Study of Elastic Modulus Determination of Polymers with Ultrasonic Method

Abstract

Elastic modulus is one of the mechanical properties of the material that often used in industry or research field as a benchmark to determine materials’ performance in term of withstanding load without being deformed. Destructive testing is perpetually used to determine this property. However, destructive testing needs a sample, and in situ testing is implausible. Various types of materials are used in the production process of the industry, e.g., polymers. Polymers have time-dependent properties, which can result in high variety value. By principle, ultrasonic inspection, which depends on sound velocity and density of materials, can be used to determine elastic modulus. Ultrasonic test with through-transmission method has been studied to determine elastic modulus and dynamic elastic modulus for polymers. For the sake of quality control and engineering design, ultrasonic pulse-echo contact is preferable. Ultrasonic testing was conducted with GE USM 35X device, which is a Pulse-Echo method and also contact method type of ultrasonic testing machine. Experiments were conducted on several types of polymers with frequency and thickness as experiment parameters. With an input of specimens’ thickness, materials’ sound velocity (ν) could be obtained. Thus results of ν were counted to attain the elastic modulus. Comparison between ultrasonic testing results and mechanical testing results of polymers’ elastic modulus were performed to analyze the data. In this research, elastic modulus value obtained from the ultrasonic test has a profound error, up to 65% (minimum) and 388% (maximum), especially for a polymer with an eminently low density. Further research should be conducted because of the attenuation effect. Also, lower probe frequency eases the detection of alternating ultrasonic wave. Specimens’ thickness adjusted with near-field calculation can eliminate the near-field effect, which is a natural phenomenon of the ultrasonic wave. However, it would not have yielded an accurate value because an excessive thickness will give an attenuation effect.