共查询到19条相似文献，搜索用时 281 毫秒
1.
2.
3.
《林业工程学报》2017,(1)
对人工林杉木层板按照GB/T 50708—2012进行目测分级和机械弹性模量分级,探讨两种分级方法的适用性和科学合理性。通过测定各层板的年轮宽度、绝干密度、弹性模量和静曲强度并进行处理与分析发现:对于目测分级,各等级层板的弹性模量值其离散度非常大且没有规律性,其特征值(平均值和5%分位值)也达不到标准规定的要求,静曲强度值的离散度也很大但其特征值随层板等级的提高而增大,等外层板的弹性模量和静曲强度值反而比等内层板的要大;层板密度与其静曲强度基本上没有相关性,而层板的年轮宽度与其静曲强度有一定的负相关性;层板的弹性模量与其静曲强度有较好的正相关性,采用机械弹性模量分级,静曲强度的特征值随层板等级的提高而成比例地提高。研究表明,目前的目测分级方法不适合于人工林杉木层板的分级,目测分级层板因弹性模量达不到要求不能用于胶合木制造,而采用机械弹性模量分级法则可以制造出强度性能可靠的胶合木。 相似文献
4.
5.
利用超声波检测杉木抗弯弹性模量 总被引：7，自引：0，他引：7
以大尺寸杉木板材为研究对象，通过超声波测试仪对其动态弹性模量进行无损检测及用微机控制电子式木材万能试验机测试其静曲弹性模量，并分析了两种试验方法测定结果之间的关系。结果表明：（1）杉木板材的静曲弹性模量E1和动态弹性模量E2之间呈线性相关，不同厚度的试样无论是作为独立样本还是合并成总体样本空间，其相关性都非常显著，相关系数为0．75～0．95；（2）各种规格的杉木静曲弹性模量平均值E1与动态弹性模量平均值E2的比值E1／E2受杉木板材的厚度影响较小，其值为0．768～0．837。 相似文献
6.
胶合板模板使用过程中抗弯性能衰减修正系数的确定 总被引：2，自引：0，他引：2
从建筑工地上连续抽取使用不同次数的胶合板模板，按GB／T17656—1999测试其静曲强度和弹性模量。对测试数据进行计算分析，提出使用过程中胶合板模板静曲强度和弹性模量的衰减修正系数。 相似文献
7.
按照GB/T 17657—2022《人造板及饰面人造板理化性能试验方法》中的三点弯曲法,先测试竹条径向两面(近竹青面和近竹黄面)各节间和节部的抗弯弹性模量,然后将试件从宽度方向一分为二,测试其各对应位置的弦向抗弯弹性模量和静曲强度。探讨竹条节间中心位置不同方向的弹性模量相互之间及其与弦向静曲强度之间的关系,并建立相应的数学模型;分析竹节对竹条弹性模量的影响,确定侧压型竹层板用竹条的实用分级方法;按中间点径向抗弯弹性模量对竹条进行分级,并测试其弦向静曲强度,分析竹条分级的可靠性;将不同等级的竹条分别制备侧压型竹层板试件,测试其静曲强度和抗弯弹性模量,验证竹条分级的有效性。结果表明：通过测量竹条节间径向两面抗弯弹性模量并计算其平均值,可以较准确地推测其弦向抗弯弹性模量值;通过测试竹条某节间径向两面抗弯弹性模量的平均值,可以很好地预测该部位的弦向静曲强度;仅测量竹条中间点(无论是节间还是节部)的径向抗弯弹性模量就能较好地推测出整根竹条的弦向抗弯弹性模量;采用竹条中间点径向抗弯弹性模量分等可以对竹条(弦向静曲强度)进行有效分级;按竹条中间部位的径向抗弯弹性模量对竹条进行分级,其侧压型竹层板的分... 相似文献
8.
9.
对落叶松胶合木用层板进行目测分级并测定其弹性模量和静曲强度,研究各等级层板的弹性模量和静曲强度及其相互之间的关系,探讨层板目测分级和机械弹性模量分级的科学性、合理性。结果表明:根据层板缺陷进行目测分级,等级高的层板其弹性模量和静曲强度的平均值和5%分位值高,目测分级能够基本反映其材质性能,具有一定的科学性与合理性;但目测分级层板弹性模量和静曲强度值的离散度很大,目测分级所能达到的准确与可靠程度决定其不能替代机械弹性模量分级。机械弹性模量分级层板的静曲强度与弹性模量呈正相关性,但各等级层板的静曲强度与弹性模量的相关系数大不相同,其静曲强度值的离散度也比较大,说明该分级方法还有改善的余地。更加科学、可靠的胶合木层板分级方法还有待进一步的探索研究。 相似文献
10.
11.
Hem-fir plywood were exposed to two brown rot fungi, Gloeophyllum trabeum and Postia placenta, and one white rot fungus, Trametes versicolor, to investigate the effect of fungal decay on mechanical properties of plywood. Results showed that modulus of rupture （MOR） and modulus of elasticity （MOE） of hem-fir plywood declined significantly by inoculating fungi, and weight loss of sample had a modest decrease. The fungi also made a greater effect on MOR than on MOE. Of three fungi, Postia placenta caused a most significant weight loss, and Gloeophyllum trabeum resulted in a largest flexural properties loss. Substantial declines in MOR and MOE of hem-fir plywood were also observed when the plywood samples were stored under wet conditions over 15 weeks, even in the absence of fungal attack. 相似文献
12.
13.
Christoph Buksnowitz Robert Evans Ulrich Müller Alfred Teischinger 《Wood Science and Technology》2012,46(6):1239-1246
This study presents three-point bending test results of Norway spruce clear wood specimens loaded on the radial-longitudinal plane in two different load cases. The tested samples were graded as resonance wood for instrument making and were characterised by narrow annual rings and relatively low density. The modulus of elasticity (MOE) and the corresponding modulus of rupture (MOR) are illustrated separately for the samples with straight grain and the group showing the specific growth pattern of indented rings (‘hazel growth’). With the longitudinal wood anatomical direction parallel to span width, the fibre deviation caused by the indents reduces MOE and MOR values, whereas a ‘reinforcing’ effect of the indents could be observed for the load case with span width parallel to the radial direction. Both aspects lead to a reduction in anisotropy for hazel-growth Norway spruce (anisotropy MOE: indented rings 11.6, straight grain 14.7, anisotropy MOR: indented rings 6.9, straight grain 8.9), which partly explains the exceptional position of this growth pattern for the construction of high-class musical instruments with outstanding mechanical and acoustical performance. 相似文献
14.
Anita Firmanti Efendi Tri Bachtiar Surjono Surjokusumo Kohei Komatsu Shuichi Kawai 《Journal of Wood Science》2005,51(4):339-347
Some reports have shown that for single species the correlation between modulus of elasticity (MOE) and modulus of rupture (MOR) in bending is quite high. Tropical timbers consist of hundreds of species that are difficult to identify. This report deals with the mechanical stress grading of tropical timber regardless of species. Nine timber species or groups of species with a total number of 1094 pieces measuring 60 × 120 × 3000 mm, were tested in static bending. The MOE was measured flat wise, while MOR was tested edge wise. Statistical analysis of linear regression with a dummy model and analysis of covariance were used to analyze the role of MOE and the effect of species on prediction of MOR. The analysis showed that using MOE as a single predictor caused under/overestimation for one or more species and/or groups of species. The accuracy of prediction would be increased with species identification. An allowable stress and reference resistance for species and/or groups of species were provided to compare with the prediction of strength through timber grading. The timber strength class for species and/or groups of species was also established to support the application of mechanical timber grading. 相似文献
15.
To provide data and methods for analyzing stem mechanics, we investigated bending, density and growth characteristics of 207 specimens of fresh wood from different heights and radial positions of the stem of one mature Norway spruce (Picea abies L. Karst.) tree. From the shape of each stress-strain curve, which was calculated from bending tests that accounted for shear deformation, we determined the modulus of elasticity (MOE), the modulus of rupture (MOR), the completeness of the material, an idealized stress-strain curve and the work involved in bending. In general, all mechanical properties increased with distance from the pith, with values in the ranges of 5.7-18 GPa for MOE, 23-90 MPa for MOR and 370-630 and 430-1100 kg m(-3) for dry and fresh wood densities, respectively. The first three properties generally decreased with stem height, whereas fresh wood density increased. Multiple regression equations were calculated, relating MOR, MOE and dry wood density to growth properties. We applied these equations to the growth of the entire stem and considered the annual rings as superimposed cylindrical shells, resulting in stem-section values of MOE, MOR and dry and fresh densities as a function of stem height and cambial age. The standing tree exhibits an inner stem structure that is well designed for bending, especially at a mature stage. 相似文献
16.
17.
The bending and growth characteristics of large fresh stems from four silver fir (Abies alba Mill.) and three Norway spruce (Picea abies (L.) Karst.) trees were studied. Twenty logs taken from different stem heights were subjected to four-point bending tests. From the bending test records, we calculated stress-strain curves, which accounted for detailed log taper, shear deformation and self weight. From these curves we determined, among other parameters, the modulus of elasticity (MOE), the modulus of rupture (MOR) and the work absorbed in bending (W). No significant differences were found between species for the wood properties examined. Values of MOE, MOR and W generally decreased with stem height, with MOR in the range of 43 to 59 MPa and MOE ranging from 10.6 to 15.6 GPa. These MOE values are twice or more those reported for stems of young Sitka spruce (Picea sitchensis (Bong.) Carr.) trees. Based on the radial growth properties measured in discs from the logs, we calculated predicted values of MOE and MOR for the stem cross section. The predictions of MOE were precise, whereas those of MOR were approximate because of a complex combination of different failure mechanisms. Methods to test and calculate MOE, MOR and W for the stems of living trees are discussed with the aim of improving analyses of tree biomechanics and assessments of forest stability protection. 相似文献
18.
19.
In this report, the 575 specimens were divided into ten groups based on range of growth ring width. The modulus of elasticity
(MOE) and modulus of rupture (MOR) of 45 × 90 mm specimens of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantation dimension lumber were analyzed by average growth ring width and average density of each group.
The results showed that the average growth ring width was in inverse proportion to density, MOE, and MOR of the dimension
lumber. Furthermore, average density was in direct proportion to MOE and MOR of the dimension lumber. The coefficient of determination
(R
2) for all the regression equations ranged from 0.7340 to 0.9207 at a significance level of 0.001. However, without such group
classification, there was poor relationship between growth ring width, density, MOE, and MOR with a determination coefficient
of 0.0901–0.1855. This finding suggested that it was feasible to predict the flexural properties of Chinese fir plantation
dimension lumber by average growth ring width after specimen group classification. 相似文献