| Nowdays, the amount of thinned wood and thinned wood are increasing due to the implement of natural forest protection project. In China, the amount of Chinese fir is the third biggest species in Chinese forestry. The percentage of this species is 4.91%, and the percentage of Chinese fir which diameter blow 16 cm is about 65-70%. However, the low cutting yield, automation and added value of products are major issue to be addressed during wood industry. This paper, as a important part of the "Twelfth Five-Year" national science and technology support project(2012BAD24B01), aim to study the optimiztion of gluing process, technology for hexagonal cutting method, the working performance of machines which used for manufacture hexagonal glulam, compression strength and performence of glulam in varying invironment, via response surface methodology, mathematical modeling, Solidworks, computed tomography(CT), and finite element modeling. The results of this study are shown as follows:(1)The surface wettability of Chinese fir was studied.The results showed that the wettability in radial direction is better than it in tangential direction, and it also better in sapwood than in heartwood. As to the surface roughness,the wettability increase as the surface roughness increasing. Different standards for glueline block shear strength were compared and analyzed in this study.The results showed that the tested shear strength is not the true shear strength in glueline,but a combination of shear strength and normal stress.So a non-standard testing method was proposed in this study. A means for selecting the optimal process parameters for the gluing process, based on the design of experiments(DOE) approach, was presented.The adhesive spread, pressing time and pressure were chosen as processing parameters.And the mathematical models between prcoessing parameters and responding parameters were created.The optimal combination of processing parameters for PVAc adhesive is 341g/m2, 3h and 1.2MPa, for adhesive spread, pressing and pressure, respectively. But for PU adhesive, the optimal combination of processing parameters is 260g/m2,1h and 1.2MPa, for adhesive spread, pressing and pressure, respectively.(2) A novel sawing method(hexagon sawing) was proposed in this study.The methmatical models for the yield of different sawing methods were created.The logs with the top diameter of 80,100,120 mm were chosen to calculate the yield of these sawing mathods.A comparison was made between the volume yield for the most common sawing method in China, and the yield produced by a novel sawing method.The results showed that the volume yield of hexagon sawing is higher than the other sawing methods.The hexagon sawing includes the following processes:cross-cutting,bilateral trimming,four-sides cutting, comb extension and shape processing.(3) The machines which used in hexagoanl cutting processing were tested in this study. The working performance of these machines conform to the standard requiements(GB5226.1-2008 and GB/T14384-2010). Some samples were processed by these machines. The tolerance of straightness and parallelism are about 88-119μm and-0.16-0.3μm, respectively. The straightness and depth of parallelism of the processed samples can be used during gluing process. This means the design of these machines are reasonable and effective.(4)The mechanical modeling was developed by ABAQUS software, aim to analyze the pressure distribution in press prosessing. The results got from FEM shown that: the pressure in different gluing surface is suitable for gluing. The pressure which get from the simulation were used for gluing process. After shear testing, the shear shtength of the glue line can meet the standard for glulam(GBT 26899-2011).(5) The Luikov mass transport model was applied to discribe the water transport in glulam.And the X-ray CT scanning technique was also used as a nondestructive testing method to detect the mositure distribution in glulam when the invironment condition varies.The result from the Luikov model have a good agreement with the result from the CT scanning. It means the selected model is acurate enough to discribe the moisture transport in glulam. During the moisture transporting, hygrothermal stress will be induced because of the moisture gradients in glulam.In the begining, the tress in the surface of glulam is tensile stress, but the pressure stress in the middle of glulam. If the stress reaches a certain level, wood may fracture. In this study, the crack appeared in the glulam which is the region of stress concentration got from ABAQUS model.(6) The samples with the length of 1000 mm were test in this study, the results showed that: the modulus of elasticity decreased as the area of cross section increased. The effects of slenderness ratio were also researched in this study, the results showed that: the bearing capacity of the hexagonal glulam decreased as the slenderness ratio increased. During the test, the turning angle and deflection increased as the slenderness ratio increased. The stiffness and stability were worse for the samples which with higher slenderness ratio. The failure mode were buckling failure and strength failure for type B(samples with the length of 3000mm) and A(samples with the length of 1000mm), respectively. |
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