A structural health monitoring technique for the reconstruction of impact forces in aerospace components

Despite composite materials are widely used in aerospace components, they are characterized by low-impact resistance and, therefore, subject to barely visible damage. This can be due to a number of sources such as hailstones, tools drop, runaway debris and bird strikes. Hence, the real time knowledge of low-velocity impact magnitude on aeronautical composite structures is certainly one of the most demanded goal for structural health monitoring (SHM). This article proposes a novel ultrasonic SHM method for the reconstruction of the impact force history on composite components. The research work is based on an inverse problem applied to composite samples of unknown mechanical properties, whose global characteristics are obtained through the knowledge of the structural transfer function measured by a sparse array of surface-bonded piezoelectric sensors. Hierarchical interpolation methods are then used to reconstruct the magnitude of the impact force over the entire structural domain. Since the proposed methodology only requires the knowledge of the material response at discrete locations, it does overcome the limitation of current impact force reconstruction techniques, which require the use of either analytical models based on classical plate theory or numerical finite element simulations. This technique is experimentally validated on a composite panel with complex geometries by considering low-velocity impacts at multiple locations and different levels of magnitude.