Damage tolerance assessment of the fighter aircraft 37 Viggen main wing attachment

The Swedish fighter aircraft 37 Viggen, designed some 25 yr ago on a safe life basis, has been reassessed in terms of a damage tolerance evaluation. The aim was to ensure structural safety and to investigate the possibilities for extending the service life of the aircraft. This article deals with the reassessment of the newest wing attachment frame for the fighter version of the aircraft. The purpose of this article is to briefly show the extent and complexity of the assessment. Because of the original safe life design, resulting in rather high stresses, very extensive finite-element analyses were necessary in order to obtain accurate stress distributions and three-dimensional stress intensity factors in critical sections. Also, high demands have been placed on the accuracy of the crack growth predictions. Hence, extensive validation of the crack growth prediction technique was required. Structural testing, including artificial flaws, was carried out with the aim or obtaining crack growth data for correlation to the prediction technique. It is concluded that the state-of-the-art methodology used was successfully verified. Furthermore, damage tolerance of the considered parts were analytically proven and experimentally verified. Finally, extension of the original design life may be possible following further considerations.