Analytical and numerical modeling of light scattering in composite transmission laser welding process

Analytical and numerical models for laser beam scattering in the thermoplastics composites are presented. The numerical model is based on Ray Tracing, an optical method to compute the optical propagation of laser beams in inhomogeneous media with spatially varying dispersion of the refractive index. In this study, only the case of unidirectional thermoplastic composites (UD) is presented. During transmission laser welding process, a divergence of the laser beam is observed in the first part (transparent in the laser wavelength) due to the internal refraction at the microscopic scale of the beam at each matrix-fiber interface. At the macroscopic scale, this phenomenon leads to the light scattering of the laser beam in this heterogeneous media. Under these conditions, a modeling of the propagation of a laser beam appears essential. An analytical model compared to numerical model is proposed, that enables to simulate and to optimize the laser source at the welding interface. This model provides a good estimation of the laser beam intensity profile at the welding interface (radiative heat well defined) and the beam widening. Those steps are necessary to describe the heat source in the laser welding process thermal simulations. The distribution of the heat source at the interface is one of the most important parameter in the description of the laser welding process.