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Article & Data Composite Pipes

Composite Pipe

Composite Pipes

Nonlinear Viscoelastic Analysis of Thick Walled Cylindrical

R.M. Guedes
INEGI - Mecânica Experimental e Novos Materiais, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal

This paper analyzes the effect of the polymer matrix non-viscoelastic behaviour in the mechanical behaviour of thick multilayered cylinders. Composite Pipe The original contribution of this work is to provide novel approximate analytical solutions to compute the timedependent internal stress state throughout the pipe thickness within the framework of nonlinear viscoelasticity theory. The structures considered are thick, multilayered anisotropic infinitive long cylinders subjected to axisymmetric mechanical loading.

Under such conditions there is an exact elastic solution which naturally satisfies equilibrium, strain-displacement, compatibility and boundary conditions for the stated constitutive equations and loading. Due to the continuous stress variations throughout the cylinder thickness, the proposed nonlinear viscoelastic solution assumes the averaged stress state to calculate the nonlinear elastic and viscoelastic factors in each layer. Furthermore the solution is obtained assuming that the creep strains, within each layer, are constant through the thickness. The proposed algorithm converges to the exact solution when the number of layers is artificially increased. For the linear viscoelastic case the proposed solution proved to match the exact known solution for isotropic viscoelastic materials. Finally several invented cases are run to illustrate the importance of the viscoelasticity phenomenon on the internal stress field throughout thick laminated cylinders.

INTRODUCTION

The hollow cylinders or cylinders are Composit Pipe very common structural elements, used in many applications including trusses, hoses, piping systems and drive shafts. The effort to improve oil production riser performance lead to the possible use of risers made of polymer matrix composites to bring the oil to surface platforms in the offshore exploration at waster depth of 2 km or more. Consequently the increasing use of polymer matrix composites in civil engineering applications has renewed interest in problems of stress analysis of cylindrical laminated composite structures.

Many analytical works about stress analysis of composite cylindrical shells have been done during the past years. This is related with the increase use of composite shells in many applications, such as civil engineering structures and aeronautical industry. The static behaviour of thin shell panels has been investigated by using two-dimensional shell theories based on the Love-Kirchhoff hypotheses.

Chandrashekhara and Kumar presented and assessed these shell theories. The laminated shell theories provide an accurate solution for thin-walled cylinders but for thick-walled cylinders elasticity solutions are required for an accurate determination of the three-dimensional stress states.

The nonlinear viscoelastic analysis of thick laminated composites, using the Schapery nonlinear visceolastic constitutive equations , has been preformed, essentially, using finite elements (FE) formulations whether using a ply-by-ply classical approach or using a more sophisticated approach based on multi-scale approach.

The laminated cylinder is one Composite Pipe of a very few structural cases for which an exact elasticity solution is available. The analytical solution for multilayered cylinders is described in detail by Herakovich . This is based on the early works of Lekhnitskii and Pagano among others. Based on this elastic solution a novel nonlinear viscoelastic analytical approximate solution was developed, using the Schapery non-linear viscoelastic constitutive equations, to compute the stress state of nonlinear viscoelastic polymer matrix fiber reinforced laminated thick cylinders. The present solution considers that the material is linear elastic in the fiber direction and nonlinear elastic-viscoelastic in transverse and shear directions to the fibre. It is also assumed that the material is transversely isotropic. Since the stress state changes continuously throughout each layer thickness, the averaged stress state is used when computing the nonlinear elastic and viscoelastic factors for each layer. Furthermore the solution is obtained assuming that the creep strains, within each layer, are constant through the thickness.

The present analytical approximate solution converges to the exact solution when the number of layers is artificially increased. The proposed approximated solution matches the exact known solution for the pressurization of a compressible linear viscoelastic isotropic cylinder constrained by an elastic case.

Finally several invented cases are run to simulate the mechanical behaviour of a nonlinear viscoelastic T300/5208 composite cylinder under internal pressure, external pressure and axial force. These cases are used to demonstrate the importance of the viscoelasticity effect over the time-dependent internal stress field evolution throughout thick laminated cylinders.