ANALYTICALLY - EXPERIMENTAL STUDY OF DAMAGE TOLERANCE OF AIRCRAFT STRUCTURES

Presented in this paper are the results of the research on some actual problems on ensuring damage tolerance of the airplanes. The first problem considered is the fatigue crack growth under random spectra. The analytically experimental study of fatigue crack growth in specimens was conducted at a regular and random spectrum of loading. Generalized Willenborg model was used for the calculations of crack growth under the spectrum of transport airplane wing loading. The second problem considered is the residual strength of the stiffened structure such as skin with stringers. An effective engineering method using the R- curve of the material was proposed for analysis of the residual strength. In that case the experimental investigation of the R- curve of the material of a passenger airplane fuselage skin was conducted. The results of the analysis were compared to the experimental results, published in the literature. Also the experimental research of the residual strength in case of multiple site fatigue damages was carried out and the criterion of the residual strength in such case was proposed. The third problem considered is the influence of the airplane long operation on the fatigue properties of structure material. In the tests of the specimens that were cut from a wing skin of long operated airplanes, the change of material properties was observed.