Effects of thermal loading and material distribution on the vibration characteristics of rotating double tapered blades

Abstract

To begin with, this study is aimed to evaluate effects of thermal loading and material distribution on the vibration characteristics of rotating double tapered blades. An important topic of research into designing helicopter rotor blade is helicopter vibration control. A selection of material in designing helicopter rotor blade has a great impact on vibration characteristics. Functionally graded materials (FGMs) are multifunctional materials, which contain a spatial variation in composition and/or microstructure for the specific purpose of controlling variations in thermal, structural or functional properties. In consequence of the improvement of composite material technology, usages of FGMs have begun to increase in such engineering applications. Their material properties are continuous along the structure; thus, stress concentrations are decreased regularly. While structural integrity of FGM is sustained, it can endure against high temperatures. This makes FGMs preferable for aerospace structural applications. Also, this qualification makes this paper significant in respect to evaluate effects of thermal loading and material distribution on the vibration characteristics of rotating double tapered blades made of FGMs. In rotor blade design process, natural vibration frequencies need to be calculated accurately to avoid resonance which damages structural integrity. The beam model is used as the first approach in solving many engineering problems in the field of aviation, such as aircraft wings, helicopter blades, turbine blades. In this study, Euler-Bernoulli Beam Theory is applied on the beams in the modeling of helicopter blades. Furthermore, Euler–Bernoulli beam theory can provide the closed form solutions for different types thermal loadings. So that, blade formulations were obtained from Euler-Bernoulli Beam Theory. Finite Element Method (FEM) was applied on these formulations. Finite element method provides an approximation of the meshed surface (for which there exists an infinite number of vibration modes and frequencies). Therefore, this provides a good approximation for the first natural frequencies. In general, only the first few modes are important for practical applications. In this study, the first four natural frequency values were taken into account to evaluate the vibration characteristics.The computational mathematical software MATLAB has been used to carry out the numerical calculations to examine the free vibration behavior of rotating tapered functionally graded blades under effects of different material distribution and thermal loading. Finally, when the calculation results were compared with the literature, it was observed that the consistent results were obtained and low deviation rates were revealed.