Indentation Characteristic Of Bamboo Or Fast Growing Wood And Its Composite

Indentation technology arises from hardness testing, having various advantages whencharacterizing materials property, such as simple, convenient and local measurement etc., whichcould be divided into nano-scale indentation, microcosmic indentation and macroscopicindentation. This study taken up the macroscopic indentation to investigate the relationshipbetween load and time of bamboo and fast-growing wood with spherical indenter, which basedon the wood hardness test under the guidance of contact mechanics, plastoelasticity andviscoelastic mechanics of wood materials, and further more analyzed indentation creepmechanism, and characterized the indentation property of bamboo, fast-growing wood andcontaining glue-line part of its composite. The results indicated that:The indentation creep test conducted at three levels20%,40%,60%of the reference loadof1600N, the indentation creep on bamboo cross-section was smaller than radial-section, thecreep curves consisted two parts: fast-growing deformation and slow-growing deformationtrending to stable. Fitting degree was0.64~0.80when simulating indentation creep curves byBurger models. The indentation morphology at60%of the reference load was observed withthe help of SEM, the cell lumen and intercellular space were compressed, for the sphericalindenter, there were tensile stress circumferentially and compressive stress radially, this resultedin that, fibers slipped, vascular bundle and ground tissue were torn on the cross-section, andfibers cracked along the fiber direction on the radial section indentation.The creep stress exponent obtained from tensile creep test in fiber direction andindentation creep test on the cross-section were1.36and1.47respectively, indicating a goodconsistency, fitting degree of indentation creep was larger than0.97when shielding the data at60%of the reference load.The indentation creep on the containing glue line part and bamboo of bamboo laminatedlumber was both increased with the press load increasing under the constant test force, the creeprate had not obvious difference. Under the conditions pressing different loads in stages, theindentation deformation was diminished in the later stage, and creep rate slowed during theholding time in the later stage, and indentation work reduced, however, the indentation elasticwasn’t change. The larger load on previous phase, the more obvious influence on the later one.Fast-growing wood composite structure: poplar/poplar, poplar/black locust, black locust/black locust. The shear strength of black locust/black locust composite was larger thanpoplar/poplar composite significantly, there was not evident difference between poplar/black locust composite made under two kind of bonding pressure, but both lower than poplar/poplarcomposite and black locust/black locust composite. The penetration of adhesive in the interfaceof poplar/poplar and poplar/black locust made under the same bonding pressure was differentobserved by SEM. Indentation on poplar and black locust were simulated by finite elementsimulation, the stress nephogram and strain nephogram under spherical indenter showed that,the distribution of stress and strain of poplar and black locust on the combined parts wasasymmetric, which reflected the shear strength indirectly. The bonding pressure had obviouseffect on indentation creep of containing glue-line part of poplar/black locust composite whenthe test force was460N, the higher bonding pressure, the smaller indentation creep. Thedifference of indentation creep on containing glue line part of poplar/poplar composite andblack locust/black locust composite was not evident. The indentation creep between two kind ofpoplar/black locust composites hadn’t obvious different at the test force240N. The ratio ofplastic deformation indentation work to total indentation work of containing glue-line part ofthe poplar/black locust composite was between the poplar/poplar composite and blacklocust/black locust composite, the existence of glue layer enhanced the plastic deformationresistance ability of poplar, while the enhancement effect is not obvious on black locust.