冷压成型工艺及取材部位对结构用重组竹力学性能的影响

Influence of cold compression molding process and extraction location on the mechanical properties of structural bamboo scrimber

为了对比“热压”和“冷压-热固化”两种工艺重组竹的材料强度等级,并探明“冷压-热固化”制备工艺对重组竹方材表、芯层材力学性能的影响,以及为丰富方材二次加工切割板材的应用场景和提高力学性能稳定性提供试验分析基础,设计并开展了两种工艺重组竹的力学性能试验。试验采用了抗弯弹性模量、抗弯强度、顺纹抗拉强度、顺纹抗压强度、顺纹抗剪强度、横纹全部抗压比例极限、横纹局部抗压比例极限等7个指标,420个试件。结果表明:热压成型重组竹除抗弯弹性模量和顺纹抗拉强度相对较低外,其他力学性能均明显优于冷压-热固化工艺制备的重组竹,且两种工艺制备成型的重组竹的强度等级均达到10E-90f;冷压成型-热固化重组竹表、芯层材试件的顺纹抗拉、抗压强度和横纹比例极限应力具有极显著性差异,下表层顺纹抗压强度和横纹抗压比例极限应力低于芯层和上表层,而其顺纹抗拉强度高于后两者;冷压成型-热固化工艺重组竹的横纹全部抗压比例极限应力在厚度方向上变异最大,变异系数为20.9%,顺纹抗拉强度变异系数为10.61%。冷压重组竹方材力学性能在厚度方向上较大的变异性由板坯胶黏剂分布不均、固化分层和受热不均导致。

In order to compare the strength levels of bamboo scrimber by"hot pressing"and"cold press-ing-thermal curing",and to investigate the effect of"cold pressing-thermal curing"on the surface and core layers of reconstituted bamboo square lumber,as well as to provide a basis for experimental analysis to enrich the appli-cation scenarios of secondary processing of square lumber into panels and to improve the stability of mechanical properties,mechanical property tests were designed and carried out for two processes of bamboo scrimber.The test used 7 indices and 420 specimens,including modulus of elasticity,longitudinal flexural strength,longitudinal tensile strength,longitudinal compressive strength,longitudinal shear strength,full and local compressive behav-ior perpendicular to the grain.The results showed that,except for modulus of elasticity and longitudinal tensile strength,the mechanical properties of hot-pressed bamboo scrimber were significantly better than that of cold-pressed bamboo scrimber,and the strength class of hot-pressed and cold-pressed bamboo scrimber reached 10E-90f.There were highly significant differences in the mechanical properties of the surface and core materials of the cold-pressed bamboo scrimber,such as longitudinal tensile strength,longitudinal compressive strength and compressive perpendicular to the grain.The longitudinal compressive strength and compressive perpendidular to the gain of the lower surface material were lower than those of the material located in the upper surface and core region,while the longitudinal tensile strength was higher than the last two.The ultimate longitudinal compressive strength of cold-pressed bamboo scrimber had the largest variation in the thickness direction,which was deter-mined as 20.9%,and the variation coefficient of longitudinal tensile strength was 10.61%.The variation in the mechanical properties of cold-pressed bamboo scrimber squares in the thickness direction was inferred to be due to uneven adhesive distribution,curing delamination and uneven heating of the slabs.