The influence of wood polymer composite (WPC) specimen composition and dimensions on wave propagation

Wave propagation velocity has been used to characterize and classify different types of materials. Proper use of this parameter means, it is necessary to know which variables affect it. This study therefore aims to evaluate the influence of composite type and specimen dimensions on the velocity of ultrasonic and stress wave propagation in compression and injection molded specimens produced with 12 different wood-polymer-composite (WPC) formulations and with high-density polyethylene (HDPE), low-density polyethylene (LDPE) and polypropylene (PP) thermoplastics. For wave propagation velocity analysis, the compression-molded specimens were cut into pieces of four different lengths with a nominal thickness of 10 mm, while the injected ones were produced in two lengths and 4 mm nominal thickness. 22 and 45 kHz transducers were used for the ultrasound wave propagation tests. Specimen size affect wave propagation velocity, showing that in the WPC classification the relationships between cross section dimensions (width and thickness) and length and cross section dimensions are important, as are the relationships between these dimensions and wavelength. The type of WPC polymer affected wave propagation velocity, showing that it is feasible to use this parameter in the classification of different polymers. Composition also affected velocity when a single polymer was used, but the influence of the dimensions hinders more conclusive results regarding wave propagation velocity sensitivity in the differentiation of different compositions.