No abstract available

[en] In the probabilistic context of structural safety, it is commonly accepted that, in order to judge the adequacy of a structure to sustain an assigned set of loads, the strength of the structure be described as a random variable, and that the significant parameter is the probability of failure. The paper deals with the problem to calculate as small as possible upper bounds on the collapse probability of a perfectly plastic isotropic supported plate subject to uniform loading. (Auth.)

[en] The aim of the present paper is to show on the basis of equations and the analysis of creep mechanisms the possibilities of a description of the creep behavior of material under variable temperature and loading conditions. Also the influence of cyclic proportional loading and temperature gradient upon the rupture life and strains of a thick cylinder is investigated in detail. The obtained theoretical creep curves coincide with the experimental results for investigated steel in the temperature range from 500⁰C to 575⁰C. The constitutive equations together with the functions determined previously are applied to solve the problem of thick cylinder subjected to cyclic proportional pressure and temperature gradient. Numerical results for the thick steel cylinder are presented both in diagrammatical and tabular form. The obtained new results clearly show the significant influence of temperature gradient, cyclic temperature gradient, and cyclic pressure upon the stress redistribution, the magnitude of deformation, the propagation of the front damage and the rupture life. It was found that small temperature fluctuations at elevated temperature can shorten the rupture life very considerably. The introduced description of the creep rupture behavior of material under variable temperature and loading conditions together with the results for the thick cylinder indicate the possibilities of solutions of practical problems encountered in structural mechanics of reactor technology

[en] A simple model of the cyclic behaviour of materials and structures where hardening and creep have to be considered is given. In order to help in understanding it, the full analysis of an elementary example is first given. Then its generalisation and its practical use for any structure is explained. (author)

[en] The WHAMS-2D and WHAMS-3D codes were used to analyze the dynamic response of the RAS/TREAT shielded shipping cask subjected to transient leadings for the purpose of assessing potential damage to the various components that comprise the the cask. The paper describes how these codes can be used to provide and intermediate level of detail between full three-dimensional finite element calculations and hand calculations which are cost effective for design purposes. Three free drops were adressed: (1) a thirty foot axial drop on either end; (2) a thirty foot oblique angle drop with the cask having several different orientations from the vertical with impact on the cask corner; and (3) a thirty foot side drop with simultaneous impact on the lifting trunnion and the bottom end. Results are presented for two models of the side and oblique angle drops; one model includes only the mass of the lapped sleeves of depleted uranium (DU) while the other includes the mass and stiffness of the DU. The results of the end drop analyses are given for models with and without imperfections in the cask. Comparison of the analysis to hand calculations and simplified analyses are given. (orig.)

[en] Elastic follow-up (EFU) is a complex phenomenon which affects the behaviour of some structural components, especially in high temperature operations. One of the major problems encountered by the designer is the quantitative evaluation of the amount of elastic follow-up that must be taken into account for the structures under examination. In the present paper a review of the guidance furnished by the ASME Code regarding EFU is presented through an application concerning a structural problem in which EFU occurs. This has been carried out with the additional purpose of comparing the percentage EFU obtained by two simplified methods: an inelastic simplified method involving relaxation analysis; the reduced elastic modulus procedure generally used for EFU problems in piping systems. The results obtained demonstrate a substantial agreement between the two methodologies when applied to a general type structure. (author)

[en] A simplified method is proposed based on a cyclic elasto-plastic constitutive model of a metal for elasto-plastic analysis of mechanical structures under cyclic loading. The results from this method show a satisfactory consistency with those from detailed analyses by the elasto-plastic finite element method. (author)

[en] Simple expressions are proposed for predicting the notch stress and strain, by applying the concept of the state of small-scale and large-scale creep conditions with the path-independence of the J-integral. A simple equation is obtained, which predicts a stress concentration factor varying with time under the small-scale creep conditions from the elastic stress concentration factor K^*_t. An ordinary differential equation is derived for estimating the stress concentration factor under the small-scale to large-scale creep conditions. Expressions for a strain concentration factor are also proposed. The applicability of the proposed predictions is demonstrated using finite element calculations. (orig.)

[en] A combined experimental and numerical approach was used for viscoelastic analysis of polymeric materials. Relaxation tests were conducted at two different temperatures to determine a master curve of the tensile relaxation modulus of epoxy. By assuming the constant Poisson's ratio, Prony series representation of the tensile relaxation modulus was obtained and was used for viscoelastic finite element program. The specimen geometry selected for simulation was an edge-cracked bimaterial strip. Three different rates of bond-normal and bond-tangential displacements were chosen for the loading condition. Near-tip fracture parameters and the reactions along the edges were computed. The results showed very little differences in stress intensity factors and crack opening displacements in comparison with elastic solutions. The reactions, however, changed with time, which was different from the elasticity. (Author)

[en] With the radial and axial displacements and the angle of rotation of the normal to the midsurface as the kinematic variables in the nodal circles, the properties of a finite element are derived on the basis of Kirchhoff's hypothesis. The deformation of the element is determined by seven generalized strains. For the dual generalized stresses the constitutive equations are derived by application of the local constitutive equations in sampling points. For the elastic behaviour they are taken to be two Gaussian integration points, while for the creep and plasticity properties a number of points along the normal in the middle section are used. Since in the case of creep and plasticity the variation of the state of stress over the thickness is history dependent, only one section is considered, thus limiting the number local stresses, that have to be stored in the course of a loading program. A strategy of solution is discussed that is robust and that will give qualitative insight, without undue emphasis on the representation of the local creep and plasticity model, which generally is also of a qualitative nature. (orig.)