本文選題：鈦合金電子束焊接接頭 + 裂紋萌生模擬　； 參考：《南京航空航天大學(xué)》2017年碩士論文

【摘要】：結(jié)構(gòu)疲勞研究中,廣泛采用唯象模型。由于唯象模型無(wú)法揭示疲勞破壞的物理機(jī)制和過(guò)程,使得對(duì)疲勞的研究難以深入。近年來(lái),從細(xì)觀角度來(lái)研究材料的疲勞失效成為研究的新熱點(diǎn)。本文以TC4-DT鈦合金電子束焊接頭為研究對(duì)象,針對(duì)接頭不同區(qū)域的裂紋萌生展開(kāi)數(shù)值模擬和試驗(yàn)研究,主要研究?jī)?nèi)容如下:論文采用元胞自動(dòng)機(jī)法模擬獲得了焊接接頭焊縫區(qū)柱狀晶組織;采用泰森多邊形法模擬獲得了母材區(qū)及靠近母材處熱影響區(qū)的等軸晶組織,經(jīng)與對(duì)應(yīng)區(qū)域的實(shí)際組織進(jìn)行對(duì)比,證明模擬結(jié)果可以很好地描述所研究區(qū)域的組織特點(diǎn)。論文基于組織模擬結(jié)果,利用自主開(kāi)發(fā)的前處理程序,將所獲得的微觀組織轉(zhuǎn)入Abaqus平臺(tái)中;為研究不同晶粒取向?qū)?xì)觀破壞的影響,在前處理中賦予晶粒不同的局部坐標(biāo)系和滑移帶,據(jù)此建立了TC4-DT鈦合金電子束焊接頭不同區(qū)域不同組織的有限元模型;通過(guò)Python語(yǔ)言對(duì)Abaqus進(jìn)行二次開(kāi)發(fā),將Tanaka位錯(cuò)模型和有限元法結(jié)合,完成了對(duì)TC4-DT鈦合金電子束焊接頭不同區(qū)域裂紋萌生的過(guò)程的模擬,并完成了不同區(qū)域疲勞裂紋萌生壽命的模擬。模擬從多維度出發(fā),分別考慮了不同區(qū)域、不同載荷水平作用以及晶粒取向不同時(shí)的裂紋萌生情況,并對(duì)比探索了對(duì)裂紋萌生的影響因素,建立了可用于材料細(xì)觀組織裂紋萌生及循環(huán)壽命預(yù)測(cè)的分析方法和數(shù)值模擬模塊。論文對(duì)TC4-DT鈦合金電子束焊接接頭進(jìn)行原位疲勞試驗(yàn),實(shí)時(shí)觀察了微觀尺度上裂紋的萌生和擴(kuò)展過(guò)程,研究了裂紋萌生的機(jī)制并探索了裂紋萌生與TC4-DT鈦合金電子束焊接頭微觀組織的關(guān)系。論文將數(shù)值模擬結(jié)果與本試驗(yàn)及文獻(xiàn)中的相關(guān)疲勞試驗(yàn)的壽命數(shù)據(jù)進(jìn)行了對(duì)比,初步驗(yàn)證了數(shù)值模擬方法的合理性。論文初步探索出了一種基于材料細(xì)觀組織模擬裂紋萌生的計(jì)算模型,能夠有效地模擬合金材料及焊接接頭焊縫區(qū)域的裂紋萌生及壽命。相對(duì)傳統(tǒng)的唯象模型,效率更高且經(jīng)濟(jì)性更好。此外,原位疲勞試驗(yàn)得出了TC4-DT焊接接頭短裂紋萌生的過(guò)程,從本質(zhì)上揭示了該材料疲勞的微觀機(jī)理。
[Abstract]:Phenomenological model is widely used in structural fatigue research. Because phenomenological model can not reveal the physical mechanism and process of fatigue failure, it is difficult to study fatigue deeply. In recent years, it has become a new research hotspot to study the fatigue failure of materials from the viewpoint of meso-scale. Taking TC4-DT titanium alloy electron beam welding joint as the research object, the numerical simulation and experimental study on crack initiation in different regions of the joint are carried out in this paper. The main research contents are as follows: in this paper, the columnar crystal structure in the weld zone of welded joint is simulated by cellular automata method, and the equiaxed crystal structure in the base metal region and the heat-affected zone near the base metal is obtained by Tyson polygon method. By comparing with the actual organization of the corresponding region, it is proved that the simulation results can well describe the organizational characteristics of the studied region. Based on the results of microstructure simulation, the microstructures obtained are transferred to Abaqus platform by self-developed pre-processing program. According to the local coordinate system and slip band of different grains in pretreatment, the finite element model of different structures in different regions of electron beam welding joint of TC4-DT titanium alloy is established, and the secondary development of Abaqus is carried out by Python language. By combining Tanaka dislocation model with finite element method, the process of crack initiation in different regions of electron beam welding joint of TC4-DT titanium alloy has been simulated, and the fatigue crack initiation life in different regions has been simulated. The simulation considers the crack initiation of different regions, different load levels and different grain orientation from multi-dimension, and compares and explores the influence factors on crack initiation. An analytical method and a numerical simulation module are established for predicting the crack initiation and cyclic life of microstructures of materials. In this paper, the in-situ fatigue test of TC4-DT titanium alloy electron beam welded joint was carried out, and the crack initiation and propagation process on the micro scale was observed in real time. The mechanism of crack initiation and the relationship between crack initiation and microstructure of electron beam welding joint of TC4-DT titanium alloy were studied. In this paper, the numerical simulation results are compared with the fatigue life data in this experiment and in the literature, and the rationality of the numerical simulation method is preliminarily verified. In this paper, a computational model for simulating crack initiation based on the microstructure of materials is proposed, which can effectively simulate the crack initiation and life in the weld zone of alloy materials and welded joints. Compared with the traditional phenomenological model, the efficiency is higher and the economy is better. In addition, the process of short crack initiation in TC4-DT welded joint was obtained by in-situ fatigue test, and the microscopic mechanism of fatigue of the material was revealed in essence.
【學(xué)位授予單位】：南京航空航天大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG407

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