Research On Residual Stress And Machining Distortion Of Aeronautic Weak Rigidity In Aluminum Structure

At present, integral structural design is widely accepted in modern aerospace and aeronautics industry. Monolithic parts are difficult to guarantee dimensional accuracy due to bad rigidity, weak intensity and high material removal rate. This dissertation elaborates the nature of distortion phenomenon based on strain energy theorem. Weak rigidity structures are theoretically and experimentally investigated to develop a methodology of distortion minimization. The main researches are as follows:(1) Residual stress measurement and stress field modeling are studied based on experimental mechanics. Based on Saint-Venant principle, design rule of sample’s size is proposed. Stress field corrections of plate, beam, cylinder and block are systematically investigated. For three dimensional problems, model correction is performed based on experimental test and numerical simulation. Stress field of block die forging is established and validation experiment is employed.(2) Machining distortion and its influencing factors are studied using strain energy theorem. Initial residual stress of material is induced by residual energy of manufacturing process. Machining distortion can be minimized by employing appropriate machining strategies. Machining-induced residual stress is inevitable external energy which is imported in part during machining process. The nature of machining-induced stress is the load of plane-stress state. Shape deflection is dominated by different factors at different stages of machining process. In rough machining stage, part distortion is caused by initial residual stress relaxation. In semi-finish/finish stage, part distortion results from bad rigidity and machining-induced stress.(3) A thermo-displacement coupled analysis is performed based on part manufacturing process. Residual stress in specific region is precisely measured by contour method. Stress field is corrected and established based on experimental measurement and numerical simulation. A distortion analysis is undertaken, and then a method for minimizing machining distortion is proposed. This method is validated by proportional and full-size experiment.(4) A weak rigidity, thin walled part is studied by using single-factor experiment. The influencing factors of initial residual stress, machining-induced residual stress, milling force and clamping methods are also analyzed. Distortion caused by initial residual stress occurs in rough machining stage. And it has light effect on the following dimensional accuracy. Machining-induced residual stress leads to shape deflection of web structure. Milling forces are responsible for distortion of rib structure. Clamping methods have a strong effect on material removal. Machining distortion of part is minimized by optimizing machining craft and structural rigidity.