断裂力学——1绪论.ppt

1、,Shanghai University,断裂力学 Fracture Mechanics 郭战胜,我的联系方式,E-mail：,办公地点：延长校区 力学所317室,断裂力学第一讲,我的希望,希望大家喜欢 希望大家参与 勇于回答问题 勇于提出问题 勇于参与讨论 希望大家能够有所收获 收获一点新意,断裂力学第一讲,课堂讲授,课堂讨论,课外学习研究,课外个别学习指导与互动,断裂力学第一讲,考试、考核方法,1. 期末考试：考试内容课外作业 考试方式笔试，闭卷 成绩认定70分。 课外作业 ：成绩认定20分,3. 平时分：1) 课堂表现：5分； 2) 出勤：5分。,断裂力学第一讲,解决问题的四个步骤,问题

2、陈述-State the Problem 计划求解（数学化、模型化)-Plan the Solution 求解-Carry Out the Solution 结果判断、评价-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 m

3、aterials 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.,Co

4、urse Objectives,教材及参考书目,程靳，赵树刚 编. 断裂力学. 北京：科学出版社，2006 王铎，杜善义 编. 断裂力学. 哈尔滨：哈尔滨工业大学出版社，1989 范天佑. 断裂理论基础. 北京：科学出版社，2003 王自强，陈少华. 高等断裂力学. 北京：科学出版社，2009 杨卫. 宏微观断裂力学. 北京：国防工业出版社，1995,断裂力学第一讲,绪论,结构失效的类型Types of structural failure,History of fracture mechanics,In the early days of World War II. the United S

5、tates 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 sh

6、ips,Arthur M. Huddell one of the last World War II,Liberty ships,Under 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 kn

7、own as the Liberty ships, had an all-welded hull, as opposed to the riveted construction of traditional ship designs. The 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 fractur

8、es 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

9、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

10、 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 Griffith,Alan Arnold Griffith (13 June 1893 13 Oct 1963) was an English engineer, who, among many other contributions, is best known

11、 for his work on stress and fracture in metals that is now known as metal fatigue, as well as being one of the first to develop a strong theoretical basis for the jet engine. He took a first in mechanical engineering, followed by a Masters Degree and a Doctorate from Liverpool University.,Alan Arnol

12、d 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，194

13、1年当选皇家学会院士，1960年退休，1963年辞世，享年70岁,Alan Arnold Griffith,In 1915 he was accepted by the Royal Aircraft Factory as a trainee, before joining the Physics and Instrument Department the following year in what was now been renamed as the Royal Aircraft Establishment (RAE). Some of Griffiths earlier works re

14、main in widespread use today. In 1917 he and G. I. Taylor suggested the use of soap films as a way of studying stress problems. Using this method a soap bubble is stretched out between several strings representing the edges of the object under study, and the coloration of the film shows the patterns

15、 of stress. This method, and similar ones, were used well into the 1990s when computer power became generally available that could do the same experiment numerically.,Alan Arnold Griffith,The work, published in 1920 (The phenomenon of rupture and flow in solids), resulted in sweeping changes in many

16、 industries. Suddenly the hardening of materials due to processes such as cold rolling were no longer mysterious. Aircraft designers immediately understood why their designs had failed even though they were built much stronger than was thought necessary at the time, and soon turned to polishing thei

17、r metals in order to remove cracks. The result was a series of particularly beautiful designs in the 1930s, such as the Boeing 247. This work was later generalized by G. R. Irwin, in the 1950s, applying it to almost all materials, not just rigid ones.,Alan Arnold Griffith,The theory was considered t

18、o apply only to a limited class of extremely , such as glasses or ceramics,Griffith theory-1920,In a body of a glass cracks pre-exist. The tip of such a crack concentrates stress. The intense stress breaks atomic bonds one by one, like opening a zipper. As the crack advances, fresh surfaces are crea

19、ted. The surface energy increases, but the elastic energy decreases. The crack advances if the advance reduces the sum of the surface energy and elastic energy.,Alan Arnold Griffith,From this work Griffith formulated his own theory of brittle fracture, using elastic strain energy concepts. His theor

20、y described the behavior of crack propagation of an elliptical nature by considering the energy involved. The equation basically states that when a crack is able to propagate enough to fracture a material, that the gain in the surface energy is equal to the loss of strain energy, and is considered t

21、o be the primary equation to describe brittle fracture. Because the strain energy released is directly proportional to the square of the crack length, it is only when the crack is relatively short that its energy requirement for propagation exceeds the strain energy available to it. Beyond the criti

22、cal Griffith crack length, the crack becomes dangerous.,Alan Arnold Griffith,Griffith is more famous for a theoretical study on the nature of stress and failure in metals. At the time it was generally taken that the strength of a material was E/10, where E was the Youngs modulus for that material. H

23、owever it was well known that those materials would often fail at 1000 times less than this predicted value. Griffith discovered that there were many microscopic cracks in every material, and hypothesized that these cracks lowered the overall strength of the material. This was because any void in a

24、solid concentrates stress, a fact already well known to machinists at the time. This concentration would allow the stress to reach E/10 at the head of the crack long before it would seem to for the material as a whole.,the father of Fracture Mechanics,Dr. George Rankin Irwin (February 26, 1907 Octob

25、er 9, 1998) was an American scientist in the field of fracture mechanics and strength of materials. He was internationally known for his study of fracture of materials,George Rankin Irwin,George R. Irwin was born in El Paso, Texas. His family moved to Springfield, Illinois where he went to school. H

26、e attended Knox College in Galesburg, Illinois and earned an A.B. degree in English in 1930. After an additional year studying physics(get bachelors degree in physics at 1931) An elder brother, William, had studied engineering at the University of Illinois (later to be Vice-President of the Springfi

27、eld 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 Irwin,It permitted him to acquire his masters degree in 1933, and subsequently a PhD in physics in 1937. M

28、eanwhile, 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. A Member of the American National Academy of Engineering, Royal Society of London, an Honorary Member and winner of prizes and awards of m

29、any American and European scientific societies. 1986 Timoshenko Medal,George Rankin Irwin,G R Irwin, Fracture Dynamics, Fracturing of Metals, American Society for Metals, 1948, p 147166 GR Irwin Analysis of stresses and strains near the end of a crack traversing a plate. J. Appl. Mech. 1957, 24 (3),

30、 361364. Discussion, J. Appl. Mech., 25, No. 2, 299-303 (1958).,George Rankin Irwin,Irwin defined the fundamental concept of a Stress Intensity Factor and the critical stress intensity factor (KIC) which is a material property. His ideas very important for practical use and subsequent works devoted

31、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 va

32、rious materials.,E 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

33、 crack surfaces.,E 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, (

34、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).,G C Sih (薛昌明) Mechanics of Fracture. Leyden: Noordhoff International Publishing, 1973-1979共六卷 H Tada, P

35、 C Paris, and G R Irwin The stress Analysis of Cracks Handbook. St. Louis: Paris Productions Inc., 1985 3rd edition 2000,标志着线弹性断裂力学趋于成熟,Other contribution,Paul Paris in developing methods for predicting crack growth and its control in aircraft structures; F. Erdogan on cracks in thin-walled shell st

36、ructures; A. A. Wells of the on characterizing fracture in normally ductile steel structures; F. A. McClintock, Massachusetts Institute of Technology and John W. Hutchinson, Harvard University, on the development of fracture mechanics procedures in the presence of substantial ductility; James R. Ric

37、e, Harvard University, on developing the J integral approach for characterizing the onset of crack growth in ductile materials; L. B. Freund, Brown University, and , Southwest Research Institute, on the dynamics of inertial limited crack propagation and arrest,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

38、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 examples,蒸压釜发生爆炸,2010年11月7号凌晨1点45分左右 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,2008年8月6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吊断裂事故,钢缆吊杆,2001年11月8号 此次事故是连接拱体和桥面预制板的4对8根钢缆吊杆断裂，北端长约10米、南端长20余米的桥面预制板发生

39、坍塌。 四川宜宾南门大桥断裂事故,“过山车”半轴断裂,2003年8月31日重庆游乐园“过山车”半轴断裂事故,图说明：过山车最后停车点;半轴断裂段及撞伤轨道点共7条横档及右侧轨道变形处;撞断脱件飞出砸伤雷车停车港防雨棚;半轴断裂后被撞伤轨道的第二段共14条横档;过山车始发车站台。,半轴的断裂属于疲劳断裂,管道断裂,2009年3月23日云南省水富县，云南云天化股份有限公司合成氨装置合成塔出口管道断裂事故 受伤人数至17人。,起重机断裂,2008年3月15日，纽约曼哈顿中城东侧一处建筑工地的起重机断裂，砸到附近建筑物，造成4人死亡，多人受伤。有报道说，事故可能是由于一个钢块坠落，切断了固定起重机塔体

40、的一根缆绳引起的,飞机,2010年7月27日德国汉莎航空一架MD-11货机在沙特首都利雅得的哈立德国王国际机场坠毁,吊桥断裂,2009年4月13日秘鲁吊桥断裂事故 秘鲁南部阿亚库乔省科拉科拉县日发生一起严重的吊桥断裂事故，造成至少7名学生、2名老师、人受重伤。,据当地媒体报道，当天下午，科拉科拉县一所学校的多名师生放学后从一座吊桥上走过时，吊桥突然从中间断裂，桥上的师生几乎都摔入距离桥面约米的河中,Cleveland East Ohio Gas explosion,Cleveland East Ohio Gas Explosion occurred on the afternoon of Fr

41、iday, October 20, 1944. The resulting gas leak, explosion and fires killed 130 people and destroyed a one square mile area on Cleveland, Ohios east side.,Ariel view of damage from East Ohio Gas Explosion,San Francisco Oakland Bay Bridge,Oct. 27, 2009 -Dec. 22, 2009,Oil spill of Gulf of Mexico,The De

42、epwater Horizon drilling rig collapsed in the Gulf of Mexico on April 22, 2010,Titanic,At 2:20 a.m., April 15, 1912, the Titanic sank with the loss of more than 1,500 lives.,A metallurgical analysis of steel taken from the hull of the Titanics wreckage reveals that it had a high ductile-brittle tran

43、sition temperature, making it unsuitable for service at low temperatures; at the time of the collision, the temperature of the sea water was -2C. The analysis also shows, however, that the steel used was probably the best plain carbon ship plate available at the time of the ships construction.,Bosto

44、n Molasses Disaster-January 15,1919,Cylinder stress failure,Damage to the Boston Elevated Railway due to the flood,Boston Molasses Disaster-January 15,1919,a molasses tank 15m tall, 27m in diameter and containing as much as 2,300,000USgal (8,700m3) collapsed. Witnesses stated that as it collapsed, t

45、here was a loud rumbling sound, like a machine gun as the rivets shot out of the tank, and that the ground shook as if a train were passing by. The collapse unleashed a wave of molasses 25 feet (7.6m) high at its peak, moving at 35 miles per hour (56km/h). The molasses wave was of sufficient force t

46、o damage the girders of the adjacent Boston Elevated Railways Atlantic Avenue structure and tip a railroad car momentarily off the tracks. Author Stephen Puleo describes how nearby buildings were swept off their foundations and crushed. Several blocks were flooded to a depth of 2 to 3 feet (60 to 90

47、cm). Puleo quotes a Boston Post report:,The Silver Bridge was an eyebar-chain suspension bridge built in 1928 and named for the color of its aluminum paint. The bridge connected Point Pleasant, West Virginia and Gallipolis, Ohio, over the Ohio River. On December 15, 1967, the Silver Bridge collapsed

48、 while it was full of rush-hour traffic, resulting in the deaths of 46 people. Two of the victims were never found.,The collapsed Silver Bridge, as seen from the Ohio side,The bridge failure was due to a defect in a single link, eyebar 330, on the north of the Ohio subsidiary chain, the first link b

49、elow the top of the Ohio tower. A small crack was formed through fretting wear at the bearing, and grew through internal corrosion, a problem known as stress corrosion cracking. The crack was only about 0.1inch (2.5mm) deep when it went critical, and it broke in a brittle fashion. Growth of the crac

50、k was probably exacerbated by residual stress in the eyebar created during manufacture.,When the lower side of the eyebar failed, all the load was transferred to the other side of the eyebar, which then failed by ductile overload. The joint was then held together only by three eyebars, and another s

51、lipped off the pin at the center of the bearing, so the chain was completely severed. Collapse of the entire structure was inevitable since all parts of a suspension bridge are in equilibrium with one another. Witnesses afterward estimated that it took only about a minute for the whole bridge to fal

52、l.,King Street Bridge (Melbourne),Overlooking the King Street Bridge and Crown Casino and Entertainment Complex,The bridge was designed in 1959 by Utah Australia for the Country Roads Board, and constructed over the next two years, being opened on 12 April 1961. It was of a welded, deck-girder, susp

53、ended-span construction with spans up to 160 feet (49m) long.,King Street Bridge (Melbourne),Soon after completion, on 10 July 1962, one span collapsed under the weight of a 47 ton semi-trailer, though the weight was within the bridge limits. The subsequent Royal Commission found that bridge failed

54、with a brittle fracture on a very cold Melbourne winter day. The Commission identified the cause of girder failure was due to cracked welds.,King Street Bridge (Melbourne),The fabricator was not familiar with welding low-alloy steel and the steel supplied was high in carbon making it difficult even

55、for an experienced fabricator. The cracks in the welds were not discovered by inspectors of both the fabricator and the Country Roads Board. The south end of the bridge has been undergoing differential settlement between the approach ramps resting on fill, and the suspended section supported by bore

56、d piles. The embarrassing incident was widely satirised at the time; most notably by the Melbourne TV clowns Zig and Zag and was the inspiration for a Spike Milligan radio comedy.,Structural Failure of Alohas 737,28 April 1988,caused by fatigue failure,Other examples,Fractured leg in plaster cast,Cr

57、acked concrete,Dried Ground,Examples,Dry mud texture,bullet hole,x-ray showing femur fracture from auto accident,Winter ice layer,美国硅谷埃及博物馆盛装人木乃伊的棺材,1943-47年, 美国近500艘全焊船1000多起脆性破坏，238艘报废。总是在焊接缺陷等应力集中区域，-34C水 1947年，苏联4500m3石油储罐，-43C，底部和下部壳连接处，大量裂纹。（低温、脆性、焊点应力集中、内外温差） 五十年代，美国北极星导弹固体燃料发动机壳体试验，发生爆炸。高强度合金，传统强度和韧性指标合格，爆炸时工作压力远低于许用应力。（裂纹） 1963年，美国F-111飞机训练中，左翼脱落，飞机坠毁，而当时飞行速度、负荷远低于设计指标。（热处理不当、机翼枢轴出现缺陷，疲劳载荷，裂纹）,一系列严重灾难，这些事故中毁坏的结构是经过传统强度理论严格设计的，为什么不断出现断裂呢？,（屈服），,为屈服应力，塑性材料,（破坏），,为强度极限，脆性材料,循环加载,这些结构大多由高与超高强度材料制造，高强度刚屈服应力,而普通钢仅200MPa，且材料韧性也很好,(材料可按延伸律分为脆性和韧性两大类，5为界限 ),由上