Development of Hybrid Piezoelectric-Fibre Optic Composite Patch Repair Solutions

Abstract

This paper proposes a hybrid structural health monitoring (SHM) solution for a smart composite patch repair for aircraft structures based on piezoelectric (PZT) and fibre optic (FO) sensors to monitor the integrity of a the bondline and detect any degradation. FO sensors are used to acquire guided waves excited by PZT transducers to allow the advantages of both sensor technologies to be utilised. One of the main challenges of guided wave based detection methodologies is to distinguish the effect of temperature on the propagating waves, from that of an existing damage. In this research, the application of the hybrid SHM system is tested on a composite step sanded repair coupon under operational condition (temperature variation) representative of an aircraft for the first time. The sensitivity of the embedded FO sensor in recording the strain waves is compared to the signals acquired by PZT sensors under varying temperature. A novel compensation algorithm is proposed to correct for the effect of the temperature on the embedded FO sensor spectrum in the hybrid set-up. The repaired specimen is then impacted with a drop mass to cause barely visible impact damage (BVID). The hybrid SHM system is then used to detect the damage, and its diagnosis results are compared to a PZT only based smart repair solution. The results show promising application of the hybrid solution for monitoring bondline integrity as well as highlighting challenges of the embedding of FO sensors for a reliable and repeatable diagnosis.

Accuracy of Distributed Strain Sensing with Single-Mode Fibre in Composite Laminates under Thermal and Vibration Loads

“…Te SMF and strain gauges are bonded to the surface of the specimen by a thermoplastic adhesive flm based on modifed polyolefns (Pontacol 22.100). Tis type of thermoplastic adhesive flm is adopted because of advantages including easy maintenance, high peel strength, and controllable thickness [17,[38][39][40]. As shown in Figure 1, two "S" shape SMF, called SMF1 and SMF2, are mounted on each side of the specimen independently, to provide strain readings in diferent directions.…”

“…For example, buckling detection based on distributed FO sensors [10], a hybrid piezoelectric-fbre optic system based on fbre Bragg gratings (FBG) [11,12], embedded FBG sensors in SHM of complex composite structures [13], and sandwich panel [14]. In addition, FO sensors are adopted in composite manufacturing monitoring [15,16] and damage detection [17,18]. For in-feld applications, however, many more FBG sensors are required than distributed FO sensors to obtain sufcient measurements, which results in higher system weight and cost.…”

Temperature calibration for guided wave hybrid system with FBG-based Fabry-Perot sensor

“…Their disadvantage, however, is that they are passive sensors and can only record the changes in the structures. Therefore, by combining the FO sensors with PZT actuators, the advantages of both technologies are enhanced, including embedding of the FO sensors in the composite (De Pauw et al, 2017; Lambinet and Sharif Khodaei, 2021). Consequently, the number of PZT transducers is significantly decreased, leading to a reduction in the additional weight, wiring, connectors, and electromagnetic interference.…”

Through thickness inspection in various structures using ultrasonic wave coupling in an embedded fiber optical sensor

“…84 0.57 2.51 0.17 1.44 0.45 0.40 0.37 In this experimental case for investigating the wave interaction phenomena only the excitation from PZT (50 kHz frequency) is used. The obtained signals are divided using the conversion factor[13] (Rconv) as shown in Fig 3, the response of sensors is proportional to the slope. To compare measurements from different sensors, the response was normalized with the slope of the FBG.…”