UBC Theses and Dissertations
Creep behaviour of wood-plastic composites Chang, Feng-Cheng
In this research, a series of experiments have been conducted, including mountain pine beetle attacked wood/plastic composite (MPB-WPC) prototype product development, dynamic mechanical analysis (DMA), short-term creep tests for master curve construction based on the time-temperature-stress superposition principle (TTSSP), and a long-term creep test. Moreover, a newly established stress-temperature incorporated creep (STIC) model, a modified Williams-Landel-Ferry (WLF) equation that incorporates the variables of temperature and stress, and a newly developed temperature-induced strain superposition (TISS) method were introduced. The MPB-WPC products showed definite potential as a value-added product option for MPB-attacked wood. The formulation affected the MPB-WPC products’ properties. The capacity of the products without a coupling agent was considerably inferior to the product formulations that included a coupling agent. The surface condition of the product was also influenced by the formulation. The dynamic mechanical properties were studied. The mechanical and viscoelastic behaviours of the MPB-WPC products were considerably influenced by the formulation of wood and plastic and the presence of a coupling agent, which can be attributed to modification of the interface property and the internal structure. The new STIC model smoothly introduced the effect of temperature into a conventional power law creep equation, and the model can be applied to predict the creep strain in which the effect of temperature is involved. Moreover, the temperature-stress hybrid shift factor and a modified WLF equation were studied; and, the parameters were successfully calibrated. Temperature-induced strain was observed in the results of the 220-day creep test. For a temperature-sensitive material like WPCs, the information obtained from conventional creep studies is not sufficient to predict long-term performance. The comparison between the long-term creep data and the master curves showed that master curves tended to overestimate the creep strain. Generally, the master curves constructed based on TTSSP cannot precisely predict the long-term creep strain, but can provide conservative estimations. To deal with the effect of fluctuating temperatures on the creep strain, the STIC model and the proposed temperature-induced strain superposition (TISS) method were established and employed. The additional temperature-induced creep strain and overall behaviour were successfully simulated.
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