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Detection of Damage in Stiffeners of Aircraft Wing Structure Based on Induced Skin Strains and Lateral Deflections

In this paper, the technique of structure health monitoring was applied to detect damage occurrence in the stiffeners of wing structure. A wing structure of airfoil shape according to digital NACA 0015 was considered for modelling the aerodynamic wing shape. Finite element models of the wing structure were created included undamaged and damage wing structures using high order eight nodes and six nodes shell elements. The damaged wing models included damaged at the main spar at 20%, 40%,60% and 80% the distance than the root chord. A mathematical model was developed using high order shell elements and programmed via MATLAB. The load cases were predicted experimentally using wind tunnel test on a wood airfoil prototype such that the pressure distributions through upper and lower wing skins measured at different attack angles. The static solutions were achieved for each finite element model under action of maximum pressure distribution at attack angle of 100. Strains distributions and lateral deflections through lower skin were estimated. The results of strains through lower skin showed occurring of climax in strain values initiated in the distribution at the location of the damage for all the cases of damaged structures, which not appeared in the undamaged wing structure. The results of lateral deformations through lower skin showed indicating variations in the shape of the curves, such that the curve appeared to be gradually increased the region between the chord and the damage. Semi to rapid increasing in the lateral deformation occurred in region between the damage and the end tip of wing. The difference in the behavior of the induced strains and lateral deformation between undamaged and damaged wing structures is intended to a technique predicting of the occurrence of the damage in the wing structure. The present of a climax in the strain distribution lead to presence of damage near the climax value of strain. Also, the indicating of variations in the shape of the lateral deformations of skins semi or rapid increasing lead to presence of damage near the rejoin of that variation. It is concluded the possibility of using the strain and deflection analysis for the wing structure to investigate occurring damage in the structure due to variation in the strains and lateral deflections between different damage locations.