Fatigue properties of a glass-fibre-reinforced polyester material used in wind turbine blades

Abstract

Glass-fibre-reinforced polyester (GFRP) is a composite commonly used in the manufacture of wind turbine blades. In the present work, one such material has been subject to static and dynamic tests in order to obtain data that can be applied to the design of wind turbine blades and other machine elements. The results of the static tests established a basis for the determination of a set of tension-tension (constant amplitude and sinusoidal load) dynamic tests with the aim of establishing a mathematical model in order to predict life as a function of the load state and calculate the fatigue limit. The multiplicative model (y ¼ ax b ) for y ¼ log of life and x ¼ transformed stress (a and b are characteristic parameters of the material obtained from data) matches the data quite well. The conclusion is that the GFRP studied has no fatigue limit. The possible decrease of fatigue strength of the material with solar radiation and moisture absorption was also investigated, with a negative result.

Prediction of the Deterioration of FRP Composite Properties Induced by Marine Environments

“…The classification societies' rules prescribe the procedure for obtaining S-N curves for composite materials. Various authors have reported results obtained in modeling S-N curves for composites [29,34,35] and the prediction of the fatigue life of composite structures [27,43,44]. A failure model for groups of similar glass/polyester composites, such as the ones used in this research, can be defined in the form:…”

“…The fatigue of composites immersed in water has been investigated in the past [27,28]. Early research assumed that the absorbed moisture has no influence on the material fatigue strength in sinusoidal tension conditions, with a moisture content no greater than 0.2 percent [29]. However, newer research acknowledges the effects of water absorption on the fatigue strength of composites [30,31].…”

Strain analysis of a glass-fibre-reinforced polyester under dynamic loads

“…If R is found to have no effect on GFRP life expectancy (Vázquez et al, 1998) and the effect of R on strain is confirmed, the conclusion would be that the failure point for a given σ max would be the same for different strain processes, 56 A. Silvera et al / Span J Agric Res (2011) 9(1), 49-58 4 Number of cycles at failure.…”

“…The moisture absorbed reduced ultimate tensile strength by 15% and fatigue strength by 35% (through 1,000 cycles) and 10% (through 10 7 cycles). Vázquez et al (1998) submerged samples in water at ambient temperature (24°C) for 45 days. The tests were conducted at laboratory temperature, i.e., 25°C.…”

“…Andersen et al (1988) and Bach (1988Bach ( , 1991 reported that the fatigue life of a material can be predicted with an equation proposed by Mandell (1982) that relates the applied stress to the number of cycles: σ = σ U (1 -y 0 log N) [1] where σ (MPa) is the applied stress; σ U the ultimate tensile strength (MPa), N the number of cycles and y 0 a coefficient dependent on the stress ratio R and the type of material. Vázquez et al (1998) developed a model to predict the expected number of cycles based on fatigue test data for different values of R. Their model is as follows:…”