本文關(guān)鍵詞：激光沖擊強化鈦合金圓角構(gòu)件的殘余應(yīng)力分布及其抗疲勞研究　出處：《江蘇大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 激光沖擊強化 TC4-DT鈦合金 殘余應(yīng)力 圓角構(gòu)件 曲率半徑 疲勞壽命

【摘要】：機械領(lǐng)域中零部件大多帶有復(fù)雜的曲面特征,如結(jié)構(gòu)圓角、溝槽等,這些曲面結(jié)構(gòu)的臨界區(qū)曲率變化較大,往往存在應(yīng)力集中,在外載荷的作用下易萌發(fā)疲勞裂紋,進而發(fā)生斷裂,是疲勞薄弱區(qū),而激光沖擊強化能有效提高曲面部件的疲勞壽命。但激光沖擊誘導(dǎo)曲面結(jié)構(gòu)殘余應(yīng)力的分布規(guī)律不能基于平面結(jié)構(gòu)獲得的趨勢進行預(yù)測,因此研究曲面結(jié)構(gòu)激光沖擊強化的殘余應(yīng)力分布,提高曲面構(gòu)件疲勞性能,具有重要的意義。本文通過理論分析、數(shù)值模擬以及試驗驗證等手段,以TC4-DT鈦合金圓角構(gòu)件為研究對象,探討了激光沖擊強化對曲面結(jié)構(gòu)殘余應(yīng)力分布及其疲勞性能的影響。本文主要研究工作如下:(1)論述了激光誘導(dǎo)沖擊波的產(chǎn)生及其與材料相互作用過程,分析了沖擊波作用下殘余應(yīng)力場的形成機制,探討了激光沖擊作用下曲面結(jié)構(gòu)殘余應(yīng)力產(chǎn)生的機理以及曲率與殘余應(yīng)力之間存在的可能關(guān)系;采用ABAQUS有限元分析軟件建立了凹面、平面和凸面三種幾何模型,研究了激光多點搭接沖擊下曲面結(jié)構(gòu)的幾何效應(yīng)。結(jié)果表明,三種幾何模型之間的殘余壓應(yīng)力大小及影響層深度存在以下關(guān)系:凹面平面凸面。對于凹面結(jié)構(gòu),殘余壓應(yīng)力隨曲率半徑的增大而減小,最后趨于平面結(jié)構(gòu);而對于凸面結(jié)構(gòu),殘余壓應(yīng)力隨半徑的增大而增大,最后趨于平面結(jié)構(gòu);對于圓角構(gòu)件,R3模型表面的殘余壓應(yīng)力分布要優(yōu)于R6模型。(2)基于ABAQUS有限元分析軟件對圓角結(jié)構(gòu)在不同激光沖擊參數(shù)下殘余應(yīng)力的分布規(guī)律進行了研究。結(jié)果表明:對于圓角結(jié)構(gòu),殘余壓應(yīng)力大小隨峰值壓力的增大而增大,但存在一個飽和值,而殘余壓應(yīng)力影響層深度一直增加;隨著激光脈寬的增大,各路徑上殘余壓應(yīng)力呈增大的趨勢,殘余壓應(yīng)力影響層深度也隨之增加;沖擊次數(shù)增加到一定次數(shù)后作用不明顯,甚至起反作用,而沖擊次數(shù)對深度方向上的殘余應(yīng)力分布影響較小。(3)對TC4-DT鈦合金R3、R6圓角雙聯(lián)試樣進行了激光沖擊強化試驗和疲勞拉伸試驗。結(jié)果表明,試樣經(jīng)激光沖擊強化后,疲勞壽命大幅增加,雖然不同條件下疲勞增益各不相同,但R3和R6試樣的疲勞增益卻相差無幾。(4)通過對疲勞斷口形貌的微觀分析發(fā)現(xiàn),比較沖擊前后:在疲勞源區(qū),試樣未沖擊端斷口上疲勞源均位于圓角根部相切處,而沖擊端疲勞源向沖擊深度方向轉(zhuǎn)移,且均位于側(cè)面;在疲勞穩(wěn)定擴展區(qū),相同位置處沖擊端斷口上的疲勞條帶間距明顯小于未沖擊端,說明激光沖擊強化能有效抑制疲勞裂紋的擴展;在最終瞬斷區(qū),試樣沖擊端瞬斷區(qū)上的韌窩尺寸較未沖擊端大。通過對激光沖擊強化改善圓角結(jié)構(gòu)抗疲勞特性的研究發(fā)現(xiàn):激光沖擊通過引入殘余壓應(yīng)力來減小裂紋尖端有效應(yīng)力強度因子幅,抑制疲勞裂紋的擴展,達到提高圓角構(gòu)件疲勞壽命的目的;而曲率半徑則通過對集中應(yīng)力和殘余應(yīng)力分布的共同作用來影響圓角構(gòu)件的疲勞性能。
[Abstract]:In the field of mechanical parts with the most complex surface feature, such as the structure of the trench, rounded, critical curvature changes of the surface structure is large, there is stress concentration, it was easy to fatigue crack under external loading, and fatigue fracture is the weak area, and laser shock peening can improve the fatigue life of surface the distribution of components. But not laser shock induced surface residual stresses in plane structure trend based on the forecast, so the research on surface structure of the residual stress distribution of laser shock strengthening, improving fatigue properties of surfaces, is of great significance. In this paper, through theoretical analysis, numerical simulation and experimental verification method based on TC4-DT the rounded titanium alloy component as the research object, discusses the laser shock stress distribution and fatigue properties of surface residual structure. This paper mainly research The work is as follows: (1) discusses the shock wave induced by laser and its interaction with the process of the material, analyzes the formation mechanism of shock wave under the action of the residual stress field, discusses the mechanism of laser shock surface structure under the effect of residual stress and curvature and residual stress exist in the relationship between the force is established; concave using finite element analysis software ABAQUS, and the three plane convex geometry model, the geometric effect of surface structure of multi point laser lap under the impact. The results showed that three kinds of residual geometric model between compressive stress size and influence depth has the following relations: concave convex concave plane. The structure, the compressive residual stress the force decreases with the increase of the radius of curvature, and finally tends to planar structure; for convex structure, the residual compressive stress increases with the increase of the radius, and finally tends to planar structure; for fillet component, R3 model The surface residual stress distribution is better than the R6 model. (2) based on finite element analysis software ABAQUS on distribution of fillet structure under different laser shock parameters of residual stress were studied. The results show that: for the fillet, the residual compressive stress with the size of the peak pressure increased, but there is a a saturation value, and the residual stress influence depth has been increased; with the increase of pulse width, the path of the residual compressive stress increases, the compressive residual stress influence depth increases; the impact number increased to a certain number of aftercrop is not obvious, or even counterproductive, and impact times on the residual stress distribution in the depth direction has little influence. (3) of TC4-DT titanium alloy R3, R6 double fillet samples by laser shock test and fatigue tensile test. The results show that after laser shock peening, the fatigue life significantly Although the gain increase, fatigue under different conditions are different, but the fatigue gain R3 and R6 samples but not much difference between. (4) through microscopic analysis on the fatigue fracture morphology found that: in the comparison before and after the impact fatigue source region, the sample fracture fatigue impact end source are located in the root of the fillet tangent at the impact end the impact of fatigue source transfer to the depth direction, and are located in the expansion zone on the side; fatigue and stability, at the same position of impact fatigue fracture end on band spacing is significantly lower than that of non impact end, which indicates that the extended LSP can effectively inhibit the crack; in the final fracture zone, specimen fracture zone on the end of the impact toughness nest size is not large. The impact end by strengthening the research on improving the fatigue resistance of the fillet on laser shock: laser shock by introducing compressive residual stress near the crack tip to reduce the effective stress intensity factor range, inhibition of fatigue crack The purpose of improving the fatigue life of fillet members is to expand, while the radius of curvature influences the fatigue performance of fillet members by the combined action of concentrated stress and residual stress distribution.

【學(xué)位授予單位】：江蘇大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG665

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