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针对应力场强法中场径计算方法存在争议且不易求取的问题,基于应力场强法假设,研究了场径参数计算方法的理论依据;在考虑场径求取可行性的基础上,提出一种在任意载荷条件下确定试件场径的方法.给出了场径的求取步骤,选取6块不同应力集中系数的缺口试件在4种应力比下,按照步骤求取场径.对场径计算结果拟合并作图,由图所示分析影响场径大小的因素.得出结论:在相同应力比下,场径与应力集中系数呈很强的线性关系;在相同应力集中系数下,场径与应力比呈很强的二次曲线关系.通过实例对所提出的方法进行了验证,结果表明:由提出方法确定的场径计算得出的疲劳寿命更贴近于试验寿命,在保证安全的基础上提高了疲劳寿命预测的准确性. 相似文献
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疲劳是涡轮叶片的一种主要失效模式.本文开展了DD11单晶合金在650℃中温条件下2种应力集中系数(K_t=1(光滑状态)、K_t=3(缺口状态))的旋转弯曲疲劳性能研究,对比了2种应力集中系数下的疲劳强度,并开展了相关断口分析.结果表明:应力集中系数由K_t=1增大到K_t=3时,疲劳极限由446 MPa降低为311 MPa,说明DD11单晶合金疲劳性能存在应力集中敏感性;疲劳寿命由10~5提高到10~7时,光滑状态由600 MPa降低为420 MPa,疲劳强度降低幅度为180 MPa,而缺口状态由370 MPa降低为290 MPa,降低幅度为80 MPa,说明应力集中条件下DD11单晶合金的疲劳寿命对于外载变化较敏感.断口分析表明,光滑试样断口(应力500 MPa/疲劳寿命9.7×10~5)由几个相交的光滑晶体学平面组成,疲劳源萌生在距表面100μm左右的铸造孔洞;缺口试样断口(应力340 MPa/疲劳寿命8.1×10~5试样)呈平面状,与应力轴垂直,为多源疲劳模式,疲劳源观察到小刻面,在加工刀痕不连续位置萌生. 相似文献
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针对航空用TB6高强钛合金,本工作研究了应力集中条件下喷丸对其疲劳性能的影响规律.采用旋转弯曲疲劳试验机分别测试了两种应力集中系数的试棒的疲劳寿命及极限,采用扫描电镜分析了疲劳断口,采用MTS试验机测试了试棒的拉伸性能,并采用白光干涉仪测试了试样的表面形貌.结果表明:当应力集中系数由Kt=1提高至Kt=2时,TB6钛合金试棒的疲劳极限从537.5 MPa下降至335.5 MPa,表现出明显的应力集中敏感性.而经过喷丸后,Kt=1和Kt=2的试棒的疲劳极限分别提高了33.5%和22.2%,缺口敏感性下降了48%.喷丸有利于降低TB6钛合金的疲劳应力集中敏感性. 相似文献
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骆文娟 《中国新技术新产品》2009,(8):80-81
本文分析了库伦土压力理论在其计算回填土墙的土体侧压力的计算值与实际值之间产生误差的原因,根据实际测试结果提出了修正系数,使得计算结果与实际结果相一致。 相似文献
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本文给出了一个新的针对应力控制接触疲劳问题的寿命预测模型。在该模型中,选用Mises等效应力作为接触疲劳应力控制参量;引进了非零的接触疲劳应力强度值,根据损伤力学理论,分析了接触疲劳应力强度值与基体材料性质,第二相夹杂之间的关系,同时考虑了表面起裂和亚表面起裂两种失效形式,并将对这两种失效形式的寿命预测统一到一个公式中,引进一个与油膜系数Λ有关的系数f(Λ),来表征润滑程度对接触疲劳寿命的影响。应用该模型来预测一些实验的接触疲劳寿命,计算值与实测值吻合很好。 相似文献
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通过计算裂纹尖端应力强度因子及疲劳裂纹扩展速率da/d N,由C.Paris模型推导出安全寿命Nf,由Bathias公式计算"哑铃"状钛合金试样的裂纹扩展寿命。通过理论计算和有限元分析超声疲劳"哑铃"状试样,得出应力最大位置。利用有限元仿真和实验数据分析TC4钛合金疲劳寿命。在20 k Hz的超声疲劳试验中,试样的断口位置表明:TC4钛合金材料内部缺陷是试样萌生裂纹使断裂位置偏离最大应力处的主要原因。并得出疲劳裂纹萌生阶段寿命决定"哑铃"状试样的疲劳寿命。 相似文献
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C. D. Lykins S. Mall & V. Jain 《Fatigue & Fracture of Engineering Materials & Structures》2001,24(7):461-473
The purpose of this study was to investigate the fretting fatigue crack initiation behaviour of titanium alloy, Ti–6Al–4V. Fretting contact conditions were varied by using different geometries of the fretting pad. Applied forces were also varied to obtain fretting fatigue crack initiation lives in both the low- and high-cycle fatigue regimes. Fretting fatigue specimens were examined to determine the crack location and the crack angle orientation along the contact surface. Salient features of fretting fatigue experiments were modelled and analysed with finite element analysis. Computed results of the finite element analyses were used to formulate a shear stress-based parameter to predict the fretting fatigue crack initiation life, location and orientation. Comparison of the analytical and experimental results showed that fretting fatigue crack initiation was governed by the maximum shear stress, and therefore a parameter involving the maximum shear stress range on the critical plane with the correction factor for the local mean stress or stress ratio effect was found to be effective in characterizing the fretting fatigue crack initiation behaviour in titanium alloy, Ti–6Al–4V. 相似文献
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Fatigue life prediction of a rubber mount based on test of material properties and finite element analysis 总被引:5,自引:0,他引:5
Failure analysis and fatigue life prediction are very important in the design procedure to assure the safety and reliability of rubber components. The fatigue life of a rubber mount was predicted by combining test of material properties and finite element analysis (FEA). The natural rubber material material’s fatigue life equation was acquired based on uniaxial tensile test and fatigue life tests of the natural rubber. The strain distribution contours and the maximum total principal strains of the rubber mount at different loads in the x and y directions were obtained using finite element analysis method. The critical region cracks prone to arise were obtained and analyzed. Then the maximum total principal strain was used as the fatigue parameter, which was substituted into the natural rubber’s fatigue life equation, to predict the fatigue life of the rubber mount. Finally, fatigue lives of the rubber mount at different loads were measured on a fatigue test rig to validate the accuracy of the fatigue life prediction method. The test results imply that the fatigue lives predicted agree well with the test results. 相似文献
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W.‐B. Shangguan T.‐K. Liu X.‐L. Wang C. Xu B. Yu 《Fatigue & Fracture of Engineering Materials & Structures》2014,37(6):623-636
A method for modelling fatigue life of rubbers and rubber isolators is presented in this paper. Firstly, a fatigue experiment is carried out for a rubber dumbbell cylindrical specimen and a rubber isolator. Based on the finite element analysis, the damage parameters including the strain energy density, the maximum principal Green–Lagrange strain and the effective stress are calculated and discussed. Secondly, three fatigue life prediction models are established by using the three damage parameters and using the relation between the measured fatigue life of a dumbbell cylindrical specimen and the computed value of the damage parameters. Thirdly, three proposed prediction models are used to investigate which one can be best used to predicting fatigue life of rubber isolators, taking a typical powertrain rubber isolator as studying example. The fatigue lives of the rubber isolator predicted by the three models are compared with the experimental life. The results demonstrate that the predicted fatigue lives of the rubber isolator using the three fatigue models agree well with the experimental fatigue life within a factor of four, and the model using the effective stress as the damage parameter can predict the fatigue life within a factor of two, which has the best accuracy among the three models. 相似文献
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In the present paper, a computational model for crack growth analysis under Mode I/II conditions is formulated. The focus is on two issues – crack path simulation and fatigue life estimation. The finite element method is used together with the maximum principal stress criterion and the crack growth rate equation based on the equivalent stress intensity factor. To determine the mixed-mode stress intensity factors, quarter-point (Q-P) singular finite elements are employed. For verification purposes, a plate with crack emanating from the edge of a hole is examined. The crack path of the plate made of 2024 T3 Al Alloy is investigated experimentally and simulated by using the finite element method with the maximum tangential stress criterion. Then, the validation of the procedure is illustrated by applying the numerical evaluation of the curvilinear crack propagation in the polymethyl methacrylate (PMMA) beam and the Arcan specimen made of Al Alloy for which experimental results are available in the literature. In order to estimate fatigue life up to failure of the plate with crack emanating from the edge of a hole, the polynomial expression is evaluated for the equivalent stress intensity factor using values of stress intensity factors obtained from the finite element analysis. Additionally, the fatigue life up to failure of the Arcan specimen is analyzed for different loading angles and compared with experimental data. Excellent correlations between the computed and experimental results are obtained. 相似文献
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This paper describes the high temperature multiaxial creep–fatigue life prediction for type 304 stainless steel. Finite element analyses were performed for determining the stress–strain state in the gage part of a cruciform specimen subjected to creep–fatigue loading under four strain waves at three principal strain ratios. Creep–fatigue lives of cruciform specimens were discussed in relation to the principal stress amplitude calculated by finite element analysis. Creep–fatigue damage was evaluated by linear damage rule and the suitability of three low cycle fatigue and three creep damage parameters was discussed. 相似文献
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Effects of mean stress and stress concentration on fatigue behavior of short fiber reinforced polymer composites
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S. Mortazavian A. Fatemi 《Fatigue & Fracture of Engineering Materials & Structures》2016,39(2):149-166
An experimental study was conducted to evaluate the effect of mean stress on fatigue behavior of two short glass fiber reinforced thermoplastic composites and the effect of stress concentration on fatigue behavior of an unreinforced and a short glass fiber reinforced thermoplastic. Load‐controlled fatigue tests were conducted on unnotched (smooth) specimens at R ratios of ?1, 0.1, and 0.3 in different mold flow directions or fiber orientations and at a range of temperatures between ?40 and 125 °C. Effect of mean stress on fatigue life was found to be significant at all temperatures. Several mean stress parameters including modified Goodman, Walker, and Smith–Watson–Topper were evaluated for their ability to correlate mean stress data. A general fatigue life prediction model was also used to account for the effect of mean stress, temperature, and fiber orientation. Notched fatigue tests of an unreinforced polymer and a short glass fiber thermoplastic composite were also conducted using plate type specimens with a central circular hole and with or without the presence of mean stress. Effect of stress concentration was found to be considerable, with or without mean stress and in both the longitudinal and transverse directions. The commonly used Neuber's rule for metallic materials, nonlinear finite element analysis, as well as critical distance approaches were utilized for notch deformation and fatigue life analyses. 相似文献
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Minoshima Nagashima & Komai 《Fatigue & Fracture of Engineering Materials & Structures》1998,21(12):1435-1446
We describe an investigation into the fatigue fracture behaviour under combined tension–torsion loading of a SiC whisker-reinforced A6061 aluminium alloy fabricated by a squeeze casting process. Special attention was paid to the environmental effects on fatigue fracture behaviour. Tests were conducted on both the composite and its unreinforced matrix material, A6061-T6, under load-controlled conditions with a constant value of the combined stress ratio, α = τmax /σmax in laboratory air or in a 3.5% NaCl solution at the free corrosion potential. The corrosion fatigue strength of both the matrix and composite was less in the solution than in air. The dominating mechanical factor that determined the fatigue strength in air was either the maximum principal stress or the von Mises-type equivalent stress, depending on the combined stress ratio. However, in the 3.5% NaCl solution, the corrosion fatigue strength of both materials was determined by the maximum principal stress, irrespective of the combined stress ratio. In the case of the matrix material, crack initiation occurred by a brittle facet normal to the principal stress due to hydrogen embrittlement. However, in the composite material, the crack was initiated not at the brittle facet, but at a corrosion pit formed on the specimen surface. At the bottom of the pit, a crack normal to the principal stress was nucleated and propagated, resulting in final failure. Pitting corrosion was nucleated at an early stage of fatigue life, i.e. about 1% of total fatigue life. However, crack initiation at the bottom of a pit was close to the terminal stage, i.e. about 70% or more of total fatigue life. The dominating factor which determined crack initiation at a pit was the Mode I stress intensity factor obtained by assuming the pit to be a sharp crack. Initiation and propagation due to pitting corrosion and crack growth were closely examined, and the fatigue fracture mechanisms and influence of the 3.5% NaCl solution on fatigue strength of the composite and matrix under combined tension–torsion loading were examined in detail. 相似文献
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应力强度因子在断裂力学中广泛应用于预测由远程载荷或残余应力引起的裂缝尖端附近应力状态。本文基于平面应力条件下应力强度因子建立WCP形状与其尖端应力之间的规律,利用有限元分析软件对含不同形状WCP的WCP/Fe复合材料的热应力进行模拟仿真,研究WCP形状对WCP/Fe复合材料热疲劳裂纹扩展行为的影响。研究结果表明,WCP的形状显著影响应力强度因子,进一步影响WCP/Fe复合材料的热疲劳裂纹扩展行为。含球状和不规则状WCP的WCP/Fe复合材料的极限抗压强度分别约为460 MPa和370 MPa。含不规则状WCP的WCP/Fe复合材料因应力集中而容易产生脆性开裂现象。通过热震实验进行验证,发现实验结果与模拟仿真结果相近,说明有限元法的准确性,同时为WCP/Fe复合材料的热疲劳裂纹扩展行为研究提供科学依据和理论基础。 相似文献
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《Engineering Fracture Mechanics》1986,25(4):403-413
A comprehensive plane stress finite element study is made of the effect of three different types of defence hole systems (A, B and C) upon the stress concentration in a uniaxially-loaded plate with two coaxial holes. Throughout this project, the geometry definition, model creation aspects for meshing the plate and generating elements and nodes, model preparation for applying the appropriate loads and restraints, model checking for coincidence nodes and element distortion, and output display of the many cases investigated were all carried out interactively using SDRC (SUPERTAB-IDEAS) pre- and post-processors. The finite element analysis was carried out in the analysis section of the package, known as SUPERB. The study reveals that the introduction of defence holes on either side of the main holes helps to smooth the flow of the tensile principal stress trajectories past the original holes, and thus effect a reduction in stress concentration factor (SCF), an improvement in component strength and a reduction in its weight. Reductions in maximum SCF ranging from 7.5% to 11% have been achieved by the present technique. With such reductions in maximum stress levels, the improvement in fatigue life of a component can be significant. 相似文献