Analysis of fatigue and damage in glass-fibre-reinforced polypropylene composite materials

Abstract

This paper concerns fatigue studies of polypropylene/glass-®bre thermoplastic composites produced from a bi-directional woven cloth of co-mingled E-glass ®bres and polypropylene ®bres with a ®bre volume fraction V f of 0.338. The eect of lay-up design and load conditions on fatigue performance were investigated. The S-N curves, the rise in the temperature of the specimens, and the loss of stiness during the tests, are discussed. Fatigue tests were performed in controlled displacement mode and in an imposed stress range. Similar results were obtained for both load conditions. The loss of stiness was used as a damage parameter and related to the rise of temperature. The results show that the damage parameter E present a nearly linear relationship with the rise in temperature. A small deviation was probably caused by the stress release observed in the ®rst period of fatigue life. #

On the tension–tension fatigue behaviour of a carbon reinforced thermoplastic part II: Evaluation of a dumbbell-shaped specimen

“…This is shown in Figure 1. It should be noted that the geometry differs from the ones mostly found in literature: in most cases, there is a constant section in between the two curved areas [12,15], whereas here, the curved section has a constant radius and thus a constantly varying width. The reason for the constant radius will become clear in the finite element assessment.…”

“…This was the case in [15], where a dogbone shape is used for fatigue testing of glass fibre reinforced polypropylene. A dogbone shape, similar to the one considered in this manuscript, was also considered for bending fatigue in [16] and uni-axial faituge of a carbon-epoxy in [17], but they also did not draw any attention to it.…”

Carbon laminates with RE doped optical fibre sensors

“…In metallic structures, damage is often localized in the form of cracks, however, in composite materials, damage accumulates throughout the structure. In terms of composites, the damage mechanisms are also very well-known and include fibre breakage, matrix cracking, debonding, transverse-ply cracking and delamination [2][3][4][5][6]. Several techniques have been used to assess damage evolution in composite structures [3,[7][8][9].…”

“…For this purpose, it is essential to resort to non-destructive techniques (NDT) in order to detect and evaluate the fatigue damages and the consequent loss of fatigue strength. Temperature, for example, increases with fatigue life, especially when close to final failure, and can be related with damage [5,6,[10][11][12][13][14][15]. Reis et al [9] found three stages, which are related with the different damage mechanisms along the fatigue process.…”

Evaluation of Structural Degradation of Polymeric Composites Subjected to Self-Heating by the Thermal Diffusivity Analysis

“…This is because a major amount of dissipated mechanical energy transforms into heat; however, a small amount of this energy dissipates toward development of plastic mechanisms [2] and microcracking [3]. The degradation process of a composite structure under conditions of fatigue loading accompanied with the self-heating effect can be featured with a characteristic three-stage degradation model, which is observable both in decrease in mechanical properties [4,5] as well as in evolution of the self-heating temperature [1,6,7]. The selfheating effect, due to the character of its development, can be classified into two types: In the first case, when stationary self-heating occurs, the self-heating temperature grows until reaching a certain temperature value and stabilizes at this value due to reaching a thermal equilibrium between the generated and convected thermal energy, while in the second case, the self-heating temperature growth has nonstationary character, which leads to significant influence and domination on the fatigue process.…”