Structural health monitoring for impact damaged composite: a new methodology based on a combination of techniques

Advanced aerospace materials, including fibre-reinforced polymer and ceramic matrix composites, are increasingly being used in critical and demanding applications, challenging not only the current damage prediction, detection and quantification methodologies, but also the residual life of the structure. The main objective of this work consists of developing a new methodology based on different techniques to be applied on structural health monitoring system for impacted composite aeronautic structures. For this, it is necessary to identify, and to localise damage, as well as to calculate the severity of the damage and to predict the residual strength of the composite structure. To achieve these goals, the research methodology should consider three methods: (1) vibration-based method, (2) shearography speckle and (3) flexural after impact. Composite plates, made of epoxy resin reinforced by carbon fibre, are evaluated. First, vibration-based method provides frequency response functions to be analysed by a new metric, which is compared in terms of their capability for damage identification and global location. Afterwards, the extension of impact damage is determined using shearography speckle. This technique has demonstrated great potential for damage detection in composite-laminated structures. A flexure after impact test is used to evaluate its limitations and potentialities as a damage-tolerance technique. The residual flexural strength of damaged specimens is evaluated by quasi-static four-point bending test. A new criterion based on a relationship between damage metric from vibration-based method and flexure after impact analysis is presented and discussed. Finally, it discussed the advantages and limitations of this combination of techniques into the context of structural health monitoring systems.