Study on Porosity and Material Parameters of Hot Moulded Resin Matrix Composites using Nondestructive Laser Ultrasound Technique

This research aims to measure the material parameters and porosity of the resin matrix composite material produced by hot moulding process under various pressures. The laser ultrasonic technique has been used as the measurement technique and the guided wave dispersion relationship was obtained in the resin matrix. In the resin substrate, the single-layer flat plate Lamb wave model was applied to inversely calculate the material parameters and compared with tensile test and traditional ultrasonic measurements. In the woven composite laminate, the specimens were produced with different porosity using the hot pressing moulding process, scanned with computed tomography to confirm the porosity under different pressure and the dispersion curve changes were observed using the laser ultrasonic technique. Result showed that the inversely calculated thickness of pure resin test pieces were consistent with the laser ultrasonic measurement within an error of 5%. The elastic modulus of inverse calculation and the actual tensile test values showed within 12% of error. In the woven fibre composite, the dispersion curve obtained by the laser ultrasonic measurement showed that, as the porosity increases, the dispersion curve tends to shift to a lower wave velocity. In addition to that, the porosity of the woven composite is not changed under different hot pressing pressures. The computed tomography scanning indicated that the pores are mostly concentrated in the overlap of the carbon fibre weaving and extended along the fibre warp and weft directions, showing cross-shaped pores.