【作者】 薛冰；

【导师】 胡英成；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2013， 博士

【摘要】 为了考察单板层积材的力学性能与可靠性,本文运用了纵波传播法、纵向共振法、弯曲振动法等无损检测方法、复合材料力学分析、计算机模拟及静态力学试验等方法来进行研究。主要内容包括：不同压缩率的桦木、杨木、樟子松单板层积材、不同组坯的桦木与杨木单板层积材、不同单板厚度的樟子松单板层积材、不同环境相对湿度下杨木与樟子松单板层积材,建立单板层积材力学性能预测公式,探讨ANSYS程序分析单板层积材力学性能的可行性,分析了各种无损检测动态杨氏模量与静态弯曲弹性模量(MOE)及静曲强度(MOR)间的线性关系,分析了各种无损检测方法的可靠性与不同因素影响下单板层积材的结构可靠性。在不同压缩率影响下单板层积材性能研究中,考察了压缩率对桦木、杨木、樟子松单板层积材力学性能的影响并分析了原因；在对单板层积材力学性能研究中,从复合材料力学角度分析单板层积材的力学性能；建立了单板层积材力学性能的计算公式；分析了树种、压缩率对单板层积材可靠性的影响,以及不同因素下不同使用工况的单板层积材结构可靠性。在不同组坯影响下单板层积材性能研究中,对杨木和桦木制作的单板层积材进行力学试验研究,主要研究不同组坯对单板层积材垂直加载的MOE与MOR的影响,共运用了复合材料力学、计算机模拟和静力学试验三种分析方法,运用了蒙特卡洛法对不同组坯单板层积材的可靠性进行了评估。在对不同单板厚度单板层积材性能研究中,考察了单板厚度对樟子松单板层积材力学性能的影响并分析了原因；分析了各种无损检测的动态杨氏模量与静态弯曲弹性模量及静曲强度间的线性关系；并研究了各种无损检测方法的可靠性。在不同环境相对湿度影响下单板层积材性能研究中,考察了环境相对湿度对杨木、樟子松单板层积材力学性能的影响并分析了原因：分析了环境相对湿度对各种无损检测的动态杨氏模量与静态弯曲弹性模量及静曲强度间线性关系的影响,运用模糊数学与经典数学对无损检测回归分析结果进行了对比分析。本研究结果归纳如下：(1)对于不同压缩率单板层积材的研究表明：复合材料力学分析方法可用于压缩率对单板层积材力学性能影响的分析,运用分析得到的力学性能参数与单板层积材压缩率的关系式求得单板层积材力学性能指标MOE与MOR,其分析结果与静力学试验结果相接近。当压缩率不太大时,桦木、杨木和樟子松三个树种单板层积材的MOE与MOR随着压缩率的增长而增长,符合本文研究的力学模型；通过微观结构分析可知,当压缩率较大时,部分单板层积材在热压的过程中,由于压力作用部分细胞出现了压溃现象,使其力学性能降低。各树种单板层积材在不同压缩率时所表现出来的可靠性不一致,而加载方向不同时也不一致。(2)对于不同组坯单板层积材的研究表明：运用复合材料力学、有限元分析程序及静力试验,对桦木与杨木不同组坯单板层积材的力学性能与可靠性进行了分析。每种组坯单板层积材的MOE与MOR理论分析结果、计算机模拟结果与试验结果都非常接近,复合材料力学与ANSYS软件分析适用于单板层积材的力学性能分析。在桦木与杨木单板用量相同的情况下,单板层积材的MOE是比较接近的,正常使用极限状态可靠性也较接近；桦木单板放置于顶底层的单板层积材强度要高于杨木单板置于顶底层的单板层积材强度,极限状态可靠性要大一些。(3)对于不同单板厚度单板层积材的研究表明：运用弯曲振动(面内、面外)、纵向共振、纵波传播四种无损检测的方法,检测了单板层积材的力学性能。不同单板厚度樟子松单板层积材动态模量结果与静态弯曲弹性模量、静曲强度有密切线性相关性,垂直加载方向与平行加载方向的相关性系数都远大于相关系数1%分位的临界值,线性相关性最好的是与静力试验加载方向同向的弯曲振动检测方法。这四种无损检测方法均可用于樟子松不同单板厚度单板层积材的静态弯曲弹性模量、静曲强度检测。直接使用无损检测结果与弹性模量或静曲强度回归方程得到的力学性能指标结果并不可靠,选择回归分析的95%置信区间下限方程的可靠性有所提高,能够满足工程实际要求。樟子松单板层积材主要力学性能指标MOE与MOR均随着单板厚度的增大而降低。(4)对于不同环境湿度下单板层积材的研究表明：将上述四种无损检测方法运用于不同环境湿度下的杨木、樟子松单板层积材力学性能的检测,除樟子松单板层积材垂直加载方向纵波传播无损检测方法外,其它杨木与樟子松单板层积材的每种动态杨氏模量结果与静态弹性模量或静曲强度之间的线性相关性较好,四种方法都可用于杨木或樟子松单板层积材的力学性能检测。各种无损检测方法结果回归分析的模糊贴近度与相关性系数大小变化是一致的,检验线性回归分析时贴近度可做为参考。单板层积材的力学性能都随着相对湿度的增长而降低,特别是相对湿度由60%增长到70%时下降最为明显；相对湿度由40%增长到70%时,杨木单板层积材的力学性能下降了21%-37%,樟子松单板层积材的力学性能下降了25%-41%。相对湿度对单板的强度有一定的影响,但是对于胶层的剪切强度没有明显的影响；相对湿度对单板层积材力学性能的影响主要因素来源于湿度影响下木材的力学性能变化。更多还原

【Abstract】 In order to investigate mechanical properties and reliability of laminated veneer lumber (LVL), the longitudinal transmission, longitudinal vibration, flexural vibration, etc non-destructive testing (NDT) methods, composite material mechanics analysis, computer simulation and static mechanical tests were utilized. The main contents including:different compression ratio LVL made from birch, poplar and pine, different assembly pattern LVL made from birch and poplar, the pine LVL of different thickness veneer and the poplar and pine LVL in different relative humidity. The presuppositions model of LVL mechanical properties were found. The feasibility that ANSYS program analyze mechanical properties of LVL were discussed, The linear relationship between the dynamic modulus of various non-destructive testing and static bending modulus of elasticity (MOE) and modulus of rupture (MOR), the reliability of various non-destructive testing methods and LVL mechanical properties with different factors influence were analyzed.For different compression rate, the effects of compression rate on the birch, poplar and pine LVL mechanical properties were investigated and the reasons were analyzed for that. For the mechanical properties of laminated veneer lumber, the composite material mechanics were utilized to analyze LVL mechanical properties. The effects of tree species and compression ratio on the reliability of LVL were analyzed. The reliability of LVL was analyzed with different factors under different loads using the method of advanced first order and second moment (AFOSM). For different assembly pattern, LVL panels made from poplar and birch veneers were tested for mechanical properties. The effects of the assembly pattern on the MOE and MOR of the LVL with vertical load testing were investigated. Three analytical methods were used:composite material mechanics, computer simulation, and static testing. The reliability of the different LVL assembly patterns was assessed using the method of Monte-Carlo. For different veneer thickness, the effects of veneer thickness on the pine LVL mechanical properties were investigated and the reasons were analyzed for that. The linear relationships between various dynamic modulus and MOE or MOR were analyzed. And the reliability of various NDT was analyzed. For different relative humidity, the effects of relative humidity on the poplar and pine LVL mechanical properties were investigated and the reasons were analyzed for that. The effects of relative humidity on linear relationships between various dynamic modulus and MOE or MOR were analyzed. And NDT regression analysis results were compared with the fuzzy mathematical analysis and the classical mathematical analysis results.The results were summarized as follows:(1) For LVL of different compression ratio:The composite material mechanics analysis method can be used to analyze the effect of compression ratio on mechanical properties of LVL The theoretical results of MOE and MOR of LVL could be obtained from formula between mechanical properties parameters and compression ratio, its analysis results were consistent with the statics experimental results. The MOE and MOR of birch, poplar and pine LVL were increased with compression rate increasing when the compression rate was not very large, and it accord with the mechanical model was found in this paper. There were some horizontal cracks and some small compression failure were found through the microscopic structure analysis, so the mechanical properties reduced, the major reson was that the pressing load was larger during hot pressing. The reliability of three species LVL were not consistent in different compression rate and loading direction.(2) For different assembly pattern:Three analytical methods were used to analyze the mechanical properties and reliability of LVL:composite material mechanics, computer simulation, and static testing. The MOE and MOR results of theoretical analysis and computer simulation of each LVL assembly pattern were very close to the test results. The composite material mechanics and ANSYS simulation analyses were appropriate for the LVL mechanical property analysis. When the veneer dosages were the same, the MOE of each LVL assembly pattern was very close, and the serviceability limit state reliabilities were close as well. The strength limit state reliability was different, however, with the reliability of LVL with birch veneers on the outer surface being greater. Although the veneer dosages were the same, the strength of LVL with birch veneers on the top and bottom were much greater than the strengths of LVL with poplar veneers on the top and bottom. A good assembly pattern can improve the utility value of wood and provide a better strength-to-price ratio.(3) For the studies of different thickness of veneer LVL:Four NDT methods were used to test the mechanical properties of LVL, including the longitudinal transmission, longitudinal vibration, flexural vibration(in and out plane). The linear correlation between various dynamic modulus results and MOE or MOR were strong, the linear correlation coefficients of vertical and parallel load were much larger than the threshold of1%sub-bit. The method of best linear correlation was flexural vibration in same direction with the static test loading.Therefore the NDT methods can be used for MOE and MOR test of pine LVL with different thickness of veneer in this study. The theoretical result of LVL mechanical properties index that was obtained using the regression equation between NDT results and static results was not reliable. But its reliability was improved as choice of regression analysis equation of the95%confidence interval lower limit, and it can meet the engineering requirements basically. The MOE and MOR of pine LVL decreased with increase of veneer thickness.(4) For LVL in different relative humidity environments:The linear correlation between various dynamic modulus results and MOE or MOR were better, except the longitudinal transmission on pine LVL with vertical load, when hereinbefore four NDT methods were used to test poplar and pine LVL mechanical properties in different relative humidity environments, the NDT methods can be used for MOE and MOR test of poplar and pine LVL in different relative humidity. The size relationship of each NDT method fuzzy neartude was same with the size relationship of correlation coefficient, the fuzzy neartude can be as a reference for the feasibility analysis linear regression results on LVL NDT. The mechanical properties of poplar and pine LVL decreased with relative humidity increased, the most obvious decrease occurred from60%to70%. The mechanical properties of poplar LVL decreased in21%～37%and pine LVL decreased in25%～41%, as relative humidity increased from40%to70%. The effect of relative humidity on mechanical properties of pine LVL was greater. The origin of effect of relative humidity on LVL mechanical properties was the change of wood, because the strength of veneer changed as relative humidity increased, but the shear strength of layer was no decrease.更多还原