【作者】 王钟羡；

【导师】 王良国； 范进；

【作者基本信息】 南京理工大学 ， 工程力学， 2008， 博士

【摘要】 论文在分析孔口应力场的基础上,从灰色系统的观点出发,探讨灰色预测模型在应力集中等工程力学问题中的应用。首先对灰色预测模型进行研究。根据GM（1,1）灰色模型的指数特性,通过区间求积给出了关于背景值的一个计算公式,讨论由此建立的GM（1,1）改进模型的适用范围和预测精度。同时,对原始数据序列一次累加生成时,考虑序列的间距,提出一种建立非等间距序列GM（1,1）模型的方法。进而,研究灰色预测模型在应力集中测试中的应用。根据六种典型应力集中试件的应变电测试验,用电测数据建立灰色模型,预测应力集中问题的峰值应力。研究表明,灰色预测具有所需要的测试数据较少、预测值精度较高的特点,用灰色预测模型得到的预测值可以符合工程实际的需要。论文在分析裂纹尖端应力场的基础上,采用J-A₂双参数弹塑性理论对裂纹尖端的约束效应进行评估。探讨如何依据裂纹尖端的约束水平,将由实验室试件测试得到的断裂力学参数转移应用到实际裂纹构件。分析不同温度和不同载荷情况下,浅裂纹试件和标准深裂纹试件裂纹尖端区域的应力场。根据约束参数A₂的特点,对单边缺口拉伸试件进行加载设计,用不同的偏心载荷来模拟各种载荷形式和约束水平。在韧脆转变区,建立约束参数A₂与主曲线参考温度T₀之间的关系,根据裂纹的约束水平预测断裂韧性随温度的变化。提出一种二点匹配方法,使J-A₂修正解适用于深裂纹、大范围屈服情况,J-A₂的控制区得到进一步扩大,断裂韧性测试对试件尺寸的要求将更加宽松。进而,根据J-A₂控制扩展理论,建立J_R曲线与约束参数A₂之间的关系,根据裂纹的约束水平预测其扩展阻力。此外,为方便工程应用,给出单边缺口弯曲试件和单边缺口拉伸试件的约束等效曲线和各试件构形间约束参数的转化关系式。建立J-A₂双参数断裂准则,对不同裂纹深度的管道进行弹塑性断裂预测。对双向荷载下,多裂纹问题进行弹塑性分析,研究载荷比、裂纹间距、相邻裂纹长度对主裂纹J-积分和约束参数A₂的影响,给出相应的影响系数。更多还原

【Abstract】 Stress concentration is a main cause of the damage in engineering structures, and the evaluation of stress concentration factors is important to engineering analysis. In the first part of this paper, the investigation of gray model approach and the application of gray model to some stress concentration problems were studied.According to the exponential form of GM （1,1 ） model, a new formula about the background value was established by a definite integral. The application domain and the prediction precision of the consequent improved GM（1, 1） model were discussed. In addition, considering the spacing interval in the primary accumulating generating of primitive data sequence, a approach for establishing a GM（1,1） model for non-equidistant sequence was presented. Furthermore, the gray model was applied in the stress concentration test. The strain electrical measurement tests were taken on six typical components. The test data were obtained to establish the gray models, which was applied to predict the maximun stress values of stress concentration problems. It is shown that the predicted data agree very well with the experimental data. The gray modeling method need less test data and is of high precision in prediction. Therefore, the gray model is feasible to a real time test of the strain or stress concentration problem.Fierce stress concentration occurs on the crack-tip. In the second part of this paper, the two parameters J-A₂ theory in fracture mechanics was used to analyze the elastic-plastic stress fields and to evaluate the constraint levels on the crack-tips. The transferability of constraint was discussed.The elastic-plastic stress fields on the crack-tips were obtained by use of the finite element analysis to the single edge notched bend（SENB） and single edge notched tension（SENT） specimens at the different temperatures and the various loading levels. SENT specimens were loaded with different eccentricity tension to simulate different loading configurations and the constraint levels. The relation between eccentricity e and parameter A₂ is obtained. Over the ductile-brittle transition region, the relationship between constraint parameter A₂ and reference temperature T₀ of the master curve was obtained. Therefore, according to the constraint level on the crack-tip one can forecast the fracture toughnesses K_JC at different timperatures. A bending correction factor was included in the J-A₂ asymptotic solution by two points matching method to improve the theoretical prediction of the stress field for deep cracks under large scale yielding condition. As a result, the valid region for J-A₂ controlled crack growth is extended, and the ASTM specimen size requirements for fracture toughness testing can be relaxed. And then, the functional dependence of J_R curves on A₂ was established and the predicted J_R curves agree very well with the experimental curves. This ensures the transferability of laboratory test data to an actual structure provided the constraint level A₂ of the cracked structure is known or determined. Farther, the constraint parameters A₂ as a function of the crack lengths were presented for the SENT samples and the SENB samples for convenience in actual application. Also, the conversion formula of the crack lengths was obtained between them. According to the fracture rule with two parameters J and A₂, the fracture press values of some cracked inner-pressed-pipelines were forecasted. Finally, the J-A₂ theory was performed to study the collinear two cracks in plate under biaxial loading. The influence to J-integral and constraint parameter A₂ of the main crack were researched with the different sizes and the different distances of adjacent crack in biaxial loading condition for different load ratios. The influence coefficients were also presented.更多还原