Viscoelastic Modelling and Dynamic Analysis of CNT-based Composite Shell Panels

Abstract

Conventional carbon fiber reinforced polymer (CFRP) composites find many applications in the aerospace and allied industries but these are vulnerable to dynamic loading which causes vibration with long settling time due to low inherent damping property. Recently, carbon nanotubes (CNTs) are well known for its application in the areas of advanced composite materials for their improved elastic and damping properties. The large aspect ratio of the CNTs make them very ideal for damping applications in engineering structures/systems.
The present research work deals with the viscoelastic modelling and dynamic responses of the three types of proposed CNTs – based composite material systems (such as CNHNC, CNHWC and FGNC). In the proposed material systems CNHNC and CNHWC, the primary phases are CNT, polymer and fiber, whereas in FGNC the primary phases are only CNT and polymer. In all the proposed composite material system the polymer is reinforced with CNT. In this present work, CNHNC represents CNT-based Hybrid Nanocomposite whereas CNHWC is the CNT-based Hybrid Woven Composite whereas, FGNC stands for Functionally Graded Nanocomposite.
The Mori – Tanaka (MT) micromechanics in conjunction with weak interface (WI) theory has been developed for the mathematical formulations of the viscoelastic modelling of CNTs-based polymer matrix phase. Further, strength of material (SOM) method has been employed to formulate frequency and temperature dependent viscoelastic material behaviour of the homogenized hybrid CNHNC composite materials. The same methodology is also applied in order to determine the viscoelastic properties of straight yarn in case of CNHWC. Finally, viscoelastic properties of the representative unit cell (RUC) is established based on the unit cell method (UCM). In case of FGNC, the Mori – Tanaka (MT) micromechanics with weak interface (WI) theory is implemented in order to obtain the frequency and temperature dependent viscoelastic properties. Five types of linear distributions of CNTs (such as UD, FGX, FGV, FGO and FGΛ) in the thickness directions are considered.
An eight-noded shell element with five degrees of freedom per node has been formulated to study the vibration damping characteristics of proposed composite shell panels. The shell finite element formulation is based on the transverse shear effects as per the Mindlin’s hypothesis and the stress resultant-type Koiter’s shell theory. Frequency and temperature dependent material properties of such proposed composite materials have been obtained and analysed based on the developed mathematical formulations.
Impulse and frequency responses of such structures have been performed to study the effects of various important parameters (such as volume fraction of CNTs, fiber volume/packing fraction, interfacial condition, agglomeration, geometry of weave pattern, temperature and geometries of shell panel) on the dynamic responses. The effects of distributions of CNTs of FGNC shell panels on the vibration damping characteristics have also been studied and analysed. Obtained results demonstrate that problems associated with vibration may be mitigated using such proposed composite materials which are desirable to overcome the drawbacks of conventional CFRP composite materials.