Speaker
Description
Laser transmission welding is a widely used process for joining thermoplastics. Of the two materials involved in the welding process, one should be transparent/semi-transparent to laser wavelength, and the other absorbent to the same wavelength. A laser beam is transmitted through the transparent material and is absorbed at the interface of the two materials.
During laser welding of thermoplastic composites, a divergence of the laser beam is observed due to internal refraction of the beam at microscopic scale at each matrix-fibre interface. At the macroscopic scale, this phenomenon leads to scattering of the laser beam in this heterogeneous media, resulting in reduction of energy reaching the weld interface. This work presents a numerical study of the effect of fibre orientation in structural composites during the laser transmission welding simulation.
A 3D structure is generated with an aim to take into account the real morphology of a composite material with short fibres. The information about fibre volume fraction, fibre length distribution and fibre orientation distribution is extracted from µCT observations. Fibre orientation distribution is extracted from fibre orientation tensors. Closure approximation is used to calculate fourth order from second order tensor. The change in fibre orientation tensor is investigated by numerical simulations.
An algorithm is developed to trace rays propagating in the composite material at two scales: micro and macro. This algorithm uses ratio of refractive index of the fibre and the matrix to simulate laser beam reflection and refraction in the complex structure. Laser beam distribution at the weld interface is calculated with this algorithm for various orientation distributions. The effect of fibre orientation on the light scattering phenomenon of laser is studied. The intensity of laser beam at the interface can be used to determine temperature field at weld interface and to optimise the quality of the weld.
| Speaker Country | France |
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