共查询到20条相似文献,搜索用时 31 毫秒
1.
Fretting causes considerable reduction in the fatigue strength of a shrink-fit assembly and failures through fretting are as numerous as failures from normal fatigue. The purpose of this investigation was to determine the effect of contact pressure and slip amplitude on the fatigue limit, and a favourable value for overhang of hub and fillet radius with constant diameter ratio, at which fretting failure can be avoided and the maximum normal fatigue strength will be obtained. The torsional fatigue strength of shrink-fitted shaft couplings was estimated by tests performed by varying the overhang of the hub, the fillet radius of the shaft and the contact pressure of the shrink-fitted assembly. Press-fitting of the hub overhanging the shoulder was used to increase the contact pressure. The tests were performed using a grooved hub. These experiments showed that fretting was reduced with an increase in contact pressure, because the slip amplitude decreased. The shaft was fractured just inside the end of the fit by fretting fatigue with low contact pressure, but if the contact pressure was very high, the shaft fractured at the fillet by normal fatigue. The fretting fatigue limit at a constant diameter ratio increases with an increase in the fillet radius, and reaches its maximum value at a certain radius using the grooved hub. 相似文献
2.
3.
4.
为有效降低齿轮箱故障特征的维数并提高诊断效率,提出了基于邻域属性重要度与主成分分析法相结合的齿轮箱故障特征约简方法,并利用支持向量机和BP神经网络对诊断的准确率进行对比分析。针对齿轮箱中具有不同程度裂纹的齿轮,选取其时域、频域和基于希尔伯特变换的36个特征;将邻域模型引入到特征属性的约简,构造前向贪心算法,以邻域属性重要度较大的9个特征作为特征集,提取累积贡献率达到95%以上的主成分,分别输入支持向量机和BP神经网络分类器中进行分类识别,并与不经过特征优选的主成分特征融合相对比。结果表明,采用基于邻域属性重要度与主成分分析法相结合的特征约简方法,既可以降低齿轮箱故障特征的维数,又不影响对其运行状态的表征,有助于识别不同裂纹水平的齿轮,与不经过特征优选直接进行融合的方法相比,所提出方法诊断准确率更高,训练时间更短。 相似文献
5.
车轮多边形是高速列车运行过程中常见的磨耗现象,该现象使轮轨作用力增大,齿轮箱持续异常振动,并会影响其疲劳寿命。为研究高速列车车轮多边形对齿轮箱疲劳寿命的影响,建立了含有齿轮箱支撑轴承的驱动系统和柔性齿轮箱的刚柔耦合整车动力学模型,采用数值仿真分析方法,通过分析不同车轮多边形幅值下轮轨垂向力和齿轮箱垂向振动加速度确定极端工况,对该工况下的齿轮箱进行应力分析并确定危险点,进而分析这些点的疲劳寿命。研究发现:列车在350 km/h三阶0.1 mm车轮多边形极端工况时,轮轨垂向力及齿轮箱垂向加速度明显增大,齿轮箱剧烈振动,此时齿轮箱多处出现应力集中,存在多个危险点。其中齿轮箱输出轴轴承端支撑筋处应力最大,该危险点疲劳寿命只能达到256万km,远小于1200万km的正常寿命。因此,在高速列车实际运营中要高度重视车轮多边形对齿轮箱疲劳寿命带来的影响,可通过车轮镟修来降低车轮多边形对齿轮箱疲劳寿命的影响。 相似文献
6.
7.
Sung Ho Kim Rjeon Hwan Bae Jae Do Kwon 《Journal of Mechanical Science and Technology》2012,26(7):2107-2110
Wire rope in elevators can become disconnected by tensile stress from friction between the rope and sheave, and by repeated stress including bending stress from various effects formed during contact between the rope and sheave. It is known that in designing wire rope, its strength is affected when wire disconnection occurs. However, insufficient related data is available. Therefore, fracture strength reduction and the effect of bending fatigue on wire rope life is difficult to evaluate. We considered the effects of wire rope diameter and tensile stress on fracture strength and wire rope life. We observed that fracture strength rapidly decreased when bending fatigue accumulated at the same time that the wire became disconnected. Moreover, bending fatigue was shown to be a crucial factor in decreased wire rope life. 相似文献
8.
To clarify the effect of hydrogen gas on fretting fatigue strength of the materials, which supposed to be used for hydrogen utilization machines, fretting fatigue tests were conducted in hydrogen gas. It is important to take fretting fatigue into account in strength design, because many fatigue failure accidents have occurred at joints or contact parts between components. As a part of the experiments, an austenitic stainless steel was focused in this paper. The material was SUS 304. Fretting fatigue strength in hydrogen gas decreased compared with that in air. Tangential force coefficient increased in the reverse order of fretting fatigue strength. Therefore, one of the reasons of the decrease of fretting fatigue strength was that tangential force was different depending on the environment. Absorption of hydrogen occurred during fretting in hydrogen gas was detected. The absorption could be considered as one of the causes of the decrease of fretting fatigue strength, since fretting fatigue life of pre-charged specimen was decreased and also the crack propagation threshold of short fatigue crack was reduced by hydrogen charge. 相似文献
9.
10.
11.
The cause of the ICE train derailment, which occurred in 1998 at Eschede, was fatigue failure originating on the inside of the wheel tire. Rubber-sprung resilient wheels were used for the trailer cars. The wheel tire is mounted on the wheel disc. Thirty-four rubber pads were arranged between the wheel disc and the wheel tire. It was postulated that fretting fatigue between the rubber block and the inner side of the tire might have an influence on the initiation of the incipient crack. In order to clarify the influence of the rubber contact on the fatigue strength of the tire, fretting fatigue experiments under rubber contact conditions were performed. During the fundamental fretting fatigue test using bridge pads and small size carbon steel specimens, no typical fretting damage such as fretting wear and minute cracks were observed due to contact of the rubber. Stress conditions of the rubber-sprung wheel under vertical and lateral wheel loads were evaluated by a three-dimensional elastic stress analysis. Since the rubber is a super-elastic material, the Mooney-Rivlin model was used in the FEM calculation. It was found that the wheel tire is subjected to a cyclic stress during one revolution of the wheel and the maximum stress occurred at the center of the inner surface of the tire where the fatigue crack initiated. Fatigue strength of the wheel tire was determined by the rotating bending fatigue testing of specimens taken from the tire. It was found that the tire with an 862 mm diameter at a wheel load of 80 kN had a safety factor more than 3.5 from a fatigue limit diagram with a failure probability of 0.01. To confirm the fretting damage under the rubber contact and the result of the fatigue strength evaluation, fatigue tests of a full size wheel were made. After 20 million cycles at the wheel load of 280 kN, which was just below the endurance limit estimated by the endurance limit diagram, no fretting damage and no fatigue cracks were observed. The wheel was, however, fractured at 1.56 million cycles under the maximum load of 308 kN, which was just above the endurance limit. The estimation of the safety factor of 3.5 estimated from the endurance diagram was confirmed by the full size fatigue testing. It was concluded that there was no effect of fretting due to the rubber contact on the fatigue strength of the rubber-sprung single-ring railway wheel. 相似文献
12.
雷达天线座方位减速箱箱体的有限元分析 总被引:2,自引:0,他引:2
对箱体的方案设计进行有限元分析。运用Pro/E软件建模,考虑到分析的侧重点,对模型进行适当简化。用ANSYS软件对箱体结构进行分析,得到位移和应力分布以及固有频率等结果,藉此反映箱体的设计效率和可靠性,为箱体的优化设计提供帮助。 相似文献
13.
14.
The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines 总被引:1,自引:0,他引:1
The objective of this study is the characterization of the fretting fatigue strength in a hydrogen gas environment. The test materials were a low alloy steel SCM435H, super alloy A286 and two kinds of austenitic stainless steels, SUS304 and SUS316L. The test was performed in hydrogen gas at 0.12 MPa absolute pressure. The purity of the hydrogen gas was 99.9999%. The fretting fatigue limit was defined by the fretting fatigue strength at 30 million cycles. For all materials, the fretting fatigue strength in the hydrogen gas environment increased in the short-life region. However, the fretting fatigue strength in the hydrogen gas environment decreased in the long-life region when exceeding 10 million cycles except for SCM435H, while there was no reduction in the fretting fatigue strength in air between 10 and 30 million cycles. The reduction rate was 18% for A286, 24% for SUS304 and 7% for SUS316L. The tangential force coefficient in the hydrogen gas environment increased when compared to that in air. It can be estimated that this increase is one of the causes of the reduced fretting fatigue strength found in a hydrogen gas environment. In order to discuss the extension of the fretting fatigue life in hydrogen gas observed at the stress level above the fretting fatigue limit in air, continuous measurement of the fretting fatigue crack propagation was performed in a hydrogen gas environment using the direct current potential drop method. As a result, it was found that the extension of the fretting fatigue life was caused by the delay in the start of the stable crack propagation. 相似文献
15.
16.
Utilisation of hydrogen is expected to be one of the solutions against the problems of exhaustion of fossil fuels and reduction of carbon dioxide emissions. Evaluation of the materials for hydrogen utilisation machines is required. The objectives of this study are the characterisation of fretting fatigue strength of low‐alloy steel SCM435H and heat‐resistant steel SUH660, and the validation of effectiveness of nitriding in hydrogen gas environment. Fretting fatigue tests were conducted up to 3 × 107 cycles. The decrease of fretting fatigue strength in hydrogen gas environment was found at the long‐life region exceeding 107 cycles. The amount of the decrease of the fretting fatigue limit at 3 × 107 cycles was 11% for SCM435H and 15% for SUH660. However, at the stress level above the fretting fatigue limit in air, the finite life in hydrogen gas increased more than that in air. The cause of extension of fatigue life was the delay of start of stable crack propagation. Fretting fatigue crack, which was smaller than 200 µm in length, consumed approximately 60% of the fatigue life in hydrogen gas environment. Fretting fatigue crack was steadily propagated after the test was started in air. Observations of the fretted surface showed that the fretting wear process in hydrogen gas environment was dominated by adhesion. Tangential force coefficient was higher in hydrogen gas environment than that in air. It is considered that the adhesion has a close relation to crack initiation in hydrogen gas environment, and as a result, the failure of specimen occurred at a lower stress level comparing the fretting fatigue limit in air. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
17.
18.
Rolling bearings in wind turbine gearboxes occasionally fail prematurely due to white etching cracks. The appearance of preparatively opened fracture faces indicates damage initiation from the surface in most cases due to brittle spontaneous tensile stress–induced cracking. Under the influence of decomposition products of the penetrating lubricant, branching crack growth is subsequently driven by corrosion fatigue. The material response analysis of rolling bearings from all gearbox locations, based on X-ray diffraction residual stress measurements, reveals vibrations in service as the root cause of surface crack initiation. The occurrence of high local friction coefficients in the rolling contact is described by a tribological model. Depth profiles of the equivalent shear and normal stresses are respectively compared with the measured residual stress patterns and a relevant fracture strength. White etching crack failures are experimentally reproduced on a rolling contact fatigue test rig under increased mixed friction. Causative vibration loading is evident from material response analysis. The generation of compressive residual stresses by cold-working the surface is proven to be an effective countermeasure. 相似文献
19.
根据起重机车轮的工作应力和疲劳强度的概率分布,采用疲劳可靠性设计方法,对车轮进行分析计算,建立车轮许用轮压与起重机机构工作级别、车轮直径、轨道曲率半径及材料疲劳强度极限等因素之间的关系,为起重机车轮的合理选用提供了一种理论依据。 相似文献