Session: 04-09-01: Materials and Structures for Extreme Environments
Paper Number: 71743
Start Time: Monday, 11:35 AM
71743 - Generalized Study on Time-Dependent Creep Analysis of Functionally Graded Thick-Walled Cylinders Under Thermal and Mechanical Boundary Conditions
This study delineates with the time-dependent creep analysis of functionally graded thick-cylinders under various thermal and mechanical boundary conditions. Aerospace and energy production applications demand components to withstand high temperature, and demonstrate high strength at the same time. This can be achieved by designing advanced composites by utilizing special characteristics of different materials e.g. combining high strength of metals with high temperature resistance of ceramics. Coating of ceramic layers onto a metal surface leads high stress concentration due to abrupt transition of material properties at the interface, resulting in failures of the coating surfaces by cracking, spalling, delamination, etc. In order to mitigate these impairments, materials with smooth spatial gradient in properties, known as Functionally Graded Materials (FGM) were developed in the 1980s by Japanese scientists working on thermal shock in Space shuttles. The analytical studies are applicable only to limited cases, and cannot be used directly for quantitative evaluation in design and decision-making. This limitation can be overcome by moving towards advanced multiscale methods by unifying the creep behavior of FGMs at the microstructural level to the stress-strain response at the macroscale.
For ultimate multiscale time-dependent creep analysis firstly, exact thermoelastic stress, and iterative creep solutions for a heat-generating and rotating-cylindrical vessel made of functionally graded materials (FGM) with thermal and mechanical properties are proposed. Equations of equilibrium, compatibility, stress-strain, and strain-displacement relations are solved to obtain closed-form initial stress-strain solutions. Initial investigations revealed that material gradient indices have significant influences on thermoelastic stress profiles. For Creep analysis, Norton’s model is incorporated into rate forms of the above-mentioned equations to obtain time-dependent stress and strain results using an iterative method. Validity of our solutions are at first verified using finite element analysis, and numerical results found in the recent literature have been enhanced. Investigation of effects of material gradients reveals that radial variation of density and creep coefficient have significant effects on strains histories, while Young’s modulus and thermal property distributions only influence stress redistribution at an early stage of creep deformation.
Next, a more realistic model of introducing microscale creep effects into a macroscopic modeling is employed to investigate the creep behavior of functionally graded hollow cylinders. Finite element (FE) simulations are employed to evaluate the position-dependent parameters associated with creep constitutive law at the microscale. A macroscopic FE model solves the non-linear boundary value problem to determine the time-varying creep stresses and strains. The framework proposed is capable of predicting the creep response of functionally graded pressure vessels based on the constitutive behavior of the creeping matrix, and volume fraction profile. Effective creep properties have been computed using three different micromechanical models and the homogenized creep response and its effect on the macroscopic behavior are compared. Considering the computational expenses associated with the large 3D- finite element models; the simple 2D- axisymmetric model is able to “closely capture” the creep behavior in such multiscale methods. Finally, a multi-objective particle swarm optimization algorithm is implemented to minimize the initial stress and final creep strain of functionally graded cylinder subjected to mechanical and thermal loads.
This study presents a multiscale framework to predict and implement local creep behavior of the FGM in the macro body to obtain numerical solutions for FGM cylinders. This research expected to enhance significantly the current ability to incorporate creep deformations into the design of FG thick-cylinders, which are potential structural components operating under severe/extreme conditions. The models are beneficial to investigate the choice of material combinations and heterogeneity profiles, thereby reducing cost of materials, fabrication, testing associated with experimental trials. In addition, to bridge the gap between the micro and macro levels a practical model for the creep behavior of FG cylindrical vessels has been developed. In this research, modeling strategies and interesting results of the multiscale creep analysis of a FG thick-walled cylinder has been described.
Presenting Author: Jasem A. Ahmed Louisiana State University
Authors:
Jasem A. Ahmed Louisiana State UniversityM. A. Wahab Louisiana State University
Generalized Study on Time-Dependent Creep Analysis of Functionally Graded Thick-Walled Cylinders Under Thermal and Mechanical Boundary Conditions
Paper Type
Technical Paper Publication