Research On Physical And Mechanical Properties Of Bamboo Scrimber

To produce bamboo scrimber, bundles of bamboo fiber are arranged in parallel, with fibers glued to each other using adhesive under a press pressure after drying. Although bamboo scrimber with high intensity has been used in demonstration building, material properties, mechanical properties, characteristic values and design values are unknown, and its promotion in timber construction is restricted. So the research on strength properties of bamboo scrimber lays the foundation for utilization of bamboo scrimber and promotion in wooden structure.In this paper, one finished product with untreated fiber bundles from a factory was selected to study its mechanical properties. Air-dry density, oven-dry density, tensile strength (UTS), compressive strength parallel to grain (UCS), local compressive strength perpendicular to grain, bending strength (MOR), bending MOE (MOE) and shear strength (SS) were studied. The main results of this research are summarized as follows:1.49 percentile values using nonparametric method were selected to fit linear model and nonlinear model (power function and exponential function). Relational models among mechanical properties were established, and accuracies of the models were tested.2. The research on influence factors of mechanical properties for bamboo scrimber:(1) The impact of moisture content on mechanical properties of bamboo scrimber was large. Mechanical properties decreased with increasing moisture content, and little changed in MOE.(2) The degree of fitting relationship between density and mechanical properties was relatively high using power function and linear function. It is recommended to use linear function in the fitting relationship. Adhesive content, which is decided by degree of cell wall tearing, has great impact on density through optical microscope images.(3) Mechanical properties decreased with increasing grain angle. A uniaxial compression test of bamboo scrimber showed wrinkled failure at 0-10°, shear failure at 20-50° and horizontal failure at 60-90°. Norris values are the lower limit of testing values, Hankinson values are close to tested values, and predictive values of GB 50005 are higher than tested values. It is not recommended to use GB 50005 to predict mechanical strength of bamboo scrimber. Maximum stress theory explained the division of failure types. Failure of 0-10° samples was caused by longitudinal compressive strength,20-50° is determined by shear strength and 60-90° is determined by horizontal compressive strength.(4) Prediction accuracy can be improved when density and grain angle were taken into account simultaneously. Prediction accuracy of 2D model was much higher than 1D model. Relative error was smaller when sample density was close to average density.(5) Temperature influences mechanical properties of bamboo scrimber greatly. Mechanical properties increased and then decreased with increasing temperature. Color of bamboo scrimber deepened gradually with increasing temperature, and cracks of cell wall increased. Fracture mode of high-temperature process8ing bamboo scrimber can determine mechanical strength, and mechanical properties reached maximum when fiber of bamboo scrimber fractured neatly.(5) Sampling method hand a significant effect on mechanical properties. Cyclic design was applied to sampling for physical and mechanical samples from each bamboo scrimber board to ensure the samples distributed at each site of the board. Significant differences of physical and mechanical properties of bamboo scrimber existed between center region and marginal region. However, mechanical properties inside center region and marginal region had no significant difference.3. Method of characteristic value for physical and mechanical properties of bamboo scrimber was determined. Normal distribution cannot fit physical and mechanical properties of bamboo scrimber, however, lognormal distribution and weibull distribution can fit these properties. Characteristic values of air dry density and oven dry density were 1.004 g/cm3 and 0.974 g/cm3, respectively. Tensile strength and tensile MOE were 119.69MPa and 24.46GPa. Compressive strength parallel to grain and local compressive perpendicular to grain were 85.65 MPa and 39.90 MPa, respectively. Bending strength and bending MOE were 151.57MPa and 23.4 GPa. Characteristic value of shear strength was 37.33MPa.4. Error of physical and mechanical properties decreased with increasing sample size, and stabilized gradually. Sampling error increased with increasing confidence level as sample size was constant. Sample sizes calculated under 75% confidence level with 5% error were 7 except compressive strength parallel to grain and total compressive perpendicular to grain, whose sample sizes were 11 respectively. Taking into account the stability of error, it is recommended to take 50 at least as the sample size of characteristic value for bamboo scrimber.