Simulation of fatigue crack propagation in the wing main spar flange

Abstract

Simulation of fatigue crack growth in the bottom flange of twin turboprop commuter aircraft wing spar is described in this paper. Analysed crack propagation scenario represents real wing fullscale fatigue test failure. Computational model of bottom flange was prepared using threedimensional fracture mechanics software FRANC3D. Calculation of crack growth under the variable amplitude loading was performed in AFGROW code using the NASGRO equation and Wheeler retardation model. It was verified with the results of wing spar specimen fatigue test and fractograpic analysis of fatigue fracture from this experiment. Computational model was applied in the prognostic algorithm of structure health monitoring system. NOMENCLATURE a crack length da/dN crack growth rate G shear modulus K stress intensity factor KC fracture toughness Kop opening stress intensity factor Kth threshold stress intensity factor range R stress ratio  constraint factor  Poisson’s ratio O flow stress YS tensile yield strength