Virtual Testing Architecture for Prediction of Effective Properties of Particulate Composites

This study has developed a computational virtual testing architecture for predicting effective properties of particulate composites. A particulate composite made up of SiC filler in an alumina matrix was used in this work. The test composite was modelled first by considering perfect bonding between the matrix and filler constituents and subsequently the effect of interphase region was assessed too

A constitutive model for semi-crystalline polymers: A multiple viscoelastic relaxation processes implementation.

The constitutive modelling of semi-crystalline polymers seeks to obtain reliable predictive tools for a wide range of their mechanical responses. Such efforts have continued to occupy computational material scientists. Although significant advances have been made regarding amorphous polymers, thanks to works by Buckley [1], Boyce [2], and Govaert [3], there is significant research scope for developing similar predictive modelling fidelity for semi-crystalline polymers. The presence of crystalline and amorphous phases in semi-crystalline polymers presents interesting constitutive modelling challenges. In this study, a physically based, three-dimensional constitutive model has been developed for simulating a wide range of features observed in deformation and processing of semi-crystalline polymers. The constitutive mathematics is based on a one-process Grass-Rubber model for amorphous polymers proposed by Buckley and colleagues [1]. The model philosophy exploits the presence of multiple relaxation processes associated with the different mechanics of the crystalline, amorphous and pseudo-amorphous parts of the polymer. The model development reasoning is inspired by a well-known physical framework of rate-dependent deformation that establishes a correlation between the observed transition in flow stress of a material and the secondary β-transition of the viscoelastic behaviour. Here, two dominant relaxation processes were identified - the α- and the β-processes. Each process was modelled using the bond-stretching and conformational stresses constitutive mathematics of the Glass-Rubber model. The model has been implemented numerically into a commercial finite element code through a user-defined material subroutine (UMAT) and validated against compression test results carried out on an isotactic polypropylene across an unusually wide range of strain rates [4]. In this study, the model predicts quite well the experimentally observed nonlinear mechanical responses like: temperature and rate-dependence, adiabatic heating effects, structural rejuvenation and post-yield de-ageing of polypropylene. It provides a viable modelling tool that can be utilized for design involving semicrystalline polymers at room temperature as well as exploring the processing response at elevated temperatures

Two-process constitutive model for semicrystalline polymers across a wide range of strain rates

The presence of crystalline and amorphous phases in semicrystalline polymers presents interesting constitutive modelling challenges. In this study, a physically based, three-dimensional constitutive model has been developed for simulating a wide range of features observed in deformation and processing of semicrystalline polymers. The proposed model combines into one constitutive model such features as: multiple viscoelastic relaxation processes, very wide strain-rate range, temperature-dependence, adiabatic heating, structural rejuvenation; in addition to it being applied to a semicrystalline polymer. The constitutive mathematics is based on a one-process glass-rubber model for amorphous polymers. It adapts that model to semicrystalline polymers by extending it to two relaxation processes: one associated with the glass transition of the mobile amorphous phase; the other associated with relaxation of the crystalline fraction and its associated rigid amorphous phase. In particular, two dominant processes were identified: the α-process and the β-process. The model has been implemented numerically into a commercial finite element code through a user-defined material subroutine (UMAT). The model has been validated against compression test results carried out on polypropylene. Also, the model predicts very well the experimentally observed nonlinear rate-dependent response and post-yield de-ageing of polypropylene

Virtual geometric realization of woven textile composites

Several methods for describing meso-mechanical virtual domains of woven textiles exist. Such approaches utilize equations conjured directly from independent textile manufacturing/machining processes. Therefore, extensions beyond cases considered by the originating authors is technically challenging because it requires machining process experience. Consequently, an intuitive, yet simple, method for developing a variety of complex woven textiles is desirable. The proposed approach uses a simplistic geometric philosophy similar to Peirce's. Nevertheless, it implements advancedcross-sectional shape functions such as power-elliptical functions etc., capable of describing a plethora of cross-sections. Also, non-circular arcs, adapted from local cross-sectional geometry of yarns, are used to define yarn paths. In addition, more complex woven fabrics such as 3D angle and orthogonal interlocking textiles are considered. Generation of desired woven fabrics is defined by a set of inherent physical geometric arguments which are implemented using numerical techniques. This numerical solution strategy, based on physical arguments, negates the requirement of defining equations restricted to specific textiles, making the proposed technique universally adaptable. The requisite arguments of this approach are implemented in MATLAB using an in-house algorithm, TextCompGen. It receives arguments about desired textile architectures, and outputs MATLAB-based plots of the expected geometry alongside a complementary Python-script for automatically re-creating the same geometry in ABAQUS/CAE—a widely-used finite element (FE) preprocessor. The latter feature is included to facilitate subsequent FE analyses, if required

The mechanism of rate-dependent off-axis compression of a low fibre volume fraction thermoplastic matrix composite

This paper reports on the mechanism of rate-dependent off-axis compression of a unique unidirectional composite with unusually high matrix volume fraction of 65%. The test material is an E-glass fibre reinforced polypropylene composite and was subjected to quasi-static, medium and high strain rates (with strain rates from 10-3 s−1 to 103 s−1). This paper has shown experimental evidence of significant rate-dependence of yielding, strain softening and fracture strain of the test composite. Also, the study reports on the effect of strain rates on evolution of different failure modes of the composite. The observed rate-dependence was shown to result from the influence of the pure matrix on the constitutive behaviour of the composite. The work has used a two-process Ree-Eyring yield model of the matrix to demonstrate the origin of the observed rate-dependent yielding of the composite. The data derived in this study will be significant for further micro-mechanical modelling of finite deforming composites used in especially damage tolerant applications. Composite design engineers and stress analysis experts should benefit also from the findings in this work