Fatigue damage in GFRP

Abstract

Purpose -Composite materials are increasingly used in the structural and mechanical fields, thanks to their high strength-to-weight ratios and the possibility of tailoring them to meet specific requirements. This study is focused on the damage to a glass fiber reinforced composite under different loading conditions. The aim is to find, by coupling mechanical tests with thermal analyses, a damage parameter, able to define the damage initiation in the studied material. Design/methodology/approach -The object of this work is a glass-fiber reinforced plastic (GFRP) laminate. To study the damage of this material under different loading conditions, static, dynamic and fatigue tests were carried out. During these tests, the surface temperature of the specimens was monitored by means of an IR-camera. In the dynamic tests, a D-mode (dissipation mode) analysis was also performed allowing the dissipated energy to be determined. Findings -In the literature, thermography is an experimental technique which has always been applied to the study of homogeneous materials. Results obtained from the proposed experimental tests on this GFRP composite show how this practice can be applied also to this kinds of materials, to identify their damage initiation. From these observations, the results can be used to definite a stress corresponding to the damage initiation, which can be related to the fatigue behavior, and useful in design stage with these materials. Originality/value -This paper provides for a useful tool to understand and predict fatigue behavior of a GFRP composite, from thermographic observations. Applications of thermography to the study of composite materials is an innovative research field, and the presented results seems satisfactory and promising for further experimental investigations.

Impact behaviour of 3-layered metal-polymer-metal sandwich panels

“…(2): where DT is the temperature variation, K is the thermoelastic constant, T 0 is the room temperature in absolute value and D(r 1 -r 2 ) is the variation in principal surface stresses. At the end of the thermoelastic linear stage, the damage stress r D [22,23,26,27] can be identified, as in Fig. 11.…”

“…Analysing this trend, a stress corresponding to the end of the thermoelastic stage, r D (end of the linear decreasing stage of the temperature) can be detected. According to some recent studies on composite fibre reinforced materials, it is related to the beginning of damage into the material and it is called damage initiation stress [22,23,26,27]. As far as the authors know, no works are present in the literature dealing with the application of this experimental technique to sandwich panels.…”

“…Infrared thermography is a non-contact and non-destructive experimental technique, based on the concept of surface temperature scanning during the application of a mechanical or thermal load to a structural component. In the literature different methods have been developed by means of thermography, initially applied to homogeneous materials [21], and recently applied also to composite structures [22,23]. The attention is focused on the correlation between the thermal response of the material under mechanical loads, either static or dynamic, and the detection of the damage initiation.…”

“…In particular, this technique can detect the damage initiation at very early stage, in correspondence of the stress at the end of thermoelastic trend, during tensile test. This stress is called damage initiation stress, r D [22].…”

Influence of delamination on fatigue properties of a fibreglass composite

“…Comparisons are proposed with undamaged material, already presented and discussed in [15]. Innovative features of the work are not only the quantification of fatigue lifespan reduction due to the presence of a delamination, but also the possible identification of a high cycle fatigue limit characteristic of the studied material.…”