Elastic Modulus Determination of Thermoplastic Polymers with Pulse-Echo Method Ultrasonic Testing

Abstract

The determination of the elastic modulus of the structural thermoplastic polymers is especially required during in-service monitoring of the components. This elasticity modulus determination can simplify the inspection process and predict the lifetime of the polymer being used. The elastic modulus of the polymer can be determined by pulse-echo method testing ultrasonic which is easier to use than transmission method. This research aims to determine elastic modulus of thermoplastic polymers i.e. polymethylmethaacrylate (acrylic), polyamide (nylon) and low density polyethylene (LDPE) calculated from measurement of velocity and attenuation of ultrasonic pulse-echo. The research begins by looking at the effect of the use of three different probes to ultrasonic velocity readings. Then elastic modulus of material polymers from ultrasonic velocity was calculated using standard equation. The elastic modulus was compared with the elastic modulus from mechanical testing. A linear model elastic modulus from ultrasonic reading which consists of velocity and apparent attenuation was developed. The results were elastic modulus value obtained from ultrasonic velocity and standard equation had a profound error 98% to 158%, especially for polymer with an eminently low density and high ratio of viscous property to elastic property. The attenuation from ultrasonic reading was influenced by the viscoelastic properties and the elastic modulus from ultrasonic velocity reading was influenced by the density. A linear model for thermoplastic elastic modulus determination based on ultrasonic pulse echo testing has been developed and could reduced the error to 3.45%.