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Effects of cold climate exposure on composite material structures are scarcely documented. As a result, even if exceptional wind conditions prevail in some cold regions, uncertainties related to composite materials durability at low temperatures may hinder development of wind energy projects in those regions. Therefore, as part of the Wind Energy Strategic Network (WESNet) of the Natural Sciences and Engineering Research Council (NSERC) of Canada, efforts were made to evaluate the effects of cold climate exposure on the mechanical properties of glass-epoxy composites. Tensile and compressive quasi-static tests as well as tensile (R = 0.1) and fully-reversed (R = −1) fatigue tests were performed on vacuum-infused [±45] 2s glass-epoxy composites at -40 and 23 . Results for quasi-static tests show an increase of tensile, compressive and shear strengths and moduli at low temperatures. It is also demonstrated that for the stress range under scrutiny, fatigue performance is improved at −40 for both the R = 0.1 and R = −1 loading cases. Moreover, the failure mode for R = −1 fatigue changed from compressive failure due to buckling of delaminated plies to tensile failure, suggesting a more efficient use of the material. However, if R = −1 fatigue results at low temperature are extrapolated towards the very low stresses that are also part of wind turbine blades fatigue load spectrum, fatigue life may be degraded compared to that at ambient temperature. Finally, evidence of visco-elastic behaviour leading to changes in s − N curve slope parameter are reported. 1

Ethynyl‐terminated polysulfones and ethynyl‐terminated polyether‐ketones were prepared in a one‐step polyetherification reaction using new end‐capping agents, respectively 4‐ethynyl‐3′‐nitrodiphenylsulfone and 4‐ethynyl‐4′‐nitrobenzophenone. These reagents were prepared according to a three‐step route each. End‐capping of the polymers involve the nitro displacement by a phenoxide ion. The nitro group was found to be more reactive than the fluoro one as a leaving group. Due to the thermally induced reaction of their ethynyl end‐groups, the polymers lead to materials with improved glass transition temperatures and good thermostability.

No abstract

Predicting the fatigue performance of composites has proven to be a challenge both conceptually, due to the inherent complexity of the phenomenon, and practically, because of the resource-intensive process of fatigue testing. Moreover, mechanical behaviour of polymer matrix composites exhibits a complicated temperature dependence, making the prediction of fatigue performance under different temperatures even more complex and resource intensive. The objective of this paper is to provide a method for the prediction of fatigue life of glass-polymer composites loaded in the fibre direction at various temperatures with minimal experimental efforts. This is achieved by using a static strength degradation approach to fatigue modelling, where only two parameters (including static strength) are temperature dependent, in conjunction with relationships for these two fatigue model parameters temperature dependence. The method relies on fatigue data at a single temperature and simple static tests at different temperatures to predict the effects of temperature on the material's fatigue behaviour. The model is validated on experimental data for two unidirectional (UD) and one woven glass-epoxy composites and is found to accurately predict the effect of temperature on fatigue life of composites. A method to obtain probabilistic stress-life (P − S − N) fatigue diagrams including temperature effects is also discussed. 1

As wind turbines are likely to be installed in a wide variety of environments, knowledge of their materials mechanical properties under extreme environments is needed. The project presented herein aims at evaluating the effects of temperatures of -40 ℃, 23 ℃, and 60 ℃ on the static properties and fatigue lives of unidirectional glass-epoxy composites as found in wind turbine blades load bearing structures. Tensile and compressive static properties, as well as fatigue lives under R = 0.1 and R = −1 loading are evaluated. Moreover, in an attempt to reduce future tests time by using the highest frequency possible, efforts are spent in evaluating the effects of loading frequency on specimen fatigue lives. Frequencies ranging from 1 Hz to 24 Hz are studied. Results show that even if the static strength of the composite is much improved at low temperature, this does not translate to improved fatigue performances and may actually cause a reduction of fatigue lives. On the other hand, static strength degradation at higher temperatures does equate to a significant reduction in fatigue life. This is particularly true for fully reversed fatigue loading. It is also shown that higher loading frequencies are rapidly deleterious at room and elevated temperatures. However, considering the limited effect of low temperatures on fatigue performances, it is believed that cooling could be coupled to higher frequencies in order to accelerate fatigue testing.

No abstract

SynopsisDifferent main chain acetylene terminated polyethers with various molecular weights were prepared in a one-step polyetherification reaction. This process requires the synthesis of new acetylene end-capping agents, 4-ethynyl-4'-fluorobenzophenone and 4-ethynyl-4'-fluorodiphenyl sulfone. These reagents were prepared with good yields in a three-step route. The thermally induced reaction of the ethynyl groups in an easy process leads to materials with improved solvent resistance and good thermostability. The fracture toughness was evaluated and was found to increase with the molecular weight of the precursor oligomers. High values were obtained, especially when 4,4'benzophenone and 4,4'-diphenyl sulfone units are present in the polymer main chain.