Impact Of Density And Thickness On Internal Stress Of Bamboo Scrimber

To research the impact of density and thickness on its internal stress, this study presses several bamboo scrimbers with three kinds of density and thickness. It tests the temperature of the mat central layer’s temperature, discusses the physical and mechanical properties, such as MOE, MOR, water absorption, moisture content, density, vertical density profile and so on, and uses the prong test method and electronic speckle pattern interferometry (ESPI) to measure its internal stress. The results showed that:1. The heating rate of the bamboo scrimber mat in central layer decreased in the rapid heating stage and the time for slowly heating stage became longer as the density or thickness increased. Besides, the time difference for the mat of different density to heating its central layer to equilibrium temperature was much smaller than that of different thickness.2. The MOE, MOR of bamboo scrimber increased as density increased, but the influence of thickness on the bending properties had no rules to follow. The impact of density of bamboo scrimber on the length and width swelling was not significant after water absorption, but on its water absorption rate and thickness swelling was significant. The impact of thickness of bamboo scrimber on the length swelling was not significant after water absorption, but on its water absorption rate, length and thickness swelling was significant.3. The mean value and volatility of moisture content of different parts in bamboo scrimber increased as the density or thickness increased. The volatility of density of different parts in bamboo scrimber decreased as density increased, and increased as the thickness increased.4. The shape of Vertical Density Profile (VDP) of bamboo scrimber became steeper and the fluctuation became more obvious as thickness increased. The VDP of bamboo scrimber moved up as the density increased, and the shape became steeper, the fluctuation became more obvious, but the variation was smaller.5. As the density or thickness increased, the released width and thickness direction internal stress of bamboo scrimber after sawing increased and the residual thickness direction stress decreased, while the residual width direction stress had no rule to follow after heat-moisture treatment.6. Combining electronic speckle pattern interferometry (ESPI) technique and hole-drilling method to measure the internal stress of bamboo scrimber, it was found that:released internal stress of longitudinal grain specimen increased as the density increased, but the effect of density on the released internal stress of lateral grain specimen was not significant. Released internal stress of longitudinal grain specimen decreased as the thickness increased, but the effect of thickness on the released internal stress of lateral grain specimen was not significant. With the same density of1.2g/cm3, the released internal stress of lateral grain specimens with the thickness of25mm and15mm was both much smaller than that of longitudinal grain specimens.