Effect of fibre orientation on the light scattering during laser transmission welding

Abstract

During laser welding of thermoplastic (LTW) composites reinforced with short fibres, a divergence of the laser beam is observed due to internal refraction of the beam at each matrix–fibre interface. This phenomenon leads to scattering of the laser beam in this heterogeneous medium, resulting in reduction of energy reaching the weld interface. This work presents a numerical study of the effect of fibre orientation in fibre-reinforced composites during the laser transmission welding simulation. A three dimensional (3D) numerical structure is generated to take into account the real microstructure of a composite material reinforced with short fibres. The information of fibre volume fraction, fibre length distribution and fibre orientation distribution is extracted from injection moulding simulations. Fibre orientation distribution function is extracted from fibre orientation tensors. An algorithm is implemented to trace rays propagating through composite material at two scales: microscopic and macroscopic. This algorithm uses optical properties of the composite material to simulate laser beam reflection and refraction in a complex structure. Laser beam scatter at the weld interface is simulated in 3D geometries with various fibre orientation distributions. The effect of fibre orientation on the light scattering phenomenon of laser is compared for different cases of fibre orientation. The simulation results are validated experimentally.