerically the damage of composite laminates with more plies under low velocity impact loading. The Puck criterion for 3D stress states is adopted to model the intralaminar damage including matrix cracking and fiber breakage, and to obtain the orientation of the fracture plane due to matrix failure. According to interlaminar delamination mechanism, a new delamination criterion is proposed. The influence of transverse and through-thickness normal stress, interlaminar shear stress and damage conditions of adjacent plies on delamination is considered. In order to quickly and efficiently predict the impact-induced damage of composite laminates with more plies, an approach, which can predict the specific damage of several plies in a single solid element, is proposed by interpolation on the strains of element integration points. Moreover, the proposed model can predict specific failure modes. A good agreement between the predicted delamination shapes and sizes and the experimental results shows correctness of the developed numerical method for predicting low velocity impact damage on composite laminates. [ABSTRACT FROM AUTHOR]

In current design methodologies for composite aircraft structures, design parameters are considered as deterministic variables while their random are ignored. In fact, many parameters affect aircraft structures safety, and some of them have obvious random features which can not be ignored. Therefore a probabilistic design methodology must be developed with the consideration of main random variables. However, probabilistic design methodologies have been gradually developed and used for composite structure design. Six popular probabilistic design methodologies are discussed in details and their benefits and potential problems are summarized. Finally, the issues to be adressed are recognized in the probabilistic design of composite structures, which provides some helpful suggestions for further study. [ABSTRACT FROM AUTHOR]

Abstract: A modified Hertz contact law is proposed for the contact problem of a laminated plate indented by a rigid sphere, which involves the effects of the thickness, in-plane dimensions and boundary conditions of the plate. The model shows that the deflection difference between the center and the edge of the contact area is a key factor dominating the effects of these variables on the force–indentation response. The modified contact law is assumed to follow the same mathematical formulation as the Hertz law. However, the contact stiffness is no longer constant but varies as a function of the contact force due to the thickness effect. The predictions of the force–indentation response show improved agreement over early work by Yang and Sun. Over the present analysis range, the thickness effect may be negligible if the plate thickness is greater than 2mm. On the other hand, the thickness has a more significant effect on the force–indentation response if the plate thickness is less than 2mm. Moreover, the in-plane dimensions and the boundary conditions of the plate show little influence on the force–indentation response within the present scope of analysis. [Copyright &y& Elsevier]

A new cohesive damage model was proposed to analyze the Mode I, Mode II, and mixed-mode bridging micromechanisms of a single Z-pin in the quasi-isotropic laminate. One zero-thickness cohesive element was embedded into each pair of adjacent elements in the damage zone to model the multi-directional Z-pin failure including splitting and rupture, snubbing damage in the resin-rich region, and interfacial debonding during bridging. The FE predicted bridging laws and damage modes of the Z-pin under Mode I, 30° and 60° mixed-mode, Mode II loading all agreed well with the experimental results. Besides, it was found that the splitting damage of the Z-pin and the snubbing damage in the resin-rich region were non-negligible. [ABSTRACT FROM AUTHOR]

This study investigated the effect of the fusion-bonded dots of veil interleaves on the crack propagation path of the interlaminar fracture of continuous carbon fiber reinforced epoxy resin. Two thin fiber layers (i.e., nylon veil (NV) with fusion-bonded dots and Kevlar veil (KV) physically stacked by fibers) were used to toughen composites as interleaves. Result shows that the existence of fusion-bonded dots strongly influenced the crack propagation and changed the interlaminar fracture mechanism. The Mode I fracture path of the nylon veil interleaved composite (NVIC) could propagate in the plane where the dots were located, whereas the path of the Kevlar veil interleaved composite (KVIC) randomly deflected inside the interlayer without the pre-cracking of the dots. The improvement of Mode I toughness was mainly based on fiber bridging and the resulting fiber breakage and pull-out. Fiber breakage was often observed for NVIC, whereas fiber pull-out was the main mechanism for KVIC. For the Mode II fracture path, the fusion-bonded NV dots guided the fracture path largely deflected inside the interlayer, causing the breakage of tough nylon fibers. The fracture path of the physically stacked KVIC occurred at one carbon ply/interlayer interface and only slightly deflected at fiber overlapped regions. Moreover, the fiber pull-out was often observed. [ABSTRACT FROM AUTHOR]