Hơn nữa, đối với các cánh phẳng, sự phân bố hợp âm lý tưởng có thể đạt được với mỗi phần Cl và Cd tối đa / của nó và sự phân bố inviscid thang máy tối ưu. Đối với đôi cánh không phẳng này không còn là trường hợp và các hợp âm tối ưu và phân phối tải trọng kéo tối thiểu là một chút phức tạp . | Materials Choice of materials emphasizes not only strength weight ratio but also Fracture toughness Crack propagation rate Notch sensitivity Stress corrosion resistance Exfoliation corrosion resistance Acoustic fatigue testing is important in affected portions of structure. Doublers are used to reduce stress concentrations around splices cut-outs doors windows access panels etc. and to serve as tear-stoppers at frames and longerons. Generally DC-10 uses 2024-T3 aluminum for tension structure such as lower wing skins pressure critical fuselage skins and minimum gage applications. This material has excellent fatigue strength fracture toughness and notch sensitivity. 7075-T6 aluminum has the highest strength with acceptable toughness. It is used for strength critical structures such as fuselage floor beams stabilizers and spar caps in control surfaces. It is also used for upper wing skins. For those parts in which residual stresses could possibly be present 7075-T73 material is used. 7075-T73 material has superior stress corrosion resistance and exfoliation corrosion resistance and good fracture toughness. Typical applications are fittings that can have detrimental preloads induced during assembly or that are subjected to sustained operational loads. Thick-section forgings are 7075-T73 due to the possible residual stresses induced during heat treatment. The integral ends of 7075-T6 stringers and spar caps are overaged to T73 locally. This unique use of the T73 temper virtually eliminates possibility of stress corrosion cracking in critical joint areas. Miscellaneous Numbers Although the yield stress of 7075 or 2024 Aluminum is higher a typical value for design stress at limit load is 54 000 psi. The density of aluminum is .101 lb in3 Minimum usable material thickness is about inches for high speed transport wings. This is set by lightning strike requirements. Minimum skin gauge on other portions of the aircraft such as the fuselage is about inches to permit
