空客A380疲劳裂缝交通运输管理知识分析(英文版)(DOC 75页).ppt

1、空客A380出现裂缝？ 当今天上的飞机都在拿自己做实验. Cracks in Airbus380? Every plane now in the air is an experiment by itself,Airbus A380 TheAirbus A380is adouble-deck,wide-body, four-enginejet airlinermanufactured by theEuropeancorporationAirbus, a subsidiary ofEADS. It is the worlds largest passenger airliner and due t

2、o its size,amazing numbers,Production,Major structural sections of the A380 are built in France, Germany, Spain, and the United Kingdom. Due to their size, they are brought to the assembly hall(theJean-Luc Lagardre Plant) inToulousein France by surface transportation, though some parts are moved by

3、theA300-600ST Beluga aircraft used in the construction of other Airbus models. A380 components are provided by suppliers from around the world; the five largest contributors, by value, areRolls-Royce,Safran, United Technologies, General Electric andGoodrich,But when an aircraft becomes bigger and he

4、avier,the size of the turbines and wings also increase, which in turn increases weight and fuel consumption. On the other hand, the European megaliner was also required to be 20 percent more efficient than the competing Boeing 747. Tom Williams, the executive vice president of programs at Toulouse-b

5、ased Airbus, and his creative engineers were told to subject the A380 to a radical diet. Innovative composite material and extremely lightweight aluminum alloys, even for important parts of the wings. Weve used this alloy in many other aircraft in the past says A380 designer Williams. issue 12/2012

6、(Mar. 19, 2012) of DER SPIEGEL,Engine Failure,On 4 November 2010, a Rolls Royce Trent 972 powered Airbus A380-842 (Registration VH-OQA) of Qantas Flight QF32suffered anuncontained engine failure in engine number 2 en route from Singapore to Sydney and returned to Singapore Changi Airport where it la

7、nded safely. Qantas grounded its fleet of six A380s for over three weeks after the accident pending the investigation and said it may replace up to 16 engines after identifying potential problems,Following an unscheduled internal inspection of an A380 wing, some rib feet have been found with cracks,

8、So EASA called for a general inspection on all A380 in Europe,EASAsays that there may bea risk Airbus NO! Repair How,Areas wherethe crackshave been identified,An Update by Doric Asset Finance & Verwaltungs GmbH,Temporary repair and replacement,According to Airbus, the damage to the wings is not very

9、 dangerous, because there are 4,000 of the brackets in question. Nevertheless, the hairline cracks have to be repaired, and the large number of defective brackets makes it a costly and complex procedure. But simply replacing the brackets is not a permanent solution to the problem because hairline cr

10、acks can also occur in the new brackets. Because the same Alloy is still being used in production, the repair remains a patchwork solution,At first, Airbus officials said that it would have to sell about 250 aircraft to recoup its costs. But according to the Latest estimates by aviation experts, the

11、 company will have to sell at least 600 units of the worlds largest aircraft to make a profit. But with a total of 253 orders on its books so far, Airbus is still a long way from that target. 350 MORE A380 FOR BREAK EVEN POINT, i.e. US$ 100Bn! issue 12/2012 (Mar. 19, 2012) of DER SPIEGEL,A380-800 Fu

12、ll Scale Fatigue Test,On September 1st 2005 the A380-800 Full Scale Fatigue Test in Dresden started conducted by teams of IABG and IMA. It is the worlds largest Full Scale Fatigue Test on a civilian aircraft. The specimen consists of the A380 fuselage and two wings. It is mounted in a test rig made

13、of 1800 tons of steel with 190 hydraulic jacks. The wings will move 4,2 meters upwards and 1,3 meters downwards. http:/,Within 26 months 47.500 flights will be simulated in Dresden. This corresponds to a life span of appr. 25 years. One important milestone are the first 5000 flights which are expect

14、ed to be completed at the beginning of 2006. Progress as scheduled is a pre-condition for the certification of the Airbus double-decker. Informationdisclosed by http:/www.ima-dresden.de,But why then they did not find any cracks,Howisit possible that,despite thecertification effort,thesecrackshave ap

15、peared,Plausible hypothesis is thatthese components were notconsidered structurallysignificant.andtherefore no studies conductedon itsfatiguebehavior,EASA Certification Specifications for Large Aeroplanes CS25,EASA Certification Specifications for Large Aeroplanes CS25 Book 2,Are the rib fits are PR

16、INCIPAL STRUCTURAL ELEMENTS OR NOT,Other implications,Currentdesign methodologieshave been observedagain unreliable! These defectswere only discoveredthrougha random (notplanned) inspection! EASA & Airbus disagree on critically of these parts,This reminds me of a famous sentence, in the early train

17、days. There is not a single rail now down in England or elsewhere which in not an experiment in itself The Engineer (1867,Twode Havilland Cometpassenger jets broke up in mid-air and crashed within a few months of each other in 1954. As a result systematic tests were conducted on afuselageimmersed an

18、d pressurised in a water tank. After the equivalent of 3,000 flights investigators at theRoyal Aircraft stablishment(RAE) were able to conclude that the crash had been due to failure of the pressure cabin at the forwardAutomatic Direction Finderwindow in the roof. This window was in fact one of two

19、apertures for theaerialsof an electronic navigation system in which opaquefibreglass panels took the place of the window glass. The failure was a result ofmetal fatiguecaused by the repeated pressurisation and de-pressurisation of the aircraft cabin,Fatigue and aircraft accidents,and others,Fail saf

20、ety (redundancy,Structures upon which human life depends have long been recognized as needing an element of fail-safety. When describing his flying machine, Leonardo Da Vinci noted that In constructing wings one should make one chord to bear the strain and a looser one in the same position so that i

21、f one breaks under the strain, the other is in the position to serve the same function.1 REDUNDANCY CONCEPT. Also in human body for critical components,Air Force Aircraft Structural Integrity Program ASIP (1958,In the final approval letter establishing the Air Force Aircraft Structural Integrity Pro

22、gram which still holds true today: The successful accomplishment of this program is vital to the Air Forces capability to perform its assigned mission, and requires complete and active support and cooperation of all staff and command levels of the Air Force organization. General Curtis E. LeMay, U.S

23、. Air ForceVice Chief of Staff, 19 November 1958,ASIP (USAF, 1958,The objectives of ASIP are to: a) Establish, evaluate, and substantiate the structural integrity (airframe strength, rigidity, damage tolerance, and durability) of the airplane. b) Acquire, evaluate, and utilize operational usage data

24、 to provide a continual assessment of the in-service integrity of individual airplanes. c) Provide a basis for determining logistics and force planning requirements (maintenance, inspections, supplies, rotation of airplanes, system phase-out, and future force structure). d) Provide a basis to improv

25、e structural criteria and methods of design, evaluation, and substantiation of future systems. http:/,Safe life” approach for critical parts,Not all structure need be damage tolerant of fatigue loading to ensure safety of operation. Some structures operate under the safe-life design principle, where

26、 an extremely low level of risk is accepted through a combination of testing and analysis that the part will ever form a detectable crack due to fatigue during the service life of the part. This is achieved through a significant reduction of stresses below the typical fatigue capability of the part.

27、 Safe-life structures are employed when the cost or infeasibility of inspections outweighs the weight penalty and development costs associated with safe-life structures.3 An example of a safe-life component is the helicopter rotor blade. Due to the extremely large numbers of cycles endured by the ro

28、tating component, an undetectable crack may grow to a critical length in a single flight and before the aircraft lands, result in a catastrophic failure that regular maintenance could not have prevented,Safe life Wohler or Basquins law,ANOTHER EMPIRICAL LAW! There is no strong reason why the law sho

29、uld hold at all, despite some attempts to justify power-laws coming from critical phenomena (also of Coffin-Manson,Crack growth Paris law 1963,Paris law 1963,KthKKIc(1-R,Damage tolerance,Approach to engineering design based on the assumption that flaws can exist in any structure and such flaws propa

30、gate with usage. This approach is commonly used in aerospace engineeringto manage the extension of cracks in structures through the application of the principles of fracture mechanics. A maintenance program is implemented that will result in the detection and repair of accidental damage, corrosion a

31、nd fatigue cracking before such damage reduces the residual strength of the structure below an acceptable limit,multiple-site damage,many small cracks grow slowly by themselves, to join one another over time, creating a much larger crack, and significantly reducing the expected time until failure 2,

32、Non-Destructive Inspections,Manufacturers and operators of aircraft have a financial interest in ensuring that the inspection schedule is as cost-efficient as possible. Because aircraft are often revenue producing, there is an opportunity cost associated with the maintenance of the aircraft (lost ti

33、cket revenue), in addition to the cost of maintenance itself. Thus, this maintenance is desired to be performed infrequently, even when such increased intervals cause increased complexity and cost to the overhaul. The exponential growth of cracks in structure has led to the development of non-destru

34、ctive testing methods which allow inspectors to look for very tiny cracks which are often invisible to the naked eye. Examples of this technology include eddy current, ultrasonic, dye penetrant, and X-ray inspections. By catching structural cracks when they are very small, and growing slowly, these

35、non-destructive inspections can reduce the amount of maintenance checks, and allow damage to be caught when it is small, and still inexpensive to repair,How many Paris laws,But how solid is Damage Tolerance if everything is based on fracture mechanics, and Paris law, how reliable is Paris law? How m

36、any Paris laws How robust is it with respect to random loading? How many assumptions in predicting effect of load sequence How robust is the calculation of loading in service to reproduce in testing How important are extreme events,Barenblatt & Botvina demonstrated that Paris law would be a true str

37、ong power-law (complete scaling), only if the power came directly from dimensional analysis, implying m=2). WE HAVE A STRONG SIZE EFFECT,Z = 52,CRITICISM TO DAMAGE TOLERANCE AND PARIS “LAW,Incomplete self-similarity in 1, 5, 6 and 7 gives,Therefore, the experimentally observed deviations from the si

38、mplest power-law regime suggested by Paris is the result of incomplete self-similarity in the various dimensionless numbers,where the exponents i can be functions of i,Complete similarity, m=2,Corresponds to early models, but is hardly ever observed,incomplete self-similarity in 1, 5, 6 and 7 gives,

39、Therefore, the experimentally observed deviations from the simplest power-law regime suggested by Paris is the result of incomplete self-similarity in the various dimensionless numbers, for example Z. We found in particular a correlation between C and m based on the dimensionless number Z (size of t

40、he specimen). M. Ciavarella, M. Paggi and A. Carpinteri, (2008), One, no one, and one hundred thousand crack propagation laws: a generalized Barenblatt and Botvina dimensional analysis approach to fatigue crack growth, Journal of the Mechanics and Physics of Solids, Volume 56, Issue 12, 3416-3432,Pa

41、ris m for all materials,(size) dependence of m: ductile materials,Al alloys,4340 steel,ASTM steel,Low carbon steel,Al alloys,4340 steel,High strength concrete,Normal strength concrete,dependence of m: quasi-brittle materials,Exponential vs. power-law Z-dependence of C,4340 steel,4340 steel,ASTM stee

42、l,ASTM steel,High strength concrete,High strength concrete,Normal strength concrete,Normal strength concrete,Exponential vs. power-law Z-dependence of C,Correlation between C and m,4340 steel,ASTM steel,High strength concrete,Normal strength concrete,Tanaka,Paggi & Carpinteri,Tanaka,Paggi & Carpinte

43、ri,Paggi & Carpinteri,Paggi & Carpinteri,45,Paris Erdogan law (1963) NASGRO law (Newman Forman) PREFFAS Davy, 1985 Strip Yield model (NASGRO) Dugdale & Barenblatt, 1960,How to use Paris law for numerical crack growth models,Kth,R: stress ratio,Law for macro cracks,Part of this uncertainty is reflect

44、ed in poor predictions using Paris law-based methods,Merging of safe life with damage tolerance - various attempts 2003 2012 (El Haddad equation to finite life,M. Ciavarella,Log Dsg,finite” life diagram,Atzori B, Lazzarin P, (2000) Analisi delle problematiche connesse con la valutazione numerica del

45、la resistenza a fatica, convegno AIAS, Lucca, e Quaderno AIAS n.7, p.33-50,safe life,damage tolerance”,safe life notches,The Kitagawa diagram & EH eqt,1 from Multiaxial Fatigue, Analysis & Experiments, Eds. G.E. Leese, D.Socie, SAE Pub. AE-14, 1989. Also, in Fatigue Database of the Lifest software d

46、atabase of Somat http:/,Region above the threshold but below fat limit Region above fat limit but below fat threshold Region above both, fat limit and fat threshold EH beatifully expresses the condition for non propagation of cracks or crack self-arrest,safe life,damage tolerance”,short cracks,Short

47、 cracks break Parislaw,Pugno, Ciavarella et al - 1,A modified Paris law adding an intrinsic crack in the Irwin SIF N. Pugno, M. Ciavarella, P. Cornetti and A. Carpinteri, (2006) A generalized Paris law for fatigue crack growth, Journal of the Mechanics and Physics of Solids, Volume 54, Issue 7, Page

48、s 1333-1349,Ciavarella Monno - 2006,M. Ciavarella, F. Monno, (2006) On the possible generalizations of the Kitagawa-Takahashi diagram and of the El Haddad equation to finite life, International Journal of Fatigue 28 18261837,Result of previous approach (2,Curious lack of continuity with the El Hadda

49、d equation,As a SN curve,A new contribution 2012,Fatigue & Fracture of Engineering Materials & StructuresVolume 35, Issue 3, pages 247256, March 2012 A simple approximate expression for finite life fatigue behaviour in the presence of crack-like or blunt notches M. Ciavarella,A simple approximate ex

50、pression,r= 3, k=10 (a metal) r=10 , k=10 (a ceramic,Results in Kitagawa diagram,Crack Propagation Laws Corresponding to a Generalized El Haddad Equation,International Journal of Aerospace and Lightweight Structures (IJALS) Volume 1 Number 1 (2011)doi: 10.3850/S2010428611000109 M. Ciavarella Politec

51、nico di Bari, 70125 Bari, Italy ABSTRACT The El Haddad equation permits to deal simply with both short and long cracks, and we have recently suggested a generalization for finite life, defining a “finite life intrinsic crack size”, as a power law of number of cycles to failure. Here, we derive the c

52、orresponding crack propagation law, finding that it shows features similar to Paris law in the limit of long cracks, but shows some dependence of the “equivalent” $C,m$ Paris material “constants” with applied stress range. The increase of crack propagation speed is obtained for short cracks, but add

53、itional size effects are derived, which may require quantitative validation, and correspond to the intrinsic difference with respect to the standard Paris law,Derivation of crack prop law,Special case r = k,Approximate law,r=3 , k=10,r=10 , k=10,Damage tolerance & safe life with notches are two different worlds,On fatigue limit in the presence of notches: classi