Experimental investigation of residual strength of aged aircrat structures

Nowadays, aging of aircraft is one of the most important problems in evaluation of their airworthiness. In structural area, it is very important to assess the rate of degradation of the material properties of aircraft after their long time service. Therefore, this subject is practiced in this article. In order to evaluate the effect of aging of aircraft on deterioration of the mechanical properties, some specimens are prepared from the structural units of a few aged aircraft in Air Force to do the tensile and fracture tests. Also in order to evaluate the results, similar tests are accomplished on unused ingot materials. In this manner, source values are obtained from reference books too. The tensile tests are accomplished on some parts of upper and lower skin of trailing edge flap torque box and also unused sheets of similar materials either in rolled direction and the opposite direction. The fracture toughness tests are accomplished on some parts of lower skin of center wing and upper skin of middle area of two wings in several directions. The results show that because of precipitation hardening of being tested alloys, the yield and ultimate strength are increased but, decrease of fracture toughness make it leads to brittle fracture.