共查询到20条相似文献，搜索用时 671 毫秒
1.
带锯条挂锯位置对锯条宽度应力分布和稳定性的影响 总被引：1，自引：0，他引：1
本试验采用应力应变法测试锯条宽度上应力分布,并在等精度条件下研究锯条的振动,以确定带锯条宽度应力分布与振动的关系。试验结果证明,带锯条宽度上应力分布图与锯条挂于锯轮上的位置有关。在锯条直线段,挂锯伸出量以22毫米左右为宜。在锯条弯曲段,局部高应力区产生于靠近锯条齿根部位,这些高应力区在锯条弯曲脉动循环作用下易于发生应力集中性裂纹。带锯条振动的平均幅值和标准偏差与张紧应力具有显著的线性关系。振幅随张紧系统的压铊重量的增加而减小。 相似文献
2.
带锯机切削木材时,影响带锯条稳定性的因素很多,如带锯条的张紧应力,锯条的热应力、锯轮倾斜度、轮缘断面形状、锯条齿型、锯条导向装置结构型式及其同锯条之间的间隙等。本文拟对影响锯条稳定性的二个关键性因素——张紧应力与热应力进行探讨。 相似文献
3.
测定带锯条的断面应力和张紧力,目前皆是利用电测或拉力传感器来完成。但上述仪器设备价格高、操作不方便,特别不适应于生产单位或科研单位用来快速测定带锯条的张紧力和锯条断面上的应力分布。从而,为制定合理的制材工艺规范提供科学依据。南京林业大学木工教研组最近试制了TQ—1型 相似文献
4.
在带锯机—锯条—木材—进料机构的刚度系统中,带锯条是最软的弹性薄壁构件,带锯条的传动是属于挠性传动。因此,在传动中将受到很多外干扰,例如带锯条张紧力、上锯轮倾斜度、带锯条的适张度和锯背挠度、导向装置(锯卡子)的调整间隙和上下导向装置间的自由长度等。 相似文献
5.
以MJ345A型木工带锯机为研究对象,空载下,运用先进的北京波普振动分析仪和Vib’sys振动信号采集、处理和分析软件进行振动信号采集和分析,通过锯条横向振动位移、自功率谱分析得出:对锯条横向振动位移影响最为显著的因素为主轴转速,其次为锯条张紧力,皮带张紧力为不显著因素;最佳工艺参数为锯轮主轴转速831 r·min-1、锯条张紧力22N、皮带张紧力34.9394 N。在调锯最佳工艺参数下,使用宽度16 mm、厚度0.7 mm的带锯条的MJ345A型细木工带锯机,对锯条产生裂纹前后的振动信号进行相关分析表明:横向振动位移如果在0.65~0.77μm之间,振动主频率在420~446Hz之间,则说明锯条已经产生至少1条超过3 mm裂纹缺陷,需要及时更换带锯条。 相似文献
6.
7.
木工适张带锯条的振动分析 总被引：4，自引：0，他引：4
应用振动理论,对经过适张处理后的木工带锯条进行研究,确定张紧力与系统固有频率之间的关系,提出将带锯条的振动简化为弦的振动与受拉伸的梁振动.用电测法测应变换算张紧力,用频谱分析法测量系统的固有频率,理论解得到试验支持,同时计算张紧力和张紧应力. 相似文献
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9.
吕天赦 《中南林业科技大学学报(自然科学版)》1983,(1)
本文对带锯条辊压后的变形、应力变化、张紧应力以及由此而导出的其他问题进行了分析,提出不同于《带锯条辊压的应力分析》一文的见解。 相似文献
10.
一、绪言研究予测带锯条的跑锯现象,必须弄清锯条厚度、张紧力等带锯条件和扭曲载荷的力学关系,以及锯割时产生压缩力即塞进齿室的锯屑压缩力(也包括锯齿切削时的背分力)的大小。但是,关于锯割时产生的锯屑压缩力发生机理,至今,除推定以外尚无其它方法,发生压缩力本身的大小及发生状况还不大清楚。关于扭曲时锯割条件,也用锯屑的母材 相似文献
11.
This study established a prediction model for bending properties of glued-laminated timber (glulam) using optimized knot and
modulus of elasticity (MOE) distributions of lumber laminate as the main input variables. For this purpose, knot and MOE data
were investigated for all pieces of lumber that were prepared for glulam manufacturing, and statistical distributions of knot
size, knot number in one lumber, and MOE of each laminate were optimized as distribution functions. These knot and MOE data
were used as input variables in the prediction model for bending properties, and were also used in generating virtual glulam
using the inverse transform method. Prediction of bending properties for glulam was carried out using the transformed section
method, which is partially provided in ASTM D 3737 (Annex A4). Predicted values were compared with those from full-scale four-point
bending tests for 60 six-layered glulams with 10 different laminar combinations. Finally, the allowable bending properties
of glulam for each specific laminate combination were determined by calculating the fifth percentile of the modulus of rupture
and the average modulus of elasticity from virtual test results of more than 1000 virtual glulams. From the results of this
study, predicted bending properties for glulam and their distributions could be used for structural design in both allowable
stress design and limit state design. 相似文献
12.
Summary Compression wood (CW) of the giant sequoia studied had higher values than normal wood (NW) in crushing strength and ultimate stress in tension parallel to grain, in toughness, in modulus of rupture, and in work to maximum load and total work in static bending. In the green condition CW had higher values than NW in stress at the proportional limit and work to the proportional limit, and about the same modulus of elasticity in static bending. In the dry condition CW was about equivalent to NW in work to the proportional limit, but was slightly weaker in stress at proportional limit and modulus of elasticity in static bending. The compression wood of this giant sequoia, even though formed when the tree was suppressed and having relatively narrow rings, can therefore be said to be essentially equivalent to normal wood so far as the mechanical properties tested in this study are concerned.Given at FPRS meeting in Dallas, Texas, June 1972 相似文献
13.
Small wood beams were loaded in a controlled environment to evaluate the effect of axial stress and strain on the equilibrium moisture content (EMC) of the tensile face. It was determined that the bending stress and the associated strain caused by the loading scheme increased the EMC of the wood along the extreme tensile face at the point of maximum bending moment. 相似文献
14.
We measured Young's modulus, proportional limit stress, and bending strength by the compression bending test and examined the applicability of the testing method by comparing it with conventional bending test methods. Long columns of todomatsu (Japanese fir,Abies sachalinensis Fr. Schmidt) with various length/thickness ratios were the specimens. A compressive load was axially applied to the specimen supported with pin ends. Young's modulus, the proportional limit stress, and the bending strength were obtained from the load-loading point displacement and load-strains at the outer surfaces until the occurrence of bending failure. Four-point bending tests were also conducted, and the bending properties obtained were compared with the corresponding properties obtained by the compression bending tests. Based on the experimental results, we believe that when the stress-strain relation is measured by the load-loading point displacement relation using specimens whose length/thickness ratio is large enough, the bending properties can be obtained properly using the compression bending test. 相似文献
15.
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
16.
Distributions of growth strains in branches, straight trunks and basal sweeping trunks of Chamaecyparis formosensis Matsum. trees were measured with strain gauges. Microfibril angles (MFAs) of the S2 layer of the cell wall were measured by the iodine deposition method and their relationships with growth strain examined. The magnitude of the compressive stress on the lower side of trunks with a basal sweep was greater than that of the tensile stress at the surface of straight trunks. However, transverse compressive stress was similar around the trunk regardless of whether normal wood or compression wood was present. The released surface growth strains varied with MFA. At MFAs of 20-25 degrees , growth stress changed from tension to compression, and compressive stress increased dramatically in the compression wood region. Branches suffer bending stress due to self-loading. This stress is superimposed on the growth stress. Growth strains on the upper or lower sides of branches were larger than those in the trunks, suggesting that generation of growth stress on the lower sides of branches with extensive compression wood is affected by the gravitational bending stress due to self-loading. We conclude that branch form is affected by the interaction between the bending moment due to self-loading and that due to the asymmetric distribution of growth stress. Growth strain distribution in a branch differed depending on whether the branch was horizontal, upward bending or downward bending. 相似文献
17.
V形件自由弯曲应力分析和最大弯矩计算公式 总被引：1，自引：0，他引：1
根据金属塑性成形原理和平板理论,结合卸载前后的板料的弯曲特点,推导出了V形件自由弯曲时的应力和最大弯矩的计算公式,为研究V形件自由弯曲时的回弹、破裂和冲压设备的选型提供理论依据. 相似文献
18.
以中性层为中心,说明不同弯曲方法对沙发扶手成型的影响;分析了木材中性层的偏移量与木材极限拉伸强度、极限压缩强度的关系,以及使用钢带可有效增大中性层偏移量的原理,为沙发扶手生产成功率的提高提供理论分析方法。 相似文献
19.
Summary An adaptor for the conversion of a high-accuracy tensile creep machine to compression loading is described. It was found that a stable mechano-sorptive creep limit could be obtained by a suitable load reduction after moisture cycling; after which further creep and creep recovery just balanced each other. In this stable state the value of the longitudinal moisture-swelling coefficient depended on the strain; being less with tensile strain and more with compressive strain then in the unloaded condition. These differences in the swelling coefficient could explain the apparent recovery during subsequent sorptions in mechanosorptive creep in bending. Such a hypothesis was strongly supported by numerical comparisons of strains in bending, tension and compression.Part of the equipment used in this project was purchased with a grant from the U.K. Science and Engineering Research Council 相似文献
20.
Hiroya Ohbayashi Rudolf E. Booker Roderick D. Ball Bradley G. Ridoutt 《Journal of Wood Science》2001,47(3):233-236
New equipment was developed to measure the strength of individual annual rings in green wood under predominantly tensile stress. This equipment was then used to assess the variation of the radial modulus of rupture (rMOR) in thirty-six 25-year-old radiata pine trees taken from three sites in New Zealand. The rMOR for individual rings ranged from 4.2 to 12.7 MPa and was calculated on the assumption that during bending of the specimens fracture was caused by the tensile force in the radial direction (i.e., perpendicular to the tangential-longitudinal plane). No consistent trends were observed in rMOR from pith to bark; nor was there any evidence of differences between the three sites. However, there was substantial between-tree variability that manifested mainly in different average rMOR values for the trees rather than in variations from pith to bark. These results indicate that there are no concerns with respect to splitting resistance for the juvenile wood of radiata pine. It will be of interest to investigate whether splitting resistance is under genetic control. 相似文献