Full-Scale Testing and Analysis of Fuselage Structure Containing Multiple Cracks

Abstract : An experimental and analytical study was conducted to determine the effects of multiple cracks on the fatigue crack growth and residual strength of curved fuselage panels. Four panels were tested, two panels with a longitudinal lap splice and two with a circumferential butt joint. For each joint configuration, one panel contained only a lead crack and the other contained a lead crack with multiple cracks located along the outer critical fastener row of the joints. The panels were tested in the Full-Scale Aircraft Structural Test Evaluation and Research (FASTER) facility. First, strains were measured under quasi-static load conditions to ensure proper load introduction into the panels. Second, fatigue crack formation and growth were monitored and recorded in real time using the Remote Controlled Crack Monitoring (RCCM) system under constant amplitude loading up to a prescribed amount of fatigue crack growth. Third, the crack growth and residual strength were measured during quasi-static loading to failure. Geometric nonlinear finite element analyses were conducted to support the tests. The strain distributions and fracture parameters governing crack formation and growth were determined. Comparisons with strain-gage data verified the finite element models. For fatigue crack growth predictions, the corresponding mixed mode stress-intensity factors were calculated using the Modified Crack Closure Integral (MCCI) method. Results include comparisons of strain distributions, fatigue crack growth characteristics, and the damage growth process during residual strength test for the two joint configurations. In general, results show that multiple cracking did not have an effect on the overall global strain response. However, the number of cycles to grow a fatigue crack to a predetermined length was reduced by 37% and 27% for the longitudinal lap joint and circumferential butt joint panels, respectively. In addition, the presence of multiple cracks reduced the residua