An embedded piezoelectric [poly(vinylidene fluoride) (PVDF)] thin film sensors system for acoustic emission (AE) was realized to investigate the possibility of monitoring, in real time, the post-impact damage in aramid woven fabric-reinforced epoxy. The same sensors have been used in a previous work on similar specimens tested in flexure but not previously impacted, with the aim of verifying the suitability of these sensors to be embedded and their ability to detect AE signals under loading. This work is a continuation of the previous one aiming at evaluating the ability of these embedded PVDF sensors to point out the presence of impact damage, issue widely studied in literature.Aramid fibre/epoxy composite specimens with embedded PVDFs, previously impacted at different energies, namely 5, 10 and 15 J, were tested using three-point bending tests. It appeared from mechanical tests that the flexural strength decreased passing from non-impacted specimens to those impacted with the highest energy and that the embedment of PVDFs in the laminates did not markedly affect the structural integrity of the impacted composites. The degree of impact damage, represented by the decrease in mechanical properties, has been correlated with the AE activity by means of a parametric analysis of the AE signals detected during post-impact mechanical tests.
Cost-effective and reliable damage detection is critical for the utilization of composite
materials due to the relatively localised nature of damage formation and the resultant reduction in
structural integrity. Of the methods available, Acoustic Emission (AE) is considered as one
potential technology for on-line and in situ monitoring of structural degradation of composite
materials.
Purpose of this work was to study the interaction between embedded PVDF (polyvinylidene
fluoride) transducers and composite samples as well as detect and characterize the failure
mechanisms in aramid/epoxy flexural test specimens using acoustic emission data obtained by
embedded PVDF film sensors. Furthermore, it has been realized a comparison with surface
mounted PVDF data. Results of our previous works (Caneva et al., 2005) dealing with monitoring
tensile and flexural behaviour of glass/epoxy composites enabled to extend this methodology to
aramid/epoxy composites.
The use of Acoustic Emission and Scanning Electron Microscopy (SEM) observations enabled
to identify and understand the failure mechanisms of the composites tested. Furthermore,
satisfactory results of this work highlighted that the application of PVDF shows promise as a
suitable acoustic emission transducer for fibrous composite materials.
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