Damage detection in composite pipes during mechanical three point bending

Improvements in the design and manufacturing process for composite materials have allowed them to become a cost-effective replacement for metals in structural applications. The cost of inspection, however, continues to represent a large proportion of the life cycle costs of composite components. Since composite materials allow for the integration of sensors, with negligible effect on their mechanical properties, permanent structural health monitoring (SHM) systems have sparked a great deal of interest. The aim of this work was to combine SHM and conventional nondestructive techniques (NDT) to detect and localize the initiation and progression of damage in a tubular specimen during several cycles of flexural loading/unloading. Active infrared thermography (IRT) is used in the reflective mode to scan the specimen between loadings; from this data, thermal diffusivity mappings of the specimen are generated. Two different SHM techniques are used during mechanical loading: (i) acoustic emission (AE) event monitoring using surface mounted piezoelectric sensors, and (ii) distributed strain monitoring using surface mounted optical fibre sensors. Distributed strain data suggests that the loadings are elastic, and residual strains do not appear to be present. The collected AE data suggests significant damage on first glance, however more thorough analysis reveals that the signals are caused primarily by matrix cracking that is damage but not as critical as delamination or fibre breakage.