本文選題：焊縫 + 高應(yīng)變低周疲勞��； 參考：《東南大學(xué)》2016年碩士論文

【摘要】：在強(qiáng)震作用下,高聳高層鋼結(jié)構(gòu)焊接節(jié)點(diǎn)焊縫極易產(chǎn)生疲勞損傷累積,造成焊接節(jié)點(diǎn)的破壞甚至整個(gè)結(jié)構(gòu)的倒塌,但國(guó)內(nèi)外對(duì)焊縫在強(qiáng)震作用下的低周疲勞性能仍缺乏系統(tǒng)的研究。本文圍繞強(qiáng)震作用下高聳高層鋼結(jié)構(gòu)焊縫疲勞劣化機(jī)理與壽命預(yù)測(cè)這一主題,針對(duì)高應(yīng)變低周疲勞問(wèn)題,通過(guò)一系列焊縫軸向等幅高應(yīng)變低周疲勞試驗(yàn),系統(tǒng)研究了焊縫在高應(yīng)變循環(huán)過(guò)程中表現(xiàn)的疲勞性能,獲得了焊縫在高應(yīng)變低周疲勞中的循環(huán)應(yīng)力應(yīng)變響應(yīng)特征和循環(huán)應(yīng)力應(yīng)變關(guān)系,提取了相關(guān)性能參數(shù),揭示了焊縫在循環(huán)加載過(guò)程中應(yīng)力應(yīng)變變化規(guī)律及其機(jī)械性能、循環(huán)韌度和Masing特性等性能特征量的循環(huán)相關(guān)性,并在其疲勞性能的基礎(chǔ)上提出了基于裂紋尖端塑性應(yīng)變能的壽命預(yù)測(cè)模型,結(jié)合試驗(yàn)S-N曲線對(duì)模型進(jìn)行了對(duì)比驗(yàn)證。試驗(yàn)研究表明,對(duì)接焊縫在高應(yīng)變低周疲勞過(guò)程中,表現(xiàn)出一定程度的循環(huán)軟化特征,但是很快就進(jìn)入穩(wěn)態(tài)循環(huán)直至破壞。循環(huán)過(guò)程中,焊縫呈現(xiàn)出明顯的拉壓塑性應(yīng)變不對(duì)稱性。在塑性變形過(guò)程中,正向受拉加載引起塑性應(yīng)變強(qiáng)化,反向受壓加載時(shí)出現(xiàn)塑性應(yīng)變軟化,具有強(qiáng)烈的包辛格效應(yīng)。通過(guò)X射線衍射分析了循環(huán)過(guò)程中焊縫殘余應(yīng)力的變化,發(fā)現(xiàn)殘余應(yīng)力在循環(huán)前期即釋放,對(duì)焊縫低周應(yīng)變疲勞性能影響不大。通過(guò)不同應(yīng)變幅下穩(wěn)態(tài)應(yīng)力應(yīng)變響應(yīng)的對(duì)比,發(fā)現(xiàn)隨著總應(yīng)變幅的增加,彈性應(yīng)變幅數(shù)值變化很小,塑性應(yīng)變幅在總應(yīng)變幅中的比例逐漸增大。高應(yīng)變幅下,焊縫主要發(fā)生塑性變形。隨著總應(yīng)變幅的增大,塑性應(yīng)變幅相應(yīng)增大,焊縫的循環(huán)韌度增大,焊縫能夠吸收的過(guò)載能量增加。根據(jù)Hollmom方程擬合得到焊縫高應(yīng)變低周穩(wěn)態(tài)循環(huán)應(yīng)力應(yīng)變關(guān)系式,對(duì)比母材鋼循環(huán)應(yīng)力應(yīng)變曲線關(guān)系結(jié)果可知,焊縫的循環(huán)強(qiáng)度系數(shù)和循環(huán)硬化指數(shù)均低于母材。通過(guò)比較焊縫單調(diào)拉伸試驗(yàn)和不同循環(huán)次數(shù)拉伸階段的循環(huán)應(yīng)力應(yīng)變曲線可知,循環(huán)作用下焊縫金屬循環(huán)強(qiáng)度系數(shù)小于單調(diào)拉伸彈性模量,屈服強(qiáng)度下降,塑性性能下降。同時(shí)焊縫金屬材料穩(wěn)態(tài)滯回曲線的上半段不能完全重合,因而焊縫金屬M(fèi)asing特性不明顯。通過(guò)積分計(jì)算滯回環(huán)包絡(luò)面積求解焊縫的循環(huán)滯回能,看出在循環(huán)過(guò)程中,隨著循環(huán)次數(shù)的增加,焊縫的塑性應(yīng)變能基本保持不變,變化區(qū)間小于1%。大量塑性應(yīng)變?cè)斐傻乃苄詰?yīng)變能的累積,進(jìn)而產(chǎn)生的不可逆損傷是產(chǎn)生疲勞破壞的根本原因。伴隨著裂紋的擴(kuò)展,裂紋尖端總是存在一個(gè)變化的塑性區(qū),而循環(huán)過(guò)程中塑性應(yīng)變能具備循環(huán)穩(wěn)定性,所以裂紋尖端塑性應(yīng)變能是一個(gè)描述高應(yīng)變低周疲勞損傷的重要參量,可以用來(lái)預(yù)測(cè)低周疲勞壽命。本文按照Irwin塑性區(qū)模型,運(yùn)用Mises準(zhǔn)則,重新推導(dǎo)了裂紋尖端塑性應(yīng)變能與應(yīng)力幅的關(guān)系,取單向拉伸的極限塑性應(yīng)變幅對(duì)應(yīng)的應(yīng)力計(jì)算了臨界狀態(tài)塑性應(yīng)變能。假設(shè)臨界塑性應(yīng)變能與疲勞壽命之間為冪函數(shù)關(guān)系,考慮斷裂前最后—次彈性應(yīng)變能積累的影響,參考Manson-Coffin公式的形式,得到了基于尖端塑性應(yīng)變能的疲勞壽命預(yù)測(cè)公式,試驗(yàn)表明該模型適合焊縫高應(yīng)變低周疲勞。
[Abstract]:Under the action of strong earthquake, the weld joint weld of high rise steel structure is very easy to produce fatigue damage accumulation, cause the damage of welding node and even the collapse of the whole structure, but the low cycle fatigue performance of weld under strong earthquake is still lack of systematic research at home and abroad. For high strain and low cycle fatigue, the fatigue performance of weld in high strain cycle is studied systematically, and the cyclic stress-strain relationship and cyclic stress-strain relationship in high strain and low cycle fatigue are obtained by a series of high strain low cycle fatigue tests. The related performance parameters were extracted, and the cyclic correlation of the stress and strain changes and the mechanical properties, the cyclic toughness and the Masing characteristics were revealed. The life prediction model based on the plastic strain energy of the crack tip was put forward on the basis of the fatigue performance, and the model of the test S-N curve was combined with the model. The experimental study shows that the butt weld exhibits a certain degree of cyclic softening in the process of high strain and low cycle fatigue, but it quickly enters the steady state cycle until it is destroyed. In the process of circulation, the weld exhibits obvious tension and plastic strain asymmetry. In the process of plastic deformation, it is induced by tensile loading. Plastic strain intensification and plastic strain softening have a strong Basinger effect. The change of residual stress in the welding seam is analyzed by X ray diffraction. It is found that the residual stress is released at the early stage of circulation and has little effect on the low cycle strain fatigue properties of the weld. With the increase of the total strain amplitude, it is found that the change of elastic strain amplitude is very small, and the proportion of plastic strain amplitude in the total amplitude increases gradually. Under high strain amplitude, the plastic deformation is mainly formed. With the increase of the total strain amplitude, the plastic strain amplitude increases correspondingly, the cyclic toughness of the weld increases and the weld can absorb the overload. Energy increases. According to the Hollmom equation, the stress-strain relationship of high strain and low cycle steady state cycle is obtained. Compared to the results of the relationship between the cyclic stress and strain curves of the base metal steel, the cyclic strength coefficient and the cyclic hardening exponent of the weld are lower than that of the parent material. The stress strain curve shows that the cyclic strength coefficient of the weld metal is less than that of the monotone tensile modulus, the yield strength decreases, and the plastic properties decrease. At the same time, the first half section of the steady-state hysteresis curve of the weld metal material can not be completely overlapped, so the Masing characteristic of the weld metal is not obvious. The calculation of the envelope area of the hysteresis loop is solved by integral calculation. In the cyclic hysteresis energy of the weld, it is found that the plastic strain energy of the weld is basically kept unchanged with the increase of the number of cycles in the cycle process. The variation interval is less than the accumulation of plastic strain energy caused by the plastic strain of 1%., and the irreversible damage is the fundamental cause of the fatigue failure. There is always a changing plastic zone, and the plastic strain can have the cyclic stability during the cycle process, so the plastic strain energy at the crack tip is an important parameter to describe the high strain and low cycle fatigue damage. It can be used to predict the low cycle fatigue life. In this paper, the crack tip is rededuced by the Mises criterion in accordance with the model of the Irwin plastic zone. The plastic strain energy is related to the stress amplitude, and the critical state plastic strain energy is calculated by the stress corresponding to the ultimate plastic strain amplitude. Assuming that the critical plastic strain energy is a power function relationship with the fatigue life, the impact of the last elastic strain energy accumulation before the fracture is taken into consideration, and a reference to the form of the Manson-Coffin formula is obtained. The fatigue life prediction formula based on tip plastic strain energy shows that the model is suitable for high strain low cycle fatigue of weld.
【學(xué)位授予單位】：東南大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：TU973.13

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