Chapter 3 Failure Behaviour of Composites Under Both Vibration Loading and Environmental Conditions Georgios Voudouris, Dario Di Maio, and Ibrahim Sever Abstract The study focuses on the understanding of failure behaviour of composites which are subjected to vibration fatigue under environmental temperature conditions. The study of vibration fatigue failure in composites can be challenging because of the coupling between mechanical and thermal properties. In fact, stiffness distribution and self-heating are typically occurring under vibration conditions. As the problem stands, the sole use of either testing or simulation would not be adequate to understand the failure behaviour fully. This paper will present both an experimental and numerical work, based on a component designed with a ply-drop feature to enhance and localise the damage occurrence. The vibration testing experiments were carried while an environmental chamber was used to control the exposure temperature. Similar experimental conditions are simulated in a finite element multi-physics environment, where the crack opening is modelled by VCCT method. The simulation environment is very challenging because both mechanical (dynamics) and thermal behaviours need to be incorporated to study the failure of a given vibration loading. Both experimental and numerical results will be qualitatively compared. Keywords High cycle vibration fatigue · Environmental temperatures conditions · Carbon fibre reinforced polymers · Finite element · Virtual crack closure technique 3.1 Introduction The accurate prediction of fatigue failure, of polymer-based composites, depends on the effects of various factors, such as the environmental conditions as well as the material properties. It is understood that changes in the temperature and moisture conditions, can lead to an acceleration in the fatigue damage accumulation of composite components. Therefore, it is of greater significance to consider the role of the ambient temperature when studying the fatigue failure of composites. There are only a few references in the literature relating the surrounding temperature and the fatigue characteristics of composite materials. A typical feature of most studies is to investigate the behaviour of composites at pure mode I or II while the excitation frequency is not greater than 10 Hz [1–4]. In a recent study, Coronado et al. [1] asses the Interlaminar Fracture Toughness (IFT) of Uni-Directional carbon fibre composite (AS4/3501). Static and fatigue tests were carried out in a temperature range between−60◦Cand90◦C. The authors reported that under cyclic loading, the initiation Energy Release Rate is increased with temperature while less energy is required for the crack propagation. Overall, elevated temperatures seem to lead to higher ductility while sub-zero temperature can result in a more brittle behaviour of the material. It was also observed that the Fatigue Delamination Growth Rate (FDGR), at −30 ◦C and −60 ◦C, progressively dropped as the delamination length increased. Sjögren and Asp [2], continued the work of Asp [3], and studied the delamination characteristics of a carbon fibre system (HTA/6376), at 20 ◦C and 100 ◦C. The tests were performed for three different loading scenarios: Pure Mode I and II and for a 50% mode-mixity. It was noticed that the FDGR is accelerated at higher exposure temperatures. Furthermore, it seems that mode II can affect greatly the delamination growth. In addition to these, G. Voudouris Bristol Composites Institute (ACCIS), University of Bristol, Bristol, UK e-mail: G.Voudouris@bristol.ac.uk D. DiMaio ( ) Department of Mechanical Engineering, University of Bristol, Bristol, UK e-mail: Dario.DiMaio@bristol.ac.uk I. Sever Rolls-Royce plc, Derby, UK e-mail: Ibrahim.Sever@rolls-royce.com © Society for Experimental Mechanics, Inc. 2020 R. Barthorpe (ed.), Model Validation and Uncertainty Quantification, Volume 3, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-12075-7_3 25
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