Tensile and fatigue testing of impacted smart CFRP composites with embedded PZT transducers for nonlinear ultrasonic monitoring of damage evolution

Abstract

Ultrasonic systems based on ‘smart’ composite structures with embedded sensor networks can reduce both inspection time and costs of aircraft components during maintenance or in-service. This paper assessed the tensile strength and fatigue endurance of carbon fibre reinforced plastic (CFRP) laminates with embedded piezoelectric (PZT) transducers, which were covered with glass fibre patches for electrical insulation. This sensor layout was proposed and tested by the authors in recent studies, proving its suitability for nonlinear ultrasonic detection of material damage without compromising the compressive, flexural or interlaminar shear strength of the ‘smart’ CFRP composite. In this work, CFRP samples including PZTs (G-specimens) were tested against plain samples (P-specimens), and their mean values of tensile strength and fatigue cycles to failure were found to be statistically the same (910 MPa and 713 000 cycles) using the one-way analysis of variance method. The same tests on P- and G-specimens with barely visible impact damage (BVID) showed that the corresponding group means were also the same (865 MPa and 675 000 cycles). Nonlinear ultrasonic experiments on impacted G-samples demonstrated that embedded PZTs could monitor the growth of BVID during fatigue testing, for a minimum of 480 000 cycles. This was achieved by calculating an increase of nearly two orders of magnitude in the ratio of second-to-fundamental harmonic amplitude. Finally, PZT transducers were confirmed functional under cyclic loading up to ∼70% of sample’s life, since their capacitance remained constant during ultrasonic testing.

Multifunctional composite structures with embedded conductive yarns for shock load monitoring and failure detection

“…Despite these advancements, challenges remain, particularly in implementing these systems on a large scale [15]. Furthermore, most studies on health monitoring of structures have concentrated on fatigue [16][17][18] and impact damage [5,19,20]. While there are some studies on damage monitoring during high-strain dynamic loading [21] and in-flight conditions [3], no research has been conducted on health monitoring during shock loading-a typical loading condition for high-performance aerospace systems.…”

Lead Zirconate Titanate Transducers Embedded in Composite Laminates: The Influence of the Integration Method on Ultrasound Transduction

“…To overcome such bonding layer issues under environmental conditions and also provide protection from impacts, one solution is the integration of the SHM system directly into the material. Composite materials allow the integration of a monitoring system directly into the material during manufacturing [18][19][20][21][22][23][24][25][26][27][28][29][30]. Moreover, as a co-cured surface-mounted SHM system, the manufacturing process of the composite material can be monitored directly from the beginning of the composite fabrication with an integrated SHM system [30,31].…”

“…Liu et al [30] monitored the curing process with embedded fiber Bragg grating (FBG) and PZT sensors and used the embedded system for delamination detection. Andreades et al [26,27] studied the tensile and fatigue of CFRP material with the electric insulation, They added PZT into their previous studies. Mall et al [21] studied the difference in monotonic load and fatigue testing of a composite with embedded transducers using two methods, namely cut-out or between two plies.…”

Damage imaging method for composites laminates based on sparse reconstruction of single-mode Lamb wave

“…However, they may exhibit defects or in-service damages * Author to whom any correspondence should be addressed. like delamination and debonding, which will result in a significant reduction in structural integrity and strength [1,2]. Structural health monitoring technology can be used to detect such damages early to increase the structure's safety.…”