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

• Main Author: Claudia
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/33836
• Institution: Institut Teknologi Bandung

The properties of thermoplastic polymers in structural applications can be degraded and decreasing in mechanical properties, especially the elastic modulus. In addition, the range of elastic modulus in polymers are varies widely due to the distribution of chain length, crystallinity, functional groups, and additional additives or solvents. Testing of the elastic modulus of the polymer is required to monitor the elastic modulus of the polymer in structural applications and to determine the elastic modulus of the new polymer. Common mechanical testing to determine the elastic modulus, requires sample preparation and cannot be done directly on a field, so that non- destructive testing such as ultrasonic is needed. The ultrasonic pulse echo testing method has the advantage that only one side of the component is needed to be tested. The purpose of this study was to determine the elastic modulus of thermoplastic polymer through ultrasonic testing of the pulse echo method. The study was conducted on three samples of thermoplastic polymer namely polymethylmethacrylate (PMMA), polyamide (PA) and low density polyethylene (LDPE). The sample was verified through FTIR (Fourier Transform Infrared) Spectroscopy, DMA (Dynamic Mechanical Analysis) and density testing. Poisson ratio was obtained from literature. Determination and evaluation of probes was carried out through ultrasonic velocity measurements on variations in sample thickness and probe variation, namely probes of 24 mm 1 MHz and 12.7 mm 1.5 MHz with and without additional probe delay. The elastic modulus from tensile testing polymer based on ASTM D 638 was used as a comparison with the elastic modulus of the ultrasonic test results determined based on ASTM E 494. Probe with diameter 12.7 mm, frequency of 1.5 MHz and an additional delay probe have been selected and can be used to measure ultrasonic longitudinal velocities in PMMA, PA and LDPE without being affected by nearfield at a minimum thickness of 14 mm. The elastic modulus of thermoplastic polymer material measured through ultrasonic testing of the pulse echo method still results in a profound error of 98% - 158% which is influenced by attenuation factors due to viscoelastic properties and polymer density. The linear regression model was created and succeeded in reducing the error value of the thermoplastic polymer elastic modulus resulting form the ultrasonic test to 2.16% - 5.52%.