【作者】 龚海；

【导师】 吴运新；

【作者基本信息】 中南大学 ， 机械设计及理论， 2011， 博士

【摘要】 高强、高韧、耐腐蚀且低残余应力水平的高性能铝合金厚板,是现代航空航天领域不可或缺的关键结构材料。然而,为了获得良好的综合性能,铝合金厚板必须进行固溶和淬火、时效处理,然而淬火处理不可避免地在厚板内部引入了很大的残余应力。残余应力的存在,直接对厚板的后续机械加工造成影响,引起加工零件的变形,造成极大的危害。因此,开展高强铝合金厚板残余应力及其评估、预测方法的研究具有十分重要的意义。本文的研究工作得到了国家重点基础研究发展计划项目“高性能铝材与铝资源高效利用的基础研究”之第八子课题“大规格铝材非均匀多相组织和内应力场的产生与演变”(编号：2005CB623708),国家重点基础研究发展计划项目“航空航天用高性能轻合金大型复杂结构件制造的基础研究”之第三子课题“大型薄壁构件塑变与去除成形及其内应力与表面完整性主动控制”(编号：2010CB731703),湖南省研究生科研创新项目的资助。本文以7075铝合金轧制厚板为研究对象,采用数值模拟和实验研究的方法,围绕铝合金厚板加工制备的几个重要环节开展厚板残余应力的相关基础研究,从而为大规格高强铝合金厚板制备的工艺参数优化、残余应力调控提供理论支持。本论文的研究工作,主要包括以下几个方面：1.建立了参数化的厚板残余应力预测模型。推导了厚板淬火过程的瞬态温度场与瞬态应力场、预拉伸过程应力场的计算公式,根据厚板制备过程的三大非线性因素：材料物热参数的非线性、厚板淬火表面换热边界条件的非线性和本构非线性,建立了厚板内应力分析非线性模型,在此基础上建立了厚板内应力分析的MSC.Patran/Marc参数化模型。运用建立的计算模型,分析了厚板内应力的演变规律,总结了厚板残余应力场的分布规律和预拉伸对厚板残余应力的影响规律,研究了拉伸率对厚板应力消减的定量关系；分析了非均匀淬火引起的板形翘曲,并研究了拉伸矫直对板型的改善作用。为后续的厚板残余应力评估模型研究奠定了理论基础,为厚板制备工艺的规划提供了应力预测方法。2.研究了裂纹柔度法在铝合金厚板深层残余应力测试中的应用。对裂纹柔度法计算的不确定度进行了评定；研究了取样后试件内部残余应力的释放规律,分析了试样尺寸对计算结果的影响,并总结了合理的试件尺寸；分析了裂纹柔度法算法中的实验误差,并对实验误差进行了修正；运用有限元方法,对裂纹柔度法和层削法用于深层残余应力测试时的计算能力进行了验证；结合有限元分析与实验研究,对裂纹柔度法和层削法计算结果进行了对比分析,确定了深层残余应力测试的有效性。3.建立了厚板残余应力场评估模型。以数值计算为基础,根据获得的厚板应力分布,运用数学方法,构建了厚板内应力分布的线型函数；运用多元非线性回归理论,建立了厚板内应力分布关键点应力值的回归模型,从而构建了铝合金厚板残余应力场评估数学模型；结合厚板残余应力实验研究,获得了实验条件下的应力分布线型函数,对关键点应力值回归模型进行了修正,提高了回归模型的计算精度。为铝合金厚板产品和后续机械加工的残余应力评估提供了有效的手段,简化了应力评估工序,提高了应力评估效率。更多还原

【Abstract】 Aluminum alloy thick plates with high strength and toughness, excellent corrosion resistance and low residual stress are of great importance as structural materials in the industry of aerospace. These aluminum alloys gain their favorable integrate performance through heat treatment involving a severe quenching operation, which inevitably introduces a very high level of residual stress. The existence of residual stress in thick plates has direct influences on after machining, which results in unexpected distortion frequently. Therefore, it is of great importance to investigate residual stress and its evaluation and prediction method in aluminum alloy plates.The present dissertation is funded by the National Basic Research Program of China (2005CB623708) and (2010CB623708), Hunan Provincial Innovation Foundation for Postgraduate.A series of basic research on several key procedures for processing7075aluminum alloy thick plates is carried out with the combination of numerical simulation and experiment method, which could provide a theoretical guide for the optimization of the processing technic parameters and residual stress adjusting and controlling in large-scale high performance aluminum alloy plates. The primary investigation contents of this paper include three main parts:First, the prediction model for residual stress in aluminum alloy thick plates was built. Calculation expressions of transient temperature field and transient stress filed during quenching and transient stress filed during pre-stretching were deduced. Nonlinear analysis model of the residual stress field of the plate was established by taking the three nonlinear factors into consideration:the nonlinearity of material thermal parameters, the nonlinearity of heat transfer boundary condition on the surface of quenching plate and the nonlinearity of constitutive relation of aluminum alloy. On this basis, the MSC.Patran/Marc parametric model was built. Using the model, evolving rules of inner stress in aluminum alloy plates was analyzed, then distribution rules of residual stress in aluminum plates and the influence of pre-stretching on residual stress were summarized, a quantified effect of stretching ratio on plate residual stress was constructed. Then plates warping induced by non-uniform quenching was studied, moreover, the effect of stretching on plates shape was investigated. These works can lay a theoretical foundation for latter experiment research and provide evaluation technique of residual stress for planning the preparation of plate.Second, the application of crack compliance method for inner residual stress measurement in aluminum alloy plates was studied. The calculation uncertainty of crack compliance method was assessed. Then, the release rule of residual stress after sampling was also studied, the influence of specimen dimension on the measurement results was analysed, and the reasonable specimen dimension was summarized. The correction scheme was proposed by taking the experiment error into consideration. Using FEM, the calculation ability of crack compliance method and layer removal method for inner residual stress were validated. Combined with FEM and experiment method, the calculation results of crack compliance method and layer removal method were compared and analyzed, which conformed the validity of the methods for inner residual stress measurement.Third, an evaluation model of residual stress field in aluminum alloy plates was constructed. Based on FEM results, a shape function of residual stress distribution in aluminum plates was proposed using mathematic method, and the regression model of stress values of key points of stress distribution within aluminum plates was obtained using nonlinear regression technology. Based on experiments, a shape function of residual stress distribution from experimental results was proposed, and the accuracy of the regression model was improved by revising the model using experiment results.更多还原