發(fā)布時(shí)間：2023-02-28 17:37

  本文選題：激光沖擊強(qiáng)化　切入點(diǎn)：可靠性　出處：《江蘇大學(xué)》2017年碩士論文

【摘要】：由于小孔構(gòu)件結(jié)構(gòu)中的應(yīng)力集中問(wèn)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(qiáng)化技術(shù)可以提高材料的疲勞可靠性。激光沖擊強(qiáng)化技術(shù)主要通過(guò)改變殘余應(yīng)力場(chǎng)來(lái)提高壽命,但殘余應(yīng)力場(chǎng)影響因素眾多。對(duì)激光沖擊強(qiáng)化小孔構(gòu)件可靠性影響因素進(jìn)行系統(tǒng)分析并建立P-S-N曲線,可以在分析應(yīng)力強(qiáng)度與疲勞壽命的關(guān)系的基礎(chǔ)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(chǔ)上,通過(guò)仿真與試驗(yàn)相結(jié)合,研究在殘余應(yīng)力的基礎(chǔ)上各因素對(duì)疲勞壽命的的影響,探索各因素對(duì)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(yīng)力與壽命的關(guān)系。主要研究?jī)?nèi)容及成果如下:(1)根據(jù)彈塑性力學(xué),在分析激光沖擊后殘余應(yīng)力的形成機(jī)制,應(yīng)力強(qiáng)度因子理論和殘余應(yīng)力場(chǎng)的的基礎(chǔ)上,對(duì)疲勞裂紋擴(kuò)展速率以及疲勞擴(kuò)展壽命影響機(jī)制進(jìn)行研究。結(jié)果表明:激光沖擊可以產(chǎn)生殘余應(yīng)力場(chǎng),殘余壓應(yīng)力可以降低裂紋應(yīng)力強(qiáng)度因子與裂紋擴(kuò)展速率,殘余壓應(yīng)力導(dǎo)致循環(huán)應(yīng)力幅值降低可以提高裂紋擴(kuò)展壽命。(2)通過(guò)對(duì)激光沖擊強(qiáng)化小孔構(gòu)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(yīng)力場(chǎng)的角度,研究各因素對(duì)疲勞壽命的影響規(guī)律。結(jié)果表明:激光沖擊強(qiáng)化小孔構(gòu)件的影響因素主要有材料、厚度以及激光沖擊強(qiáng)化工藝,影響激光沖擊殘余應(yīng)力場(chǎng)的形成,進(jìn)而影響疲勞壽命。(3)通過(guò)ABAQUS軟件平臺(tái),分析不同板厚、材料、峰值壓力以及三因素聯(lián)合作用下,激光沖擊強(qiáng)化小孔構(gòu)件殘余應(yīng)力場(chǎng)的分布規(guī)律。結(jié)果表明:厚度增大會(huì)使得孔壁壓應(yīng)殘余拉應(yīng)力值和區(qū)間增大,鈦合金材料孔角的殘余壓應(yīng)力比鋁合金材料的大得多,功率密度增大殘余壓應(yīng)力增大幅度降低,對(duì)孔壁殘余壓應(yīng)力值影響最大的是材料,對(duì)表面殘余壓應(yīng)力影響對(duì)大的是功率密度。(4)采用正交試驗(yàn),運(yùn)用疲勞統(tǒng)計(jì)分析方法對(duì)壽命數(shù)據(jù)進(jìn)行處理,建立了P-S-N曲線進(jìn)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(gòu)件的壽命最高;給出了對(duì)于多點(diǎn)激光沖擊強(qiáng)化小孔的光斑大小、搭接率、沖擊層數(shù)、沖擊范圍、功率密度、能量等參數(shù)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(shí)的激光沖擊強(qiáng)化小孔構(gòu)件疲勞壽命可靠性最高;通過(guò)疲勞數(shù)據(jù)統(tǒng)計(jì)分析建立可以描述不同可靠度下壽命與疲勞強(qiáng)度的關(guān)系的P-S-N曲線,給出工藝參數(shù)的確定方法,對(duì)于提高構(gòu)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(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG665

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