Simulation of the Temperature Change Induced by a Laser Pulse on a CFRP Composite Using a Finite Element Code for Ultrasonic Non-Destructive Testing

Abstract

Laser-ultrasonic is an innovating technique developed in aeronautics for quick and contactless inspection of composite materials. For the Non Destructive Evaluation (NDE) of composites, a short and powerful laser pulse generates ultrasonic waves. A part of the incident laser beam is absorbed by the surface and induces an elevation of the temperature of the material. This temperature increase generates local stress and thermal warping that are responsible for the generation of ultrasonic waves. This chapter of contribution describes the case of the thermal interaction between a CO₂ laser beam pulse and a carbon fibre reinforced plastic (CFRP) composite material. The laser beam is considered spatially and temporally Gaussian and the material is decomposed as two media. The first one is a 40 μm thick resin and the second is a 4 mm thick CFRP. By considering the laser beam as a volumic heat source with a 120 ns pulse duration, a 90 mJ energy and a 10 ms time range between two pulses, we have developed a finite element model using the Elmer code to simulate the transient heat equation and to evaluate the composite temperature increase. The results of the thermal analyses are applied to understand the influence of resin skin thickness and pulse rate on the ultrasound generation.