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金属材料低温疲劳裂纹起始寿命的微机辅助电位法测试 总被引:1,自引:0,他引:1
本文研制了一套适用于低温环境的疲劳裂纹微机辅助电位法测试系统。该系统中采用了翻转电位法、温度补偿和控温信号锁存等技术.对16Mn 钢及 LY12cz 铝合金缺口试件低温疲劳裂纹起始寿命的实际测试结果表明,该系统可比较有效地抑制测试仪器零点飘移、温度波动等造成的干扰,提高了测试精度。实验结果表明,降低温度可使16Mn 钢及 LY12cz 铝合金的疲劳裂纹起始寿命提高。本文还对实验结果及测试系统的进一步改进做了简要讨论。 相似文献
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本文讨论了负超载对Al-2024铝合金材料疲劳裂纹扩展的影响,试验发现在大量负超载循环周次之后也有裂纹停滞现象发生。这种停滞现象的产生与剪切唇的形成有关。本文发现负超载期间的剪切唇(简称剪切唇Ⅰ)和负超载之后的剪切唇(简称剪切唇Ⅱ)对疲劳裂纹扩展速率影响的程度不同。从裂纹闭合的观点建立了负超载对疲劳裂纹扩展影响的计算模型。 相似文献
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飞机纵向运动的稳定区域 总被引:1,自引:0,他引:1
本文利用Liapunov函数方法,讨论了飞机纵向运动的稳定性,所得结果扩大了[4,6]的稳定区域,而且还给出了若干与[1,2,5]不同的新的稳定区域. ... 相似文献
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短裂纹闭合的尺寸效应分析 总被引:1,自引:0,他引:1
对循环荷作用下缺口根部静态短裂纹和扩展短裂纹的闭合现象进行了弹塑性有限元分析。考虑不同应力水平和应力比,尤其是零-压载荷对短裂纹的作用。在此基础上提出分析长,短裂纹闭合尺寸效应的修正模型。与实验结果相比,本文模型对短裂纹的闭合预测甚好。 相似文献
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近似求解了微裂纹演化系统随机偏微分方程。结果表明:当裂纹扩展速率的随机偏差正比于其平均速率时,材料损伤不随裂纹随机行为而变化。同时,还讨论了金属疲功损伤随机波动程度的变化趋势。 相似文献
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Analysis of electric boundary condition effects on crack propagation in piezoelectric ceramics 总被引:1,自引:0,他引:1
There are three types of cracks: impermeable crack, permeable crack and conducting crack, with different electric boundary
conditions on faces of cracks in piezoelectric ceramics, which poses difficulties in the analysis of piezoelectric fracture
problems. In this paper, in contrast to our previous FEM formulation, the numerical analysis is based on the used of exact
electric boundary conditions at the crack faces, thus the common assumption of electric impermeability in the FEM analysis
is avoided. The crack behavior and elasto-electric fields near a crack tip in a PZT-5 piezoelectric ceramic under mechanical,
electrical and coupled mechanical-electrical loads with different electric boundary conditions on crack faces are investigated.
It is found that the dielectric medium between the crack faces will reduce the singularity of stress and electric displacement.
Furthermore, when the permittivity of the dielectric medium in the crack gap is of the same order as that of the piezoelectric
ceramic, the crack becomes a conducting crack, the applied electric field has no effect on the crack propagation.
The project supported by the National Natural Science Foundation of China (19672026, 19891180) 相似文献
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A model for analysing a soft-hard heterogeneous body with a crack in the hard region is presented in this paper. The result of fatigue experiments shows that mechanical heterogeneity affects the rate of propagation of fatigue crack. Meanwhile the results computed by BEM for cracked heterogeneous bodies under cycling loading indicate that the smaller the distance between the crack and the interface of hard and soft regions is, the smaller the amplitude of crack opening displacement, COD and ofJ-integral as well at the same step during the fatigue crack growth will be. The effect of heterogeneity on the rate of fatigue crack propagation is shown by the variation of J. The smaller the distance of the crack to the interface is, the smaller the rate of fatigue crack growth will be. 相似文献
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本文将拉氏变换-边界元法用于表面裂纹问题的瞬态响应分析。文中讨论了拉氏反演参数的选择和动态应力强度因子的计算方法。作为程序的考核和离散方案的选择,分别地计算了水平柱体一端固定、另一端受p(t)=poH(t)载荷时的位移响应和具有贯穿裂纹的厚板在两种离散方案时的动态应力强度因子响应。最后,还计算了若干载荷工况的半圆表面裂纹板应力强度因子的瞬态响应,获得了有效的数值结果。 相似文献
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Analytical Treatment of Boundary Integrals in Direct Boundary Element Analysis of Plan Potential and Elasticity Problems 总被引:1,自引:0,他引:1
IntroductionAcomparison[1,2 ]betweentheDBEMandtheindirectboundaryelementmethod (IBEM)hasbeenmadebyearliersomeauthors.TheirmainviewpointsarethattheDBEMhasanadvantageofgettingobjectivelyphysicalquantitiesotherthanimaginaryones ,butitrequiresanintegratednumer… 相似文献
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IntroductionTheclassicalconhnuummechanicshasbeenusedtosolvemanyproblemsinmacrofracturemechanics,butencountersdifficulheswhentheeffectofITilcrocharacteristicdimensionshouldbetakenintoaccount.Thestressfieldverynearthecracktipisstillnotclear.Somephenomenaofshortcrackscannotbeexplained["']andsomemechanismoffracturehasnotbeensolvedyet.Thenon-localelashcitytheoryseemsattractivetotheseproblems.Thetheoryofnon-localelasticity,establishedanddevelopedbyEringenetal[3),connectstheclassicalcontinuummechan… 相似文献
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By coupling natural boundary element method (NBEM) with FEM based on domain decomposition, the torsion problem of the square
cross-sections bar with cracks have been studied, the stresses of the nodes of the cross-sections and the stress intensity
factors have been calculated, and some distribution pictures of the stresses have been drawn. During computing, the effect
of the relaxed factors to the convergence speed of the iterative method has been discussed. The results of the computation
have confirmed the advantages of the NBEM and its coupling with the FEM.
Foundation item: the State Key Laboratory of Science and Engineering Computation
Biography: ZHAO Hui-ming (1971-) 相似文献
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The rapid development of high-speed trains like the TGV or the ICE in recent years results in high dynamic loads causing vibrations which propagate from the train-track structure into the ground and further into nearby buildings. In this context it is important to develop rigid tracks with improved dynamic behaviour and to investigate possible means of vibration reduction. The boundary element method in frequency and time domain is used to simulate train-track structures subjected to dynamic loading and the reduction of vibrations which for instance can be achieved via a trench running parallel to the rigid track. In this context the non-causality error, which arises when the time-domain BEM algorithm is applied to mathematically concave domains, is discussed and the substructure method is proposed as a solution to this problem. A two-layered cylindrical elastic structure on a half-space with a trench is added as an example of a possible application. 相似文献
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破前漏(简称LBB)是压力容器、核电站设备结构设计与评价中的一个重要准则.表面裂纹准静态扩展的几何形貌变化规律的预测是破前漏(LBB)评判十分重要的课题之一.本文对特定焊接残余应力场加载作用下,含三维表面裂纹的压力容器模型,用有限元软件(ABAQUS)进行了表面裂纹准静态扩展模拟计算,得到在此残余应力场作用下应力强度因子沿裂纹前缘的分布规律.结合外载引起的应力强度因子,就可以判别裂纹的扩展形貌,从而判断结构是否满足LBB要求. 相似文献
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利用满足Laplace方程,线性化自由面条件及无穷远处条件的Havelock兴波源涵数,建立了关于常航速稳态船波势函数的边界积分方程.针对这个积分方程,建立了相应的数值计算方法,编制了一般三维问题的边界元法计算机程序,可用来计算全潜和半潜物体的稳态绕流场及船舶兴波阻力. 相似文献
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构造了一种适合边界元分析裂纹问题的三角形单元,该单元中的形函数包含两部分,主要部分用于捕捉裂纹尖端上位移分布的陡峭特性(性质),另一部分为常规的拟合函数,体现裂纹尖端位置附近的物理量在其他方向上的连续分布。形函数主要部分的构造充分利用了已有理论研究获得的结论,在裂纹表面,随着距离远离尖端,位移分布与■函数保持同阶变化。在传统形函数的基础上,通过先乘以一项同阶于■的变量项,再在系数中将其在形函数所在点上的值除去,便得到新型的用于拟合裂纹尖端附近位移和面力分布的形函数。新的形函数能够满足形函数的delta性质,但归一性不再满足,因此,新的形函数只用于物理量的拟合,而几何量的拟合依然采用传统方案。通过对偶边界元方法计算裂纹尖端的张开位移后,利用一种位移外插方法计算获得应力强度因子。数值算例关注了一种无限域内的圆盘裂纹,应用新构造的三角形单元于对偶边界元中计算结构在受到斜拉力时裂纹尖端的三种应力强度因子。通过与参考解进行对比,验证了该插值方案用于对偶边界元分析裂纹问题时的正确性和高精度。 相似文献