The dimension lumber （45mm×90mm×3700mm） of plantation Chinese fir （Cunninghamia lanceolata （Lamb.） Hook.） was graded to four different classes as SS, No. 1, No.2 and No.3, according to national lumber ...
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The dimension lumber （45mm×90mm×3700mm） of plantation Chinese fir （Cunninghamia lanceolata （Lamb.） Hook.） was graded to four different classes as SS, No. 1, No.2 and No.3, according to national lumber grades authority （NLGA） for structure light framing and structure joists and planks. The properties of apparent density was determined at 15% moisture content, bending strength and stiffness were tested according to American Society for Testing and Materials （ASTM） D198-99, and dynamic modulus of elasticity （Eusw） was measured by ultrasonic technique, for predicting the flexural properties of different grade lumbers. The results showed that Eosw was larger than the static MOE. The relationship between Eusw and static MOE was significant at 0.01 level, and the determination coefficients （R2） of the four grade lumbers followed the sequence as R^2No.2 （0.616）〉 R^2ss （0.567）〉 R^2No1 （0.366）〉 R^2No.3 （0.137）. The R^2 of Fusw and MOR were lower than that of the Etru and MOR for each grade. The Eusw of all the grade lumbers, except No.3-grade, had significant correlation with the static MOE and MOR, thus the bending strengthof those grade lumbers can be estimated by the E The Etru valuesof four grade lumbers followed a sequence as No.2-grade （10.701 GPa） 〉 SS-grade （10.359 GPa） 〉 No.l-grade （9.840 GPa） 〉 No.3-grade （9.554 GPa）. For the same grade dimension lumber, its Eusw value was larger than static MOE. Mean values of MOR for four grade lumbers follow a sequence as No.2-grade （48.67 MPa） 〉 SS-grade （48.16 MPa） 〉 No.3-grade （46.55 MPa） 〉 No. 1-grade （43.39MPa）.
为探究不锈钢纤维长度与填充量对导电膜片导电性能与电磁屏蔽性能的影响,将不锈钢纤维均匀地铺撒在涂有脲醛树脂和丙烯酸树脂的表层纸上热压,制备具有电磁屏蔽功能的不锈钢纤维填充导电膜片。首先通过微观结构表征,分析不锈钢纤维在导电膜片平面和断面内的搭接状况;然后采用四电极法与同轴线法测试导电膜片的体积电阻率及电磁屏蔽效能;最后通过理论模拟探究不锈钢纤维填充导电膜片的电磁屏蔽机理。结果表明：1）随着不锈钢纤维填充量的增加,导电膜片平面和断面内不锈钢纤维之间交叉排列的混乱程度不断增加,并以随机排列的形式相互交织形成了有效的＂三维导电网络＂。2）随着不锈钢纤维长度和填充量的不断增加,导电膜片的体积电阻率逐渐减小,而其电磁屏蔽效能逐渐增大。3）不锈钢纤维的填充量、导电膜片厚度对导电膜片的导电性能影响显著。4）当不锈钢纤维长度为15 mm、填充量为250 g/m2时,导电膜片的体积电阻率降低为6.493×10-3Ω·cm,电磁屏蔽效能为37.77-51.42 d B,达到中等屏蔽效果,适用于对电磁兼容要求较高的场合。5）理论模拟结果表明,吸收损耗在导电膜片对电磁辐射的屏蔽效果中占有很大的比重,导电膜片表现出了很好的吸波特性。
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