Nondestructive evaluation of wood-plastic composites

The use of wood-plastic composites in exterior structural applications is increasing due to their inherent resistance to environmental degradation, decay, and insect attack. Currently, wood-plastic composites are being used for decking material and are being considered for use in waterfront facilities. Many factors can contribute to the quality of wood-plastic composites, such as formulations and processing parameters. Nondestructive evaluation techniques are needed to continuously monitor wood-plastic composites material quality during manufacturing for process control. Strong correlations were observed between modulus of elasticity and modulus of rupture for several formulations of wood-plastic composites. As such, the research focused on acoustic wave nondestructive evaluation methods. Fundamental wave characteristics were determined, such as speed and attenuation (time and frequency domain). Ultrasonic frequencies above 200 kHz were significantly attenuated over transmission distances of 14 cm. Significant anisotropy was observed for the extruded wood-plastic composites studied. Wave speeds from impact as well as ultrasonic sources were strongly correlated to material stiffness and strength.