【作者】 王秋成；

【导师】 柯映林；

【作者基本信息】 浙江大学 ， 机械制造及自动化， 2003， 博士

【摘要】 7000和2000系列变形铝合金具有优良的力学性能与加工性能等,因此广泛地用作各种军用与民用飞机的主要结构材料。航空铝合金为了获得高强韧性,必须进行固溶与时效处理,在淬火过程中产生很大的淬火残余应力。残余应力直接影响航空铝合金结构件的疲劳强度、抗应力腐蚀能力、尺寸稳定性与使用寿命,并导致后续机械加工过程中,由于材料内部的残余应力的释放,容易产生很大的加工变形。因此,研究航空铝合金残余应力控制与消除技术是极为重要的。本论文的研究工作,主要有以下几个方面: 1.研究了铝合金构件内部残余应力的测试与评估技术。首先概述了国内外残余应力测试技术的研究历史与现状,在此基础上,分析了逐层钻孔法、X射线法测量航空铝合金结构件表层残余应力的原理与方法。其次,基于线弹性断裂力学原理,研究了一种被称为裂纹柔度法的残余应力测试新技术,详细分析了其测定原理、方法与实验装置。实验测定了7075铝合金板材在T73、T7351、T7352、T7353状态下的全厚度残余应力分布规律。研究结果表明它比逐层钻孔法及X射线衍射法具有更好的敏感性与精确度。 2.对7075铝合金板材与隔框模锻件的淬火残余应力进行了理论分析与实验研究。首先针对铝合金板材淬火过程的特点,建立了铝合金板材淬火过程的(热)弹塑性力学模型,推导了7075铝合金构件淬火过程瞬态温度场、应力场与残余应力场的计算方法,并在大型有限元软件ABAQUS、ANSYS上实现了7075铝合金板材与某飞机隔框模锻件淬火过程中温度场与热应力场的数值模拟,以及淬火残余应力形成和分布情况。进行了7075铝合金淬火时效热处理试验,并测定了7075铝合金试样在T73工艺状态、AQ工艺状态以及100℃-250℃高温条件下的机械性能,残余应力实验结果与模拟结果对比具有很好的一致性。 3.研究了机械法消除铝合金残余应力的理论与方法。首先概述了国内外机械拉伸法(Txx51)、模压法(Txx52)与模拉压法(Txx54)的研究现状;其次,建立了机械法消除铝合金板材残余应力的弹塑性力学模型,采用数值模拟方法系统分析了机械拉伸(模压)变形量、分段模压时的重叠区域等关键工艺参数对残余应力消除效果的影响。研究结果表明:机械拉伸法(Tx51)是简单形状零件消除残余应力的理想方法,仅1.O%永久拉伸变形量就基本消除了7075铝合金板材中的淬火残余应力,但需4.0%永久拉伸变形量才能完全消除残余应力。而模压时重叠区域愈大,消除残余应力效果愈好。 4.研究了深冷处理(T7x53)法消除铝合金残余应力的理论与方法。首先概括了国内外深冷处理(T7x53)法消除铝合金残余应力的研究概况;其次,在更多还原

【Abstract】 AL-Zn-Mg-Cu (7000 series) and AL-Cu-Mg (2000 series) high strength aluminum alloys have been widely used as the key materials of aircraft structures due to their high strength-to-weight ratio, excellent corrosion resistance, and high fracture resistance. These precipitation-hardened aluminum alloys gain their high strengths through heat treatment involving a severe quenching operation, which introduces a very high level of residual stresses. Residual stresses not only result in unexpected machining distortion, but also increases the possibility of unpredicted fatigue failures and stress corrosion cracks (SCC). Therefore, It is of interest to investigate residual stress measurement and prediction in aircraft aluminum parts.In this dissertation, systematical investigations are carried out on control and evaluation of residual stresses in aircraft aluminum parts. The main work done and the main results obtained are as follows.First, several residual stress measurement methods were summarized with overview of the history and the current development of residual stress research. The principles of incremental hole drilling method and X-ray diffraction method were analyzed to measure surface or subsurface residual stresses in engineering components. Based on fundamental theoretical relations of liner-elastic fracture mechanics, a novel method known as the crack compliance method was chosen for this research. Its basic theory, principle, and experimental implementation were comprehensively studied. Experimental results revealed that this proposed method can be used to evaluate through-thickness residual stress distributions in rolled 7075 aluminum plates procured in T73, T7351 , T7352 and T7353 temper designations. It further showed that measured subsurface residual stresses are more sensitive and accurate as compared with those obtained by incremental hole drilling method or X-ray diffraction method.Second, the quench-induced residual stresses in rolled 7075T73 aluminum plate and forging of bulkhead were investigated by theoretical analysis and experimentation. The heat equation for a simple geometric model, such as an infinite plate, was solved with an experimental surface conductance and a step-by-step method of determining the temperature field in the thickness of the plate. This temperature field was introduced as data for the uncoupled thermal elastic-plastic model for quenching. In the calculation of the plastic-strain path, the thermal and mechanical properties were considered as temperature dependent for a homogeneous and isotropic material. The quenching process was simulated by finite element analysis to predict the residual stress distributions that develop in aluminum plates and forgings. Experimentally, the through-thickness residual stress distributions in 7075T73 plate specimens were measured by the crack compliance method. Good agreement is found between theoretical predictions and experimental results.Third, we summarized current developments of three stress relief methods include Tx51 (stress relieved by stretching deformation), Tx52 (stress relieved by compressive in a separate die), and Tx54 (stress relieved by combined stretching compressive in a finish die). A systematic study was performed on effect of amount of stretching deformation on stress relief of 7000 series aluminum plates. The effect of更多还原