toughness levels of 55 MPa m and 80 MPa m respectively. These values give limited defect sizes of approximately 0.5 mm and 2.2 mm which can be The Future of detected by well-developed NDT tech niques. There are a number of different alloy steels used in landing gear components. Landing Gear Some of the most common are named below: Steels Grade Type Tensile Strength MPa AMS 6419 1 3/4% Ni Si Cr Mo V 1930 AMS 6418 1 3/4% Ni Si Mn Mo Cr 1520 STOCKSBRIDGE Engineering Steels The process route adopted in the AMS 6411 1 3/4% Ni Cr Mo 1520 manufacture of landing gear steels (SES) is a manufacturer of specialised AMS 6414 1 3/4% Ni Cr Mo 1795 steels for the aerospace industry, supply differs from that used for less critical 35 NCD 16 4% Ni Cr Mo 1850 DTD 5212 18% Ni Cr Mo 1800 ing major airframe, engine and aerospace industries. The majority of landing gear S98 2 1/2% Ni Cr Mo 1200 equipment companies including Airbus steels are made by double melting 3% Cr Mo V S132 1320 Industrie, Boeing, Dowty, Rolls-Royce, techniques that ensure freedom from harmful non-metallic inclusions and Messier-Bugatti and Westland Helicop ters. segregation. The process also refines the The desire of aircraft manufacturers structure and enhances toughness. Hugh Everson, SES's manager of to reduce overall weight means that Product Metallurgy explains why steel At Stocksbridge, landing gear steels traditionally bulky components such as will continue to play an important part are made to an Ultra Clean Steel landing gear are facing especial scrutiny. in critical components such as landing Practice (UCSP) to provide a premium The need to reduced weight is gear. quality electrode which is subsequently accompanied by higher performance remelted under vacuum (VAR) or Predictions about the future metal expectations from designers. Increased content of aircraft suggest a significant under a refining slag or flux (ESR). strength allows for a reduction in weight reduction in terms of the proportion of but as important as this is the concurrent Initial melting is carried out in an overall weight. Composites and ceramics need to provide improved toughness, electric arc furnace followed by refining are superseding light metals and other better temperature tolerance and im in a vacuum arc degassing vessel alloys as manufacturers look to lighten (VAD). Casting of the electrode uses proved resistance to corrosion without structures and reduce flying costs. playing. specially developed refractories and shrouded teeming techniques. Research New brake designs for modern airlines Although overall metal weight will drop significantly, the proportion of at Stocksbridge has shown that the are exerting higher transient temperatures steel is expected to see only a marginal quality of the feedstock electrode is of on landing gear components in aborted great importance in ensuring that the fall. It is widely accepted that areas of take-off situations. The fact that temp final remelted ingot has optimum clean eratures above those used in heat heavy stress and load will continue to ness and properties. Specialist ultrasonic treatment may be encountered could rely on specialist aerospace steels. inspection facilities can be used to jeopardise the continued safe service of This is largely due to the fact that for guarantee that the product meets the components which normally operate at many critical applications such as most stringent requirements. ambient temperatures. landing gear components, control surface actuators and engine gears and shafts, The current remedy for this sort of steel continues to be the only cost- eventuality is for the suspected parts to The inspectability of steel be examined and, where necessary, effective materials solution. Non-metal- One of the disadvantages of composites, lics and composites still cannot match replaced. However, Stocksbridge is non-metallics and ceramics is the diffi its combination of strength, toughness, leading research into the development culty that can be involved in examining and ductility. of materials that will withstand excur the finished product. As with steel, sions into these temperatures without On a modern civil aircraft the weight quality has to be assured by stringent affecting properties, thereby adding an of the landing gear is approximately 4% control of the manufacturing process extra margin of safety. of total aircraft weight, compared with a itself but the inspectability of steel gives it a definite advantage over composites, Despite the undisputed status of figure of around 7% in aircraft made 30 years ago. as the quality can be verified by a specialised steels as the major constituent variety of inspection techniques. of landing gear components, Stocks The reduction in landing gear weight bridge recognises the pressing need to is set against the increase in the average In ceramics, for example, the flaws continue to move forward. The require size of aircraft and the general improve responsible for failure are usually smaller ments of the aerospace industry as a ment in performance. than 50μm and are therefore not whole will best be served by close co The major constituent of the landing detectable by non-destructive testing operation between designers and steel gear in both large civil aircraft and (NDT) techniques. manufacturers to maintain research military aircraft is high strength steel, In contrast, high strength steels such programmes to optimise alloy design. the consistency and reliability of which as AMS 6419 (a high silicon nickel, has been steadily enhanced through chromium molybdenum steel commonly improved manufacturing and testing known as 300M) and 35 NCD16 used Stocksbridge Engineering Steels, procedures. in aircraft undercarriages have fracture Tel: 0742 882361. AIRCRAFT ENGINEERING — October 1991 11
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Oct 1, 1991
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