本文選題：蠕變疲勞交互 + 損傷　； 參考：《天津大學(xué)》2014年碩士論文

【摘要】：對(duì)于電廠(chǎng)高溫結(jié)構(gòu),在服役過(guò)程中,結(jié)構(gòu)除了承受高溫穩(wěn)定載荷外,由于重復(fù)的啟動(dòng)停止還會(huì)產(chǎn)生變化的載荷,啟停中變化的載荷以及運(yùn)行過(guò)程中穩(wěn)定的載荷導(dǎo)致蠕變-疲勞的交互作用。對(duì)于初始無(wú)缺陷結(jié)構(gòu),裂紋的萌生壽命在結(jié)構(gòu)失效壽命中占據(jù)很大的比例,研究蠕變-疲勞交互作用下裂紋的萌生及影響因素具有重要意義。通過(guò)結(jié)合初始應(yīng)力應(yīng)變場(chǎng)與連續(xù)損傷力學(xué)理論以及單元失效和裂紋萌生準(zhǔn)則,構(gòu)建了蠕變-疲勞交互作用下裂紋萌生的預(yù)測(cè)模型,將模型編寫(xiě)為UMAT耦合到ABAQUS有限元分析軟件中并進(jìn)行損傷的計(jì)算,實(shí)現(xiàn)了初始無(wú)缺陷結(jié)構(gòu)蠕變-疲勞交互作用下裂紋萌生的有限元模擬,分析了影響裂紋萌生位置和裂紋萌生壽命的因素。分析表明危險(xiǎn)部位的應(yīng)力水平和塑性應(yīng)變水平是影響裂紋萌生的關(guān)鍵因素,裂紋萌生于應(yīng)力集中和塑性應(yīng)變集中的位置;通過(guò)與線(xiàn)性累計(jì)損傷理論對(duì)比發(fā)現(xiàn),裂紋萌生位置蠕變損傷和疲勞損傷具有相互促進(jìn)作用,蠕變疲勞的交互作用使裂紋萌生壽命減小;模擬了三種不同的蠕變和疲勞載荷的加載順序,結(jié)果表明加載順序?qū)α鸭y萌生位置損傷的累積具有顯著影響,承受蠕變載荷后再施加后續(xù)循環(huán)載荷時(shí)結(jié)構(gòu)總損傷更嚴(yán)重,從而使裂紋萌生壽命更短;應(yīng)力集中系數(shù)與循環(huán)壽命的對(duì)數(shù)近似呈線(xiàn)性關(guān)系,且應(yīng)力集中系數(shù)越大,裂紋萌生時(shí)蠕變損傷分量越大。
[Abstract]:For high-temperature structures in power plants, in the course of service, in addition to withstanding high-temperature stable loads, because of repeated startup stops, they will also produce variable loads. The variable load during startup and stop and the steady load during operation lead to the creep-fatigue interaction. For the initial faultless structure, the crack initiation life occupies a large proportion of the failure life of the structure. It is of great significance to study the crack initiation and its influencing factors under the creep-fatigue interaction. Based on the theory of initial stress-strain field and continuous damage mechanics and the criterion of element failure and crack initiation, a prediction model of crack initiation under the interaction of creep and fatigue is established. The model is programmed as UMAT coupled to Abaqus finite element analysis software and the damage is calculated. The finite element simulation of crack initiation under the creep-fatigue interaction of the initial defectless structure is realized. The influence factors of crack initiation position and crack initiation life are analyzed. The analysis shows that the stress level and plastic strain level are the key factors affecting the crack initiation, and the crack initiation is in the position of stress concentration and plastic strain concentration, and it is found by comparison with the linear cumulative damage theory that the stress level and the plastic strain level are the key factors affecting the crack initiation. The creep damage at crack initiation position and fatigue damage promote each other, and the interaction of creep fatigue reduces the crack initiation life, and simulates the loading sequence of three different creep and fatigue loads. The results show that the loading sequence has a significant effect on the cumulative damage of crack initiation position, and the total damage of the structure is more serious when the creep load is applied after the subsequent cyclic loading, which makes the crack initiation life shorter. The logarithmic relationship between the stress concentration factor and the cyclic life is linear, and the larger the stress concentration factor is, the larger the creep damage component is during crack initiation.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：TM621

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