共查询到19条相似文献,搜索用时 62 毫秒
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提出了在非对称循环加载下,描述金属材料弹塑性材料行为的损伤演变速率方程式和各个历程与不同损伤量Doi相对应寿命Noi的估算式,其方法是采用以塑性应变幅同弹性应变幅的比值△εp/△εe作为载荷参量,以常用的材料常数作为材料参数。新计算式计算结果与Landgraf方程式计算结果一致,且计算精度较高。这对避免过多而重复的疲劳试验、方便工程应用、节约人力、时间和资金有着实际意义。 相似文献
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提出用塑性应变范围与弹性应变范围的比值作为载荷参量,以小裂纹尺寸作为损伤变量,用常用的材料参数作为小裂纹扩展方程式中的材料常数,建立描述弹塑性材料行为的小裂纹扩展速率方程式与各个历程的寿命估算式,从而计算结构材料在对称和非对称循环加载下的疲劳损伤,其计算结果与Landgraf公式一致。 相似文献
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基于裂纹尺寸a像D那样也可以作为损伤变量的观点,借助于双向组合坐标系,就弹塑性材料的小裂纹扩展速率和寿命提出三种计算方法:单参数法、比值法和乘积法。同时还给出许多新计算方程,提供一个同各个常用材料参数有着函数关系的综合性材料常数 、 、 和 的新概念。这些常用参数有:疲劳强度系数 、疲劳强度指数 、疲劳延性系数 、疲劳延性指数 、平均应力、平均应变和临界加载时间等。应用汽车的一个零件进行实例计算,并对计算结果进行比较分析,这些计算方法对避免过多的疲劳试验,节省疲劳试验的时间、人力、资金及方便工程应用在某种程度上将有着实际意义。 相似文献
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通过对零-压载荷下的疲劳裂纹扩展试验。研究LY13CZ试件在压缩循环载荷下的裂纹扩展规律。发现在压缩循环载荷下疲劳裂纹可以扩展,但不铳即发生休眠。其休眠长度与反复塑性区的尺寸相当。 相似文献
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对承受循环压载的缺口试件的疲劳问题进行了试验和理论研究。结果表明,疲劳裂纹是在残余拉应力和循环压应力作用下萌生和扩展的,压塑性变形是裂纹萌生和扩展和扩展的必要条件。循环压载下仍存在着裂纹张开和裂纹闭合,其机理与拉伸循环下不同。以试验中采用的LY12CA材料边缺口试件为例,提出了考虑裂纹闭合效应的扩展率计算模型,结果与试验吻合得较好。 相似文献
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研究了不同腐蚀预损伤对新型高强铝合金小裂纹行为的影响。小裂纹试验采用单边缺口拉伸试样(SENT),在试样半圆形缺口根部预制直径大小为100—300μm的单腐蚀坑,后在空气环境进行疲劳小裂纹实验,实验在R=0.5恒幅载荷下,采用复型法观测小裂纹的萌生及扩展情况。结果表明,与预腐蚀24h试样相比,预腐蚀240h试样产生的裂纹数量较少,裂纹萌生与扩展较快。预腐蚀240h试样裂纹绝大多数萌生于腐蚀坑处而预腐蚀24h试样并未出现类似特性。预腐蚀240h试样未显现明显的小裂纹效应,预腐蚀24h试样有较明显的小裂纹效应出现。文中还通过引入参数aT对腐蚀时间与小裂纹受微观组织影响程度的关系进行了描述。相较预腐蚀24h试样预腐蚀的240h试样的aT更短,小裂纹受微观组织影响也更小。 相似文献
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通过对中碳钢光滑试样的疲劳实验,研究了疲劳过程中短裂纹的扩展和演化行为,分析了基于短裂纹群体行为的疲劳损伤参数来描述疲劳损伤的有效性。通过研究裂纹总数和裂纹总长这两个参数在疲劳损伤过程中的动态变化,对基于短裂纹群体行为的疲劳损伤检测方法进行了评价。 相似文献
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断裂力学理论认为结构破坏是由疲劳裂纹的不断扩展所致,而损伤容限结构能够在承受一定损伤(裂纹)情况下继续安全使用。为了评估含损伤(裂纹)结构的使用危险性,提出一种以裂纹长度为参量的结构破坏危险性估计方法,详细分析了瞬时裂纹尺寸与临界裂纹尺寸的分布形式,建立瞬时裂纹尺寸与临界裂纹尺寸之间的干涉关系,利用Monte-Carlo模拟方法得出当前裂纹尺寸下结构发生破坏的概率。算例表明方法简单有效。 相似文献
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Wan Zhen-ping Liu Ya-jun Tang Yong Ye Bang-yan 《Frontiers of Mechanical Engineering in China》2006,1(2):194-198
With more and more applications of glass in advanced fields of science, the demand for glass machining precision has increased
greatly. More and more attention is being paid to glass cutting because precise glass parts with various shapes can be obtained
at high efficiency and low cost. To improve the machining precision of part surfaces and to facilitate tool design and cutting
parameter selection, the initiation and propagation laws of glass cracks in specimens subjected to normal loading by symmetric
wedges were investigated. Research results show that initiation and propagation laws are the same with interior symmetric
wedge angles of 30°–120°, while the laws are different with interior symmetric wedge angles equal to or more than ≥150°. The
relationship between medial crack length and normal loading was also investigated when specimens were indented by symmetrical
wedges with interior angles of 30°–120°.
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Translated from Journal of South China University of Technology (Natural Science Edition), 2004, 32(7) (in Chinese) 相似文献
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测试了2124铝合金TL与LT取向疲劳裂纹扩展门槛值,提出了用疲劳裂纹失稳扩展阶段最后十个循环中的最大值来估算2124铝合金TL与LT取向的断裂韧度K′C的方法,并将其与Forman公式预测的断裂韧度Kc值进行对比。结果表明:K′C与Kc值结果相近,误差分散度小;将K′C值代入全范围疲劳裂纹扩展速率表达式中,对2124铝合金TL和LT取向试验数据进行计算,预测结果与试验结果较好吻合。 相似文献
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H. Badnava S. M. Pezeshki Kh. Fallah Nejad H. R. Farhoudi 《Journal of Mechanical Science and Technology》2012,26(10):3067-3072
In this paper, experimental and numerical investigations on mechanical behaviors of SS304 stainless steel under fully reversed strain-controlled, relaxation, ratcheting and multiple step strain-controlled cyclic loading have been performed. The kinematic and isotropic hardening theories based on the Chaboche model are used to predict the plastic behavior. An iterative method is utilized to analyze the mechanical behavior under cyclic loading conditions based on the Chaboche hardening model. A set of kinematic and isotropic parameters was obtained by using the genetic algorithm optimization approach. In order to analyze the effectiveness of this optimization procedure, numerical and experimental results for an SS304 stainless steel are compared. Finally, the results of this research show that by using the material parameters optimized based on the strain-controlled and relaxation data, good agreement with the experimental data for ratcheting is achieved. 相似文献
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This paper is concerned with the mechanical property changes in drawing/extrusion operations of hardening viscoplastic materials with damage. The process model in this study includes two state variables, the hardness for strain hardening from slip dominated plastic distortion and the porosity for damage from growth of microvoids. The decrease in apparent density in strip drawing of aluminum for several die angles are computed and compared with that from experiments. Simulations of axisymmetric drawing/extrusion have shown that the accumulated porosity in drawing is much bigger than that in extrusion while the difference between the hardness distributions in these processes are insignificant. The effects of the process conditions, such as conical die angle, friction and drawing/extrusion speed, on the mechanical property changes are also examined. 相似文献
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Bing LI Xu GENG Tong LU Lei QIANG Minghang LI 《Frontiers of Mechanical Engineering》2015,10(4):380-391
The interface wave traveling along the boundary of two materials has been studied for nearly a century. However, experiments, engineering applications, and interface wave applications to the non-destructive inspection of interlaminar composite have developed slowly. In this research, an experiment that applies Stoneley waves (a type of interfacial wave between two solid half-spaces) is implemented to detect the damage in a multilayer structure. The feasibility of this method is also verified. First, the wave velocity and wave structure of Stoneley waves at a perfectly bonded aluminum-steel interface are obtained by solving the Stoneley wave dispersion equation of two elastic half-spaces. Thereafter, an experiment is conducted to measure the Stoneley wave velocity of an aluminum-steel laminated beam and to locate interlaminar cracks by referring to the Stoneley wave velocity and echo wave time. Results indicate that the location error is less than 2%. Therefore, Stoneley waves show great potential as a non-destructive inspection method of a multilayer structure. 相似文献
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本文论述了多轴载荷下的无限寿命疲劳设计方法。提供了对称循环和非对称循环下的弯扭复合疲劳设计公式和三轴应力疲劳设计公式。并出了弯扭复合应力下的试验数据和疲劳设计数据。 相似文献