The measurement of elastic modulus degradation on random glass fibre-reinforced polyester composites using ultrasonic testing pulse-echo method

Abstract

Chopped Strand Mat Fibre-Reinforced Plastics (CSM-FRP) are very popular composites which are widely used in many applications. CSM-FRP can experience degradation due to the interaction of composites with the environment and mechanical loading, resulting in the decrement of elastic modulus and finally lead to failure. Common tensile testing for determining the elastic modulus has disadvantage as it is a destructive testing. The theoretical determination of elastic modulus can be approached by non-destructive test method through utilizing the velocity of ultrasonic wave propagation in the material. The purpose of this study was to determine the elastic modulus degradation of CSM-FRP using shear wave propagation from a 90° angle probe. CSM glass fiber-reinforced polyester composites with 18% fiber volume fraction were manufactured using wet hand lay-up technique. Degradation on composites was obtained by immersion method. Ultrasonic testing using a 90° angle probe was conducted to determine the longitudinal elastic modulus of the non-degraded and degraded composites by placing the probe on the surface of a measured membrane direction. The shear wave velocity determination was conducted using the two distance method. The resulted elastic modulus degradation was validated by tensile testing results. The results showed that the use of pulse-echo ultrasonic method using probe 90° has been able to determine the degradation on longitudinal elastic modulus of CSM fiber-reinforced polyester composites with 18% fiber volume fraction. The elastic modulus results were lower up to 28% than that of from tensile test due to the wave attenuation phenomenon. The decrease in elastic modulus degradation resulting from ultrasonic measurement was only 27% compared to the tensile test results with a decrease of 41%. The discrepancy may be addressed to the cracks development which were not able to be fully detected by ultrasonic technique.