斷裂力學-1緒論課件

1、Shanghai University斷裂力學Fracture Mechanics郭戰(zhàn)勝我的聯(lián)系方式E-mail：davidzsguo辦公地點：延長校區(qū) 力學所317室斷裂力學第一講我的希望希望大家喜歡希望大家參與 勇于回答問題 勇于提出問題 勇于參與討論希望大家能夠有所收獲 收獲一點新意斷裂力學第一講課堂講授課堂討論課外學習研究課外個別學習指導與互動斷裂力學第一講考試、考核方法1. 期末考試：考試內(nèi)容課外作業(yè) 考試方式筆試，閉卷 成績認定70分。課外作業(yè) ：成績認定20分3. 平時分：1) 課堂表現(xiàn)：5分； 2) 出勤：5分。斷裂力學第一講解決問題的四個步驟問題陳述-State the Pr

2、oblem計劃求解（數(shù)學化、模型化)-Plan the Solution求解-Carry Out the Solution結(jié)果判斷、評價-Review the Solution1.) 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 enginee

3、ring 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 教材及參考書目

4、程靳，趙樹剛 編. 斷裂力學. 北京：科學出版社，2006王鐸，杜善義 編. 斷裂力學. 哈爾濱：哈爾濱工業(yè)大學出版社，1989 范天佑. 斷裂理論基礎(chǔ). 北京：科學出版社，2003王自強，陳少華. 高等斷裂力學. 北京：科學出版社，2009楊衛(wèi). 宏微觀斷裂力學. 北京：國防工業(yè)出版社，1995斷裂力學第一講緒論結(jié)構(gòu)失效的類型Types of structural failureHistory of fracture mechanicsIn the early days of World War II. the United States was supplying ships and pl

5、anes 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 shipsArthur M. Huddellone of the l

6、ast World War II Liberty shipsUnder 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 al

7、l-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 fractures occurred in other Liberty ships.

8、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. SchenectadyOn 16 January 1943, Without warning, and with a nois

9、e 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 followbut it was perhaps the most prominent; it occ

10、urred in full view of the city of Portland, and was widely reported in the newspapers even under wartime conditions. Alan Arnold GriffithAlan Arnold Griffith (13 June 1893 13 Oct 1963) was an English engineer, who, among many other contributions, is best known for his work on stress and fracture in

11、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 Arnold Griffith格氏1893年出生于倫敦，1911年畢業(yè)于曼島的一所中學，獲

12、得獎學金進入利物浦大學讀機械工程，1914年以一等成績獲得學士學位，并獲得最高獎?wù)隆?915年，格氏到皇家航空研究中心工作，并與G.I. Taylor一起發(fā)表了用肥皂膜研究應(yīng)力分布的開創(chuàng)性論文，該文獲得機械工程協(xié)會的金獎。同年，格氏獲得利物浦大學工程碩士學位。1921年，格氏以他的斷裂力學成名作獲得利物浦大學工程博士學位。其后，格氏歷任空軍實驗室首席科學家，航空研究中心工程部主管等職，在航空發(fā)動機設(shè)計方面做出了同樣卓越的貢獻，與他在斷裂方面的名望相比，這些成就就少為人知了。格氏于1939年加盟勞斯萊思公司，1941年當選皇家學會院士，1960年退休，1963年辭世，享年70歲 Alan Arn

13、old GriffithIn 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 remain in widespread use today. In 1917 he a

14、nd 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 of stress. This method, and similar ones,

15、 were used well into the 1990s when computer power became generally available that could do the same experiment numerically. Alan Arnold GriffithThe work, published in 1920 (The phenomenon of rupture and flow in solids), resulted in sweeping changes in many industries. Suddenly the hardening of mate

16、rials 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 their metals in order to remove cracks. The res

17、ult 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 GriffithThe theory was considered to apply only to a limited class of extremely

18、 , such as glasses or ceramics Griffith theory-1920In 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 created. The surface energy increases, but the el

19、astic energy decreases. The crack advances if the advance reduces the sum of the surface energy and elastic energy.Alan Arnold GriffithFrom this work Griffith formulated his own theory of brittle fracture, using elastic strain energy concepts. His theory described the behavior of crack propagation o

20、f 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 to be the primary equation to describe brittle f

21、racture. 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 critical Griffith crack length, the crack becomes da

22、ngerous. Alan Arnold GriffithGriffith 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. However it was well known that those materials wo

23、uld 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 solid concentrates stress, a fact already well k

24、nown 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 October 9, 1998) was an American scientist in the fie

25、ld of fracture mechanics and strength of materials. He was internationally known for his study of fracture of materialsGeorge Rankin IrwinGeorge R. Irwin was born in El Paso, Texas. His family moved to Springfield, Illinois where he went to school.He attended Knox College in Galesburg, Illinois and

26、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 Springfield Boiler Co.), so that GRI was known there, and wa

27、s invited after graduation at Knox to fill a graduate assistant teaching post at the University of Illinois, which he accepted.George Rankin IrwinIt 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 1

28、933, 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 many American and European scientific societies.1986 Tim

29、oshenko Medal George Rankin IrwinG R Irwin, Fracture Dynamics, Fracturing of Metals, American Society for Metals, 1948, p 147166GR Irwin Analysis of stresses and strains near the end of a crack traversing a plate. J. Appl. Mech. 1957, 24 (3), 361364.Discussion, J. Appl. Mech., 25, No. 2, 299-303 (19

30、58).George Rankin IrwinIrwin 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 to their improvement and development caused a decisive influe

31、nce 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 Orowan1949 Rep. Prog. Phys. 12 185-232was b

32、orn 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 OrowanFellow of the Royal Society, (1947)Membe

33、r 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 Engineerin

34、g 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 C Paris, and G R Irwin The stress Analysis of Cracks Handbook. St. Louis:

35、Paris Productions Inc., 1985 3rd edition 2000標志著線彈性斷裂力學趨于成熟Other contributionPaul Paris in developing methods for predicting crack growth and its control in aircraft structures; F. Erdogan on cracks in thin-walled shell structures; A. A. Wells of the on characterizing fracture in normally ductile st

36、eel 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. Rice, Harvard University, on developing the J integral approach for characterizin

37、g 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 國內(nèi)我國斷裂力學工作起步至少比國外晚了20年，直到上世紀70年代，斷裂力學才廣泛引入我國，一些單位和科技工作者逐步開展了斷裂力學的研究和應(yīng)用工作。 Disaster examples蒸壓釜發(fā)生爆炸2010年11月7號凌晨1點45分左右

38、上海建華管樁有限公司車間內(nèi)一個蒸壓釜發(fā)生爆炸5名工人不同程度受傷。原定恒壓0.92兆帕。當壓力值還在0.7至0.8兆帕時，容器突然爆炸，釜門連接處斷裂。2噸多重的釜門受巨大沖擊力作用，瞬間飛過圍墻。 塔吊斷裂2008年8月6號呼和浩特市敕勒川大街與騰飛路交匯處的金隅時代城施工現(xiàn)場發(fā)生塔吊斷裂事故 鋼纜吊桿2001年11月8號此次事故是連接拱體和橋面預(yù)制板的4對8根鋼纜吊桿斷裂，北端長約10米、南端長20余米的橋面預(yù)制板發(fā)生坍塌。 四川宜賓南門大橋斷裂事故 “過山車”半軸斷裂2003年8月31日重慶游樂園“過山車”半軸斷裂事故 圖說明：過山車最后停車點;半軸斷裂段及撞傷軌道點共7條橫檔及右側(cè)軌道

39、變形處;撞斷脫件飛出砸傷雷車停車港防雨棚;半軸斷裂后被撞傷軌道的第二段共14條橫檔;過山車始發(fā)車站臺。 半軸的斷裂屬于疲勞斷裂 管道斷裂2009年3月23日云南省水富縣，云南云天化股份有限公司合成氨裝置合成塔出口管道斷裂事故 受傷人數(shù)至17人。 起重機斷裂2008年3月15日，紐約曼哈頓中城東側(cè)一處建筑工地的起重機斷裂，砸到附近建筑物，造成4人死亡，多人受傷。有報道說，事故可能是由于一個鋼塊墜落，切斷了固定起重機塔體的一根纜繩引起的 飛機2010年7月27日德國漢莎航空一架MD-11貨機在沙特首都利雅得的哈立德國王國際機場墜毀 吊橋斷裂2009年4月13日秘魯?shù)鯓驍嗔咽鹿?秘魯南部阿亞庫喬省科

40、拉科拉縣日發(fā)生一起嚴重的吊橋斷裂事故，造成至少7名學生、2名老師、人受重傷。據(jù)當?shù)孛襟w報道，當天下午，科拉科拉縣一所學校的多名師生放學后從一座吊橋上走過時，吊橋突然從中間斷裂，橋上的師生幾乎都摔入距離橋面約米的河中Cleveland East Ohio Gas explosionCleveland East Ohio Gas Explosion occurred on the afternoon of Friday, October 20, 1944. The resulting gas leak, explosion and fires killed 130 people and destr

41、oyed 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 MexicoThe Deepwater Horizon drilling rig collapsed in the Gulf of Mexico on April 22, 2010TitanicAt 2:20 a.m

42、., 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 transition temperature, making it unsuitable for service at low temperatures; at the time of the colli

43、sion, 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. Boston Molasses Disaster-January 15,1919Cylinder stress failureDamage to the Boston Elevated Railway du

44、e to the floodBoston Molasses Disaster-January 15,1919a molasses tank 15m tall, 27m in diameter and containing as much as 2,300,000USgal (8,700m3) collapsed. Witnesses stated that as it collapsed, there was a loud rumbling sound, like a machine gun as the rivets shot out of the tank, and that the gr

45、ound 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 to damage the girders of the adjacent Boston Elevated Railways Atlantic Avenue structure and tip a railr

46、oad 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 90cm). Puleo quotes a Boston Post report:The Silver Bridge was an eyebar-chain suspension bridge built in

47、 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 while it was full of rush-hour traffic, resulting in the deaths of 46 people. Two of the victims were n

48、ever found. The collapsed Silver Bridge, as seen from the Ohio sideThe bridge failure was due to a defect in a single link, eyebar 330, on the north of the Ohio subsidiary chain, the first link below the top of the Ohio tower. A small crack was formed through fretting wear at the bearing, and grew t

49、hrough 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 crack was probably exacerbated by residual stress in the eyebar created during manufacture.When the lower sid

50、e 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 slipped off the pin at the center of the bearing, so the chain was completely severed. Collapse of the enti

51、re 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 fall.King Street Bridge (Melbourne)Overlooking the King Street Bridge and Crown Casino and Entertainment Comp

52、lexThe 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, suspended-span construction with spans up to 160 feet (49m) long.King Street Bridge (Melbourne)Soon after complet

53、ion, 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 with a brittle fracture on a very cold Melbourne winter day. The Commission identified the cause of girder fail

54、ure 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 for an experienced fabricator. The cracks in the welds were not discovered by inspectors of both the fabricator

55、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 bored piles. The embarrassing incident was widely satirised at the time; most notably by the Melbourne TV clowns Zig

56、 and Zag and was the inspiration for a Spike Milligan radio comedy.Structural Failure of Alohas 73728 April 1988caused by fatigue failureOther examplesFractured leg in plaster cast Cracked concreteDried GroundExamplesDry mud texture bullet hole x-ray showing femur fracture from auto accident Winter

57、ice layer 美國硅谷埃及博物館盛裝人木乃伊的棺材 1943-47年, 美國近500艘全焊船1000多起脆性破壞，238艘報廢?？偸窃诤附尤毕莸葢?yīng)力集中區(qū)域，-34C水1947年，蘇聯(lián)4500m3石油儲罐，-43C，底部和下部殼連接處，大量裂紋。（低溫、脆性、焊點應(yīng)力集中、內(nèi)外溫差）五十年代，美國北極星導彈固體燃料發(fā)動機殼體試驗，發(fā)生爆炸。高強度合金，傳統(tǒng)強度和韌性指標合格，爆炸時工作壓力遠低于許用應(yīng)力。（裂紋）1963年，美國F-111飛機訓練中，左翼脫落，飛機墜毀，而當時飛行速度、負荷遠低于設(shè)計指標。（熱處理不當、機翼樞軸出現(xiàn)缺陷，疲勞載荷，裂紋）一系列嚴重災(zāi)難，這些事故中毀壞的結(jié)構(gòu)是經(jīng)過傳統(tǒng)強度理論嚴格設(shè)計的，為什么不斷出現(xiàn)斷裂呢？ （屈服），為屈服應(yīng)力，塑性材料（破壞），為強度極限，脆性材料 循環(huán)加載 這些結(jié)構(gòu)大多由高與超高強度材料制造，高強度剛屈服應(yīng)力而普通鋼僅200MPa，且材料