齿面粗糙度对齿轮传动接触疲劳应力的影响

对齿面粗糙度呈余弦分布的渐开线圆柱齿轮进行热弹流润滑数值计算,分析齿面粗糙度对齿轮传动接触疲劳应力的影响。结果表明:粗糙度会使轮齿接触区次表面发生明显的应力集中,粗糙度波长愈小,应力集中愈明显,且愈贴近齿轮表面;随着粗糙度波幅的增大,平均油膜厚度单调增大,而接触区次表面主剪应力的最大值呈抛物线变化;随着粗糙度波长的增大,平均油膜厚度迅速减小而主剪应力的最大值急剧增大,但当波长增至一定值时,二者各自趋于光滑齿面接触时的相应值。

齿轮接触疲劳极限应力快速测定法的应用

齿轮的点蚀破坏,是许多闭式齿轮传动的主要破坏形式,所以,齿面抗点蚀能力、齿面接触疲劳强度计算的准确度,就直接关系着齿轮传动的质量与寿命。采用快速试验法,即罗卡提方法,只用少量试件,可快速地得出试验齿轮材料的疲劳极限应力的预估值,并用MATLAB进行数据处理做出齿轮疲劳寿命曲线和损伤累计曲线。

点线啮合齿轮接触强度计算的研究

通过对点线啮合齿轮的啮合特点分析,提出了点线啮合齿轮最大接触应力计算点,并给出了经过修正的最大接触应力计算公式,包括单对齿C点的综合曲率半径计算公式。在最大接触应力计算中增加凹凸齿廓接触线长度变化系数和单对齿C点载荷系数,反映凹凸齿廓接触对所受载荷的影响。在许用接触疲劳应力计算中增加增强系数,反映间断工作的影响。

齿轮接触疲劳极限应力快速试验法

齿轮的点蚀破坏,是许多闭式齿轮传动的主要破坏形式。因此,齿面接触强度计算的可靠程度,选用的齿轮材料的接触疲劳极限应力的准确程度,就成为一个十分重要的问题。而在国家标准“渐开线圆柱齿轮承载能力计算”(GB3480-83)中所提供的齿轮的接触疲劳极限应力的框图,系来自ISO标准。它不一定符合我国各工厂的情况。因而,就必然影响了计算的准确性。然而,用常规的办法来做齿轮试验,是费时又费钱的。本文介绍了一种快速试验法,即罗卡提(Locati)方法。它只用一对试件,就可以求出疲劳极限应力,是一种省时省钱且切实可行的方法。本文主要介绍了它的基本原理,数据处理,点蚀判据,参考曲线以及我们在CL-100齿轮试验机上试验的实例。

Finite element analysis of contact fatigue and bending fatigue of a theoretical assembling straight bevel gear pair

The aim of this work is to propose a 3D FE model of a theoretical assembling straight bevel gear pair to analyze the contact fatigue on the tooth surface and the bending fatigue in the tooth root. Based on the cumulative fatigue criterion and the stress-life equation, the key meshing states of the gear pair were investigated for the contact fatigue and the bending fatigue. Then, the reliability of the proposed model was proved by comparing the calculation result with the simulation result. Further study was performed to analyze the variation of the contact fatigue stress and the bending fatigue stress under different loads. Furthermore, the roles of the driving pinion and the driven gear pair were evaluated in the fatigue life of the straight bevel gear pair and the main fatigue failure mode was determined for the significant gear. The results show that the fatigue failure of the driving pinion is the main fatigue failure for the straight bevel gear pair and the bending fatigue failure is the main fatigue failure for the driving pinion.

Effects of thickness and elastic modulus on stress condition of fatigue-resistant coating under rolling contact

The distribution and magnitude of surface substrates were investigated by finite element method and subsurface stresses of the （FEM）. The models of coating single-layer sprayed-coatings on monolithic configurations with different thicknesses and elastic modulus ratios of coating to substrate were introduced, and the effects of thickness and elastic modulus ratio on the stresses were addressed. The calculation results show that the coating/substrate interface shear stress obviously decreases with increasing coating thickness, due to the location of the maximum shear stress moving away from the coating/substrate interface. At the same time, the magnitude of von Mises stress also declines in the case of thicker coatings. However, the high elastic modulus ratio results in extremely high maximum shear stress and the severe discontinuity of the von Mises stress curves, which leads to the intensive stress concentration on the coating/substrate interface. So the coating configurations with the larger coating thickness and lower difference of elastic modulus between coating and substrate exhibit excellent resistant performance of rolling contact fatigue （RCF）.

自动变速器行星齿轮机构的优化设计

根据自动变速器行星齿轮机构的特点和要求,在保证传动比合理和体积减小等40个约束条件下,以行星齿轮机构中各齿轮强度均等或接近于优化目标,建立齿轮齿面接触疲劳应力差值最小和齿根弯曲疲劳应力差值最小的优化模型,并用MATLAB进行优化计算。与原设计比较,优化设计的行星齿轮机构的齿面接触疲劳应力和齿根弯曲疲劳应力的最大值、应力差值以及整体应力都下降,特别是齿根弯曲疲劳应力最大值减小了12.24%,而且所有齿轮的齿根弯曲疲劳应力几乎相等,优化效果明显。优化设计的行星齿轮机构体积比原设计小3.54%,而且在传动比、尺寸参数和工艺参数方面,优化设计也都有优势。

Subsurface crack propagation under rolling contact fatigue in bearing ring

The influences of subsurface cracks,distributing along the axial direction,on the rolling contact fatigue(RCF)faliure in a bearing ring are investigated.A realistic three-dimensional model of the bearing ring containing three subsurface cracks is used to evaluate the fatigue crack propagation based on stress intensity factor(SIF)calculations.Moreover,the distributions of the subsurface cracks along the axial direction are varied to study their effects on RCF.The results provide valuable guidelines for enhanced understanding of RCF in bearings.