鼓形齿式联轴器

鼓形齿式联轴器鼓形齿式联轴器比老式直齿联轴器接触状况好，允许有一定的角位移，具有承载能力高、寿命长等特点。工业发达国家在７０年代就广泛使用该种联轴器。该技术所推广的鼓形联轴器包括ＧＩＣＬ和ＧＩＣＬ两种系列，其主要技术指标为：ＧＩＣＬ１～３０公称扭矩６...     

重点成果推广

鼓形齿式联轴器比老式直齿联轴器接触状况好,允许有一定的角位移,具有承载能力高、寿命长等特点。工业发达国家在70年代就广泛使用该种联轴器。该技术所推广的鼓形联轴器包括GⅠ CL和G Ⅱ CL两种系列,其主要技术指标为:G Ⅰ CL1～30公称扭矩630～2800000N·m;许用转速500～4000r/min;轴孔直径38～630mm;G Ⅱ CL1～25公称扭矩355～4000000N·m;许用转速460～4000r/min;轴孔直径16～1000mm。鼓形齿式     

扭矩测量方法现状及发展趋势

按照不同的测量原理,将扭矩测量方法分为平衡力法、能量转换法和传递法三大类.根据被测物理参数的不同,重点分析了应用最为广泛的传递法扭矩测量所包含的各种方法,阐述了这些方法的原理、特点和适用范围,并归纳出扭矩测量方法的主要发展趋势.     

整枝机传动装置中矩形截面弹簧的研究

整枝机传动装置中矩形截面弹簧是实现扭矩传递、速度改变、转向改变、柔性传动的重要零件,应用有限元方法分析其受力情况,并通过Hypermesh软件、ANSYS有限元软件取得弹簧的力学参量分布。本文旨在研究矩形截面弹簧在传动过程中的作用,提出一种矩形截面扭转弹簧的有限元分析方法。     

几种新型联轴器简介

1 引 言在机械行业中,联轴器是常用部件,广泛应用于各种机械传动中,用以传递运动和动力。联轴器根据内部是否包含弹性元件,可以划分为刚性联轴器和弹性联轴器两大类。其形式繁多,且大多数都是从结构上采取各种措施,使两轴偏移的状态得到改善。因各种联轴器均存在着不足之处,所以,在该领域内的创造和改进工作仍然十分活跃。笔者根据查阅的资料,介绍几种新型联轴器。     

割灌机离合器工作特性的研究

本文在简要分析割灌机离合器的构造和工作原理的基础上，讨论了离合器在能传递发动机最大扭矩的条件下，如何使离合器的扭矩特性与发动机特性合理匹配的问题．并在此基础上，提出了可作为评价离合器扭矩特性的综合结构系数的新概念．为设计者比较各种型式的离合器的性能，设计新型的、性能优良的离合器提供了参考．     

单板旋切新技术—动力防弯压辊

目前采用的旋切方法是用卡爪夹紧并旋转木段,提供木段所需的全部扭矩以克服旋切阻力。这种方法有两大缺点:①卡爪容易在木段端部打滑。木芯直径由卡爪直径决定,用较小的卡爪可减小木芯直径,但能传递的扭矩也随之降低。当旋转木段所需扭矩超过卡爪能传递的扭矩时就发生打滑现象,使旋切不能继续进行,剩下木芯的直径较大。若采用双卡轴,打滑常发生在外卡轴缩回时,估计胶合板厂的木段打滑率约占5—8%,这样降低了单板的出材率。②某些腐心材因不能被卡爪夹紧而不能旋切,缩小了旋切单板的资源。     

基于磁弹性的扭矩测量实验台设计及其技术指标分析

基于磁弹性原理设计并搭建了扭矩测量实验台,其主要技术指标为:量程0～100N.m、线性度和重复性两个误差指标均为0.1%。扭矩测量结果表明,在磁头与轴不同间隙条件下,扭矩与磁感应强度之间始终存在线性正比例关系,依据这种关系并利用磁力计先测量出磁感应强度值,然后再计算出相应的扭矩值,以实现扭矩的间接测量。     

分段式转子铁心压装工艺技术研究

针对某型异步风力发电机分段式转子铁心压装过程中存在片间压力及通风槽宽度尺寸难控制的问题,提出了保证分段式转子铁心压装可靠性的工艺方法.首先,利用最小二乘法建立发电机转子铁心压缩量与压装力的关系;其次,根据要求的片间压力值设定压装转子铁心的油压机压力和螺栓扭矩值,测定油压机泄压后转子铁心剩余压缩量及最终螺栓扭矩值,判定铁...     

竹塑复合材料流变行为分析

以竹粉和聚丙烯粉剂为原料,马来酸酐接枝聚丙烯为相容荆,通过转矩流变仪测试混合物料在熔合状态下扭矩、温度及时间的变化情况,同时分析了不同粒径竹粉对混合体系流变性能的影响.试验结果表明:混合体系的最大扭矩、平衡扭矩及平衡时间与竹粉粒径的关系基本都呈类抛物线关系,随着竹粉粒径的增大呈现先增大后减小的趋势,即竹粉粒径在20～40目、200目时,流变参数值较小,流变性能比较好.     

On the distribution of tree growth stresses

Summary Growth stress distributions in trees are derived using the hypothesis that longitudinal and circumferential growth strains are continuously induced at the periphery of the growing stem. A plane strain combined with pure torsion model is used to compute the internal stresses and strains due to forces and moments caused by the new growth increment. The twisting angle of the pure torsion model is caused by the shear stresses set up in the growth increment as the growth strains are induced along the grain axis and the coupling of axial and torsional effects due to the elastic constants for the inclined grain material. Detailed stress distributions are derived for a range of constant grain angle cases. The extreme sensitivity of the torsional shear distribution to small grain angles is noteworthy.This work was supported in part by NSF Grant ENG 74-02428     

Pseudodynamic tests and earthquake response analysis of timber structures III: three-dimensional conventional wooden structures with plywood-sheathed shear walls

Pseudodynamic (PSD) tests were conducted on plywood-sheathed conventional Japanese three-dimensional (3D) wooden structures. Lateral load was applied to the edge beam of specimen structures to generate eccentricity loading. Specimens were based on a combination of shear walls with openings in the loading direction and horizontal diaphragms with different shear stiffness. The principle deformation of the horizontal diaphragm was torsion for rigid diaphragms and shear deformation for flexible diaphragms. Lumped-mass time-history earthquake response analysis was conducted on the tested structures, and additional calculations were conducted on structures with different eccentricity rates. Dynamic analyses were conducted by varying the masses and the resistance of the walls in the loading direction. The simulated peak displacement response in the loading plane agreed comparatively well with the PSD test results. The maximum displacement response on changing the wall resistant ratio showed almost the same tendency as that obtained by changing the mass ratio up to an eccentricity rate of 0.3; however, the maximum displacement response increased markedly beyond an eccentricity rate of 0.4. It was proved that the lumped-mass 3D model proposed in this study was appropriate for conducting a parameter study on the 3D dynamic behavior of timber structures.     

林业数字式测高测距仪的研制

林业数字式测高测距仪是以测量新方法树基标尺法和前后标尺法为理论基础,以倾角传感器、单片机、显示屏等电子器件所组成的集中电路并结合机械设计与加工为技术特征的仪器装置.仪器具有结构轻巧、操作简便、高精度与高效率等特点,主要解决了森林计测中测点灵活选择与数字化测高测距问题.对其构造、原理、特点等进行了阐述,以期将科技成果迅速转化为现实生产力.     

累积流量坐标系下河流二维水质模型流管划分技术研究

针对广泛应用的河流累积流量二维水质模型手工流管划分存在的缺陷，提出了计算机流管划分的原理，并给出了详细的计算机流管划分的步骤、方法和应用实例。该方法具有很强的可编程性，能极大地减轻科研人员的劳动强度，提高科研效率，增加计算方案的灵活性。     

Viscoelastic properties of wood in swelling systems

Summary The torsion modulus and the mechanical damping were investigated on wood swollen with formamide and a series of glycols, at frequencies of 0.5 and 0.02 Hz as a function of temperature. In wood swollen with formamide to the same extent as it would swell when saturated with water, the temperature of maximum damping was about 48° and above 100°C for wood swollen with polyethylene glycols, while that of water saturated wood was 80°C. For more highly formamide swollen wood (1.2 times the swelling in water) the temperature at which maximum damping develops decreased to 30°C. With regard to the influence of swelling and temperature on the torsion modulus of wood, three regions of viscoelastic behavior were recognized in these swelling systems. They are the glassy region in non-swollen wood, where the torsion modulus decreases gradually with increasing temperature, the transition region where the torsion modulus decreases abruptly with increasing temperature and swelling, and a plateau region appearing at high temperatures for highly swollen wood where the torsion modulus remains fairly constant with temperature with a value of about one tenth the modulus for non-swollen wood.     

Fracturing of wood under superimposed tension and torsion

A testing method using circumferentially notched round bars for investigating mixed mode behaviour under loading in tension and torsion is applied to wood. The applicability of the method to anisotropic materials is investigated for two types of wood, beech and spruce, considering the longitudinal and radial orientation with respect to the stem axis of the tree. The strong anisotropy of wood requires different evaluation procedures for radial and longitudinal sample orientation. The K-concept of linear elastic fracture mechanics (LEFM) and concepts of non-linear elastic fracture mechanics (NLEFM) were used for the evaluation of radial and longitudinal samples, respectively. Differences between the investigated wood types under radial orientation, in their durability to withstand torsional loads, could be observed by examining ratios of the values of the fracture toughness in mode III against mode I. Micrographs of the fracture surfaces support the assumption that the higher amount of wood rays in beech is responsible for the higher toughness under torsion. In case of longitudinal specimen geometry it was found that at very high levels of torsional deformation beech and spruce reach similar values in their specific fracture energy in mode I.     

Variation of sapflow velocity in Eucalyptus globulus with position in sapwood and use of a correction coefficient

Sapflow sensors were used to investigate variation in sapflow velocity at different positions in the sapwood of three-year-old Eucalyptus globulus ssp. globulus Labill. trees. Sapflow velocity was measured at 5-mm intervals across the sapwood by moving two probe sets simultaneously on two opposite radii. Another probe set placed in a fixed position at right angles to the first two sets acted as a control. A sapflow velocity ratio was defined as the velocity given by each moving sensor divided by that given by the static sensor. Correlation between observations of sapflow velocity at different positions exceeded 95%, and the ratio of velocity between any pair of sensors was constant. We observed radial variation in sapflow velocity across the sapwood with the lowest velocities at the center of the tree. Variation due to sensor position was high implying the need for large numbers of sensors for accurate estimates of sap flux. To overcome this need, we used a correction coefficient, namely a simple weighted average of the sapflow ratios with depth in the sapwood, for each fixed sensor. We recommend the use of three probe sets to estimate the correction coefficient. Subsequently, two probe sets can be placed at two fixed positions for routine measurements of sap flux.     

Acoustoelastic birefringence effect in wood II: influence of texture anisotropy on the polarization direction of shear wave in wood

Ultrasonic shear waves were propagated through the breadth direction of a wood beam which was subjected to a bending load such that it was in a plane-stress state. The oscillation direction of the shear waves with respect to the wood beam axis was varied by rotating an ultrasonic sensor, and the relationship between the shear wave velocity and the oscillation direction was examined. The results indicate that when the oscillation direction of the shear wave corresponds to the tangential direction of the wood beam, the shear wave velocity decreases sharply and the relationship between shear wave velocity and rotation angle tends to become discontinuous. When the oscillation of the shear waves occurs in the anisotropic direction of the wood beam instead of in the direction of principal stress, the shear wave velocity exhibits a peak value. In addition, the polarization direction was found to correspond to the direction of anisotropy of the wood beam according to the theory of acoustoelastic birefringence with respect to plane stress. This indicates that when the acoustoelastic birefringence method is applied to stress measurement of wood, it is appropriate to align the oscillation direction of the shear wave with the principal axial direction of anisotropy in order to carry out ultrasonic measurement.     

杉木、马尾松轮作对林地土壤肥力和林木生长的影响

研究了杉木、马尾松人工林轮作对林地土壤肥力和林木生长的影响。结果表明：与连作相比，轮作林分土壤微生物数量增多，酶活性增强、土壤酚类物质减少、土壤酸度降低，盐基总量和盐基饱和度提高以及土壤有效养分增加，并由此导致了林分生长量的提高。轮作林分土壤肥力提高，林分生长量增加的实质在于：人工林林分实施轮作后，由于后茬植物与前茬植物种类的不同导致土壤微生物种类和数量增多，土壤生物活性增强，并由此而导致土壤酸度降低，有毒物质减少，速效养分增加。     

A hierarchical approach coupled with coarse DEM information for improving the efficiency and accuracy of forest mapping over very rugged terrains

Forest mapping over mountainous terrains is difficult because of high relief. Although digital elevation models (DEMs) are often useful to improve mapping accuracy, high quality DEMs are seldom available over large areas, especially in developing countries. In this study, a hierarchical approach coupled with topographic information derived from coarse DEM was developed to improve the efficiency and accuracy of forest mapping over mountainous areas. The overall idea of increasing mapping accuracy over large mountainous areas is to reduce spectral variety over areas to be mapped. The approach consists of three major steps. The first step is to partition a large mountainous area into several small mapping zones. Forest mapping is then conducted in each zone independently. At the second step, forest areas are separated from non-forest areas through a semi-automatic binary classification procedure. At the third step, forested areas are then further classified into detailed forest types by coupling Landsat ETM+ imagery and two topographic variables derived from a coarse DEM (extracted from 1:250,000 digital elevation contour layer, which are readily available). This hierarchical approach was illustrated and evaluated through a case study in Northwest Yunnan, China, a very rugged terrain in the world. Forests and non-forests were separated accurately and efficiently (the overall accuracy is 0.97 and Khat value is 0.94 of whole area). It was found that the inclusion of the coarse topographic data improved the mapping accuracy significantly (overall accuracy from 0.74 to 0.84, from 0.76 to 0.89, from 0.78 to 0.84 in three test areas, respectively), and that the difference in accuracy between the use of coarse DEM data and the use of fine DEM data for the study area is not significant (overall accuracy from 0.84 to 0.86). The results indicate that the hierarchical approach, coupled with coarse DEM information, is effective in increasing the accuracy of forest mapping over very rugged terrains when high quality digital elevation models are not available.