By using IF dryer, this paper studied the tangential shrinkage coefficient of small-diameter polygonal cutting of Larix gmelinii Rupr. The results showed that: there were two kinds of trend of shrinkage coefficient under same drying temperature. One is first decreased and then increased from pith to surface; another is increased gradually from pith to face. These trends were decided by the frequency of tensile stress in wood drying process. Moreover, drying temperature could affect the response of wood shrinkage coefficient. The shrinkage coefficient of wood was large at low temperature, and decreased firstly and then increased as drying temperature increased. Similarly, the average of shrinkage coefficient showed same variance trend with the increase of wood drying temperature. Additionally, it founded a better quadratic correlation between drying temperature and shrinkage coefficient of different part in wood. Ⅰ. MATERIAL AND METHODThe quality of forest resource in the world is decreasing gradually, thus the production of small diameter timbers are becoming more and more popular in wood industry. However, there are some limits for utilization of small diameter timbers due to its diameter and unstable quality. How to use these resources more effectively is a general problem concerned by scholars from different countries. In recent time, small diameter timbers usually are used for making chips, paper and wood-based panels, but there are some disadvantages in this way, such as great investment and low benefit. If small diameter timbers are process into glulam or reconstituted wood, that will improve its quality and meet the demand of society for wood. In the utilization of small diameter timbers, wood drying is an important part. Zhu has done some experiments on wood drying characters of nine broadleaf small diameter timbers, and imposed some measures for improving the quality of wood drying. Gong has studied the wood drying methods for three tree species grew in northeast of China and imposed a method for control the quality of wood drying. Small diameter timbers are used to make glulam using polygonal cutting method, this will overcome its shortage and improve its utilization ratio (Gong et al,1999) . Because small diameter timber has many shortages, it is necessary to study the dry process of them, watch the change of dimension stability of them in the drying process to improve the quality of wood drying. This study will select some small diameter timber of larch, cut them and do drying experiments at different temperature to them, discuss the response of shrinkage coefficient to different temperature in the drying process in order to provide some basic data of wood drying for wood industry. A. SpecimensSpecimens are green log of larch (Larix gmelinii Rupr.), cutting from Maoershan forest farm, Heilongjiang province. Those diameters range from 14 to 16cm, lengths from 2 to 3m and moisture contents above 50%. These green log specimens were cut in 60° angel and then become into six triangle samples, see figure 1...
Abstract:To study the mechanical behavior and energy absorption ability of polyurethane foam/honeycomb paperboard composite material under the static compression test.The static compression tests of polyurethane foam/honeycomb paperboard composite material are conducted by electronic universal testing machine. The mechanical behavior under the condition of static compression and the factors influencing the composite materials' static cushioning properties were analyzed. Then, a comparison was made based on the energy absorption ability between composite materials and simple materials.The yield stress, strength and other indicators of foam/honeycomb paperboard have doubled the growth after filling polyurethane. The aperture size is the main influencing factor affecting the static cushioning properties of composite material.The energy absorption amount of composite materials is about 1.85 times than the total energy of two simple materials.
In order to avoid the high brittleness of epoxy resin and the low peeling strength of its laminated composite, polyurethane was synthesized by in-situ polymerization in epoxy adhesive system. The results of IR, SEM and mechanical properties test showed that the peel strength and shear strength of laminated epoxy adhesive / aramid fabrics composites reached the optimum value when the molar ratio of NCO/OH was 1.2, the content of MoCA curing agent was 1.5% and the content of polyurethane prepolymer was 20%. The brittleness of epoxy resin was reduced to a certain degree, and the bonding properties of epoxy adhesive/aramid fabrics composites were improved.
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