Distributed Piezo-Optical Active Sensing for Damage Assessment in Composite Materials for Aerospace Application

Lead Research Organisation: University of Manchester
Department Name: Materials

Abstract

This project brings together supervisors with complementary research interests with the overarching aim of developing distributed piezo-optical active sensing for damage assessment in composite structures for aerospace applications. Structural health monitoring (SHM) of material performance is expected to be a key resource in continued safe, efficient and economically viable operation. However, development of new or advancement of SHM techniques relies on knowledge of the impact of material state on detection signals. Models that can predict the interaction of SHM signals with relevant material status could provide optimization or new directions for SHM development and deployment.
Flaws may have been initiated in the composite structures due to material degradation resulting from service conditions and environmental attack or introduced during the manufacturing process. Though SHM techniques are being developed to detect service-induced flaws (e.g., delamination, disbonds, resin cracks.) in limited-access locations, majority of the techniques have to inspect the entire structural components in order to detect the presence of flaws, which is time-consuming and costly. A consensus approach that can identify "hot spots" in the subject component for efficient inspection has not yet been established.
The project is highlighted with novel technologies including structural component evaluation using combined acoustic (passive) and ultrasonic (active) piezoelectric sensing, fibre Bragg gratings and distributed optical strain sensors. Together the proposed method can provide a sensing system that can timely interrogate the structural integrity for condition assessment and diagnosis of composite components and provide a game-changing technique of long-term online monitoring of critical structures

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509565/1 01/10/2016 30/09/2021
1830576 Studentship EP/N509565/1 19/09/2016 30/09/2020 Marilyne Philibert
 
Description A sensing method has been designed and developed for damage assessment in a carbon fibre reinforced polymer (CFRP) composite T-joint structure subjected to mechanical impacts. Ultrasonic guided Lamb waves have been monitored at different frequencies using piezoelectric lead-zirconate-titanate (PZT) discrete transducers; and the fundamental modes A0 and S0 have been identified at approximately at 30 kHz and 150 kHz respectively. Dispersion and tuning curves have been used for damage detection by signal comparison with a prior obtained baseline. This pitch-catch active structural health monitoring (SHM) approach allowed detecting and quantifying inner damage created by either 4J or 10J impact.

Nonetheless, the choice of appropriate transducers can improve efficiency of damage assessment. In this context, direct-write (DW) piezoelectric transducers made of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and comb-shaped top electrodes have been produced on CFRP plates. DW transducers newly developed benefits from customised design and improved integration with little interference, compared to discrete transducers. Moreover, electrodes can be patterned in desired shape allowing mode selection by imposing the wavelength. The DW transducers achieved strong piezoelectric response, with typical effective piezoelectric strain coefficient d33 of about -20 pm/V at 100 kHz, measured by laser scanning vibrometer under substrate clamping effect. The A0 Lamb wave mode was effectively selected at frequencies corresponding to periodicities of comb-shaped electrodes. A pitch-catch active sensing method is under development using four DW transducers fabricated on a CFRP plate for impact damage identification.
Exploitation Route Monitoring aerospace structures over time would improve safety and prevent catastrophic failure. Composite materials, which are increasingly used in aerospace applications, are prone to internal damage that should be detected and repaired before they progressively grow into critical defects. Structural Health Monitoring (SHM) techniques have been therefore developed, using a network of ultrasonic transducers, which can generate and sense guided Lamb waves travelling into carbon-fiber reinforced polymer (CFRP) structures. These waves are particularly affected by any discontinuities, such as damage but also anisotropy and discontinuities due to the multi-layer composition and the potentially complex shape of CFRP structures. Monitoring these composite structures is thus more challenging than monitoring metal structures. In addition, the ultrasonic wave attenuation in composite is higher than in metal.
Sectors Aerospace, Defence and Marine