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High density cellulose-based materials have been widely used for electrical insulation and (interior) construction or structural material. Similar to typical paper/board materials, the microstructure of high-density fibre mats consists of a porous network of cellulose fibres, which contributes to its highly non-linear mechanical response. Such fibre mats exhibit strong anisotropic material behaviour as well as significant transient (time- or rate-dependent) behaviour. The present investigation is aimed at studying the transient behaviour of high-density cellulose fibre mats, particularly during out-of-plane compression. A viscoelastic-viscoplastic constitutive model dedicated for high-density cellulose-based materials has been used to simulate the responses of the high-density cellulose-based fibre mats upon two types of transient loading, i.e. compressive creep and stress relaxation. The predictions of the model are then compared to the corresponding experimental characterization results, which indicate that material densification mechanism plays a more critical role during out-of-plane compression creep than in stress relaxation. [ABSTRACT FROM AUTHOR]

The article develops a simple homogenization scheme for multiphase microstructure. The scheme is based on the classical Taylor averaging scheme. It introduces scalar multipliers as weighting parameters in order to relax the condition of uniform strain distribution used in the classical Taylor scheme.

Because of their widely generalized use in many industries, composites are the subject of many research campaigns. More particularly, the development of both accurate and flexible numerical models able to capture their intrinsically multiscale modes of failure is still a challenge. The standard finite element method typically requires intensive remeshing to adequately capture the geometry of the cracks and high accuracy is thus often sacrificed in favor of scalability, and vice versa. In an effort to preserve both properties, we present here an extended finite element method (XFEM) for large scale composite fracture simulations. In this formulation, the standard FEM formulation is partially enriched by use of shifted Heaviside functions with special attention paid to the scalability of the scheme. This enrichment technique offers several benefits since the interpolation property of the standard shape function still holds at the nodes. Those benefits include (i) no extra boundary condition for the enrichment degree of freedom, and (ii) no need for transition/blending regions; both of which contribute to maintaining the scalability of the code. Two different cohesive zone models (CZM) are then adopted to capture the physics of the crack propagation mechanisms. At the intralaminar level, an extrinsic CZM embedded in the XFEM formulation is used. At the interlaminar level, an intrinsic CZM is adopted for predicting the failure. The overall framework is implemented in ALYA, a mechanics code specifically developed for large scale, massively parallel simulations of coupled multi-physics problems. The implementation of both intrinsic and extrinsic CZM models within the code is such that it conserves the extremely efficient scalability of ALYA while providing accurate physical simulations of computationally expensive phenomena. The strong scalability provided by the proposed implementation is demonstrated. The model is ultimately validated against a full experimental campaign of loading tests and X-ray tomography analyzes. [ABSTRACT FROM AUTHOR]