Thermomechanical creep analysis of FGM thick cylindrical pressure vessels with variable thickness

In the present study, a theoretical solution for thermomechanical creep analysis of functionally graded (FG) thick cylindrical pressure vessel with variable thickness based on the first-order shear deformation theory (FSDT) and multilayer method (MLM) is presented. To the best of the researchers' knowledge, in the literature, there is no study carried out into FSDT and MLM for creep response of cylindrical pressure vessels with variable thickness under thermal and mechanical loadings. The vessel is subjected to a temperature gradient and nonuniform internal pressure. All mechanical and thermal properties except Poisson's ratio are assumed to vary along the thickness direction based on a power-law function. The thermomechanical creep response of the material is described by Norton's law. The virtual work principle is applied to extract the nonhomogeneous differential equations system with variable coefficients. Using the MLM, this differential equations system is converted into a system of differential equations with constant coefficients. These set of differential equations are solved analytically by applying boundary and continuity conditions between the layers. In order to verify the results of this study, the finite element method (FEM) has been used and according to the results, good agreement has been achieved. It can be concluded that the temperature gradient has significant influence on the creep responses of FG thick cylindrical pressure vessel

The effect of viscoelasticity on creep behavior of double-lap adhesively bonded joints

The effect of viscoelasticity of epoxy adhesive on creep behavior in the adhesive layer of a double-lap joint is studied in this paper. The joint is comprised of three elastic single isotropic adherend layers joined by an epoxy adhesive that is under shear loading. Prony series is used to modeling the relaxation modulus of epoxy adhesive. The differential equation is derived in Laplace domain, and numerical inversion from the Laplace domain to the time domain is achieved by the Fixed Talbot method. Results show that for an impulse load of 100N, maximum shear stress in the adhesive layer is reduced to 38% of its initial value after almost 12 days and 79% of its initial value over a very long time. The rate of increase in tensile load P has a direct effect on peak shear stress developed in the adhesive layer and holding P0 as a constant, increasing t p will lower the induced peak shear stress in the joint. Also, an increase in the thickness of the adhesive layer reduced the induced peak shear stress and strain in the joint

Time-dependent thermomechanical creep behavior of FGM thick hollow cylindrical shells under non-uniform internal pressure

In this paper, a theoretical solution for time-dependent thermo-elastic creep analysis of a functionally graded (FG) thick-walled cylinder based on the first-order shear deformation theory is presented. The cylinder is subjected to the non-uniform internal pressure and distributed temperature field due to steady-state heat conduction from inner to outer surface of the cylinder. Mechanical and thermal properties except Poisson's ratio are assumed to vary along the thickness direction based on a power function. The creep constitutive model is on the basis of the Norton's law. The effects of the temperature gradient and FG grading index on the creep stresses of the cylinder are investigated. A numerical solution using finite element method is also presented and good agreement was found. Although previous publications presented analytical solutions for creep analysis of thick-walled cylindrical pressure vessels under uniform pressure, to the best of the authors' knowledge, so far, no analytical solution has been provided for time-dependent creep analysis of FG cylinder under non-uniform internal pressure. The results of this study are applicable for designing optimum FG thick-walled cylinder

Time-dependent creep analysis for life assessment of cylindrical vessels using first order shear deformation theory

In the present study, assuming that the thermo-elastic creep response of the material is governed by Norton's law, an analytical solution has been developed for the purpose of time-dependent creep response for isotropic thick-walled cylindrical pressure vessels. To study the creep response, the first-order shear deformation theory (FSDT) is applied. To the best of the researchers' knowledge, in the literature, there is no study carried out into FSDT for time-dependent creep response of cylindrical pressure vessels. The novelty of the present work is that it seeks to investigate creep life of the vessels made of 304L austenitic stainless steel (304L SS) using Larson-Miller Parameter (LMP) based on FSDT. Using this analytical solution, stress rates are calculated followed by an iterative method using initial thermo-elastic stresses at zero time. When the stress rates are known, the stresses at any time are obtained and then using LMP, creep life of the vessels are investigated. The Problem is also solved, using the finite element method (FEM), the result of which are compared with those of the analytical solution and good agreement was found. It is found that the temperature gradient distribution has significant influence on the creep life of the cylinder, so that the maximum creep life is located at the outer surface of the cylinder where the minimum value of temperature is located

Creep damage and life assessment of thick cylindrical pressure vessels with variable thickness made of 304L austenitic stainless steel

Using first-order shear deformation theory (FSDT), a semi-analytical solution is employed to analyze creep damage and remaining life assessment of 304L austenitic stainless steel thick (304L ASS) cylindrical pressure vessels with variable thickness subjected to the temperature gradient and internal non-uniform pressure. Damages are obtained in thick cylinder using Robinson’s linear life fraction damage rule, and time to rupture and remaining life assessment is determined by Larson-Miller Parameter (LMP). The thermo-elastic creep response of the material is described by Norton’s law. The novelty of the present work is that it seeks to investigate creep damage and life assessment of the vessels with variable thickness made of 304L ASS using LMP based on first-order shear deformation theory. A numerical solution using finite element method (FEM) is also presented and good agreement is found. It is shown that temperature gradient and non-uniform pressure have significant influences on the creep damages and remaining life of the vessel

Stick-slip analysis in vibrating two-layer beams with frictional interface

This paper attempts to present a new analysis for dynamical behavior of two-layer beams with frictional interface which held together in a pressurized environment, including stick-slip nonlinear phenomenon. To achieve a proper outlook of two-layer beam structures behavior, it is essential to realize the mechanisms of motion precisely. Coupled equation of transversal and longitudinal vibration of two-layers in the presence of dry friction is derived and nondimensionalized. Furthermore, free and forced vibration of the mentioned system is investigated and the system dynamics is monitored via Poincare maps and Lyapunov exponent analysis. A comparative study with ANSYS is developed to show the accuracy of the proposed approach

Theoretical modeling of low-attenuation lamb wave modes generation in three-layer adhesive joints using angle beam transducer

AbstractIn this paper, at first the attenuation of Lamb waves in three-layer adhesive joints, including two elastic plates bonded together by a viscoelastic adhesive layer, is investigated using Global matrix method and then suitable incidence angle is theoretically calculated to generate low-attenuation Lamb waves using angle beam transducer. Theoretical boundary value problem in three-layer adhesive joints with perfect bond and traction-free boundary conditions on their outer surfaces is solved to find a combination of frequencies and modes with lowest attenuation. Characteristic equation is derived by applying continuity and boundary conditions in three-layer joints using Global matrix method. Phase velocity dispersion curves and attenuation intensity plot in high and low frequencies are obtained with numerical solution of this equation by a computer code for a three-layer joint, including an aluminum repair patch bonded to the aircraft aluminum skin by a layer of viscoelastic epoxy adhesive. To validate the numerical solution results of characteristic equation, wave structure curves are plotted for a special mode in two different frequencies in the adhesive joint. Also, transducer incidence angle is calculated in terms of frequency for different modes using theoretical method to generate Lamb wave modes with low attenuation level by angle beam transducer. These modes are recognizable by transducers in inspections with Lamb waves because of low attenuation level