[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] Highlights: • Due to pre-creep, ratcheting strain of cartilage increases, while its rate reduces. • Larger ratcheting strain occurs due to residual strain after creep-recovery. • Creep-ratcheting strain is greater in spite of short peak holding time. • Creep-ratcheting strain of cartilage is dependent on its depth. • Accumulated creep-ratcheting strains can accelerate cartilage's damage. -- Abstract: Since the accumulations of ratcheting strain combined with creep deformation, which are produced in normal activities, can accelerate the fatigue damage of cartilage in joint, the creep-ratcheting and creep-recovery-ratcheting behaviors of articular cartilage are experimentally investigated under creep-fatigue loads. The effect of pre-creep on ratcheting behavior of cartilage was probed firstly and it is found that the initial ratcheting strain of cartilage presents the larger value (30% and 35%) due to its pre-creep deformation in spite of the short pre-creep time applied. With the increasing pre-creep time the ratcheting strain of sample increases while the ratcheting strain rate decreases. The effects of pre-creep and recovery on ratcheting behavior of cartilage were also investigated and it is noted that the strain of cartilage increases fast at first, decreases partly and then changes periodically with cyclic stress. The ratcheting strain evolutions of different layers are not coincident for cartilage sample after the pre-creep or pre-creep-recovery and the ratcheting strains of different layers with pre-creep are larger than them with pre-creep-recovery. Finally the creep-ratcheting strain of cartilage with different peak-holding time during cyclic compression was studied and it is found that the creep-ratcheting strain with peak-holding time is significantly greater than that without peak-holding time. The creep-ratcheting strain increases with increase of peak-holding time or stress amplitude, while it reduces with rising of stress rate. The creep-ratcheting behavior of cartilage is dependent on its depth. These findings point out that the accumulated deformations, including creep deformation and ratcheting deformation, can accelerate the cartilage's damage.

[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] The influence of peak ratchetting stress on ratchetting deformation of this alloy is investigated based on uniaxial ratchetting tests of T225NG titanium alloy at room temperature. Results show that experimental relationships between ratchetting strain and peak ratchetting stress are a tuft of linear curves, and there is a ratchetting stress threshold with constant value, which determines whether ratchetting deformation occurs. A model used to describe evolution law of ratchetting strain for the alloy under uniaxial cyclic stressing has been presented. This model is easy to be built, and is suitable to engineering prediction of ratchetting deformation of the titanium alloy

No abstract available