Damage detection & localization on composite patch repair under different environmental effects

Abstract

This paper presents a structural health monitoring (SHM) methodology for detecting damage in a composite bonded repair. The application of guided wave based techniques in a step-sanded bonded repair under operational and environmental load is thoroughly investigated. A two step damage detection and localization algorithm is presented, were in the first level the path damage indices (PDIs) for each transducer pair is calculated. The PDIs are then compared to a set threshold (based on the environmental and operational conditions) to increase the reliability of damage detection while reducing false alarm. In addition, a self-diagnosis approach based on electro-mechanical impedance (EMI) measure is proposed to identify the faulty sensors prior to the diagnosis. Once the transducer pairs with possible damage in their path has been selected, the second level of the proposed methodology is damage localization. To address the challenge of edge reflection, complex geometrical shape and layup of the repair patch which introduced anisotropy to the wave propagation, a novel damage detection based on probability imaging technique is proposed. The methodology is developed based on assigning probabilities of damage to the Minimal Intersection Score (MIS) to reduce the path saturation related to each path having the same probability of damage being located anywhere along it. The proposed method, uses a smart sub-division technique based on Voronoi Tessellation which is adaptable to any shape (circular, rectangular, elliptical). The reliability of the proposed method is then demonstrated with experimental results on a composite step-sanded repair subjected to impact damage under vibration and temperature variations, and the choice of input parameters such as wave form and excitation frequency on the probability of detecting damage is demonstrated.