Dynamic Analyses of CNT-based Viscoelastic Composite Shell Structures in Hygrothermal Conditions

Abstract

Composite materials are well known for light weight and high specific stiffness, and find many engineering applications but conventional carbon fiber reinforced polymer (CFRP) composites are vulnerable under hygrothermal conditions. Since the discovery of carbon nanotubes (CNT), it has fascinated the researchers and being used to improve the damping properties of such conventional composites due to its large aspect ratio. Dynamic mechanical analysis (DMA-8000) is used to conduct the creep test for nanocomposite (NC) samples as per ASTM-D4065 standard and obtained the frequency dependent viscoelastic properties (i.e storage modulus and loss factor) of NC samples using the Prony series. Viscoelastic properties of NC matrix based carbon fiber reinforced polymer (CNT-CFRP) laminated hybrid composite (HC) and functionally graded carbon nanotube reinforced hybrid composite (FG-CNTRHC) materials have also been determined in frequency domain. Furthermore, the vibration and damping characteristics of CNT reinforced laminated hybrid skewed shell structures under hygrothermal environments have been investigated using finite element method. Finite element modelling has been formulated using an eight noded shell element based on the Koiter’s shell formulation. The transverse shear effect is considered based on the first order shear deformation theory. Based on the above obtained frequency dependent viscoelastic properties, dynamic responses of various composite shell skewed shell panels have been determined. The effects of skewing angle and CNT volume fraction on the modal parameters (such first eigenfrequency and modal loss factor) and dynamic responses of various skewed shell structures under hygrothermal conditions have also studied and reported. The frequency dependant viscoelastic properties are directly used to obtain the frequency responses of the skewed shell panel whereas the transient responses are determined with using inverse fast Fourier transform (IFFT). The effects of staking sequence and power law index on the dynamic responses of such CNT based hybrid composite skewed shell structures have also been studied and analysed