Thermo-visco-elasto-plastic modeling of composite shells based on mechanics of structure genome
Creators: name: Long, Yufei
Publisher: name: Purdue University Graduate School
Year: 2021
Subjects: Aerospace structures
Structural engineering

description: Being a widely used structure, composite shells have been studied for a long time. The features of small thickness, heterogeneity, and anisotropy of composite shells have created many challenges for analyzing them. A number of theories have been developed for modeling composite shells, while they are either not practical for engineering use, or rely on assumptions that do not always hold. Consequently, a better theory is needed, especially for the application on challenging problems such as shells involving thermoelasticity, viscoelasticity, or viscoplasticity.<br><br>In this dissertation, a shell theory based on mechanics of structure genome (MSG), a unified theory for multiscale constitutive modeling, is developed. This theory is capable of handling fully anisotropy and complex heterogeneity, and because the derivation follows principle of minimum information loss (PMIL) and using the variational asymptotic method (VAM), high accuracy can be achieved. Both a linear version and a nonlinear version using Euler method combined with Newton-Raphson method are presented. This MSG-based shell theory is used for analyzing the curing process of composites, deployable structures made with thin-ply high strain composite (TP-HSC), and material nonlinear shell behaviors.<br><br>When using the MSG-based shell theory to simulate the curing process of composites, the formulation is written in an analytical form, with the effect of temperature change and degree of cure (DOC) included. In addition to an equivalent classical shell theory, a higher order model with the correction from initial geometry and transverse shear deformation is presented in the form of the Reissner-Mindlin model. Examples show that MSG-based shell theory can accurately capture the deformation caused by temperature change and cure shrinkage, while errors exist when recovering three-dimensional (3D) strain field. Besides, the influence of varying transverse shear stiffness needs to be further studied.<br><br>In order to analyze TP-HSC deployable structures, linear viscoelasticity behavior of composite shells is modeled. Then, column bending test (CBT), an experiment for testing the bending stiffness of thin panels under large bending deformation, is simulated with both quasi-elastic (QE) and direct integration (DI) implementation of viscoelastic shell properties. Comparisons of the test and analysis results show that the model is capable of predicting most of the measured trends. Residual curvature measured in the tests, but not predicted by the present model, suggests that viscoplasticity should be considered. A demonstrative study also shows the potential of material model calibration using the virtual CBT developed in this work. A deployable boom structure is also analyzed. The complete process of flattening, coiling, stowage, deployment and recovery is simulated with the viscoelastic shell model. Results show that major residual deformation happens in the hoop direction.<br><br>A nonlinear version of the MSG-based general purpose constitutive modeling code SwiftComp is developed. The nonlinear solving algorithm based on the combined Euler-Newton method is implemented into SwiftComp. For the convenience of implementing a nonlinear material model, the capability of using user material is also added. A viscoelastic material model and a continuum damage model is tested and shows excellent match when compared with Abaqus results with solid elements and UMAT. Further validation of the nonlinear SwiftComp is done with a nonlinear viscoelastic-viscoplastic model. The high computational cost is emphasized with a preliminary study with surrogate model.