超_超_臨界汽輪機汽缸緊固螺栓疲勞_蠕變斷裂的研究

1、第27卷第32期中國電機工程學(xué)報V ol.27 No.32 Nov. 20072007年11月Proceedings of the CSEE 2007 Chin.Soc.for Elec.Eng. 文章編號:0258-8013 (2007 32-0063-04 中圖分類號:TH140 文獻標(biāo)識碼:A 學(xué)科分類號:47030超(超臨界汽輪機汽缸緊固螺栓疲勞蠕變斷裂的研究徐鴻1,鄭善合1,MAILE Karl2(1.華北電力大學(xué)電站設(shè)備狀態(tài)監(jiān)測與控制教育部重點實驗室, 北京市昌平區(qū) 1022062.斯圖加特大學(xué)國家材料測試中心,斯圖加特70569,德國Research on the Fatigue

2、-creep Rupture of Fastening Bolts of Ultra-supercritical SteamTurbine Cylinder CaseXU Hong1, ZHENG Shan-he1, MAILE Karl2(1. Key Laboratory of Condition Monitoring and Control for Power Plant Equipment of Ministry of Education, North ChinaElectric Power University, Changping District, Beijing 102206,

3、 China;2. State Material Testing Institute, University Stuttgart, Stuttgart 70569, GermanyABSTRACT: Loading of peak generator units were changed frequently. The fastening bolts of steam turbine cylinder case were in fatigue-creep interaction. It was important to study fatigue-creep interaction damag

4、e of fastening bolts under multiaxial stress. Fatigue-creep rupture experiments of Nimonic 80A uniaxial specimen and hollow bolts at 550C were carried out. Fatigue-creep process was simulated by ABAQUS using Chaboche-Nouaihas fatigue creep model. It is indicated that fatigue-creep rupture of hollow

5、bolt is different from simple creep rupture. Hollow bolt rupture of fatigue-creep is taking place at the position of the first screw thread root, where the stress is concentrated. A good coincidence comparing the result experiment with finite element calculation can be observed. KEY WORDS: ultra-sup

6、ercritical steam turbine; fastening bolt; fatigue-creep; damage model; rupture摘要:調(diào)峰機組頻繁調(diào)整負荷,汽輪機汽缸緊固螺栓處于疲勞蠕變交互作用,對緊固螺栓多軸應(yīng)力下疲勞-蠕變損傷的研究對調(diào)峰機組安全運行和維修具有重要意義。該文對鎳基合金Nimonic 80A進行了550下單軸及空心螺栓的疲勞蠕變斷裂實驗,應(yīng)用Chaboche-Nouaihas模型,用有限元軟件ABAQUS模擬了空心螺栓的疲勞蠕變過程。結(jié)果表明,與空心螺栓的純?nèi)渥償嗔巡煌?疲勞蠕變斷裂發(fā)生在應(yīng)力集中的螺紋處,有限元計算結(jié)果與實驗結(jié)果吻合較好。關(guān)鍵詞:

7、超(超臨界汽輪機;緊固螺栓;疲勞蠕變;損傷模型;斷裂0 引言汽輪機汽缸緊固螺栓在機組穩(wěn)定運行時受蠕變載荷的作用,在機組啟動、停機和負荷變動過程中受低周疲勞與高溫蠕變的交互作用。筆者在文獻1中對空心螺栓的純?nèi)渥償嗔堰M行了研究?？招穆菟ㄔ诟邷睾愣☉?yīng)力作用下,斷裂部位在螺桿處,而不在應(yīng)力集中的螺紋處。調(diào)峰機組負荷調(diào)整頻繁,隨著電網(wǎng)峰谷差的加大,越來越多的超(超臨界機組也參與調(diào)峰?？招穆菟ㄔ谘h(huán)應(yīng)力作用下,疲勞損傷斷裂部位與純?nèi)渥償嗔巡课徊煌?。本文主要對空心螺栓的高溫疲勞蠕變斷裂進行研究,對鎳基合金幾組單軸試棒及空心螺栓進行了疲勞蠕變實驗。疲勞壽命評估的模型2-6比較多,本文采用Chaboche模型7

8、-10對單軸試棒和空心螺栓進行了有限元計算,計算結(jié)果與實驗結(jié)果相吻合。1 耦合損傷Chaboche粘塑性統(tǒng)一本構(gòu)方程1.1 應(yīng)力應(yīng)變關(guān)系在小變形范圍內(nèi),總應(yīng)變可以分解為e inij ij ij=+(1 各向同性的彈性應(yīng)變服從廣義虎克定律e1ij ij kk ijE E+=(2式中:E,分別為彈性模量、泊松比;ij為Kronecker 符號。64 中 國 電 機 工 程 學(xué) 報 第27卷應(yīng)力增量可以描述為d (d d ijkl t c = (3式中E ijkl 為彈性剛度矩陣。表面應(yīng)力可以表達為(F J X R k = (4式中:k 為與加載速率相關(guān)的初始屈服應(yīng)力;X 為運動硬化量的背應(yīng)力(ba

9、ck stress11;R 為各向同性硬化變量;J (X 為第二應(yīng)力不變量,定義為(J X = (5 式中s 為偏差應(yīng)力張量。 1.2 流動準(zhǔn)則粘塑性應(yīng)變率張量為32(pl F X p pJ X = s (6 式中p為準(zhǔn)則參數(shù),定義為11 11/22(:exp(3nn v vp p p aKK+= (71.3 運動硬化準(zhǔn)則為了增加模型的應(yīng)用范圍,Chaboche 提出用多個分量來描述運動硬化變量X 121Mi i X X = (8當(dāng)忽略溫度和屈服應(yīng)力的影響,每個分量都遵循相同形式的演化方程11/223(:32i r i i i i p i i i i X c a c p X pX X X =

10、(9式中:,c i ,a i ,i ,r i 均為與溫度相關(guān)的材料參數(shù)。等式右端分別是應(yīng)變硬化項、動態(tài)恢復(fù)項和穩(wěn)態(tài)熱恢復(fù)項。Marquis 13對(p 進行了改進(1exp(s s p b p =+ (10 1.4 損傷描述在高溫條件下金屬受應(yīng)力的作用會產(chǎn)生損傷,反之,材料的損傷也會影響到應(yīng)力和應(yīng)變的分布。Kachanov 提出連續(xù)損傷機理14,Lemaitre 和Chaboche 提出等效應(yīng)力的概念15-16,名義應(yīng)力和等效應(yīng)力的關(guān)系為0D 0D 00(1/(1F F FS S S S S S D = (11式中:S 0為試件的截面面積;S D 為損傷產(chǎn)生的空穴總面積。損傷D 定義為D 0/

11、D S S = (122 實驗及結(jié)果實驗用Nimonic 80A 制作的單軸試棒和空心螺栓,實驗溫度均為550。采用HT DMS 高溫應(yīng)變片測量試件應(yīng)變。單軸試棒采用標(biāo)準(zhǔn)試件,進行6組實驗(UF1- UF6,采用等應(yīng)變幅控制,各組實驗加載見表1。螺栓實驗進行了5組(NB1-NB5,空心螺栓試件結(jié)構(gòu)與論文第一部分蠕變實驗相同,螺桿直徑為41mm ,中間孔直徑為18mm ,螺栓總長度為284mm ,兩端以螺紋連接,螺紋直徑為52mm 。螺栓左右螺母材料以及循環(huán)應(yīng)力加載見表2。表1 550下單軸等應(yīng)變幅控制實驗Tab. 1 Conventional strain controlled fatigue

12、 test of uniaxialspecimen at 550C編號應(yīng)變幅拉應(yīng)力/MPa壓應(yīng)力/MPa 循環(huán)周次應(yīng)變率UF10.01830797.8 2000.0002UF20.004646.3572.3 22476 0.0002UF30.006735 695.7 789 0.0002UF 40.008784 776.0 484 0.0002UF 50.005649.3 627.8 6708 0.0002UF 60.009796762.0 416 0.0002表2 550下螺栓疲勞蠕變實驗Tab. 2 Fatigue creep experiments of bolt at 550螺栓編號螺

13、母材料(左螺母材料(右加載應(yīng)力/MPa a m p 保持時間/min t a t m t p 總時間/hNB1GS17CrMoV 511Nimonic 80A 400 250 175 20 60 202265NB2GS17CrMoV 511Nimonic 80A 600 375 262.5 20 60 20815NB3GS17CrMoV 511Nimonic 80A 760 475 332.5 20 60 201153 計算與實驗結(jié)果分析3.1 疲勞蠕變損傷公式參數(shù)的確定根據(jù)單軸疲勞蠕變實驗數(shù)據(jù),擬合得到鎳基合金Nimonic 80A 的材料參數(shù)17-20,見表3。有限元計算結(jié)果與實驗結(jié)果相吻

14、合。圖1為應(yīng)用本構(gòu)方程實驗UF1中5個循環(huán)疲勞理論計算結(jié)果與實驗結(jié)果的比較(total =0.01。單軸理論計算結(jié)果與實驗結(jié)果一致,擬合的各參數(shù)可以用于多軸疲勞蠕變的模擬。表3 Nimonic 80A 在550下的材料參數(shù)Tab. 3 Material parameters of Nimonic 80A at 550 C參數(shù) 數(shù)值 參數(shù)數(shù)值參數(shù)數(shù)值a 1 318.6 Q 41.8 k 220.7 a 2 354.7 n 18.39 K 1070 c 1 106.6 m 1 2.16b 2.114c 2 217.3 m 2 6.35 1 2.14109r 1 2 1 8.11011 2 8.07

15、1015r 222 1.141014 R1第32期徐 鴻等: 超(超臨界汽輪機汽缸緊固螺栓疲勞蠕變斷裂的研究 65400 800 4008008004000400 800應(yīng)變 應(yīng)變0 0 0.0040.0040.0040.004(a計算結(jié)果(b實驗結(jié)果應(yīng)力/M P a應(yīng)力/M P a圖1 應(yīng)用本構(gòu)方程5個循環(huán)疲勞理論計算結(jié)果與實驗結(jié)果 (total = 0.01Fig. 1 Comparison between experimental fatigue test results and theoretical results by means of the used constitutive

16、equation for 5 cycles (total = 0.013.2 螺栓疲勞蠕變結(jié)果將Chaboche-Nouaihas 粘塑性方程寫入ABAQUS ,有限元計算結(jié)果與實驗結(jié)果吻合。實驗用高溫應(yīng)變片測量試件的軸向變形,圖2為實驗螺栓NB3(表2軸向應(yīng)變實驗結(jié)果與有限元計算結(jié)果的比較。圖3顯示了螺栓第一螺紋根部前26個循環(huán)軸向、徑向和周向應(yīng)力與應(yīng)變的計算曲線。對螺栓螺紋處和螺桿處的損傷進行比較,結(jié)果顯示損傷最大的部位在第一螺紋根部。圖4顯示實驗NB4第一螺紋根部與螺桿損傷隨時間的變化曲線。與第一部分純?nèi)渥冇嬎憬Y(jié)果相同,第一螺紋根 0.004時間/min0.0080.012軸向應(yīng)變圖2

17、有限元計算結(jié)果與實驗結(jié)果(NB3 Fig. 2 Comparison of finite element results withexperimental data (No. NB3800 4000 1200 1600 應(yīng)力/M P a200 400 600 800 400 200600 800 1000 0 0.004 0.008 應(yīng)變 0.008 0應(yīng)變 0 0.0001 應(yīng)變(a 軸向 (b 徑向 (c周向圖3 螺栓第一螺紋根部前26個循環(huán)計算曲線(NB3Fig. 3 Calculated curves of stress-strain for the first 26 cycles a

18、t the first screw root of the bolt (No. NB3部是應(yīng)力集中部位,實驗NB2斷裂時間的V onMises 應(yīng)力分布如圖5(a所示,實驗斷裂也在此部位如圖5(b所示,計算結(jié)果與實驗結(jié)果吻合較好。0 400 800 1200時間/ min 損傷因子 D 圖4 螺桿與螺紋損傷隨時間的變化曲線(NB4 Fig.4 Time-dependent damage D in screw and in whorl(No.NB4100221.4343464586707829950(a計算 Fig. 5 Results of stress calculation and exp

19、eriment4 結(jié)論根據(jù)鎳基合金單軸疲勞蠕變交互作用實驗數(shù)據(jù),擬合了Chaboche-Nouaihas 模型的材料參數(shù),多軸應(yīng)力下疲勞蠕變損傷計算結(jié)果與實驗吻合 較好。對于高溫循環(huán)應(yīng)力下的空心螺栓,斷裂部位與高溫純?nèi)渥儾煌?純?nèi)渥償嗔巡课辉诼輻U上,而疲勞-蠕變斷裂部位在第一螺紋根部,在此部位容易發(fā)生疲勞蠕變斷裂。參考文獻1 徐鴻,鄭善合,Maile Karl .超(超臨界機組螺栓高溫蠕變斷裂的研究J.中國電機工程學(xué)報,2007,27(29:80-83.Xu Hong ,Zheng Shan-he ,Maile Karl .Research on creep rupture of ultra-

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