【作者】 杨洋；

【导师】 申士杰；

【作者基本信息】 北京林业大学 ， 木材科学与技术， 2011， 硕士

【摘要】 木材作为一种生物质高分子材料,其本身存在较大的变异性。这种变异性不但会对木材的力学性质造成较大影响,更会给其加工利用带来很大的不确定性。为了科学合理的使用木材,有效提高木质资源的利用率,保证各种木质产品在建筑上的安全可靠应用,必须对其力学性质进行准确预测以实现等级区分。目前,国内外常用的分等方法有目测分等和无损检测两类。通过对木材进行无损检测和破坏性试验,探究无损检测结果与力学性能的关系,不但可以较为全面的了解木材的各项力学性质,更能为实现快速准确的强度分级提供科学依据,具有很大的理论意义和实用价值。本文首先依据美国ASTM D245、日本JAS 1152、德国DIN 4074三种目测分等标准对694根足尺落叶松天然林锯材和221根足尺落叶松人工林锯材进行了目测分等,然后分别运用四种无损检测方法(机械应力分等、横向振动、纵向振动和应力波)和两种静态弯曲测试方法(ASTM D4761三点平弯、四点侧弯)对试材动、静态弹性模量进行了测试,最后通过对整体样本随机抽样,进行四点平弯破坏,获得了试材的抗弯强度。通过分析不同力学性质之间的关系,得到了以下主要研究结论：1、目测等级与静态抗弯性能(三点平弯静曲弹性模量E3s、四点侧弯静曲弹性模量E4s,抗弯强度MOR)之间具有密切的相关性。2、三点平弯与四点侧弯测试方法结果之间(E3s与E4s)具有良好的线性回归关系,相关系数R为0.8049,E4s平均值比E3s高8.13%(1.3GPa)。3、动态MOE与静态MOE的相关性存在较大差异,R范围为0.4989-0.7330。其中以EMSR与E4S的相关性最好,R达到0.7730；ELV与E3S的相关性最差,R仅为0.4989。4、静态MOE与MOR的相关性(R范围0.6552～0.7535)优于动态MOE与MOR的相关性(R范围0.3087-0.6439),其中以E4s与MOR的相关性最好,R为0.7535。5、机械应力法、横向振动法、应力波法、纵向振动法所建立的MOR预测模型,相关系数分别为0.6439、0.5914、0.5035、0.3087,表明利用机械应力分等法预测MOR的效果最好,其次分别是横向振动法、应力波法,纵向振动法预测MOR的效果最差。更多还原

【Abstract】 As biomass polymer material, wood has great variability. It will not only affect the mechanical properties of wood, but also cause great uncertainty in wood processing and utilization. In order to make the most use of wood resources, pre-tests must be done to achieve the class differentiation. At present, visual grading and non-destructive testing (NDT) are two effective methods.Using NDT and destructive testing to test wood materials and finding the relationship between NDT results and static properties can not only gain a more comprehensive understanding of mechanical properties, but also provide a scientific basis for strength grading, which has a very theoretical and practical value.In this paper, six hundred and ninety-four full-size Chinese larch (Larix gmelin (Rupr.) Rupr.) sawn lumber and two hundred and twenty-one Larix olgensis sawn lumber were studied. Visual grading was firstly conducted according to ASTM D 245、JAS 1152、DIN 4074, then four NDT methods (mechanical stress grading, transverse vibration, longitudinal vibration and stress wave)and two static bending test methods (ASTM D 4761 center-point flat-wise bending, third-point edge-wise bending) were used to determine the dynamic and static modulus of elasticity (MOE). Finally, modulus of rupture (MOR) was measured by bending flat-wise (third-point loading). By analyzing the relationship between NDT results and static bending properties, we got the main conclusions as follows:1、The relevance of visual grades and static properties (E3S、E4S、MOR) were obvious.2、There was a good correlation between center-point flat-wise bending and third-point edge-wise bending, the correlation coefficient between E3S and E4S was 0.8049, the mean value of E4S was 8.13% (1.3GPa) greater than E3S.3、Relationship between dynamic MOE and static MOE showed large variability, R ranged from 0.4989 to 0.7330. E4S and EMSR had the highest correlation coefficient, R was 0.7330.4、Correlation between static MOE and MOR (R range of 0.6552～0.7535) was better than correlation between dynamic MOE and MOR (R range of 0.3087～0.6439), E4S best correlated with MOR, R is 0.7535.5、Strength prediction model created by MSR, transverse vibration, stress wave and longitudinal vibration were different, the correlation coefficients were 0.6439,0.5914,0.5035 and 0.3087. It showed that using MSR to predict MOR was the best, followed by the transverse vibration and stress wave, the longitudinal vibration method was the worst.更多还原