A PVDF Sensor for the In-situ Measurement of Stress Intensity Factors During Fatigue Crack Growth

Several analytical and numerical studies of inverse analysis are performed to verify the feasibility and accuracy of the proposed K-sensor. At first, the application to cracks in sheets under in-plane stresses is investigated and compared with the analytical solution for the GRIFFITH's crack under mixed mode. It was found that the convergence radius, where the electrodes have to be placed, must be smaller than half of the crack length, which is sufficient for real cracks of several millimeters. The obtained accuracy of crack tip location and (KI, KII)-factors is better than 1%. Second, the technique is applied to cracks in thin-walled plates of KIRCHHOFF type under bending and torsion moments. In this case, the plate intensity factors (k1, k2) are of interest. Again, the inverse identification procedure is studied by synthetic analytical and numerical solutions of simple crack configurations. Due to the assumptions of the KIRCHHOFF plate model, the sensors have to be placed outside a radius of 3 times plate thickness h. The obtained accuracy in position and intensity factors is quite sufficient as well. The practical realization of the K-factor sensor requires good electric signal measurement and amplification. Its experimental testing on components is ongoing work.