Development of testing methods for endurance trials of composites components

Abstract

Endurance of composites materials is a critical and important factor that enables engineers to design structural components more efficiently. In fact, what it matters for many industries is to define the life of their products and, within that life, their safe operational conditions. Endurance of composites materials goes by the definition of failure criteria that can be obtained by cooperation between research groups acting both in a modelling and in an experimental framework. This research work is focussed on the development of an experimental test planning directed at testing composites components. Endurance trials for full reverse loading conditions, such as R = −1, can be executed by exploiting the first resonant mode of a beam, or a narrow plate. The major obstacles for this type of testing are (a) the fixture of the sample and (b) the amplitude of vibrations required for initiating fatigue behaviours. This paper will present two experimental methods based on (i) pulsed air-jet contactless excitation method and (ii) a novel fixture for electromagnetic shaker type testing. These methods will show how to overcome these obstacles in order to perform endurance trials on Carbon Fiber Reinforced Polymer (CFRP) components. The experimental results obtained from two sets of components are presented here and an interpretation of the fatigue behaviour of the trialled specimens will be also attempted.

Experimental fatigue behaviour of CFRP composites under vibration and thermal loading

“…It can, therefore, be readily understood that test can be time-consuming and costly, but also not carryed out with a representative loading enviroment. However, recent studies introduced testing methods to overcome these limitations [4,5]. Thus, the fatigue tests were performed at high frequencies and resonance conditions; drawing from the knowledge developed for metals [6].…”

“…Thus, the fatigue tests were performed at high frequencies and resonance conditions; drawing from the knowledge developed for metals [6]. One of the most significant challenges investigated in [4] was about an excitation method capable of delivering enough excitation force to reach the lowest fatigue threshold. A contactless excitation system based on compressed pulsed jets delivered the right force for achieving vibration fatigue.…”

“…The excitation method was not tuneable for a definitive study of failure criteria. In a later study, Magi further investigated some of the insights gathered from [4] to the study the fatigue behaviour of tapered Carbon Fibre Reinforced Polymers (CFRP) composite components [5]. The latter presents, as the most significant scientific novelty, a change from tracking the resonance frequency to track, instead, the response phase.…”

Criticality of the Self-Heating Effect in Polymers and Polymer Matrix Composites during Fatigue, and Their Application in Non-Destructive Testing

“…Therefore, in order to avoid self-heating or at least to minimize its influence, various approaches were applied. In many cases, the loading frequency was significantly decreased (see e.g., [119]), which allows for the neglect of the self-heating effect, while another approach was based on cooling the surface of a tested structure subjected to fatigue loading [44,46,50,120,121]. The self-heating effect, however, can be utilized for the material characterization and diagnostic problems of polymeric and PMC structures.…”

Nonlinear Modal Testing Performed by Pulsed-Air Jet Excitation System

“…Several measurements to experimentally quantify the influence of some design parameters were carried out. For example, the ducting (comprising of orifice, sampling hole and nozzle) or the addition of a double nozzle were presented in [8]. To characterize the excitation force with respect of the measured pressure at the nozzle and the excitation frequency, a small test rig was configured as shown in Figure 2.…”