Contribution à l’étude de fatigue des structures endommagées et réparées : analyse et optimisation

Abstract

In this study, the fatigue crack repair techniques, several methods have been proposed so far, (drilling with and without expansion, shot peening, patching, etc.). Depending on the structure, the material and the conditions of service, the choice of the method of repair becomes a problem, since each method has a specific character having its advantages and disadvantages. The objective of this study is to take stock (state of the art on the repair methods validated in the literature and certified by the control and aeronautical safety organizations), then a very detailed analysis on a reliable method gain in residual life. This study is composed of two parts; a 3-D finite element analysis was conducted on a thin aluminum plate with a 45 °inclined central crack. A modeling of the bonding repair with composite patch of different shapes was carried out. In addition to the patch shapes studied in the literature, a new butterfly shape was proposed. A length H, a width B and a neck C in the middle define the latter. The main objective is to analyze the effect of patch shape on the rate of decrease of stress intensity factors. This rate is characterized by a coefficient R that combines between the mode I and the mode II of the rupture (KI and KII). In the second part of this study, the impact of the shape of the crack front was studied on the stress intensity factor and the crack propagation behavior of the aluminum plate, repaired asymmetric by composite patch. As a result, skew degree has a significant impact on the distribution of stress intensity factor along the crack front in thicker plates than thin plates. In addition, the fatigue life was calculated using different factors of average stress intensity factor of the repaired plate determined from crack front obtained from FEM.