發(fā)布時間：2018-04-04 04:03

  本文選題：鋼橋　切入點(diǎn)：焊接接頭　出處：《西南交通大學(xué)》2015年博士論文

【摘要】：環(huán)境腐蝕和疲勞是影響鋼橋耐久性的重要因素,實(shí)際工程中鋼橋焊接接頭大多處于復(fù)雜應(yīng)力狀態(tài),因此本文針對預(yù)腐蝕及復(fù)雜應(yīng)力場下鋼橋焊接接頭的疲勞性能展開研究。(1)介紹了疲勞壽命評估方法、多軸疲勞破壞準(zhǔn)則以及多軸疲勞試驗(yàn)的研究情況。歸納總結(jié)了鋼橋腐蝕類型、影響因素、腐蝕預(yù)測模型和腐蝕試驗(yàn)方法。闡述了腐蝕疲勞裂紋萌生機(jī)理和擴(kuò)展機(jī)理的研究現(xiàn)狀,概述了國內(nèi)外學(xué)者對腐蝕疲勞壽命評估的研究進(jìn)展。(2)參考國內(nèi)外文獻(xiàn),構(gòu)造不同傾角(0°、15°、30°、45°)全熔透承載角焊縫十字形焊接接頭來模擬正應(yīng)力和剪應(yīng)力共同作用下的復(fù)雜應(yīng)力場。采用線性外推、二次外推和1 mm法計算焊接接頭的熱點(diǎn)應(yīng)力,根據(jù)不同網(wǎng)格尺寸的計算結(jié)果來確定合適的網(wǎng)格密度。分析熱點(diǎn)正應(yīng)力集中系數(shù)和熱點(diǎn)剪應(yīng)力集中系數(shù)隨傾角的變化情況。最后,分別采用等效應(yīng)力法、相互作用方程法和雙參數(shù)臨界面法進(jìn)行疲勞壽命評估,并與試驗(yàn)結(jié)果進(jìn)行對比分析,推薦采用線性外推法計算熱點(diǎn)應(yīng)力,等效應(yīng)力法來預(yù)測復(fù)雜應(yīng)力場下焊接接頭的疲勞壽命。(3)總結(jié)了大量的腐蝕坑深度模型,介紹了腐蝕坑缺口和裂紋當(dāng)量化技術(shù),最終采用最簡單的冪函數(shù)模型表示蝕坑深度與時間的關(guān)系,為了研究當(dāng)單個蝕坑尺寸對疲勞壽命的影響,把蝕坑當(dāng)作形狀規(guī)則的球形缺口來處理,并且考慮兩種不同的蝕坑深度。(4)對3種不同腐蝕程度下的45°傾角全熔透承載角焊縫十字形焊接接頭進(jìn)行疲勞試驗(yàn),得到了它們的S一N曲線。研究不同腐蝕損傷對焊接接頭熱點(diǎn)應(yīng)力集中系數(shù)和疲勞缺口系數(shù)的影響,提出了一種考慮腐蝕深度和應(yīng)力幅的腐蝕疲勞壽命影響系數(shù)定義方式,根據(jù)試驗(yàn)結(jié)果擬合得到了它的表達(dá)式。結(jié)果表明蝕坑缺口對焊接接頭的疲勞性能有一定影響,但不是很敏感；不同腐蝕深度和應(yīng)力幅下焊接接頭的疲勞強(qiáng)度降低程度不同。(5)以不同腐蝕程度下45°傾角全熔透承載角焊縫十字形焊接接頭為研究對象,采用數(shù)值方法計算焊接接頭表面裂紋的應(yīng)力強(qiáng)度因子,分析不同蝕坑尺寸、裂紋形狀比和裂紋深度對焊接接頭應(yīng)力強(qiáng)度因子的影響規(guī)律。結(jié)果表明蝕坑深度對應(yīng)力強(qiáng)度因子的影響起主要作用,蝕坑球半徑的影響比較��；裂紋表面點(diǎn)為Ⅰ型開裂,而最深點(diǎn)為Ⅰ+Ⅱ復(fù)合型開裂；蝕坑深度、裂紋形狀比和裂紋深度對表面點(diǎn)應(yīng)力強(qiáng)度因子影響大于最深點(diǎn)。(6)根據(jù)不同腐蝕程度下十字形焊接接頭的S-N曲線計算疲勞裂紋擴(kuò)展速率公式參數(shù),采用數(shù)值方法模擬不同復(fù)合型裂紋擴(kuò)展準(zhǔn)則下十字形焊接接頭的疲勞裂紋擴(kuò)展,基于多項(xiàng)式擬合得到了不同復(fù)合型裂紋擴(kuò)展準(zhǔn)則下的裂紋形狀修正系數(shù),最終采用最大周向應(yīng)力準(zhǔn)則對裂紋擴(kuò)展速率公式進(jìn)行修正。給出了不同應(yīng)力幅和腐蝕程度下有效應(yīng)力強(qiáng)度因子幅、裂紋擴(kuò)展角與裂紋深度的關(guān)系,裂紋深度與循環(huán)次數(shù)的關(guān)系,對比分析了模擬和實(shí)際裂紋擴(kuò)展路徑。結(jié)果表明裂紋擴(kuò)展模擬路徑與實(shí)際路徑符合較好,修正后的裂紋擴(kuò)展速率得到的疲勞壽命與試驗(yàn)結(jié)果吻合較好,基于最大周向應(yīng)力準(zhǔn)則的裂紋形狀修正系數(shù)能夠用于疲勞壽命計算。(7)從損傷力學(xué)角度出發(fā)提出焊接接頭疲勞損傷模型,采用裂紋尺寸來定義損傷變量,給出了兩種損傷演化模型：Chaboche模型和Lemaitre模型,結(jié)合疲勞試驗(yàn)結(jié)果確定了不同腐蝕程度下十字形焊接接頭Chaboche損傷演化方程的材料參數(shù),得到了十字形焊接接頭的損傷曲線和疲勞壽命預(yù)測方程。結(jié)果表明裂紋尺寸能夠作為焊接接頭的損傷變量,Chaboche模型能夠用于焊接接頭的損傷評估。
[Abstract]:Environmental corrosion and fatigue are important factors affecting the durability of steel bridge, steel bridge welded joints in practical engineering are mostly in the complex stress state, this paper carries out research on the fatigue performance of pre corrosion and complex stress field of steel welded joints. (1) introduced a method to estimate the fatigue life of multiaxial fatigue damage criterion and research multi axial fatigue test. Summarizes the steel corrosion types, influence factors, models and methods for corrosion testing of corrosion prediction. Describes the present situation of the initiation mechanism and propagation mechanism of corrosion fatigue crack, research progress of domestic and foreign scholars on the evaluation of corrosion fatigue life is summarized. (2) refer to the domestic and foreign literature, construct different angle (0 degrees, 15 degrees, 30 degrees, 45 degrees) full penetration weld carrying cruciform welded joints to simulate normal stress and shear stress under the complex stress field. By linear extrapolation, two time extrapolation 1 and the MM method to calculate the hot stress of welded joints, to determine the appropriate grid density according to the calculation results of different mesh size. Analysis of hot spots is the stress concentration coefficient and hot shear stress concentration coefficient changes with angle. Finally, using the equivalent stress method, interaction method and parameters of critical plane method of fatigue life assessment, and the results were compared with experimental results, recommend the use of linear extrapolation method to calculate the hot spot stress, to predict the complex stress field of welded joints fatigue life equivalent stress method. (3) summarized a lot of deep pit corrosion model, introduces corrosion pits and cracks when the gap of quantitative techniques eventually, the exponential function model is the simplest representation of relationship between corrosion pit depth and time, in order to study the effect of a single pit when the size of the fatigue life, the spherical gap pits as shape rules to handle, and the test About two different depth of corrosion pit. (4) of 3 different corrosion degree under the angle of 45 DEG full penetration weld cross bearing fatigue tests of welded joints, the S N curve. They study different corrosion damage effect on stress concentration coefficient and fatigue notch factor of welded joints of hot spot that is put forward by considering the corrosion depth and stress amplitude of the corrosion fatigue life influence coefficient is defined, according to the test results obtained by fitting its expression. The results show that the pit gap has a certain effect on the fatigue performance of welded joints, but not very sensitive; reduce the fatigue strength of welded joints with different corrosion depth and stress amplitude under the different degree. (5) under different corrosion degrees to 45 degrees angle of full penetration weld carrying cruciform welded joints as the research object, the numerical calculation method of welding joint surface crack stress intensity factor analysis Different pit size, crack shape ratio and crack depth on stress intensity factor of welded joints. The results showed that the effect of corrosion pit depth and stress intensity factor plays the main role, effect of pit radius is relatively small; the crack surface point type cracking, and the deepest point is I + II compound cracking; corrosion pit depth, crack shape ratio and crack depth on the surface of the stress intensity factor effect is greater than the deepest point. (6) according to the different corrosion degree of cruciform welded joint S-N curve calculation formula of fatigue crack propagation rate parameters, the numerical simulation of different compound crack propagation of fatigue crack in welded joint shape under the criterion of cross crack shape polynomial fitting obtained for different composite crack propagation criterion correction coefficient based on the maximum circumferential stress criterion of crack growth rate formula is corrected. Given the different effective stress intensity factors stress amplitude and corrosion degree, relationship between the crack angle and the crack depth, the relationship between the depth and the number of cycles to crack, comparative analysis of the simulation and actual crack propagation path. The results show that the simulation of crack propagation path and actual path is consistent with the crack growth rate was revised the fatigue life and the test results are in good agreement, based on the maximum circumferential stress criterion of crack shape correction coefficient can be used for the calculation of fatigue life. (7) from the perspective of damage mechanics, the fatigue damage of welded joint model is proposed, using the crack size to define the damage variable, gives two kinds of damage evolution model: Chaboche model and Lemaitre model, combined with the the fatigue test results of different corrosion degrees of cruciform welded joints of Chaboche material parameters evolution equation of damage is determined by cruciform welded joints The damage curves and fatigue life prediction equations show that the crack size can be used as a damage variable of welded joints, and the Chaboche model can be used for damage assessment of welded joints.

【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：U441.4;U445.583
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本文編號：1708283