INVESTIGATION OF AN IN-SERVICE CRACK SUBJECTED TO AERODYNAMIC BUFFET AND MANOEUVRE LOADS AND EXPOSED TO A CORROSIVE ENVIRONMENT

摘要

During routine inspection of a vertical tail attachment stub former from a combat aircraft, cracking was found about an attachment bolt. This former was replaced and was made available for examination. The cause of the cracking was found to be fatigue. The stub had experienced both aerodynamic buffeting and manoeuvre loads (often in combination) and these had produced many prominent fatigue progression markings on the crack surface, and by assuming that these marks were caused by similar events evenly distributed across the service life of the stub a crack growth curve was derived. During the life of the aircraft, significant down-time periods for maintenance had occurred and evidence of corrosion was found in discrete areas of the fatigue crack's surface that suggested that they were the result of these periods of inactivity. By assuming that the corrosion occurred whilst the aircraft was on the ground it was possible to correlate the crack growth curve to known flight hours.