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  本文選題：激光沖擊強化　切入點：可靠性　出處：《江蘇大學》2017年碩士論文

【摘要】：由于小孔構件結構中的應力集中問題,循環(huán)載荷下的疲勞是其失效的主要原因,利用激光沖擊強化技術可以提高材料的疲勞可靠性。激光沖擊強化技術主要通過改變殘余應力場來提高壽命,但殘余應力場影響因素眾多。對激光沖擊強化小孔構件可靠性影響因素進行系統分析并建立P-S-N曲線,可以在分析應力強度與疲勞壽命的關系的基礎上更好地控制影響因素,因此工作具有十分重要的究意義。本文在理論分析的基礎上,通過仿真與試驗相結合,研究在殘余應力的基礎上各因素對疲勞壽命的的影響,探索各因素對疲勞壽命的影響規(guī)律,建立P-S-N曲線,得出不同可靠度下應力與壽命的關系。主要研究內容及成果如下:(1)根據彈塑性力學,在分析激光沖擊后殘余應力的形成機制,應力強度因子理論和殘余應力場的的基礎上,對疲勞裂紋擴展速率以及疲勞擴展壽命影響機制進行研究。結果表明:激光沖擊可以產生殘余應力場,殘余壓應力可以降低裂紋應力強度因子與裂紋擴展速率,殘余壓應力導致循環(huán)應力幅值降低可以提高裂紋擴展壽命。(2)通過對激光沖擊強化小孔構件的失效分析,研究疲勞壽命的主要影響因素,并從影響殘余應力場的角度,研究各因素對疲勞壽命的影響規(guī)律。結果表明:激光沖擊強化小孔構件的影響因素主要有材料、厚度以及激光沖擊強化工藝,影響激光沖擊殘余應力場的形成,進而影響疲勞壽命。(3)通過ABAQUS軟件平臺,分析不同板厚、材料、峰值壓力以及三因素聯合作用下,激光沖擊強化小孔構件殘余應力場的分布規(guī)律。結果表明:厚度增大會使得孔壁壓應殘余拉應力值和區(qū)間增大,鈦合金材料孔角的殘余壓應力比鋁合金材料的大得多,功率密度增大殘余壓應力增大幅度降低,對孔壁殘余壓應力值影響最大的是材料,對表面殘余壓應力影響對大的是功率密度。(4)采用正交試驗,運用疲勞統計分析方法對壽命數據進行處理,建立了P-S-N曲線進行可靠性分析與正交分析。研究得出:在相同可靠度條件下4mm鈦合金大功率密度下的小孔構件的壽命最高;給出了對于多點激光沖擊強化小孔的光斑大小、搭接率、沖擊層數、沖擊范圍、功率密度、能量等參數的確定方法。研究表明,較小厚度下采用大功率密度沖擊鈦合金材料時的激光沖擊強化小孔構件疲勞壽命可靠性最高;通過疲勞數據統計分析建立可以描述不同可靠度下壽命與疲勞強度的關系的P-S-N曲線,給出工藝參數的確定方法,對于提高構件疲勞可靠性以及選擇最優(yōu)工藝方案的選擇有重要意義。
[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.
【學位授予單位】：江蘇大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG665

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