Aircraft structures

Fokker Bond Tester. An ultrasonic inspection technique commonly used for aircraft structures is based on ultrasonic spectroscopy [2]. Commercially available instruments (bond testers) used for this test operate on the principle of mechanical resonance in a multi-layer structure. A piezoelectric probe shown in Figure 3b, excited by a variable frequency sine signal is placed on the surface of the inspected structure. A frequency spectrum in the range of some tens of kHz to several MHz is acquired by the instrument, see Figure 3a. 

D. H. Middleton, ed.. Composite Materials in Aircraft Structures, Longman Scientific and Technical, London, 1990. 

Smith, H. Jr 1995 Applications in Aircraft Structures. In Sundararajan, C. (ed.). Probabilistic Structural Mechanics Handbook Theory and Industrial Applications. NY Chapman Hall. 

W. Elber, The Significance of Fatigue Crack Closure , Damage Tolerance in Aircraft Structures, ASTM STP 486, 1971, pp. 230 242. 

Baker, A.A., Bonded Composite Repair of Metallic Aircraft Components — Overview of Australian Activities, AGARD (Advisory Group for Aerospace Research and Development) Conference of Composite Repair of Military Aircraft Structures, 3-5 October 1994, Seville. 

As mentioned above, aircraft structure is typically quite thin with numerous small fasteners to achieve efficient load transfer through joints. Mechanical fasteners are laborious to install. Adhesive bonding of large area doublers and joints can be accomplished at significant labor hour savings over equivalent mechanically fastened designs. 

Other natural glues common at the time, such as plant starch and fish glues, were not used for aircraft structure because they are even more sensitive to moisture. 

Adhesive strength is evaluated at room temperature as well as at the extreme temperatures of —65°F and 180°F. Aircraft structure can reach —65°F at cruise altitudes and 180°F on the ground in a hot, sunny location. The types of toughened epoxies commonly used for metal bond adhesives have glass transition temperatures not much greater than 200°F, so properties fall off drastically at higher temperatures. 

Higgins, A., Adhesive bonding of aircraft structures. Int. J. Adhes. Adhes., 20, 367-376... 

The operating cost includes items like fuel and other consumables. Maintenance costs are obviously repairs and periodic reworking of the structure. After the passage of years, nearly the entire aircraft structure has often been replaced part by parti The final category is the salvage value. What is the object worth at the end of its life Consider an aluminum airplane for which some scrap value exists at the end of its useful life. When the structure is no longer suitable to be flown, and there we... 

As a summary of nonlinear behavior, it appears possible to eliminate the nonlinear behavior, and at the same time, you typically do not want to operate in that nonlinear behavior regime anyway, so you are both able to, and want to, design out nonlinear behavior. That observation is true generally in aircraft structures, but there are other structures, which are subjected to higher temperatures, for which you simply cannot avoid some of the nonlinear behavior aspects, so you must take them into account in any rational design analysis. 

B. C. Hoskin and A. A. Baker, Composite Materials for Aircraft Structures, AIAA Publ. Inc., New York (1986). 

The largest application of polycyanurates is in circuit hoards. Their transparency to microwave and radar energy makes them useful for manufacturing the housing of radar antennas of military and reconnaissance planes. Their impact resistance makes them ideal for aircraft structures and engine pistons. ... 

Coatings consisting of a mixture of equal parts of cadmium and tin are particularly suitable for the protection of steel fasteners in contact with aluminium in aircraft structures where electrochemical corrosive attack is prone to occur under adverse conditions. The protection afforded is... 

Of historical interest may be the use of a half dollar coin (the lighter weight 250 not as efficient). During the early 1940s the coin tap test was used very successfully in evaluating the performances of plastics, particularly RP primary aircraft structures. With a good ear (human hearing ear) there was (and is) a definite different sound between a satisfactory and unsatisfactory RP product. The unsatisfactory product would contain voids, delaminations, defects in fiber distribution, etc. In... 

Performance of plastics , W. Brostow Hanser Gardner Pubis (1999) ISBN 1569902771. Comprehensively covers the behavior of the most important polymer materials. Subject areas range from Computer Simulations of Mechanical Behavior to Reliability and Durability of aircraft structures made of fiber-reinforced hydrocarbons. 

Recently, a method for predicting the remanent life of a reinforcing geotextile was proposed [1] in which the strain to failure of a sacrificial sample was divided by the current creep rate. This requires verification. However, very few methods have so far been proposed or used for monitoring plastics in service and at the same time providing a numerical prediction of their remaining life. The reason for this is not just that the methods are likely to be expensive and complicated, but that there are few applications of plastics which can compete in risk and replacement cost with a high temperature boiler or aircraft structure. 

Substrate Characterization. Test coupons and panels of 7075-T6 aluminum, an alloy used extensively for aircraft structures, were degreased In a commercial alkaline cleaning solution and rinsed In distilled, deionized water. The samples were then subjected to either a standard Forest Products Laboratories (FPL) treatment ( 0 or to a sulfuric acid anodization (SAA) process (10% H2SO4, v/v 15V 20 min), two methods used for surface preparation of aircraft structural components. The metal surfaces were examined by scanning transmission electron microscopy (STEM) In the SEM mode and by X-ray photoelectron spectroscopy (XPS). 

Holt, D.J. (1982). Future composite aircraft structures may be sewn together. Automotive Eng. 90, 46- 9. 

Defense Advanced Research Projects Agency (DARPA) begins a project, Morphing Aircraft Structures, to investigate the potential of such technology as shape-changing wings. 

Aircraft Sealants. Polysulfides have been used for sealing fuel tanks and aircraft structural components since the 1940s. There are stringent requirements for these sealants. They must have outstanding resistance to fuels and excellent adhesion to many different materials such as various metal alloys and protective coatings used in aircraft construction. The sealants must also perform in extremely variable weather conditions (10). The polysulfides have an excellent performance record. 

Aircraft structures Aircraft windshields Air drying Air electrode... 

BISMALEIMIDE POLYMERS. These relatively new polymeric materials were developed to serve the increasing requirements for materials of high strength in high-temperature applications. Currently, a high percentage of the bismaleimides produced are used for printed circuit boards (PCBs). The materials usually are cured with aromatic amines and then compression molded into the PCBs. Future uses include aircraft structural components where bismaleimides may prove superior for high-temperature skin surface applications as compared with present epoxy composites. 

Alloy with Memory. In seeking a way to reduce the brittleness of titanium, U.S. Navy researchers serendipitously discovered a nickel-titanium alloy having an amazing memory. Previously cooled clamps made of the alloy (nitinol) are flexible and can be placed easily in position. When warmed to a given temperature, the alloy hardware then exerts tremendous pressure. Use of conventional clamps for holding bundles of wires or cables in a ship or aircraft structure requires special tools. For this and other applications in industry and medicine, nitinol has been in demand. The alloy, however, is not easy to produce because only minor variations in composition can affect the snap back" temperature by several degrees of temperature. 

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