Time-temperature effects on early-stage primary thermal creep of plywood and oriented strand board (OSB) at elevated temperatures

This study examined the effects of elevated temperatures on plywood and Oriented Strand Board (OSB) subjected to a constant load. Due to the short duration and the absence of a steady-state, this behavior was classified as "Early-Stage Primary Thermal Creep." Deflections at each elevated temperature, ranging from 120°C to 200°C, were analyzed to assess the thermal effects. Statistical analysis of the maximum deflections indicated the onset of thermal degradation at around 170°C for both plywood and OSB. Notably, a significant increase in deflection was observed between 180°C and 190°C for OSB, suggesting adhesive thermal decay. In addition to the statistical analysis, a numerical model was fitted to the experimental data to create temperature-dependent deflection curves, revealing an exponential trend. To understand the combined effects of temperature and time on early-stage primary thermal creep, two models were evaluated: a modified rational function model and a modified power model. The temperature-dependent power-exponential creep model provided a superior fit for both plywood and OSB, as indicated by higher R² values and lower root mean square errors.