Results 1 - 10 of 485
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[en] The effect of quenched disorder on the underdamped motion of a periodically driven particle on a ratchet potential is studied. As a consequence of disorder, current reversal and chaotic diffusion may take place on regular trajectories. On the other hand, on some chaotic trajectories disorder induces regular motion. A localization effect similar to the Golosov phenomenon sets in whenever a disorder threshold that depends on the mass of the particle is reached. Possible applications of the localization phenomenon are discussed
[en] From the practical point of view, the classical elastic shakedown methods are not very useful for design, since in most components the stresses can safely exceed the elastic limit locally. This paper generalizes the static shakedown theorem (Melan's theorem) to allow the analysis of plastic shakedown. Since the method is derived from a lower bound formulation in shakedown, it is very useful for the design purposes (safe). The ratchet boundary is analytically determined using the proposed method for several examples with uniform stress distributions. The numerical implementation of the method along with several examples is discussed in an accompanying paper.
[en] This report is a draft of an enactment of KEPIC MNH based on 2007 ASME Boiler and Pressure Vessel Code, Section III, Division 1 Subsection NH for Class 1 Components in Elevated Temperature Service and contains of ASME Article NH-3000 design, the mandatory appendix I-14, and non-mandatory appendices T and X
[en] This study discusses an experimental investigation of the effect of the mean moment on the response and collapse of sharp-notched circular tubes subjected to cyclic bending. To highlight the influence of the mean moment effect, five different moment ratios r (minimum moment / maximum moment) were experimentally investigated. We found that the moment-curvature loop gradually shrinks, and stabilizes after a few cycles for r = -1. However, the moment-curvature loop exhibits ratcheting and increases with the number of cycles for r ≠ -1. In addition, the ovalization-curvature curve shows unsymmetrical, ratcheting and increasing manner with the number of cycles for any r. Finally, the empirical formulation proposed by Chang et al. was modified to simulate the relationship between the controlled moment range and the number of cycles necessary to produce buckling. The results of the experimental investigation and the simulation were in good agreement with each other.
[en] Thermal ratcheting tests are carried out to simulate the thermal cycling due to free level variations as in the main vessel of pool type nuclear reactors. The tests were performed at two different temperatures to capture the shakedown and ratcheting behavior of cylindrical specimens of SS 316 L. The ratcheting behavior is numerically predicted using Armstrong-Fredrick (AF) and Chaboche three back stress (CH3) rule. The ratcheting predictions using CH3 rule demonstrates its capability of capturing non saturating behavior aptly. Further, the thermal ratcheting with thermo-mechanical interaction is studied numerically by subjecting the cylinder to a traveling temperature front with the concurrent change in peak temperature. The analysis demonstrates the pronounced influence of thermo-mechanical interaction on the deformation mode of expansion and contraction of the cylinder during thermal ratcheting. (author)
[en] This article is concerned with a review of the literature on shakedown problems of complex structures according to various hardening rules. Although many hardening rules have been developed, shakedown analyses for hardening materials in the literature are limited to the simple kinematic hardening rules of Prager and Armstrong-Frederick. In other words, much more advanced hardening rules may not be vital to decide whether a structure will shakedown or not. Results of shakedown analyses for some complex structures are included
[en] The ITER Torus Cryo-Pump Housing (TCPH) is a penetration located on the Cryostat cylinder with main functions to accommodate and support the Torus Cryo-Pump (TCP), connect it to the Vacuum Vessel and provide tritium confinement and primary vacuum boundary. TCPH consist of inner cylinder to support cryopump and tritium confinement whereas the outer rectangular box structure provides Re-generation volume for TCP. They are interconnected through vertical ribs for providing stiffness and transferring load of cryopump to the Cryostat. This poster shows the structural integrity assessment of TCPH based on ASME Section VIII Div. 2 Part 5 for Protection against Plastic Collapse, Local Failure, Ratcheting, Buckling and Fatigue
[en] In this paper, an investigation of various inelastic ratcheting constitutive models for a GEN-IV reactor structural design subjected to elevated temperature operations is carried out. For a inelastic analysis of a ratcheting strain, various nonlinear kinematic hardening models such as the Prager Model, Armstrong and Frederick Model, Chaboche Model, Chaboche Model with a Threshold, and Ohno and Wang Model are investigated. To carry out the simulations for all the models, the computer program PARA-ID code is developed. This code implements the radial return algorithm to simulate the cyclic behavior for each model with extracted plastic modulus
[en] Strain is an important factor in evaluating structure integrity. It is primarily measured using contact type methods such as an electric resistance strain gage. However, an electric resistance strain gage is sensitive to the external environment. Moreover, it cannot be relocated or reused, and it has a limited measurement range. Therefore, measuring a large strain is difficult. Therefore, a method for measuring the strain from a remote distance, without attaching any sensor, is required. In this study, the ratcheting strain was measured efficiently by using the image signal. The ratcheting strain of the steel pipe elbow was measured using the image signal. The accumulative strain is expected to be of use when estimating the failure criteria. In addition, by using the image signal, the ratcheting strain at a remote distance can be measured without the installation of a conventional sensor.
[en] A fine modelling of the material' behaviour can be necessary to study the mechanical strength of nuclear power plant' components under cyclic loads. Ratchetting is one of the last phenomena for which numerical models have to be improved. We discuss in this paper on use of radial evanescence remain term in kinematic hardening to improve the description of ratchetting in biaxial loading tests. It's well known that Chaboche elastoplastic model with two non linear kinematic hardening variables initially proposed by Armstrong and Frederick, usually over-predicts accumulation of ratchetting strain. Burlet and Cailletaud proposed in 1987 a non linear kinematic rule with a radial evanescence remain term. The two models lead to identical formulation for proportional loadings. In the case of a biaxial loading test (primary+secondary loading), Burlet and Cailletaud model leads to accommodation, when Chaboche one's leads to ratchetting with a constant increment of strain. So we can have an under-estimate with the first model and an over-estimate with the second. An easy method to improve the description of ratchetting is to combine the two kinematic rules. Such an idea is already used by Delobelle in his model. With analytical results in the case of tension-torsion tests, we show in a first part of the paper, the interest of radial evanescence remain term in the non linear kinematic rule to describe ratchetting: we give the conditions to get adaptation, accommodation or ratchetting and the value of the strain increment in the last case. In the second part of the paper, we propose to modify the elastoplastic Chaboche model by coupling the two types of hardening by means of two scalar parameters which can be identified independently on biaxial loading tests. Identification of these two parameters returns to speculate on the directions of strain in order to adjust the ratchetting to experimental observations. We use the experimental results on the austenitic steel 316L at room temperature to study the new model capabilities. We get a good modelling of ratchetting in biaxial loadings. (author). 4 refs., 5 figs