单板条层积材(PSL)力学性能的各向异性

Study on the anisotropy of mechanical properties of parallel strand lumber

为研究单板条层积材(PSL)的力学性能,以5和20 mm两种宽度的杨木单板条PSL为材料,对垂直和平行于单板条层积材层积方向分别进行了抗弯、冲击韧性及握钉力的试验,并对两个方向结果进行了差异显著性分析,探究单板条层积材不同加载方向力学强度指标的差异。结果表明:PSL力学性能存在各向异性,5和20mm宽单板条制成的PSL抗弯强度、抗弯弹性模量均为平行加载大于垂直加载,冲击韧性和握钉力为垂直加载大于平行加载;5 mm宽单板条制成的PSL抗弯强度、抗弯弹性模量、冲击韧性值在两个方向差异不显著,只有握钉力在0.05水平下差异显著,20 mm宽单板条制成的PSL所有强度指标在两个方向上差异均显著(P<0.01)。单板条宽度的增加,使得PSL主要力学强度指标各向异性更为显著。

This study explored the differences in the mechanical properties of parallel strand lumber with different loading directions. Parallel strand lumber（ PSL） were made of poplar strands with 5 mm and 20 mm width. The test was carried out to measure the flexural,impact and nail-holding forces in load perpendicular to wide face of strand and load parallel to wide face of strand,and an analysis of variance was performed on the results in both directions. The results showed that the PSL mechanical properties were anisotropic. The flexural strength and flexural modulus in parallel loading were higher than those in perpendicular loading. When vertical loading was applied,the interface layer between the adhesive layer and the single strand was prone to be damaged at the adhesive layer and early wood thin cell walls. When parallel load was applied,the strands were cracked along the glue line. The impact toughness for vertical loading was greater than that of parallel loading. When vertical loading was used,wood was cracked along the wood ray stretching,resulting in a rough fracture surface. When parallel load was used,the shear layer was either a layer of glue or strand,and the layer of glue was more fragile than plywood. The nail-holding forces in the vertical direction was greater than that in the parallel direction. When the screw was fastened in the vertical loading direction,the combined shearing and extruding actions of the thread on the single-strand fiber of poplar made the pull-out force of the screw large. When the screw was fastened parallel with the loading direction,a part of the contact area between the screw and the test piece might be a glue area,and the extrusion function and the pull-out resistance were small.Only the nailing force of the PSL,made of 5 mm wide strands,showed significant differences of P value at 0.05 level in both directions. All the mechanical properties of the PSL,made of 20 mm wide strands,showed significant differences in both directions. The increase of the width of the strands made more significant anisotropy of the main strength index of the PSL.