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应力集中和表面完整性对平尾大轴抗疲劳性能的影响 总被引:4,自引:0,他引:4
某型飞机平尾轴在进行台架试验时发生断裂,失效分析表明,该轴的断裂性质为疲劳断裂,裂纹起源于大轴筒体内腔变截面过渡圆弧根部的加工刀痕谷底。通过对大轴进行扫描电镜观察分析,发现使用过的旧大轴内表面存在10~16 μm厚的“疏松”层,疏松层内有较多的疲劳微裂纹和孔洞,该“疏松”层是大轴服役中氧化腐蚀和疲劳损伤所形成的。“疏松”层的存在破坏了大轴的表面完整性,降低了大轴材料的抗疲劳性能。有限元建模分析表明,变截面台阶造成的结构应力集中和粗糙加工刀痕形成的附加应力集中是造成大轴疲劳断裂的力学因素,两种应力集中因素的联合作用降低了大轴的疲劳寿命,导致大轴在变截面过渡圆弧根部的加工刀痕谷底萌生疲劳裂纹。综合分析表明,大轴内表面“疏松”层的存在以及变截面台阶造成的结构应力集中和粗糙加工刀痕形成的附加应力集中是大轴发生疲劳断裂的主要原因。 相似文献
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本文对在役压力容器表面凹坑的实验作了介绍,分析了凹坑处应力集中系数与凹坑几何参数之间的关系,给出了最大应力集中系数和应力分布的经验公式。 相似文献
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用有限元法对内压柱壳开孔平齐接管的应力集中系数研究 总被引:1,自引:0,他引:1
本文在微机(IBM-PC/XT)上用有限元法对内压柱壳开孔平齐接管的应力集中系数进行了研究。为了在微机上能实施这种问题的研究,本文在程序设计上选择Q_(c5)、Q_6三维块体单元,使用波前法解方程,使所解问题的规模、结果精度和计算速度能保证在微机上进行。对计算模型、网格划分和单元形态方面做了若干数值试验,并同已知柱壳接管结构的实验结果比较,验证了本程序和所建立的柱壳接管有限元模型的可靠性。在0.05≤r/R≤0.7,0≤t/T≤1.4范围,取容器内外径比为1.05,进行了31个内压下开孔接管模型的计算,并根据柱壳、接管结构中应力集中系数与无量纲参数r/R、R/T和t/T的关系,将计算结果整理成不同几何参数下应力集中系数的曲线。该曲线用t/T=0.5、1.0和容器内外径比不同的实验结果作了验证,符合较好,可供设计者参考。 相似文献
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针对一种磨削表面微观形貌的应力集中问题提出了一种应力集中系数的精确计算方法。通过实验观察磨削工件表面微观形貌在进给方向具有沟壑状形貌特征,采用缺口模型分析计算磨削表面微观形貌应力集中系数;提出基于二维表面轮廓数据的缺口表征参数计算方法,建立无限大平面缺口模型并采用迭代法对模型进行修正,并用有限元方法进行对比验证。针对磨削表面微观形貌的应力集中系数与缺口模型特征参数-缺口的宽度、深度和谷底半径的定量关系,提供了对应的经验公式。研究工作为磨削表面微观形貌与应力集中系数关联规律研究提供一种定量计算方法,对分析磨削工件表面微观形貌的疲劳性能具有基础作用。 相似文献
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为了揭示Ni-P-Al2O3复合涂层的失效机理,对Ni-P-Al2O3复合涂层进行划痕试验和划痕过程的有限元模拟。划痕试验表明在Ni-P-Al2O3复合涂层的划痕表面上产生了一定间隔距离的横向表面裂纹。划痕过程的有限元模拟揭示在划痕过程的不同阶段涂层表面和界面上应力分布规律,揭示涂层表面裂纹产生的模式和形成的机理。划痕过程分为划针尖端压入涂层表面、在涂层表面上滑动和从涂层表面升高等3个阶段。前两个阶段由于划针尖端对涂层表面的作用,在涂层表面形成划痕沟槽,引起涂层表面产生裂纹。应力分析表明在划痕过程中涂层表面裂纹形成有两种方式。第一种方式是首先在涂层界面产生裂纹,然后裂纹向表面扩展形成表面裂纹;第二种方式是涂层表面直接形成表面裂纹。表面裂纹是最大拉应力引起的,因此,表面裂纹是第一型裂纹。划针尖端从涂层表面升高后在涂层中留下了较大的残余应力,最大残余拉伸应力是出现在接触中心之下的界面上的第一残余主应力。这些结果将为涂层设计和应用提供依据。 相似文献
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Neuber rule and Arola-Ramulu model are widely used to predict the stress concentration factor of rough specimens. However, the height parameters and effective valley radius used in these two models depend strongly on the resolution of the roughness-measuring instruments and are easily introduce measuring errors. Besides, it is difficult to find a suitable parameter to characterize surface topography to quantitatively describe its effect on stress concentration factor. In order to overcome these disadvantages, profile moments are carried out to characterize surface topography, surface topography is simulated by superposing series of cosine components, the stress concentration factors of different micro cosine-shaped surface topographies are investigated by finite element analysis. In terms of micro cosine-shaped surface topography, an equation using the second profile moment to estimate the stress concentration factor is proposed, predictions for the stress concentration factor using the proposed expression are within 10% error compared with the results of finite element analysis, which are more accurate than other models. Moreover, the proposed equation is applied to the real surface topography machined by turning. Predictions for the stress concentration factor using the proposed expression are within 10% of the maximum stress concentration factors and about 5% of the effective stress concentration factors estimated from the finite element analysis for three levels of turning surface topographies under different simulated scales. The proposed model is feasible in predicting the stress concentration factors of real machined surface topographies. 相似文献
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B. A. Shcheglov N. A. Makhutov N. V. Sharyi 《Journal of Machinery Manufacture and Reliability》2008,37(6):565-567
The influence of internal pressure on hardness of an elastic finite pipe element has been determined. This hardness increases under pressure under both compressive and stretching axial strains. 相似文献
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The use of conductivity as a means to determine the volume fraction of solids in a suspension of poorly conductive solids in water combines the benefits of high sampling rates and ease of use at the cost of a high sensitivity to salinity and fluid temperature. In this paper we investigate a custom built CCM, to which a third parameter was found to be of much influence: the grain size of the suspended phase. This paper describes a calibration experiment with which the influence of grain size on the CCM output has been investigated. The data give rise to an alternative calibration curve which is different from the regular effective media theories. 相似文献
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A method is given for the calculation of creep rupture strength of parts containing stress concentrations. The creep theory takes account of the damage and anisotropy of materials. which arise during deformation. For the example of a plane specimen with a notch, results of calculations are compared with experimental data. The results of an investigation into the creep strength of the fir-tree root of a turbine blade at non-stationary loading is given. 相似文献
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基于钢制薄壁压力容器的可靠性研究,确定了超高压圆筒在耐压试验与正常操作状态下的许用可靠度系数,采用应力-强度干涉模型,建立了超高压圆筒爆破安全系数、试验压力系数与许用可靠度系数三者之间的关系。研究表明:1)超高压容器爆破压力许用可靠度系数,在耐压试验时的范围应不小于3.31且不大于6.81,在正常操作时应不小于3.91且不大于7.57。2)基于满足许用可靠度系数范围,采用福贝尔(Faupel)公式设计径比在1.33与4.71之间的超高压圆筒,当圆筒材料的屈强比在0.4997与0.8852之间时,爆破安全系数的最小值为2.50,对应的试验压力系数应不小于1.08且不大于1.25。 相似文献