Crack arrestor

A crack arrestor (otherwise known as a rip-stop doubler) is a structural engineering device. Being typically shaped into ring or strip, and composed of a strong material, it serves to contain stress corrosion cracking or fatigue cracking, helping to prevent the catastrophic failure of a device.

The crack arrestor can be as simple as a thickened region of metal, or may be constructed of a laminated or woven material that can be designed to withstand deformation without failure. When correctly applied, the technique is capable of redirecting movement and safely distributing stresses.[1] The crack arrestor is considered to be compatible with fail-safe design practices.[2]

Applications

Crack arrestors have seen extensive use in the aviation sector, particularly upon large pressurised aircraft as a means of guarding against progressive metal fatigue.[3] Specifically, the skin of the fuselage skin typically has a large number of high stress locations, rivetting being a leading cause, making these points of potential crack initiation. Calculations are frequently used to simulate crack propagation, as well as the effectiveness of mitigating measures, such as crack arrestors, in ensuring the aircraft can be safely operated.[3]

Following two catastrophic airframe failures in 1954, crack arrestors were used as additional reinforcement of the fuselage of the de Havilland Comet, although this was only one of several design changes made to address structural design weaknesses related to metal fatigue and skin stresses that had been previously unknown to the aviation industry.[4][5]

Naval vessels are another place where crack arrestors have been extensively used. As of the 2010s, the United States Navy frequently applies them to areas of the ship that have been damaged or otherwise have received repairs in order to ensure that the affected element is not lacking in either strength or durability. It has been acknowledged that ships primarily composed of aluminium are significantly more prone to crack propagation than older steel counterparts, thus the use of mitigating measures is likely to become more commonplace.[6]

Crack arrestors have also been used in civil engineering. They have long been used in the nuclear industry as a structural element of reactors.[7] Numerous pipelines used from transporting chemicals have been reinforced with such devices to protect against bursting and exterior damage alike.[8] While commonly applied to metal alloys, appropriately designed crack arrestors have been used with composite materials as well.[9][10] During 2008, Airbus Group was awarded a patent for a new design technique for a crack arrestor component.[11]

Citations
  1. "High strain deformation" (PDF). uobabylon.edu.iq. 20 June 2020.
  2. Sairam Kotari, S.M.Gangadhar, A. Amala, P.Poornima, P.Janaki Ramulua (1 February 2014). "Design and Analysis of Crack Stopper" (PDF). International Journal of Current Engineering and Technology.CS1 maint: uses authors parameter (link)
  3. Venkatesha, B K (January 2012). "Analytical Evaluation of Fatigue Crack Arrest Capability in Fuselage of Large Transport Aircraft". pp. 13–22.
  4. R.J. Atkinson, W.J. Winkworth and G.M. Norris (1962). "Behaviour of Skin Fatigue Cracks at the Corners of Windows in a Comet Fuselage". Aeronautrical Research Council Reports and Memoranda. CiteSeerX 10.1.1.226.7667.
  5. Faith, Nicholas. Black Box: Why Air Safety is no Accident, The Book Every Air Traveller Should Read. London: Boxtree, 1996. ISBN 0-7522-2118-3. p. 72.
  6. "Effective Crack Arrestors for On-Board Fatigue Crack Repair of Aluminum Ship Structures". Department of Defense. 17 February 2016.
  7. G. R. Irwin, J. M. Krafft, P. C. Paris, and A. A. Wells (21 November 1967). "Basic Aspects of Crack Growth and Fracture" (PDF). apps.dtic.mil.CS1 maint: uses authors parameter (link)
  8. Brauer, H.; Knauf, G.; Hillenbrand, H.-G. (9–12 May 2004). "Crack arrestors" (PDF). Ostend, Belgium: 4th International Conference on Pipeline Technology. Archived from the original (PDF) on 7 July 2011. Retrieved 11 June 2010.CS1 maint: uses authors parameter (link) CS1 maint: date and year (link)
  9. Harris, Bryan (2003). "Fatigue in composites: Science and technology of the fatigue response of fibre-reinforced plastics" (PDF). dl.polycomposite.ir. p. 198.
  10. Kruse, Thomas., Thomas Körwien, Roman Ruzek, Robert Hangx, Calvin Rans (2007). "Fatigue behavior and damage tolerant design of bonded joints for aerospace application on Fiber Metal Laminates and composites" (PDF). 29th ICAF Symposium.CS1 maint: uses authors parameter (link)
  11. "DE102008023495A1: Component for an aircraft structure, method for producing a component for an aircraft structure and use of the component as a crack stopper". 2008.
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