飞机结构件“残余应力-结构”的耦合加工变形预测及结构优化设计方法

From the unified viewpoint of blank manufacturing, structure design and workpiece machining, an "analysis - prediction - control" method is investigated for the "residual stress - structure" couple deformations of aircraft structural parts. Firstly, based on the fact that the machining deformations is far less than geometric dimensions, the mechanical models of workpiece deformation and residual stress redistribution are formulized to realize the connection of FEM with analytical method for the high speed milling of aircraft structural parts. Secondly, the determination method for the position and stress intensity of crucial points is suggested to linearly approximate the distribution curve of residual stress. By taking the stress intensity of crucial points as input samples, the neural network model can be established to predict the workpiece deformations. And then, a stress optimal model is established with the multi-objective of maximizing both stress amplitude and workpiece deformations within the machining requirements. By equivalently transforming the multi-objective optimal model into the simple-objective optimal model, a genetic algorithm solution technology is developed for the stress optimal model so that it can provide the residual stress specification for the upstream process of workpiece machining. Finally, the non-symmetry ratio of material removal is for the first time defined to reveal the workpiece deformation rule and in turn, the material distribution optimal model is established to minimize the compliance under the constraint condition of material reservation ration. By constructing the step function with the variable of sensibility, a heuristic optimization method is proposed to update the design variables so that it can provide a theory basis for the design of workpiece structure. Obviously, the proposed active deformation control method is of great significance in the respect of theory and engineering to improve the manufacturing capability of aircraft structural parts.

从毛坯制造、结构设计与零件加工相结合的角度，研究飞机结构件“残余应力-结构”耦合变形的“分析-预测-控制”方法。基于加工变形远小于自身几何尺寸这一事实，通过建立零件变形与残余应力再分布力学模型，实现有限元方法与解析法相结合的飞机结构件高速铣削分析方法。研究关键点位置及应力指标的确定方法完成应力分布曲线的线性近似，通过以关键点的应力指标为输入样本，构建零件变形的神经网络预测方法。建立应力幅值最大、零件变形最大但不超过加工要求的多目标应力优化模型，通过多目标向单目标的等价转换，研究优化模型的遗传算法求解技术，为切削上游工艺提供残余应力规范。研究材料去除不对称率的零件变形规律，建立以最小柔顺度为目标、材料保留比为约束的材料分布优化模型，通过灵敏度构造步长函数，提出启发式优化准则求解法，为零件结构设计提供理论依据。这种主动变形控制方法对于提高飞机结构件的制造水平具有重要的科学意义和工程应用价值。

飞机结构件“残余应力-结构”的耦合加工变形预测及结构优化设计方法的主要研究内容及取得的成果如下：.（1）飞机结构件加工变形分析研究.在测量出初始残余应力的基础上，将释放的应力等效为外力，依据弯曲变形理论创新性地建立了零件变形分析模型。零件变形的解析值与仿真值、实测值相比，无论是幅值还是变形曲线，都具有很好的一致性。 .（2）加工位置优化方法研究.为获得零件加工上下余量分配对加工变形的影响规律，提出了加工位置的变向迭代优化方法。利用该方法优化了C919飞机某直梁件的加工余量分配，与企业实际使用的中间位置法相比，加工变形减小了99%。.（3）残余应力控制规范研究 .通过单位力法将分析模型分解为影响因子与残余应力之积，以加工要求为控制限，结合残余应力的自平衡特性建立了残余应力控制规范模型。通过夹逼原则将应力控制模型转化为齐次线性不等式组，并提出了应力控制规范模型的旋转算法求解方法。 .（4）零件结构优化方法研究.从拓扑优化的角度考虑航空整体结构件加工变形控制问题，采用变密度法建立以零件变形最小为设计目标，结构体积为约束的拓扑优化设计模型。通过推导目标与约束关于设计变量的灵敏度，提出拓扑优化设计模型的MMA算法求解技术。.（5）多重夹紧力规划算法研究 .在具有力封闭的前提下，以一定步长选取相邻的两个夹紧力大小或极径，根据力可行的差异确定下一个步长，以步长不超出阈值为终止条件建立了夹紧力规划算法。通过夹紧力规划算法计算工件钻孔时的二重夹紧力，与解析法的计算结果对比分析表明，两者的相对误差最大为0.98%。.（6）淬火残余应力形成机理及调控方法研究.从温度、应力等多场耦合角度，分析了淬火残余应力产生的机理，结果显示：对流换热系数能够对淬火残余应力大小和降温速度产生较大影响，其中，对残余应力的影响主要集中在高温区，而低温区的降温过程不会对最终残余应力形成造成实质影响。

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