Mechanical and time-dependent behavior of wood-plastic composites subjected to tension and compression

Abstract

The thermoplastics within wood—plastic composites (WPCs) are known to experience significant time-dependent deformation or creep. In some formulations, creep deformation can be twice as much as the initial quasi-static strain in as little as 4 days. While extensive work has been done on the creep behavior of pure polymers, little information is available on the mechanical effects of mixing polymers with large amounts of woodbased or other bio-based fillers. As producers seek to develop structural WPC products that may be subjected to sustained loads, it is imperative that this creep behavior be understood. We characterized the quasi-static and time-dependent deformations of seven WPC formulations (primarily polypropylene, and polyethylene) in tension and compression. The quasi-static, mode-dependent response of the material to a linearly increasing strain was found to be well described by an exponential function coupled with a linear term. For most formulations, significant differences betw1en the tension and the compression University were not exhibited below 50% of the tensile capacity. The longterm creep response of the material was found to conform well to a time-dependent power-law (Findley, Shapery, etc.) at various stress levels for both loading modes.

Citation

Hamel, Scott E.; Hermanson, John C.; Cramer, Steven M. 2012. Mechanical and time-dependent behavior of wood-plastic composites subjected to tension and compression. Journal of Thermoplastic Composite Materials Volume 26, Number 7, 2012; pp. 968–987.