断裂力学——1绪论.ppt

Shanghai University 断裂力学 Fracture Mechanics 郭战胜 我的联系方式我的联系方式 E-mail： 办公地点：延长校区办公地点：延长校区 力学所力学所317317室室 断裂力学第一讲断裂力学第一讲 我的希望我的希望 希望大家喜欢希望大家喜欢 希望大家参与希望大家参与 勇于回答问题勇于回答问题 勇于提出问题勇于提出问题 勇于参与讨论勇于参与讨论 希望大家能够有所收获希望大家能够有所收获 收获一点新意收获一点新意 断裂力学第一讲断裂力学第一讲 课堂讲授课堂讲授 课堂讨论课堂讨论 课外学习研究课外学习研究 课外个别学习指导与互动课外个别学习指导与互动 断裂力学第一讲断裂力学第一讲 考试、考核方法考试、考核方法 1. 1. 期末考试：考试内容期末考试：考试内容课外作业课外作业 考试方式考试方式笔试，闭卷笔试，闭卷 成绩认定成绩认定7070分。分。 2. 2. 课外作业课外作业 ：成绩认定：成绩认定2020分分 3. 3. 平时分：平时分：1) 1) 课堂表现：课堂表现：5 5分；分； 2) 2) 出勤：出勤：5 5分。分。 断裂力学第一讲断裂力学第一讲 解决问题的四个步骤解决问题的四个步骤 l l 问题陈述问题陈述-State the Problem-State the Problem l l 计划求解（数学化、模型化计划求解（数学化、模型化)-Plan the Solution)-Plan the Solution l l 求解求解-Carry Out the Solution-Carry Out the Solution l l 结果判断、评价结果判断、评价-Review the Solution-Review the Solution 1.) Develop basic fundamental understanding of the effects of crack-like defects on the performance of aerospace, civil, and mechanical engineering structures. 2.) Learn to select appropriate materials for engineering structures to insure damage tolerance. 3.) Learn to employ modern numerical methods to determine critical crack sizes and fatigue crack propagation rates in engineering structures. 4.) Gain an appreciation of the status of academic research in field of fracture mechanics. Course Objectives 教材及参考书目教材及参考书目 程靳，赵树刚程靳，赵树刚 编编. . 断裂力学断裂力学. . 北京：科学出版社，北京：科学出版社，20062006 王铎，杜善义王铎，杜善义 编编. . 断裂断裂力学力学. . 哈尔滨：哈尔滨：哈尔滨工业大学哈尔滨工业大学 出版社，出版社，19891989 范天佑范天佑. . 断裂理论基础断裂理论基础. . 北京：科学出版社，北京：科学出版社，20032003 王自强，陈少华王自强，陈少华. . 高等断裂力学高等断裂力学. . 北京：科学出版社，北京：科学出版社， 20092009 杨卫杨卫. . 宏微观断裂力学宏微观断裂力学. . 北京：国防工业出版社，北京：国防工业出版社，19951995 断裂力学第一讲断裂力学第一讲 绪论绪论 结构失效的类型结构失效的类型 Types of structural failureTypes of structural failure History of fracture History of fracture mechanicsmechanics lIn the early days of World War II. the United States was supplying ships and planes to Great Britain under the Lend- Lease Act. Britains greatest need at the time was for cargo ships to carry supplies. The German Navy was sinking cargo ships at three times the rate al which they could be replaced with existing ship- building procedures. Liberty ships Arthur M. Huddell one of the last World War II Liberty ships lUnder the guidance of Henry Kaiser, a famous construction engineer whose previous projects included the Hoover Dam, the United States developed a revolutionary procedure for fabricating ships quickly. These new vessels, which became known as the Liberty ships, had an all-welded hull, as opposed to the riveted construction of traditional ship designs. lThe Liberty ship program was a resounding success, until one day in 1943, when one of the vessels broke completely in two while sailing between Siberia and Alaska. Subsequent fractures occurred in other Liberty ships. Of the roughly 2700 liberty ships build during World War II, approximately 400 sustained fractures, of which 90 were considered serious. In 20 ships the failure was essentially total, and about half of these broke completely in two. S.S. Schenectady On 16 January 1943, Without warning, and with a noise audible for at least a mile, the hull cracked almost in half. Only the bottom plates of the ship held. This was not the first of the war-built merchant fleet to fracture in this way there had been ten other major incidents, and several more would follow but it was perhaps the most prominent; it occurred in full view of the city of Portland, and was widely reported in the newspapers even under wartime conditions. Alan Arnold GriffithAlan Arnold Griffith Alan Arnold GriffithAlan Arnold Griffith (13 (13 June 1893 13 Oct 1963) June 1893 13 Oct 1963) was an was an EnglishEnglish engineer, engineer, who, among many other who, among many other contributions, is best known contributions, is best known for his work on for his work on stressstress and and fracturefracture in metals that is now in metals that is now known as known as metal fatiguemetal fatigue, as , as well as being one of the first well as being one of the first to develop a strong theoretical to develop a strong theoretical basis for the basis for the jet enginejet engine. He . He took a first in mechanical took a first in mechanical engineering, followed by a engineering, followed by a Masters Degree and a Masters Degree and a Doctorate from Doctorate from Liverpool Liverpool UniversityUniversity. . Alan Arnold GriffithAlan Arnold Griffith 格氏1893年出生于伦敦，1911年毕业于曼岛的一所中学 ，获得奖学金进入利物浦大学读机械工程，1914年以一 等成绩获得学士学位，并获得最高奖章。1915年，格氏 到皇家航空研究中心工作，并与G.I. Taylor一起发表了 用肥皂膜研究应力分布的开创性论文，该文获得机械工 程协会的金奖。同年，格氏获得利物浦大学工程硕士学 位。1921年，格氏以他的断裂力学成名作获得利物浦大 学工程博士学位。其后，格氏历任空军实验室首席科学 家，航空研究中心工程部主管等职，在航空发动机设计 方面做出了同样卓越的贡献，与他在断裂方面的名望相 比，这些成就就少为人知了。格氏于1939年加盟劳斯莱 思公司，1941年当选皇家学会院士，1960年退休， 1963年辞世，享年70岁 Alan Arnold GriffithAlan Arnold Griffith l l In 1915 he was accepted by the In 1915 he was accepted by the Royal Aircraft FactoryRoyal Aircraft Factory as a trainee, before joining the Physics and Instrument as a trainee, before joining the Physics and Instrument Department the following year in what was now been Department the following year in what was now been renamed as the renamed as the Royal Aircraft EstablishmentRoyal Aircraft Establishment (RAE). (RAE). l l Some of Griffiths earlier works remain in widespread Some of Griffiths earlier works remain in widespread use today. In 1917 he and use today. In 1917 he and G. I. TaylorG. I. Taylor suggested the suggested the use of soap films as a way of studying stress use of soap films as a way of studying stress problems. Using this method a soap bubble is problems. Using this method a soap bubble is stretched out between several strings representing the stretched out between several strings representing the edges of the object under study, and the coloration of edges of the object under study, and the coloration of the film shows the patterns of stress. This method, the film shows the patterns of stress. This method, and similar ones, were used well into the 1990s when and similar ones, were used well into the 1990s when computer power became generally available that computer power became generally available that could do the same experiment numerically. could do the same experiment numerically. Alan Arnold GriffithAlan Arnold Griffith The work, published in 1920 (“The work, published in 1920 (“The phenomenon of The phenomenon of rupture and flow in solidsrupture and flow in solids“), resulted in sweeping “), resulted in sweeping changes in many industries. Suddenly the “hardening“ of changes in many industries. Suddenly the “hardening“ of materials due to processes such as materials due to processes such as cold rollingcold rolling were no were no longer mysterious. Aircraft designers immediately longer mysterious. Aircraft designers immediately understood why their designs had failed even though understood why their designs had failed even though they were built much stronger than was thought they were built much stronger than was thought necessary at the time, and soon turned to polishing their necessary at the time, and soon turned to polishing their metals in order to remove cracks. The result was a metals in order to remove cracks. The result was a series of particularly beautiful designs in the 1930s, such series of particularly beautiful designs in the 1930s, such as the as the Boeing 247Boeing 247. This work was later generalized by . This work was later generalized by G. R. IrwinG. R. Irwin, in the 1950s, applying it to almost all , in the 1950s, applying it to almost all materials, not just rigid ones.materials, not just rigid ones. Alan Arnold GriffithAlan Arnold Griffith The theory was considered to apply only to a limited class of extremely , such as glasses or ceramics Griffith theory-1920Griffith theory-1920 l l In a body of a glass cracks pre-exist. In a body of a glass cracks pre-exist. l l The tip of such a crack concentrates stress. The tip of such a crack concentrates stress. l l The intense stress breaks atomic bonds one by The intense stress breaks atomic bonds one by one, like opening a zipper. one, like opening a zipper. l l As the crack advances, fresh surfaces are As the crack advances, fresh surfaces are created. The surface energy increases, but the created. The surface energy increases, but the elastic energy decreases. elastic energy decreases. l l The crack advances if the advance reduces the The crack advances if the advance reduces the sum of the surface energy and elastic energy.sum of the surface energy and elastic energy. Alan Arnold GriffithAlan Arnold Griffith From this work Griffith formulated his own theory of From this work Griffith formulated his own theory of brittle fracture, using elastic brittle fracture, using elastic strain energystrain energy concepts. concepts. His theory described the behavior of crack propagation His theory described the behavior of crack propagation of an elliptical nature by considering the energy of an elliptical nature by considering the energy involved. The equation basically states that when a involved. The equation basically states that when a crack is able to propagate enough to fracture a crack is able to propagate enough to fracture a material, that the gain in the surface energy is equal to material, that the gain in the surface energy is equal to the loss of strain energy, and is considered to be the the loss of strain energy, and is considered to be the primary equation to describe brittle fracture. Because primary equation to describe brittle fracture. Because the strain energy released is directly proportional to the strain energy released is directly proportional to the square of the crack length, it is only when the the square of the crack length, it is only when the crack is relatively short that its energy requirement for crack is relatively short that its energy requirement for propagation exceeds the strain energy available to it. propagation exceeds the strain energy available to it. Beyond the critical Griffith crack length, the crack Beyond the critical Griffith crack length, the crack becomes dangerous.becomes dangerous. Alan Arnold GriffithAlan Arnold Griffith l l Griffith is more famous for a theoretical study on the Griffith is more famous for a theoretical study on the nature of stress and failure in metals. At the time it nature of stress and failure in metals. At the time it was generally taken that the strength of a material was was generally taken that the strength of a material was E/10, where E was the E/10, where E was the Youngs modulusYoungs modulus for that for that material. However it was well known that those material. However it was well known that those materials would often fail at 1000 times less than this materials would often fail at 1000 times less than this predicted value. Griffith discovered that there were predicted value. Griffith discovered that there were many microscopic cracks in every material, and many microscopic cracks in every material, and hypothesized that these cracks lowered the overall hypothesized that these cracks lowered the overall strength of the material. This was because any void in strength of the material. This was because any void in a solid concentrates stress, a fact already well known a solid concentrates stress, a fact already well known to machinists at the time. This concentration would to machinists at the time. This concentration would allow the stress to reach E/10 at the head of the crack allow the stress to reach E/10 at the head of the crack long before it would seem to for the material as a long before it would seem to for the material as a whole. whole. the father of Fracture Mechanics the father of Fracture Mechanics Dr. Dr. George Rankin IrwinGeorge Rankin Irwin (February 26, 1907 (February 26, 1907 October 9, 1998) was an October 9, 1998) was an AmericanAmerican scientist in the scientist in the field of field of fracture fracture mechanicsmechanics and and strength strength of materialsof materials. He was . He was internationally known for internationally known for his study of fracture of his study of fracture of materialsmaterials George Rankin IrwinGeorge Rankin Irwin l l George R. Irwin was born in George R. Irwin was born in El Paso, TexasEl Paso, Texas. His . His family moved to family moved to SpringfieldSpringfield, , IllinoisIllinois where he went to where he went to school.school. l l He attended He attended Knox CollegeKnox College in in GalesburgGalesburg, , IllinoisIllinois and and earned an A.B. degree in English in 1930. After an earned an A.B. degree in English in 1930. After an additional year studying physics(get additional year studying physics(get bachelors degree in physics at 1931) lAn elder brother, William, had studied engineering at the University of Illinois (later to be Vice-President of the Springfield Boiler Co.), so that GRI was known there, and was invited after graduation at Knox to fill a graduate assistant teaching post at the University of Illinois, which he accepted. George Rankin IrwinGeorge Rankin Irwin lIt permitted him to acquire his masters degree in 1933, and subsequently a PhD in physics in 1937. Meanwhile, a unique event in Georges life occurred in 1933, with marriage to Georgia Boynton Shearer, creating a strong partnership that was to last for 65 years. lA Member of the American National Academy of Engineering, Royal Society of London, an Honorary Member and winner of prizes and awards of many American and European scientific societies. l1986 Timoshenko Medal George Rankin IrwinGeorge Rankin Irwin l l G R Irwin, Fracture Dynamics, Fracturing G R Irwin, Fracture Dynamics, Fracturing of Metals, American Society for Metals, of Metals, American Society for Metals, 19481948, p 147166, p 147166 l l GR Irwin Analysis of stresses and strains GR Irwin Analysis of stresses and strains near the end of a crack traversing a plate. near the end of a crack traversing a plate. J. Appl. Mech. 1957, 24 (3), 361364.J. Appl. Mech. 1957, 24 (3), 361364. l“Discussion,“ J. Appl. Mech., 25, No. 2, 299-303 (1958). George Rankin IrwinGeorge Rankin Irwin l l Irwin defined the fundamental concept of a Irwin defined the fundamental concept of a Stress Intensity FactorStress Intensity Factor and the critical stress and the critical stress intensity factor (KIC) which is a intensity factor (KIC) which is a material material propertyproperty. . lHis ideas very important for practical use and subsequent works devoted to their improvement and development caused a decisive influence on the progress in fracture mechanics as a new science and powerful engineering tool applicable to numerous problems connected with manufacturing and processing of materials and their failureproof operation in critical structures of various materials. E OrowanE Orowan 1949 Rep. Prog. Phys. 12 185-232 was born in Obuda, a part of Budapest Courtesy of MIT Museum The X-ray studies conducted earlier by Orowan (1955) showed that even in materials fracturing in a purely brittle manner, there was evidence of extensive plastic deformation on the crack surfaces. E OrowanE Orowan Fellow of the Royal Society, (1947) Member of the American Academy of Arts and Sciences, (1951) Member of the National Academy of Sciences, (1969); Bingham Medal of the American Society of Rheology, (1959); Gauss Medal of the Braunschweiger Wissenschaftliche Gesellschaft, (1968); Vincent Bendix Gold Medal of the American Society for Engineering Education, (1971); Paul Bergse Medal of the Danish Metallurgical Society, (1973); The Acta Metallurgica Gold Medal, (1985). l l G C Sih (G C Sih (薛昌明薛昌明) Mechanics of Fracture. ) Mechanics of Fracture. Leyden: Noordhoff International Publishing, Leyden: Noordhoff International Publishing, 1973-19791973-1979共六卷共六卷 l l H Tada, P C Paris, and G R Irwin The stress H Tada, P C Paris, and G R Irwin The stress Analysis of Cracks Handbook. St. Louis: Analysis of Cracks Handbook. St. Louis: Paris Productions Inc., 1985 3rd edition Paris Productions Inc., 1985 3rd edition 20002000 标志着线弹性断裂力学趋于成熟标志着线弹性断裂力学趋于成熟 Other contributionOther contribution l l Paul ParisPaul Paris in developing methods for predicting crack in developing methods for predicting crack growth and its control in aircraft structures; growth and its control in aircraft structures; l l F. ErdoganF. Erdogan on cracks in thin-walled shell structures; on cracks in thin-walled shell structures; l l A. A. WellsA. A. Wells of the on characterizing fracture in normally of the on characterizing fracture in normally ductile steel structures; ductile steel structures; l l F. A. McClintockF. A. McClintock, Massachusetts Institute of Technology , Massachusetts Institute of Technology and and John W. HutchinsonJohn W. Hutchinson, Harvard University, on the , Harvard University, on the development of fracture mechanics procedures in the development of fracture mechanics procedures in the presence of substantial ductility; presence of substantial ductility; l l James R. RiceJames R. Rice, Harvard University, on developing the J , Harvard University, on developing the J integral approach for characterizing the onset of crack integral approach for characterizing the onset of crack growth in ductile materials; growth in ductile materials; l l L. B. FreundL. B. Freund, Brown University, and , Southwest , Brown University, and , Southwest Research Institute, on the dynamics of inertial limited Research Institute, on the dynamics of inertial limited crack propagation and arrest crack propagation and arrest 国内国内 我国断裂力学工作起步至少比国外晚了20年，直到上 世纪70年代，断裂力学才广泛引入我国，一些单位和 科技工作者逐步开展了断裂力学的研究和应用工作。 Disaster examplesDisaster examples 蒸压釜发生爆炸蒸压釜发生爆炸 l l 20102010年年1111月月7 7号号凌晨1点45分左右 l l 上海建华管桩有限公司车间内一个蒸压釜发生爆炸上海建华管桩有限公司车间内一个蒸压釜发生爆炸 5名工人不同程度受伤。 原定恒压0.92兆帕。当压力值还在0.7至0.8兆帕时，容器突然爆炸 ，釜门连接处断裂。2吨多重的釜门受巨大冲击力作用，瞬间飞过 围墙。 塔吊断裂塔吊断裂 l l 20082008年年8 8月月6 6号呼和浩特市敕勒川大街与腾号呼和浩特市敕勒川大街与腾 飞路交汇处的金隅时代城施工现场发生塔飞路交汇处的金隅时代城施工现场发生塔 吊断裂事故吊断裂事故 钢缆吊杆钢缆吊