Transient Stress Analysis Research Articles

Evaluation of premature failure of a gas turbine component

A case study of certain gas turbine stator vanes which fail prematurely is presented, with a view to determining whether operational procedure might have caused the failures. The engines had been operated from a ‘hot-and-high’ environment, and this could have contributed to the failures. Computational fluid dynamics (CFD) techniques were employed in order to obtain an accurate design point thermal history. The resulting convection boundary conditions were then interpolated over a finite element mesh. Transient thermal and stress analyses were performed. At the same time, microstructural analyses of the service-exposed material were carried out to estimate the maximum temperature seen by the component. These showed that higher than expected vane metal temperatures were experienced. Emphasis was placed on the procedures outlined in the USAF Engine Structural Integrity Program 1, since little detail was known about the actual engine operating histories.

Transient stress analysis during quench of MRI magnets

A quench simulation model is analyzed by means of control theory for optimal computational efficiency relative to a complex network of coupled shells. The authors describe the superconducting magnet configuration and the time domain aspects. They then discuss quench transient analysis and force transient analysis. The control theory analysis derived identifies an optimal computation efficiency for the numerically intense problem of 3D quench analysis with coupled circuits. This scheme of numerical time step integration has wider applicability. >

Transient and steady state thermal and stress analysis of an insertion device beam shutter at the Advanced Photon Source

This article describes a conceptual design of an ultrahigh vacuum beam shutter for an insertion device beamline at the Advanced Photon Source. Various aspects of the design such as geometry, cooling arrangement, and material selection are optimized based on thermal and stress finite element analysis. The goal of the optimization is to assure survivability while maintaining a reasonably compact physical size.

Analysis of Tempering Stresses in Bilayered Porcelain Discs

Previous studies of opaque-porcelain/body-porcelain discs have shown that compressive stresses which develop in the porcelain surface by being tempered in air can inhibit the sizes of cracks induced within the surface. The objective of this study was to develop a theoretical model for analysis of transient and residual stresses in opaque-porcelain/body-porcelain discs which were produced under variable cooling conditions. The model incorporates the effects of stress and structural relaxation. Transient and residual stresses were calculated for bilayered porcelain discs 16 mm in diameter and 2 mm in thickness for three opaque-porcelain/body-porcelain combinations. Transient temperature distributions in the discs for simulated convective cooling were calculated by finite-element analysis. Data from microhardness indentations reported by Anusavice et al. (1989) indicate that crack lengths measured for bilayered porcelain discs subjected to slow cooling conditions, for which the model predicted residual tensile stresses, were greater than those combinations for which residual compressive stresses were calculated. Calculated values of residual compressive stress for tempered specimens were considerably higher than those for specimens that were slowly cooled and those that were cooled by free convection. In general, residual stress levels calculated by use of the analytical model were in fairly good agreement with the trends observed for crack lengths and bi-axial flexural strengths reported by Anusavice and Hojjatie (1991). The results of the present study indicate that a visco-elastic model is a viable approach for determination of transient and residual stresses in opaque-porcelain/body-porcelain discs.

TRANSIENT THERMO-VISCOELASTIC RESPONSE OF A CRACK IN A LAYERED STRUCTURE

This article examines the application of a numerical method of transient stress analysis for the study of a crack located in a viscoelatic layer bonded to an elastic substrate. The layered structure containing the defect is subjected to heat conduction and associated thermo-viscoelastic effects. The finite-element technique is used to examine the time-dependent variation in the stress intensity factor at the crack tip due to a sudden reduction in the temperature at the surface of the layered structure. Numerical results presented in the article illustrates the influence of the thermo-viscoelastic coupling on the crack behavior.

Transient stress analysis of grooved and stepped shafts by time domain semi-analytical boundary element method

A formulation and numerical solution procedure for boundary integral equation using the semi-analytical method is given for the three-dimensional transient stress analysis of a grooved cylindrical shaft with arbitrary impact loads. In this method the fundamental solution of three-dimensional elastodynamics is directly used and the general three-dimensional problem is reduced to a one-dimensional numerical one using the semi-analytical technique at the stage of discretization of the boundary. Several numerical examples are presented for verification.

Modelling of low-temperature behaviour of cracks in asphalt pavement structures

This paper examines the transient stress analysis of a multilayer pavement structure subjected to heat conduction and associated thermoelastic effects by the cooling of its surface. In particular, the layered structure contains a transverse crack which can be created either during the construction of the pavement or during its service life. The numerical treatment of the transient stress analysis is achieved using a finite element scheme, which models the heat conduction and thermoelasticity of each component in the layered system and the singular stress field at the extremities of a crack. The numerical scheme is applied to examine the manner in which the propagation of an existing crack is influenced by the thermoelastic mismatch between the layers adjacent to the crack location. The analysis also illustrates the influence of the thermoelastic mismatch between a cracked pavement and an overlay, in the suppression of crack propagation. Key words: fracture mechanics, pavement structures, low-temperature fracture, transient thermal effects, finite element modelling, stress intensity factors.

Optimum design of rotational wheels under transient thermal and centrifugal loading.

Turbine rotors and compressor rotors are subject to centrifugal and thermal loads. These loads increase proportionally with tip speed and gas temperature. Additionally, rotor weight must be decreased to improve rotor dynamics and to restrict bearing load. Thus, an optimum design technique which offers the lightest possible wheel shape under the stress-limit restriction is required. This paper introduces an optimum design system developed for turbomachinery rotors, and discusses several applications. The sequential linear programming method is used in the optimizing process, and unsteady state thermal analyses of variable thickness wheels are performed using a numerical analysis of a multiring model. Centrifugal and thermal stress analyses of these wheels are performed using Donath's method with the same multiring model. This optimum design program is applied to the design of axial flow compressor wheels. Finally, the validity of these applied results are confirmed by transient thermal and stress analyses using the finite element method.

Dynamic stress analysis of a class of geomechanics problems by the boundary element method

AbstractThis paper presents the application of an advanced BEM for periodic and transient dynamic stress analyses of a class of geomechanics problems. For transient dynamic analysis, the problem is first solved in the Laplace transform space, which happens to be similar to the periodic dynamic analysis, and then the time domain solution is obtained by numerical inversion of transform domain solutions. The numerical implementation of the BEM used to present the results in this paper is complete and most general available to date. It is capable of treating very large, multi‐layered problems by substructuring and satisfying the equilibrium and compatibilities at the interfaces. With the help of this substructuring, capability problems related to layered media and soil–structure interaction have been analysed. A number of examples are presented and through comparisons with available analytical and numerical results, the applicability and usefulness of the present analysis to real geomechanical problems are established.

Natural Frequencies and Transient Responses of 3-Phase Rotating Machine Windings

The analysis of transient electrical stresses in the insulation of high voltage rotating machines is rendered difficult because of the existence of capacitive and inductive couplings between phases. The Published theories ignore many of the couplings between phases to obtain the solution. A new procedure is proposed here to determine the transient voltage distribution on rotating machine windings. All the significicant capacitive and inductive couplings between different sections in a phase and between different sections in different phases have been considered in this analysis. The experimental results show good correlation with those computed.

Transient stress analysis of high energy gas fracture experiments

The elastodynamic solution of a cylindrical hole whose edge is subjected to the action of a transient pulse load has been obtained in this report. This problem is of interest to the high energy gas fracture experiments to be conducted by Sandia National Laboratories at the Nevada Test Site. Laplace transform technique is used to present the result in integral forms. Numerical results have been obtained and are presented in graphical forms.

TRANS2A: An Unconditionally Stable Code for Thermal Transient Stress Analysis in Piping

A technique for numerical integration of the finite difference (matrix) formulation of the unsteady heat transfer equation has been applied to the thermal stress analysis requirements of ASME B&PV Section III, Article NB-3650. This technique, with its properties of unconditional solution stability, has been incorporated into a new computer program, TRANS2A, which has been designed totally around the needs of the stress analyst. To be of maximum aid to the analyst, in addition to the necessary output of thermal gradients (ΔT2 and ΔT2) and average temperatures (Ta and Tb), TRANS2A provides a complete set of thermal stress histories and tables of thermal stress extrema. Values of the thermal stresses are output at maxima of the thermal gradient terms (with or without adjacent sections), in addition to the extrema of the secondary and secondary plus peak stresses and time of occurrence. Each solution is performed for a set of seven general and three optional stress indices. The process allows a strict and simple data interface to the combined stress analaysis computation without excessive approximations. Data may also be stored so that sections need not require repeated analyses. All computational output, from the detailed heat transfer solution to the stress summaries, may be requested or deleted at the option of the analyst. For generality, TRANS2A includes a complete set of temperature-dependent material properties for all current piping materials and a complete set of fluid properties for water, steam, and sodium. Fluid transient data are input using phase and temperature, and a choice of four flow rate specifications. Accepted heat transfer correlations for laminar and turbulent flow in liquids and gases are included, with smoothing at two-phase excursions. Samples of the TRANS2A benchmark problems are included, with discussions on data interface and sensitivity for erratic fluid transients.

An algorithm for automatically tracking ablating boundaries

AbstractAn algorithm has been developed which automatically calculates the time‐dependent positions of points on the ablating boundaries of two‐dimensional continuum structures with geometrially complex shapes. The structural boundary may consist of ablating and non‐ablating parts. The initial ablating and non‐ablating boundaries are defined by the disjoint union of piecewise linear arcs passing through a finite set of nodal points on the boundary, each defined by a pair of rectangular Cartesian co‐ordinates. For a specified ablation rate, the algorithm calculates successive positions of the boundary points at times specifiec by the user. The algorithm is designed such that it may be easily incorporated, along with an automated mesh generation procedure, into existing finite element codes for transient thermal or stress analysis of structures with ablating boundaries. Two examples are presented from the field of solid rocket analysis.

Numerical study of dynamic crack growth by the finite element method

Recent developments in numerical techniques for dynamic transient stress analysis have ensured that realistic models can now be employed in crack propagation studies. In this paper transient dynamic finite element solutions are undertaken for both double cantilever beam (DCB) and pipeline problems with propagation of the crack being permitted. Standard parabolic isoparametric elements are employed for spatial discretization with an explicit (central difference) scheme being employed for time integration. Both critical stress and energy balance crack propagation criteria are considered.

Transient Thermoelastoplastic Stress Analysis for an Infinite Medium with a Spherical Cavity

Transient Thermoelastoplastic Stress Analysis for an Infinite Medium with a Spherical Cavity

Transient thermoelastoplastic stress analysis for a hollow sphere using the incremental theory of plasticity

An analysis based on the incremental strain theory is formulated for solving the problem of an elastoplastic hollow sphere subjected to a transient temperature distribution. Thermal and material properties are assumed to be temperature dependent and the behaviour of the medium to be characterized by the Ramberg-Osgood stress-strain relation. A method of successive elastic solutions is used to obtain a numerical solution. An illustrative example shows that the effective stress is not a monotonie function of the radius, but is much dependent on the history, gradient, and distribution of the temperature in the hollow sphere. In addition, unloading in the plastically deformed region is confirmed from the detailed discussion on the distribution of strains. As a result, the analysis based on the total strain theory is not permissible for solving this kind of elastoplastic problems subjected to transient thermal loading. In the following analysis the problem is treated in a quasi-static sense and the inertia terms in the thermoelastoplastic equations are neglected.

An analysis of transient stresses produced around cavities of arbitrary shape during the passage of travelling waves. 17F, 9R : Niwa, Y Kobayashi, S Azuma, N Mem. Fac. Engng, Kyoto Univ., V37, N1, Jan. 1975, P28–46

An analysis of transient stresses produced around cavities of arbitrary shape during the passage of travelling waves. 17F, 9R : Niwa, Y Kobayashi, S Azuma, N Mem. Fac. Engng, Kyoto Univ., V37, N1, Jan. 1975, P28–46

Sudden Twisting of a Penny-Shaped Crack

A transient stress analysis for the problem of a torque applied suddenly to the surface of a penny-shaped crack in an infinite elastic body is carried out. The singular solution is equivalent to that of the sudden appearance of a crack in a body under torsion. Using an integral transform technique developed for this class of transient problems, the dynamic stresses near the periphery of the crack are found to have the same angular distribution and inverse square root singularity as in the static case. This character of the local solution prevails for all time only in a toroidal region extremely close to the crack border. Within this region, the stress intensity is found to vary with time, reaching a peak greater than the static value and subsequently oscillating about that value with decreasing amplitude. The dynamic crack-opening displacement field is also given for any instant of time after loading.