Monitoring quasi-static and cyclic fatigue damage in fibre-reinforced plastics by Poisson’s ratio evolution

Abstract

Even if the extent of fatigue damage in fibre-reinforced plastics is limited, it can already affect the elastic properties. Therefore, the damage initiation and propagation in composite structures is monitored very carefully. Beside the use of nondestructive testing methods (ultrasonic inspection, optical fibre sensing), the follow-up of the degradation of engineering properties such as the stiffness is a common approach. In this paper, it is proved that the Poisson's ratio can be used as a sensitive indicator of fatigue damage in fibre-reinforced plastics. Static tests, quasi-static cyclic tests and fatigue tests were performed on [0°/90°] 2s glass/epoxy laminates, and longitudinal and transverse strain were measured continuously. The evolution of the Poisson's ratio ν xy versus time and longitudinal strain ε xx is studied. As the transverse strain measurement is crucial to monitor the degradation of the Poisson's ratio, three techniques were applied to measure the transverse strain (strain gauges, mechanical extensometer and external optical fibre sensor). Finally, the technique has been applied to a totally different material: a carbon fabric thermoplastic composite. The results show a very similar degradation of the Poisson's ratio, although no stiffness degradation can be observed during fatigue loading of this material. It is concluded that the degradation of the Poisson's ratio can be a valuable indicator of fatigue damage, in combination with the stiffness degradation.

Finite element modelling of composite structures under crushing load

“…This approach is consistent with the experimentally observed Poisson's ratio degradation that accompanies the progression of damage in composite materials [43].…”

Monitoring Poisson’s ratio of glass fiber reinforced composites as damage index using biaxial Fiber Bragg Grating sensors

“…7(d)e(f) is that the lateral strains measured by the strain gage and FBG sensor acquire positive values under zero loading, which was also reported in [5,6] without any discussion on possible physical reason, and considered to be a peculiar behavior in sensor reading. It is inferred that this is due to the relaxation of the curing induced compressive strain in both axial and lateral directions due to the transversal crack formation discussed in the previous section.…”

“…Several researchers examined the reduction of Poisson's ratio as a damage indicator [2e5] since Poisson's ratio (n xy ¼ Àε y /ε x ) embodies both axial and transversal strain (ε x and ε y , respectively) information and is affected by the transverse cracks formed as a result of applied longitudinal strain [6e8]. Paepegem et al [6] investigated the evolution of Poisson's ratio of composite materials as a function of applied longitudinal strain, and showed that Poisson's ratio decreases with the applied strain. Smith et al [8] modelled the evolution of Poisson's ratio using a shear-lag theory under static loading conditions, correlated their analytic model with experimental results, and indicated that Poisson's ratio decreases as the transverse crack density increases.…”

Damage Signature of Fatigued Fabric Reinforced Plastics in the Pulsed Ultrasonic Polar Scan

“…However, the application of the P-UPS technique for nondestructive detection and evaluation of fatigue damage in fiber-reinforced plastics has hardly been investigated. Most fiber-reinforced composites show a progressive directional reduction in stiffness properties upon fatigue loading through fiber/matrix interface debonding, matrix cracks, fiber bridging/pull-out/failure on the micro-scale [21,22,25,27]. There where most of the existing NDT tools fail to assess the effect of fatigue damage in composites, the nature and design of the P-UPS method should perfectly match such kind of material degradation.…”