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Numerical testing is crucial for the design of composite fuselages, which have strict crashworthiness regulations. However, the majority of studies on numerical fuselage impacts do not account for the effects of strain rate in simulations. A damage model considering strain rate dependence has been implemented to accurately predict the impact behaviour of a composite fuselage structure. This model enhances the existing three-dimensional Hashin criterion by incorporating strain rate effects and its implemented numerically using a VUMAT subroutine in ABAQUS/explicit. Validation of the model is done through a low-velocity impact problem, showing a better correlation with experimental data compared to previous numerical analyses available in the literature. The study focuses on high-energy impact on a composite stanchion in the lower lobe of an aircraft fuselage. Results demonstrate that the newly proposed model effectively predicts failure zones and modes, indicating its potential in addressing dynamic composite problems typical of impact scenarios. [ABSTRACT FROM AUTHOR]

Abstract A constitutive model for an interface finite element is proposed to enable simulation of delamination in composite materials with R-curve effects. The constitutive model is formulated in the framework of cohesive zone modelling (CZM). In essence, a multilinear CZ law with an arbitrary number of line segments is developed. The CZ law seeks to enable constitutive modelling of failure mechanisms on multiple scales within the fracture process zone and reduce conventional a priori assumptions regarding the shape of the CZ law. The CZ law relies on damage mechanics, an equivalent one-dimensional formulation, and criteria for mode interactions to simulate delamination under mixed-mode loading. Special emphasis is put on the derivation of interpolation formulas and a constitutive tangent stiffness tensor for the multilinear formulation. The constitutive model is implemented in the commercial FE program ANSYS Mechanical, for implicit finite element analysis (FEA), using user-programmable features. The implementation is verified through single interface element numerical studies, and its applicability is demonstrated by simulating an experiment of quasi-static delamination showing large-scale fiber bridging in pure mode I DCB glass-fiber epoxy specimens. Experimental measurements and simulation outputs using the novel cohesive element is compared to those of the conventional bi- and trilinear CZ laws. [ABSTRACT FROM AUTHOR]

The paper aims to present a novel mathematical formulation for the modelling of damage. In particular, the decay of the mechanical properties of the elastic media is modeled by means of two-dimensional smooth functions, which are the Gaussian and the ellipse shaped ones. Various damaged configurations are obtained as concentrated variations of the elastic properties of the materials by setting properly the parameters that define the distributions at issue. This approach is employed to investigate the dynamic behavior of damaged plates and shells made of composite materials. In particular, a massive set of parametric studies is presented for this purpose. The results are obtained numerically by means of the Generalized Differential Quadrature (GDQ) method and are presented in terms of natural frequencies. Several Higher-order Shear Deformation Theories (HSDTs), which can include also the Murakami’s function to capture the so-called zig-zag effect, are used and compared. [ABSTRACT FROM AUTHOR]

In order to reduce weight and to create efficient construction, fiber reinforced plastics are of general interest. Hence, the understanding of the material behavior is very important to build safe structures. For composite structures, existing of several stacked layers, which behave transversely isotropic, different failure mechanisms may appear. The considerations in this paper deal with the failure analysis of one layer of a laminated structure with unidirectionally orientated fibers. The possible failure mechanisms are described with failure criteria. So-called damage models include these criteria and the behavior of damaged structures, formulated in degradation models. Damage models usually show a strong mesh dependency in their inelastic part, which begins with an initial failure in the structure and ends with the total loss of stiffness. This mesh dependency is characterized by the concentration of the occurring damage only within a small zone, which generally corresponds e.g. with one element row and thus with the mesh refinement. In order to develop a regularized damage model for transversely isotropic materials a gradient enhancement based on the Helmholtz free energy function is used. With the introduction of a new field, coupled with the inelastic variables, the model gets a non-local character, preserving C 0 -interpolation order. Formulated as a pure minimization problem, the elimination of the mesh dependency due to the unambiguity of the solution is illustrated by numerical examples. [ABSTRACT FROM AUTHOR]

This paper presents a detailed numerical analysis of two types of 3D woven composite architecture. a unit cell, full finite element meso model, and a mosaic macro model are developed to simulate the elastic and damage progression behaviour of the two weave types. Both models predicted the tensile modulus and strength within 20% of the experimentally measured values, and the predicted failure sequence was similar to the experimental observation. [ABSTRACT FROM AUTHOR]

Abstract: Failure mechanisms of fibre reinforced composite structures are closely related to processes within the heterogeneous material. In order to include these processes in numerical simulations a micromechanical model needs to be coupled to the finite element solution. This two-scale framework has in the current work been achieved using the reformulated High Fidelity Generalized Method of Cells (HFGMC) micromechanical model and the finite element code Abaqus/Explicit. The two-scale approach enables calculation of the stress field within the unit cell, based on the constitutive behaviour of each subcell and the unit cell morphology. As the stress distribution is determined for the representative unit cells, calculation of failure criteria and constitutive response of the composite are performed at the micro-level. Damage effects are also being modelled on the micromechanical level. Failure initiation has been predicted using three micromechanical failure criteria found in the literature – the 3D Tsai–Hill model, the MultiContinuum Theory model and the 3D Hashin type strain based failure criteria. Degradation of mechanical properties of the composite material has been introduced to the model using the damage model described in the work of Bednarcyk et al. [19]. The damage model relies on the 3D Hashin type strain based failure criteria and shows good agreement with experimental results. [Copyright &y& Elsevier]

Abstract: Understanding the failure behaviour of three-dimensional weaved composites is necessary to allow the design of weave forms appropriate for application, or to predict the failure mode a component will undergo. The different effects at different length-scales call for multi-scale simulation. In this work, a finite-element model is proposed using the asymptotic homogenisation method to distribute macro-scale stresses to the micro-scale, i.e. yarns and matrix, in a repeating unit cell (RUC) model. The stresses in the yarns and matrix are then used in a continuum damage model to determine localised stiffness degradation, and the cell properties are homogenised to determine the macro-scale effect. The model is demonstrated by simulating a through-the-thickness reinforced orthogonally weaved composite, undergoing tensile, compressive and shear loading. The stress–strain response and failure are reproduced and shown to match experimental results. The model reveals the locations of damage initiation, and the progress of damage through the RUC. It is observed that the binder yarns create localised stress concentrations from which the failure process is initiated. It is concluded that the use of such a model can be critical to designing a 3D weave with optimal behaviour. [Copyright &y& Elsevier]

The main challenge for realizing competitive hybrid steel-FRP structures, such as bridges, carparks, is to make the steel and FRP components work together. In this study shear resistance, stiffness and ductility of three types of demountable bolted shear connectors are examined. Two blind-bolted M20 shear connectors and a novel, injected steel-reinforced resin (SRR) connection are selected to perform push-out experiments in web-core FRP decks. Failure modes of excessive bearing in FRP and bolt shear failure for blind-bolted and injected connectors, respectively, are identified. Nonlinear, highly detailed finite element (FE) models were also built and validated by results of the push-out tests to provide insights to the load-transfer mechanism. Analysis of internal forces and deformation through FE results reveals that blind bolted shear connectors provide high shear resistance and slip capacity thanks to the shear sleeves and catenary effects. The injected SRR connector shows distinct and centric load transfer owing to gapless design. [ABSTRACT FROM AUTHOR]