激光冲击强化小孔构件可靠性影响因素及P-S-N曲线研究

发布时间：2023-02-28 17:37

本文选题：激光冲击强化　切入点：可靠性　出处：《江苏大学》2017年硕士论文

【摘要】：由于小孔构件结构中的应力集中问题,循环载荷下的疲劳是其失效的主要原因,利用激光冲击强化技术可以提高材料的疲劳可靠性。激光冲击强化技术主要通过改变残余应力场来提高寿命,但残余应力场影响因素众多。对激光冲击强化小孔构件可靠性影响因素进行系统分析并建立P-S-N曲线,可以在分析应力强度与疲劳寿命的关系的基础上更好地控制影响因素,因此工作具有十分重要的究意义。本文在理论分析的基础上,通过仿真与试验相结合,研究在残余应力的基础上各因素对疲劳寿命的的影响,探索各因素对疲劳寿命的影响规律,建立P-S-N曲线,得出不同可靠度下应力与寿命的关系。主要研究内容及成果如下:(1)根据弹塑性力学,在分析激光冲击后残余应力的形成机制,应力强度因子理论和残余应力场的的基础上,对疲劳裂纹扩展速率以及疲劳扩展寿命影响机制进行研究。结果表明:激光冲击可以产生残余应力场,残余压应力可以降低裂纹应力强度因子与裂纹扩展速率,残余压应力导致循环应力幅值降低可以提高裂纹扩展寿命。(2)通过对激光冲击强化小孔构件的失效分析,研究疲劳寿命的主要影响因素,并从影响残余应力场的角度,研究各因素对疲劳寿命的影响规律。结果表明:激光冲击强化小孔构件的影响因素主要有材料、厚度以及激光冲击强化工艺,影响激光冲击残余应力场的形成,进而影响疲劳寿命。(3)通过ABAQUS软件平台,分析不同板厚、材料、峰值压力以及三因素联合作用下,激光冲击强化小孔构件残余应力场的分布规律。结果表明:厚度增大会使得孔壁压应残余拉应力值和区间增大,钛合金材料孔角的残余压应力比铝合金材料的大得多,功率密度增大残余压应力增大幅度降低,对孔壁残余压应力值影响最大的是材料,对表面残余压应力影响对大的是功率密度。(4)采用正交试验,运用疲劳统计分析方法对寿命数据进行处理,建立了P-S-N曲线进行可靠性分析与正交分析。研究得出:在相同可靠度条件下4mm钛合金大功率密度下的小孔构件的寿命最高;给出了对于多点激光冲击强化小孔的光斑大小、搭接率、冲击层数、冲击范围、功率密度、能量等参数的确定方法。研究表明,较小厚度下采用大功率密度冲击钛合金材料时的激光冲击强化小孔构件疲劳寿命可靠性最高;通过疲劳数据统计分析建立可以描述不同可靠度下寿命与疲劳强度的关系的P-S-N曲线,给出工艺参数的确定方法,对于提高构件疲劳可靠性以及选择最优工艺方案的选择有重要意义。
[Abstract]:Fatigue under cyclic load is the main cause of failure due to the stress concentration in small hole structure. The fatigue reliability of materials can be improved by laser shock strengthening technology, which can improve the life of materials by changing the residual stress field. However, there are many factors affecting the residual stress field. A systematic analysis of the factors affecting the reliability of small hole members strengthened by laser shock and the establishment of P-S-N curves can better control the influencing factors on the basis of analyzing the relationship between stress intensity and fatigue life. Therefore, the work is of great significance. On the basis of theoretical analysis, this paper studies the influence of various factors on fatigue life on the basis of residual stress through the combination of simulation and experiment. This paper explores the influence of various factors on fatigue life, establishes P-S-N curve, and obtains the relationship between stress and life under different reliability. The main contents and results are as follows: 1) according to elastoplastic mechanics, the formation mechanism of residual stress after laser shock is analyzed. On the basis of stress intensity factor theory and residual stress field, the influence mechanism of fatigue crack growth rate and fatigue propagation life is studied. The results show that laser shock can produce residual stress field. Residual compressive stress can reduce the crack stress intensity factor and crack growth rate, and the cyclic stress amplitude decreases due to residual compressive stress, which can improve the crack propagation life. The main influencing factors of fatigue life are studied, and from the point of view of influencing residual stress field, the influence law of various factors on fatigue life is studied. The results show that the main factors affecting the fatigue life of small hole members strengthened by laser shock are material. Thickness and laser impact strengthening process affect the formation of laser shock residual stress field, and then affect fatigue life. Through ABAQUS software platform, we analyze different plate thickness, material, peak pressure and three factors combined action. The distribution of residual stress field of small hole member strengthened by laser shock is studied. The results show that the thickness increases the value and interval of residual tensile stress, and the residual compressive stress of titanium alloy is much larger than that of aluminum alloy. The increase of power density decreases the increase of residual compressive stress, the material has the greatest influence on the residual compressive stress of the hole wall, and the influence on the surface residual compressive stress is the power density. The fatigue statistical analysis method is used to process the life data, and the P-S-N curve is established for reliability analysis and orthogonal analysis. The results show that: under the condition of the same reliability, the life of 4mm titanium alloy with high power density is the highest; The determination methods of spot size, lap ratio, number of impact layers, impact range, power density, energy and so on for multipoint laser shock strengthened holes are given. The fatigue life reliability of small hole members strengthened by laser shock is the highest when large power density impact titanium alloy is used in small thickness. Through the statistical analysis of fatigue data, the P-S-N curve which can describe the relationship between life and fatigue strength under different reliability is established, and the method of determining process parameters is given. It is of great significance to improve the fatigue reliability of components and to select the optimal process scheme.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665

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