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A three-dimensional explicit finite element method was presented to investigate the bearing failure of single- and double-shear composite bolted joints. To predict the various failure modes of composite laminates, three-dimensional solid elements accompanied by mixed-mode failure criteria considering nonlinear shear behavior were employed in the model. A linear damage propagation law based on the fracture energy and the characteristic length was adopted to alleviate the mesh dependency. In addition, reduced integration elements were used in the models of single- and double-shear joints to avoid the overstiffness. The simulated models were implemented in the Abaqus/Explicit solver with a user-defined material subroutine. The numerical analysis run successfully without any convergence issues. The predictions of mechanical behavior agreed well with the experimental results, with typical damages in the laminates including matrix crack and fiber failure. The effect of secondary bending in the single-shear bolted joint was also analyzed in the explicit modeling. [ABSTRACT FROM AUTHOR]

Carbon fiber laminated composites are widely used in the aerospace industry due to their excellent lightweight and excellent mechanical properties. However, when subjected to external impact, delamination damage occurs between the layers of composite materials, and thus how to suppress delamination and improve the interlaminar strength of composite laminates has become the focus of the research field. Based on the idea of interlayer toughening, a new double-sided-loop two-dimensional (2D) woven laminated composites (DWLC) is designed, woven and laminated using the RTM molding process. DWLC is based on a 2D fabric with the introduction of loop warp yarns in thickness direction, which form Z-directional loops and thus form a synergistic toughening layer with the resin matrix between the layers after lamination during the forming process. In order to study the mechanical properties of DWLC, the tensile, compressive, interlaminar shear mechanical properties and damage behavior of DWLC are experimentally and numerically investigated. In addition, the internal damage and failure fracture are examined using micro computed tomography (Micro-CT). Strength prediction model of DWLC is established based on a representative volume element (RVE) with a mesoscopic geometric model. Three-dimensional (3D) Hashin and Von-Mises criteria are introduced as the failure criteria for the component materials. The results show that due to the existence of loops, the in-plane fiber volume content of DWLC decreases, resulting in a decrease of tensile and compressive strengths but an increase of interlaminar shear strength. [ABSTRACT FROM AUTHOR]

A transient-dynamics model based on the approximate Riemann algorithm is proposed for the failure analysis of a frangible composite canister cover. The frangible cover, manufactured with a traditional manual lay-up method, is designed to conduct a simulated missile launch test using a specially developed test device. Deformation of the cover’s centre is determined using a transient-dynamics finite element model; failure pressure for the frangible cover is obtained based on a failure criterion and compared with simulated experimental results. Weak-zone position of the frangible cover has a significant effect on failure pressure compared to that of deformation of the cover’s centre. With the same structure of the weak-zone, an increase in its height can first raise and then reduce the level of failure pressure of the frangible cover. Close agreements between the experimental and numerical results are observed. [ABSTRACT FROM AUTHOR]

A progressive damage model is proposed to predict buckling strengths and failure mechanisms for both symmetric and asymmetric patch repaired carbon-fibre reinforced laminates subjected to compression without lateral restrains. Solid and cohesive elements are employed to discretize composite and adhesive layers, respectively. Coupling with three dimensional strain failure criteria, an energy-based crack band model is applied to address the softening behaviour in composites with mesh dependency elimination. Both laminar and laminate scaled failure are addressed. Patch debonding is simulated by the cohesive zone model with a trapezoidal traction–separation law applied for the ductile adhesive. Geometric imperfection is introduced into the nonlinear analysis by the first-order linear buckling configuration. Regarding strengths and failure patterns, the simulation demonstrates an accurate and consistent prediction compared with experimental observations. Though shearing is the main contributor to damage initiation in adhesive, stress analysis shows that lateral deformation subsequently reverses the distribution of normal stresses which stimulates patch debonding at one of the repair sides. The influence of patch dimensions on strengths and failure mechanisms can be explained by stress distributions in adhesive and lateral deformation of repairs. Comparison between symmetric and asymmetric regarding strength and failure modes shows that structural asymmetry can intensify lateral flexibility. This resulted in earlier patch debonding and negative effects on strengths. [ABSTRACT FROM AUTHOR]