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71.
72.
The study aims to explore the effect of tangential force on wear and rolling contact fatigue (RCF) behaviors of wheel material using a JD-1 wheel/rail simulation facility. The normal, tangential and lateral forces between the wheel/rail rollers are controlled, and the magnetic power brake was used to generate the tangential forces (16–330 N). The results indicate that the surface hardness and wear loss of wheel rollers increase with the tangential force increasing. The surface cracks mouths are perpendicular to the resultant directions of the frictional forces. There are visible secondary cracks and multilayer cracks and the interlayer material of multilayer cracks are easy to break. The compositions of wear debris consist of Fe2O3, Fe3O4 and iron. 相似文献
73.
Over a four year period, six phases of testing were performed to observe the influence of age at loading, applied stress level, mix composition and relative humidity on the tensile creep of concrete. From these investigations it was possible to develop a model which allowed the prediction of tensile creep based on a knowledge of the compressive strength of the concrete (determined at the age of loading), the applied stress level and the relative humidity. Subsequently, this model was validated using the results from three independent investigations. Compressive creep as well as tensile creep was also obtained. This allowed a comparison of compressive creep with tensile creep and illustrated that on the basis of equal stresses, tensile creep is on average between 2 and 3 times greater than compressive creep (the maximum ratio is in excess of 8). For this investigation, however, on the basis of stress/strength ratio the difference between tensile and compressive creep is less significant. Considering a simply supported flexural reinforced concrete element, the investigation suggests that it is unwise to consider actual compressive creep equal to actual tensile creep as is often the case in design practice. 相似文献
74.
Based on experimental data found in literatures, four traditionally multiaxial fatigue life criteria are analyzed and verified. It is discovered that these conventional criteria cannot reflect well the combined effect both under tension and torsion loadings for some materials, such as 6082-T6 and AlCu4Mg1, due to lack of enough consideration about the influence of stress amplitude ratio and stress level on fatigue life even under proportional loading. In order to solve this problem, a new approach of fatigue life prediction, based on the equal-life curve, is proposed and it is composed of three parts: the multiaxial fatigue life surface, a new path-dependent factor for multiaxial high-cycle fatigue and a material parameter describing material sensitivity to non-proportional loading. Finally, the precision of the presented approach is systematically checked against the experimental data found in literatures for four different materials under proportional and non-proportional loadings. 相似文献
75.
Fatigue crack initiation and damage characterization in Brazilian test specimens for adhesive joints
D. Vicentini A. Crocombe A. Barroso F. París V. Mantič 《Journal of Adhesion Science and Technology》2014,28(14-15):1418-1431
The present study is focused on the fatigue failure initiation at bimaterial corners by means of a configuration based on the Brazilian disc specimens. These specimens were previously used for the generalized fracture toughness determination and prediction of failure in adhesive joints, carried out under static compressive loading. Under static loading, local yielding effects might affect the asymptotic two-dimensional linear elastic stress representation under consideration. Fatigue loading avoids this fact due to the lower load levels used. The present tests were performed using load control; video microscopy and still cameras were used for monitoring initiation and crack growth. The fatigue tests were halted periodically and images of the corner were taken where fatigue damage was anticipated. Damage initiation and subsequent crack growth were observed in some specimens, especially in those which presented brittle failure under static and fatigue tests. These analyses allowed the characterization of damage initiation for a typical bimaterial corner that can be found in composite to aluminium adhesive lap joints. 相似文献
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铝/镁异种金属复合结构在结构轻量化领域具有极大的应用价值。采用新型搅拌摩擦点焊-钎焊技术(friction stir spot welding-brazing,FSSW-B)对铝/镁异种金属进行搭接点焊,同时与搅拌摩擦钎焊(friction stir spot brazing,FSSB)工艺进行对比,研究焊接工具中搅拌针的存在对接头界面组织与力学性能的影响。FSSW-B接头界面中间层分为明显上下2个部分,上层界面主要为MgZn2相,下层界面主要为Mg7Zn3相;FSSB接头主要为MgZn2相。接头的断裂模式主要为界面剥离断裂,由于搅拌针的存在,出现了眉状断裂模式。搅拌针的存在提高了接头的抗拉剪性能与疲劳性能,FSSW-B接头的最大抗拉剪力为7600 N,疲劳极限为3366.6 N;搅拌针使抗拉剪性能提升了53.5%,使疲劳性能提升了11.4%;FSSW-B中搅拌针的存在增加了接头疲劳性能的分散性。 相似文献
80.
通过断口(宏观)形貌分析、微观组织分析、化学成分检测以及硬度测试等手段对SCM435钢发动机缸盖螺栓的疲劳断裂进行失效分析。结果表明,失效SCM435钢缸盖螺栓的化学成分和显微组织合格,硬度符合技术要求。失效样件1的断裂原因为表面脱碳引起的脆性断裂,螺栓断裂部位的表面脱碳层宽为120μm;失效样件2主要是非金属夹杂物所引起的疲劳断裂,近球状的CaS-CaO-Al2O3-MgO复合型冶金夹杂物造成了沿晶裂纹。对材料的塑韧性、表面脱碳及非金属夹杂物等指标,提出了改善建议。 相似文献