结构疲劳强度分析及工程应用
摘要
当机械设备承受一定交变循环载荷的时候,设备常常会在经历一定载荷次数后发生疲劳破坏而失效。有统计数据表明,在现代工业的各种领域中,因疲劳破坏而引起的结构强度破坏事件就占了80%,因此如何有效地防止服役设备发生疲劳破坏,使设备在设计疲劳寿命内不发生失效成为了人们的重要课题。
疲劳破坏的发生区域带有一定局部性,一般发生在存在应力集中、结构疲劳强度薄弱的部位。对于承受交变载荷的压力容器和输送水泥用的斗式提升机来说,前者的开孔接管处尤其是开孔率较高的一些部位如人孔结构,由于开孔破坏了容器结构的连续性,削弱了该处的承载面积,容易引起应力的高度集中和结构抗疲劳强度的降低。后者的工作环境恶劣,工况复杂多变,提升机服役时,输送链上的销轴受交变剪切和弯曲等载荷作用,销轴的中部位置受到的合应力最大,若销轴的加工过程伴有冶金缺陷,销轴的中部位置就可能成为抵御疲劳破坏的脆弱之处,在一定的受载次数后发生疲劳破坏,给企业的正常运营和生产安全带来隐患和危险。
本文首先利用有限单元法,运用计算机分析软件ANSYS,依据JB4732-1995《钢制容器——分析设计标准》,对一氧气储气罐的人孔补强管结构进行了应力强度和疲劳强度的分析和校核。在解决一个工程问题的同时,还就人孔补强管的两个几何参数即补强管向筒节的内伸深度和补强管补强段的壁厚对结构应力强度和疲劳强度的影响,对模型的计算结果进行了对比性分析,得出一些一般性的结论,即:在当前人孔开孔率下,人孔补强管相贯区附近区域将会产生应力集中现象;内伸式补强管比平齐式补强管更能有效降低结构应力,提高设备的抗疲劳性能;补强管内伸深度的增加对结构和应力线性化校核线所在部位的各类应力强度的影响则有所差别;同样内伸深度条件下,补强段壁厚的增加可以持续地对结构部分类别的应力强度和疲劳强度起降低作用,但不能有效减小峰值应力,而且最后设计所取的内伸深度和补强段壁厚应当采用“适当原则”。
随后,通过化学成分、显微组织和裂纹、断口特征的分析以及应力强度计算校核,对一斗式提升机输送链销轴的断裂原因进行了综合分析,分析结果表明销轴表面偏大的弯曲正应力和淬火裂纹的存在是导致销轴发生疲劳断裂的重要原因。同时,利用Paris公式对疲劳裂纹的扩展寿命进行了估算,结果显示如果销轴工作时存在一定尺寸的初始裂纹,则偏大的弯曲正应力以及初始裂纹尺寸的大小会成为影响销轴疲劳裂纹扩展寿命的关键性因素。
Fatigue fracture will happen when equipments bear a certain number of alternating load. Statistics have shown that 80 per cent of the structural damages were caused by the fatigue fracture. Therefore how to effectively prevent the machinery from fatigue fracturing during the time of services becomes an important subject.
Fatigue fracture frequently occurs in the places in which there is the presence of stress concentration and the structural fatigue strength is weak, limited in certain region. For the pressure vessel subject to the circular load, the manhole's opening rate is somehow higher and that will not only destroy the continuity of the equipment, but also reduce the areas used to bear the load, resulting in high stress concentration and easier structural damage. For the bucket elevator used to transport cement, the loads of the pins in the hoist chains conclude alternating shear stress and bending stress, the maximal composition of forces and some metallurgical defects will make the centre of the pin weakest point in withstanding fatigue. Damages resulting from fatigue will endanger the normal business operation and production safety.
This article firstly analyzed the stresses intensity and fatigue of the manhole in an oxygen cylinder according to the principles and methods of analytic design, using finite element method and ANSYS program. For one thing, an engineering problem was solved. For another, some general conclusions were obtained by examining the effects of some variables. That is, high stress concentration exists in the junction of the manhole and nozzle extending inside of opening. The stress can be reduced obviously by extending the nozzle inside the opening though the stress reduction effect will become different when the extending depth increases. The larger is the thickness of the tube, the smaller is the stress of the junction, except for the peak stress, but the stress declining rate will decrease.
Secondly, the stress intensity of the pins was calculated and a comprehensive research on composition, microstructure, cracks and fracture surfaces was conducted. The research showed that the maximal bending stress of the pin's surface was larger than expected and some micro cracks were generated during the quenching, which resulted in fatigue damnification on the surfaces of the pins and fracturing finally. The bending stress and the initial size of the quenching cracks are the key factors that affect the crack growth life of the pin.
疲劳破坏的发生区域带有一定局部性,一般发生在存在应力集中、结构疲劳强度薄弱的部位。对于承受交变载荷的压力容器和输送水泥用的斗式提升机来说,前者的开孔接管处尤其是开孔率较高的一些部位如人孔结构,由于开孔破坏了容器结构的连续性,削弱了该处的承载面积,容易引起应力的高度集中和结构抗疲劳强度的降低。后者的工作环境恶劣,工况复杂多变,提升机服役时,输送链上的销轴受交变剪切和弯曲等载荷作用,销轴的中部位置受到的合应力最大,若销轴的加工过程伴有冶金缺陷,销轴的中部位置就可能成为抵御疲劳破坏的脆弱之处,在一定的受载次数后发生疲劳破坏,给企业的正常运营和生产安全带来隐患和危险。
本文首先利用有限单元法,运用计算机分析软件ANSYS,依据JB4732-1995《钢制容器——分析设计标准》,对一氧气储气罐的人孔补强管结构进行了应力强度和疲劳强度的分析和校核。在解决一个工程问题的同时,还就人孔补强管的两个几何参数即补强管向筒节的内伸深度和补强管补强段的壁厚对结构应力强度和疲劳强度的影响,对模型的计算结果进行了对比性分析,得出一些一般性的结论,即:在当前人孔开孔率下,人孔补强管相贯区附近区域将会产生应力集中现象;内伸式补强管比平齐式补强管更能有效降低结构应力,提高设备的抗疲劳性能;补强管内伸深度的增加对结构和应力线性化校核线所在部位的各类应力强度的影响则有所差别;同样内伸深度条件下,补强段壁厚的增加可以持续地对结构部分类别的应力强度和疲劳强度起降低作用,但不能有效减小峰值应力,而且最后设计所取的内伸深度和补强段壁厚应当采用“适当原则”。
随后,通过化学成分、显微组织和裂纹、断口特征的分析以及应力强度计算校核,对一斗式提升机输送链销轴的断裂原因进行了综合分析,分析结果表明销轴表面偏大的弯曲正应力和淬火裂纹的存在是导致销轴发生疲劳断裂的重要原因。同时,利用Paris公式对疲劳裂纹的扩展寿命进行了估算,结果显示如果销轴工作时存在一定尺寸的初始裂纹,则偏大的弯曲正应力以及初始裂纹尺寸的大小会成为影响销轴疲劳裂纹扩展寿命的关键性因素。
Fatigue fracture will happen when equipments bear a certain number of alternating load. Statistics have shown that 80 per cent of the structural damages were caused by the fatigue fracture. Therefore how to effectively prevent the machinery from fatigue fracturing during the time of services becomes an important subject.
Fatigue fracture frequently occurs in the places in which there is the presence of stress concentration and the structural fatigue strength is weak, limited in certain region. For the pressure vessel subject to the circular load, the manhole's opening rate is somehow higher and that will not only destroy the continuity of the equipment, but also reduce the areas used to bear the load, resulting in high stress concentration and easier structural damage. For the bucket elevator used to transport cement, the loads of the pins in the hoist chains conclude alternating shear stress and bending stress, the maximal composition of forces and some metallurgical defects will make the centre of the pin weakest point in withstanding fatigue. Damages resulting from fatigue will endanger the normal business operation and production safety.
This article firstly analyzed the stresses intensity and fatigue of the manhole in an oxygen cylinder according to the principles and methods of analytic design, using finite element method and ANSYS program. For one thing, an engineering problem was solved. For another, some general conclusions were obtained by examining the effects of some variables. That is, high stress concentration exists in the junction of the manhole and nozzle extending inside of opening. The stress can be reduced obviously by extending the nozzle inside the opening though the stress reduction effect will become different when the extending depth increases. The larger is the thickness of the tube, the smaller is the stress of the junction, except for the peak stress, but the stress declining rate will decrease.
Secondly, the stress intensity of the pins was calculated and a comprehensive research on composition, microstructure, cracks and fracture surfaces was conducted. The research showed that the maximal bending stress of the pin's surface was larger than expected and some micro cracks were generated during the quenching, which resulted in fatigue damnification on the surfaces of the pins and fracturing finally. The bending stress and the initial size of the quenching cracks are the key factors that affect the crack growth life of the pin.
引文
[1]赵少汴.机械设计丛书 抗疲劳设计.北京:机械工业出版社,1994
[2]赵在理.压力容器的结构分析与安全评估研究:[博士学位论文].湖北:武汉理工大学,2006
[3]Wohler's Experiment on the Strength of Metals.Engineering,1967
[4]程育仁,缪龙秀,侯炳麟.疲劳强度.北京:中国铁道出版社,1990
[5]J.Goodman.Mechanics Applied to Engineering,1914
[6]S.S.Manson.National Advisory Committee for Aeronautics.Cleveland,1954
[7]L.F.Coffin,Jr.,ASME Transaction,Vol.16,P931,1954
[8]王勖成,邵敏.有限元基本原理和数值方法(第二版).北京:清华大学出版社,1997
[9]郭乙木,陶伟明,庄茁.线性与非线性有限元及其应用.北京:机械工业出版社,2004
[10]许尚贤.机械设计中的有限元法.北京:高等教育出版社,1992
[11]潘风文,金淼.液压机本体CAD的现状与发展.锻压机械,2000,35(2):39-40
[12]陈传尧.疲劳与断裂.武汉:华中科技大学出版社,2002
[13]薛明德.国外关于圆柱壳开孔接管问题的研究状况.压力容器,1991,8(2):9-15
[14]张卫义,俞建荣等.内压柱壳大开孔率开孔平齐式接管应力分布研究.压力容器,2000,17(6):1-5
[15]张卫义,田海晏.内压圆柱壳内伸式接管补强结构应力分布.石油化工机械,2003,32(4):24-25
[16]王磊.内压壳体开孔接管的应力分析与补强设计计算.机械科学与技术,2006,25(9):1130-1134
[17]闫胜咎,李昕,高炳军等.大开孔球壳与内伸接管连接区的实验应力分析.石油化工设备技术,2002,23(2):1-4
[18]张卫义,陈罕.内压筒体开孔接管结构应力集中系数预测.化工机械,2006,33(6):346-349
[19]王定标,魏新利,向飒等.压力容器与切向接管结构应力三维有限元分析及强度评定.湖南工程学院学报,2005,15(4):29-33
[20]毛明智,谭建平,叶云友.斗式提升机输送链销轴断裂机理分析.机械科学与技术,2001,20(6):864-865,903
[21]郭才才,尹汾.斗提机断销原因分析及改进.山西化工,2001,21(2):44-45
[22]陈灵,梁思祖,刘正义.牵引销紧固螺钉断裂分析.机械工程材料,2006,30(4):86-88
[23]冯耀荣,祁全全.曲柄销轴断裂失效分析.理化检验:物理分册,1991,27(4):52-53,51
[24]冯少陵.挖掘装载机铲斗长销轴断裂分析.工程机械,1990,21(11):52-52,32
[25]束维钧,钦培忠,杨柄南等.机械设计中销轴的计算与结构选择.农机与食品机械,1995,4:16-17
[26]李家武,彭铎.典型销轴的有限元计算研究.建筑机械化,2005,6(10):50-51
[27]董华明,王义行,乇晓虎.滚子链销轴的有限元计算及其应力场分布与变形规律.吉林工业大学学报,1996,26(4):85-89
[28]徐进永,阎树岭.工程机械铰接销轴结构设计.建筑机械,1997,5:18-19,37
[29]曹文静,景岗.提高套筒滚子链传动疲劳寿命的优化设计.机械工程师,1990,6:2-4
[30]赵永利,王春,邸玉志.防止销轴淬火开裂的措施.机械工人:热加工,2003,6:53-53
[31]何建伟,郭文华,李银风等.销轴弯曲疲劳强度的试验研究.工程机械,2003,34(4):20-23
[32]卜海峰.压力容器用钢疲劳可靠性分析:[硕士学位论文].北京:北京工业大学,2001
[33]范钦珊.压力容器的应力分析和强度设计.北京:原子能出版社,1983
[34]机械工程手册编委会编.机械工程手册:第十九篇机械结构强度.北京:机械工业出版社,1980
[35]T.V.Duggan and J.Byrne.Fatigue as a Design Criterion.The Macmillan Press Ltd.,1977
[36]李志安,金志浩,宫殿民.压力容器断裂理论与缺陷评定.大连:大连理工大学出版社,1994.8
[37]王仲仁,宛世剑,胡连喜.弹性与塑性力学基础.哈尔滨:哈尔滨工业大学出版社,2004
[38]张洪伟.圆柱壳大开孔应力分析研究:[硕士学位论文].大连:大连理工大学,2003
[39]薛明德.力学与工程技术的进步.北京:高等教育出版社,2001
[40]贺匡国.压力容器分析设计基础.北京:机械工业出版社,1995
[41]GB 150-1998,钢制压力容器
[42]JB 4732-1995,钢制压力容器——分析设计标准
[43]余伟炜,高炳军.ANSYS在机械与化工装备中的应用.北京:中国水利水电出版社,2006
[44]郑志峰.链传动设计与应用手册.北京:机械工业出版社,1992
[45]GB/T 3077-1999,合金结构钢
[46]GB/T 10561-1989,钢中非金属夹杂物显微评定方法
[47]GB/T 13320-1991,钢质模锻件金相组织评级图及评定方法
[48]张经源.链条传动及制造.杭州:浙江大学出版社,1989
[49]孟繁忠.链条链轮产品设计与检验.北京:机械工业出版社,1996
[50]夏荣海,郝玉琛.矿井提升设备.江苏:中国矿业学院出版社,1987
[51]徐尚龙.基于数值模拟的矿井提升机主轴疲劳与断裂性能研究:[硕士学位论文].陕西:西安科技学院,2003
[52]Eringen,A.C.et,"Stress concentrations in Two Normal Intersecting Cylindrical shells subject to Internal Pressure".《Wrc Bulletin》 No.139,1969
[53]Zarrabi K.,Basu A..A finite volume element formulation for solution of elastic axisymmetric pressurized components.Pressure vessels and Piping.2000,77:479-484
[54]D.Broke,et al.Fatigue crack growth:effect of sheet thickness.Aircraft Engineering.1996,38(11):31-33
[55]方佩珍,潘永亮,黄卫星等.天然气贮罐的疲劳分析.化工机械,2003,30(4):221-223,234
[56]严永德,王宽福.接管区含缺陷的压力容器的疲劳分析.石油化工设备,1989,18(2):1-4
[57]吴会超.基于ANSYS的焊接接头疲劳分析.铁道机车车辆工人,2006,6:1-4,10
[58]王磊.内压壳体开孔接管的应力分析与补强设计计算.机械科学与技术,2006,25(9):1130-1134
[59]张卫义,田海晏.内伸式接管补强结构应力分布特点.北京石油化工学院学报,2003,11(2):48-50
[60]马天兵,孙兵,杜菲.基于ANSYS对压力容器管板厚度的优化设计.煤矿机械,2004,12:23-25
[61]薛明德.国外关于圆柱壳开孔接管问题的研究概况.压力容器,1991,8(2):9-15
[62]洪德晓.有限元在压力容器应力分析设计中应用的讨论——阶段性归纳.化工设备与管道,2006,43(4):1-6,16
[63]郑津洋,董其伍,桑芝富.过程设备设计 第二版.北京:化学工业出版社,2005
[64]季建钢,寿旭日.储汽筒椭圆形封头及人孔结构应力和疲劳分析.机电设备,1998,1:34-38,42
[65]宋建华,张会平.在线化工设备疲劳分析专家系统的研究.化工机械,1996,23(5):7-11
[66]崔军,吴伟.塑性理论在疲劳分析中的应用.工程力学,1997,A01:329-332
[67]林国湘.提升机主轴疲劳强度的模糊概率设计.矿山机械,1999,27(8):34-35
[68]范国海,周庆超,张纯义.疲劳分析数值方法的关键技术及摇枕计算实例.大连铁道学院学报,2000,21(3):21-25
[2]赵在理.压力容器的结构分析与安全评估研究:[博士学位论文].湖北:武汉理工大学,2006
[3]Wohler's Experiment on the Strength of Metals.Engineering,1967
[4]程育仁,缪龙秀,侯炳麟.疲劳强度.北京:中国铁道出版社,1990
[5]J.Goodman.Mechanics Applied to Engineering,1914
[6]S.S.Manson.National Advisory Committee for Aeronautics.Cleveland,1954
[7]L.F.Coffin,Jr.,ASME Transaction,Vol.16,P931,1954
[8]王勖成,邵敏.有限元基本原理和数值方法(第二版).北京:清华大学出版社,1997
[9]郭乙木,陶伟明,庄茁.线性与非线性有限元及其应用.北京:机械工业出版社,2004
[10]许尚贤.机械设计中的有限元法.北京:高等教育出版社,1992
[11]潘风文,金淼.液压机本体CAD的现状与发展.锻压机械,2000,35(2):39-40
[12]陈传尧.疲劳与断裂.武汉:华中科技大学出版社,2002
[13]薛明德.国外关于圆柱壳开孔接管问题的研究状况.压力容器,1991,8(2):9-15
[14]张卫义,俞建荣等.内压柱壳大开孔率开孔平齐式接管应力分布研究.压力容器,2000,17(6):1-5
[15]张卫义,田海晏.内压圆柱壳内伸式接管补强结构应力分布.石油化工机械,2003,32(4):24-25
[16]王磊.内压壳体开孔接管的应力分析与补强设计计算.机械科学与技术,2006,25(9):1130-1134
[17]闫胜咎,李昕,高炳军等.大开孔球壳与内伸接管连接区的实验应力分析.石油化工设备技术,2002,23(2):1-4
[18]张卫义,陈罕.内压筒体开孔接管结构应力集中系数预测.化工机械,2006,33(6):346-349
[19]王定标,魏新利,向飒等.压力容器与切向接管结构应力三维有限元分析及强度评定.湖南工程学院学报,2005,15(4):29-33
[20]毛明智,谭建平,叶云友.斗式提升机输送链销轴断裂机理分析.机械科学与技术,2001,20(6):864-865,903
[21]郭才才,尹汾.斗提机断销原因分析及改进.山西化工,2001,21(2):44-45
[22]陈灵,梁思祖,刘正义.牵引销紧固螺钉断裂分析.机械工程材料,2006,30(4):86-88
[23]冯耀荣,祁全全.曲柄销轴断裂失效分析.理化检验:物理分册,1991,27(4):52-53,51
[24]冯少陵.挖掘装载机铲斗长销轴断裂分析.工程机械,1990,21(11):52-52,32
[25]束维钧,钦培忠,杨柄南等.机械设计中销轴的计算与结构选择.农机与食品机械,1995,4:16-17
[26]李家武,彭铎.典型销轴的有限元计算研究.建筑机械化,2005,6(10):50-51
[27]董华明,王义行,乇晓虎.滚子链销轴的有限元计算及其应力场分布与变形规律.吉林工业大学学报,1996,26(4):85-89
[28]徐进永,阎树岭.工程机械铰接销轴结构设计.建筑机械,1997,5:18-19,37
[29]曹文静,景岗.提高套筒滚子链传动疲劳寿命的优化设计.机械工程师,1990,6:2-4
[30]赵永利,王春,邸玉志.防止销轴淬火开裂的措施.机械工人:热加工,2003,6:53-53
[31]何建伟,郭文华,李银风等.销轴弯曲疲劳强度的试验研究.工程机械,2003,34(4):20-23
[32]卜海峰.压力容器用钢疲劳可靠性分析:[硕士学位论文].北京:北京工业大学,2001
[33]范钦珊.压力容器的应力分析和强度设计.北京:原子能出版社,1983
[34]机械工程手册编委会编.机械工程手册:第十九篇机械结构强度.北京:机械工业出版社,1980
[35]T.V.Duggan and J.Byrne.Fatigue as a Design Criterion.The Macmillan Press Ltd.,1977
[36]李志安,金志浩,宫殿民.压力容器断裂理论与缺陷评定.大连:大连理工大学出版社,1994.8
[37]王仲仁,宛世剑,胡连喜.弹性与塑性力学基础.哈尔滨:哈尔滨工业大学出版社,2004
[38]张洪伟.圆柱壳大开孔应力分析研究:[硕士学位论文].大连:大连理工大学,2003
[39]薛明德.力学与工程技术的进步.北京:高等教育出版社,2001
[40]贺匡国.压力容器分析设计基础.北京:机械工业出版社,1995
[41]GB 150-1998,钢制压力容器
[42]JB 4732-1995,钢制压力容器——分析设计标准
[43]余伟炜,高炳军.ANSYS在机械与化工装备中的应用.北京:中国水利水电出版社,2006
[44]郑志峰.链传动设计与应用手册.北京:机械工业出版社,1992
[45]GB/T 3077-1999,合金结构钢
[46]GB/T 10561-1989,钢中非金属夹杂物显微评定方法
[47]GB/T 13320-1991,钢质模锻件金相组织评级图及评定方法
[48]张经源.链条传动及制造.杭州:浙江大学出版社,1989
[49]孟繁忠.链条链轮产品设计与检验.北京:机械工业出版社,1996
[50]夏荣海,郝玉琛.矿井提升设备.江苏:中国矿业学院出版社,1987
[51]徐尚龙.基于数值模拟的矿井提升机主轴疲劳与断裂性能研究:[硕士学位论文].陕西:西安科技学院,2003
[52]Eringen,A.C.et,"Stress concentrations in Two Normal Intersecting Cylindrical shells subject to Internal Pressure".《Wrc Bulletin》 No.139,1969
[53]Zarrabi K.,Basu A..A finite volume element formulation for solution of elastic axisymmetric pressurized components.Pressure vessels and Piping.2000,77:479-484
[54]D.Broke,et al.Fatigue crack growth:effect of sheet thickness.Aircraft Engineering.1996,38(11):31-33
[55]方佩珍,潘永亮,黄卫星等.天然气贮罐的疲劳分析.化工机械,2003,30(4):221-223,234
[56]严永德,王宽福.接管区含缺陷的压力容器的疲劳分析.石油化工设备,1989,18(2):1-4
[57]吴会超.基于ANSYS的焊接接头疲劳分析.铁道机车车辆工人,2006,6:1-4,10
[58]王磊.内压壳体开孔接管的应力分析与补强设计计算.机械科学与技术,2006,25(9):1130-1134
[59]张卫义,田海晏.内伸式接管补强结构应力分布特点.北京石油化工学院学报,2003,11(2):48-50
[60]马天兵,孙兵,杜菲.基于ANSYS对压力容器管板厚度的优化设计.煤矿机械,2004,12:23-25
[61]薛明德.国外关于圆柱壳开孔接管问题的研究概况.压力容器,1991,8(2):9-15
[62]洪德晓.有限元在压力容器应力分析设计中应用的讨论——阶段性归纳.化工设备与管道,2006,43(4):1-6,16
[63]郑津洋,董其伍,桑芝富.过程设备设计 第二版.北京:化学工业出版社,2005
[64]季建钢,寿旭日.储汽筒椭圆形封头及人孔结构应力和疲劳分析.机电设备,1998,1:34-38,42
[65]宋建华,张会平.在线化工设备疲劳分析专家系统的研究.化工机械,1996,23(5):7-11
[66]崔军,吴伟.塑性理论在疲劳分析中的应用.工程力学,1997,A01:329-332
[67]林国湘.提升机主轴疲劳强度的模糊概率设计.矿山机械,1999,27(8):34-35
[68]范国海,周庆超,张纯义.疲劳分析数值方法的关键技术及摇枕计算实例.大连铁道学院学报,2000,21(3):21-25