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

Micromechanical modelling of finite deformation of thermoplastic matrix composites

The prediction of the constitutive behavior of thermoplastic matrix composites from quasi-static up to impact rates demands a detailed understanding of the behavior of the polymeric constituents of these materials; this is due to the pronounced rate dependence of the polymeric matrix. This paper is an attempt at approaching the prediction of finite deformation of thermoplastic matrix composites, using a multi-scale approach in which the fibre and the matrix are separately modelled and combined within a finite element scheme to determine the constitutive response of the test composite. A micromechanical model comprising a finite element implementation of constitutive laws for the fibre and matrix constituents are discussed. The robust formulation for predicting the behavior of the semicrystalline polymer was successfully developed, including the techniques of generating the 3D representative volume element (RVE) of composites as well as prescribing the periodic boundary conditions on the 3D RVE. Finally, the validation studies for predicting the elastic properties of the composite using the Finite Element (FE) methods and the effect of spatial arrangement of the fibre inclusions within the matrix at finite strains are illustrated

A computational investigation of the effect of three-dimensional void morphology on the thermal resistance of solder thermal interface materials

Process-induced solder voids have three-dimensional shapes and show spatially random distribution with polydisperse geometric dimensions. There exists no analytical formulation of thermal resistances which incorporates void shapes, distribution and polydispersity variables. This paper uses finite element methods to investigate the effect of realistic void morphology on the thermal resistance of solder thermal interface materials (STIMs). The study has developed two computationally efficient methods for generating voids that show the features of real voids. Cylindrical and spherical void morphologies have been studied. The study is the first attempt, in literature, of characterizing the holistic effects of such realistic three-dimensional void morphologies on the thermal resistance of STIM layers. We have shown a qualitative agreement between our results and simplistic analytical predictions. However, the influence of void shapes, distribution and polydispersity have been shown to contribute to increased thermal resistances. The findings should provide significant insight to electrical/electronics engineers, micro-electronics chips manufacturers and academic research groups working on thermodynamics design of chip scale package (CSP) devices. It is also a framework for investigating objectively, the consequence of voids on the thermo-mechanical response of solder joints

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

Optimisation of design and manufacturing parameters of 3D printed solid microneedles for improved strength, sharpness, and drug delivery

3D printing has emerged as a powerful manufacturing technology and has attracted significant attention for the fabrication of microneedle (MN)-mediated transdermal systems. In this work, we describe an optimisation strategy for 3D-printed MNs, ranging from the design to the drug delivery stage. The key relationships between design and manufacturing parameters and quality and performance are systematically explored. The printing and post-printing set parameters were found to influence quality and material mechanical properties, respectively. It was demonstrated that the MN geometry affected piercing behaviour, fracture, and coating morphology. The delivery of insulin in porcine skin by inkjet-coated MNs was shown to be influenced by MN design