Implementation and Validation of Schapery-Rand Anisotropic Viscoelasticity Model for Super-Pressure Balloons

Abstract

The thin film used for the NASA Ultra Long Duration Balloons (ULDB) shows considerable time-dependent behaviour. Furthermore, experiments on scaled ULDB balloons have revealed that wrinkles are present over a wide range of pressures. A numerical model has been developed describing the nonlinear anisotropic viscoelastic material behaviour by means of a Schapery-type model and this model has been extended to model wrinkling by means of a user-defined subroutine in the finite-element package ABAQUS. After a description of the viscoelastic modelling approach, a lobe of a 48 gore ULDB flat facet balloon is modelled and compared to experimental results. Additionally two test cases of anisotropic wrinkling are presented, one involving a flat membrane and one a cylindrical balloon structure.

Anisotropic Viscoelasticity and Wrinkling of Superpressure Balloons: Simulation and Experimental Verification

“…This algorithm has been implemented in Abaqus, but would be equally suitable for any displacement based finite element software, where strain components are used as the independent state variables. 2,5 Every time UMAT is called, it starts with an estimation of the biaxial trial stresses σ t,trial j based on the nonlinearity parameters at the end of the previous time increment. The principal strains and estimated principal stresses are used with a combined stress-strain criterion (Section II.C) to determine if the element is wrinkled or not.…”

Wrinkling of Orthotropic Viscoelastic Membranes

“…Kang and Im 10 proposed an iterative scheme for the finite element analysis of wrinkling in orthotropic membrane structures, which was later adopted by Gerngross and Pellegrino. [11][12][13] Alternative approaches have been proposed by Epstein and Forcinito 14 and Raible et al…”