Predicting Models Of The Mechanical Properties Of Larix Gmelinii Mature Wood And Finger-jointed Glulam

The goal of this doctoral dissertation was to model three different types of mechanical properties of Larch(Larix spp) mature wood (LMW) and its products, including the elasticity modulus (MOE) of clear wood, the ultimate longitudinal tensile strength of clear wood (UTS), and the finger-jointed lumber destruction. The Laminating Effect was also involved in this thesis. As a basis for all kinds of models, the physical and mechanical properties of earlywood (EW) and latewood (LW) were studied at the very beginning. The two forms of clear wood nodels own the ability to predict the properties of mature wood quite precisely. Under the condition of flawlessly finger-jointed process, the value of finger-jointed failure load model, which depends on the node geometry, is rather accurate.The major findings of this study are summarized as follows:(1) Earlywood and Latewood of Larch Mature WoodThe density of the LW, which is two to three times as much as it of the EW, was generally greater than 1.0 g/cm3. Microfibril angle (MFA) of the S2 has little difference between the LW and the EW. The range of LW MOE covered from 25 to 42MPa, which is beyond 3 times bigger than the value of EW MOE. It is fairly clear that MOE has positive relationship with density and negative correlation with MFA. The values of LW UTS ranged from 320 to 450MPa, while the extremes of EW UTS were 2.63 to 8.01MPa. It shows strong positive correlation between UTS and density. However, there can be no association between UTS and MFA.(2) Models of Clear Wood of Larch Mature WoodBy the X-ray method, it is rather convenient to obtain the information in the wood radial direction, including the density and the width of EW and LW. With all the details searching by X-ray method, models of mechanical properties would be established and verified. According to the classical layer thesis, the predicting model of larch mature wood MOE was established by the linear elastic properties of EW and LW. The MOE value of clear wood from LMW is calculated as follows:Here, ρE is EW mean density of the specimen(g/cm3), ρL is LW mean density of the specimen(g/cm3), PLmax is LW maximum density of the specimen(g/cm3), EE is mean value of EW elastic modulus(GPa), EL is mean value of LW elastic modulus(GPa), /ρE is mean value of EW density(g/cm3), /ρL is mean value of LW density(g/cm3), hE is EW-width sum of the specimen, hL is LW-width sum of the specimen.The result which the relative error was less than 5% shows that it would predict quite iccurate. The model of predicting the UTS of clear wood isHere, P is ultimate failure load model of LMW clear wood longitudinal tension(N), UTSL is mean value of LW tenslie strength(MPa), a is thickness of the specimen(mm). It shows rather correct as while.(3) Model of Finger-jointed LumberBy flawlessly process, the ultimate failure load model of finger-jointed lumber longitudinal tension has been built and verified. The relative error was less than 10% when the node profile was confirmed, which 27.5mm of the height,7.5mm of the bottom,2.25mm with the top and 95° of node angle. The expression isHere, H is the tooth length(mm), a is the thickness of the specimen(mm), hoL is the_W-width sum on the projection of glued area on cross-section(mm); θ is the acute angle of finger-joint(°);The tensile strength of qualified finger-jointed lumber may cover from(4) Glulam beamThe correlation between the glued area and the thickness of lumber play a vital role on predicting the tensile strength of the finger-jointed lumber. Other factors, such as the outer extension lamination and the the shear force of glue-line between the laminations, are also very crucial. The value of glulam bending strength reached the highest position when the two kinds of failure form scombined (finger-jointed failure on the outer extension lamination and shear failure of glue between two laminations).