Strength prediction for bi-axial braided composites by a multi-scale modelling approach

The final publication is available at Springer via http://dx.doi.org/10.1007/s10853-016-9901-z.Braided textile-reinforced composites have become increasingly attractive as protection materials thanks to their unique inter-weaving structures and excellent energy-absorption capacity. However, development of adequate models for simulation of failure processes in them remains a challenge. In this study, tensile strength and progressive damage behaviour of braided textile composites are predicted by a multi-scale modelling approach. First, a micro-scale model with hexagonal arrays of fibres was built to compute effective elastic constants and yarn strength under different loading conditions. Instead of using cited values, the input data for this micro-scale model were obtained experimentally. Subsequently, the results generated by this model were used as input for a meso-scale model. At meso-scale, Hashin’s 3D with Stassi’s failure criteria and a modified Murakami-type stiffness-degradation scheme was employed in a user-defined subroutine developed in the general-purpose finite-element software Abaqus/Standard. An overall stress–strain curve of a meso-scale representative unit cell was verified with the experimental data. Numerical studies show that bias yarns suffer continuous damage during an axial tension test. The magnitudes of ultimate strengths and Young’s moduli of the studied braided composites decreased with an increase in the braiding angle

Study of black silicon obtained by cryogenic plasma etching: approach to achieve the hot spot of a thermoelectric energy harvester

International audiencen this paper, we study the enhanced absorption properties of micro/nano structured silicon surface under incident electromagnetic illumination and its capacity to convert light into heat. We simulate the optical reflectance of three-dimensional micro/nano silicon cones of different dimensions and under different electric field incident angles. According to the favorable simulation results, we fabri- cate black silicon with conical microstructures that exhibits excellent anti-reflectivity behavior. Plasma etching under cryogenic temperatures is used for this purpose in an induc- tively coupled plasma-reactive ion etching reactor. The reflectance of the black silicon is measured to be approxi- mately 1 % in the optical wavelength range, by using an integrating sphere coupled to a calibrated spectrometer. Fur- thermore, a device integrating a resistance temperature detector in a black silicon area is developed in order to investigate its efficiency as a photo-thermal converte