This paper presents an experimental and analytical study about the mechanical response at a different temperature on glass fiber-reinforced polymer laminates. The effect of different environmental conditions on compressive, tensile, stiffness, and viscoelastic behavior (storage modulus, loss modulus and damping ratio) of laminates were investigated. Before testing, laminates were preserved in a deep freezer at −80 °C, −20 °C, 0 °C, and room temperature (25 °C) for up to 60 days. Results confirmed that temperatures ranging from −80 to 50 °C, which were below the glass transition temperature of the epoxy resin, did not significantly affect the compressive, tensile, and stiffness performance of all laminates. When the testing temperature increased to 100 °C, the properties were decreased significantly due to the damaging of the fiber/matrix interface. Additionally, results obtained from dynamic mechanical analyses tests showed a drop-in storage modulus, high peaks in loss modulus and high damping factor at the glass transition region of the epoxy resin. The highest storage modulus, two phases of glassy states and highest damping ratio on the −80/G group of laminates were obtained. The accuracy of experimental results was assessed with empirical models on the storage modulus behavior of laminates. The empirical model developed by Gibson et al. provided accurate estimates of the storage modulus as a function of temperature and frequency. The remaining empirical models were less accurate and non-conservative estimations of laminates stiffness.

This paper presents the results of an experimental program to study the mechanical properties of currently available composite materials for the construction of wind turbine blade. The materials identified for this purpose include unidirectional glass fibre/epoxy (GFRP), carbon fibre/epoxy (CFRP) and hybrid combinations of these two materials to be used in a laminated design and at elevated temperatures. The tests conducted in the present programme includes short beam shear test and dynamic mechanical analysis tests after the specimens are exposed to temperatures ranging from 25 to 140°C. The results indicate that the inter-laminar shear failure strength and stiffness of GFRP, CFRP and hybrid specimens degrade with increasing temperature. However, the degradation is observed to be higher in single material specimens in comparison to hybrid specimens. In particular, stiffness of CFRP specimens decreased linearly as the temperature approached 40°C and increased up to the glass transition temperature of epoxy. Experimental results indicated that damping properties of Glass-Carbon-Glass/epoxy specimens improved at elevated temperatures which is important for noise and vibration control. In the present study, empirical models are proposed based on the test data to predict the variation of inter-laminar shear failure stress and stiffness as a function of temperature. The experimental results and proposed model can be used as input parameters to design and construct composite wind turbine blades to be used in tropical wind farms.

This paper presents a theoretical and computational study to determine the optimal positions of airfoils along the length of the horizontal axis wind turbine blade. We used four and five-digit NACA airfoils to model a 54-meter blade. The lift, drag coefficient, and lift-to-drag ratio of each airfoil are determined by using QBlade software. The aerodynamic performance of the airfoils is studied based on the blade element momentum theory, and Matlab software is used for numerical implementation. The velocity and pressure distributions on each airfoil are assessed using computational fluid dynamics. We implement the thickness distribution techniques to adjust the positions of the airfoils along the length of the blade. It is noted that stresses reach their maximum values at the root and minimum at the tip section. Thus, the thicker (NACA 4420) and thinner (NACA 23012) airfoils are set at 20% of the maximum chord and 91.11% at the tip sections of the blades. The remaining sections of the blade are configured using linear interpolation methods. Specifically, the maximum chord length of the new design is reduced by 18.06% compared to the NACA 23012 rotor blade. Finally, the recommended tip speed ratio for the designed rotor blade is estimated using the graphs of the normal and tangential forces, thereby producing a safe and efficient design.

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