DMMCTE - NSM - Comunicaciones en Congresos y otros eventos

Permanent URI for this collection


Recent Submissions

Now showing 1 - 2 of 2
  • Publication
    Assessment of residual stresses in ITER CS helium inlet welds fatigue tested at cryogenic temperature
    (IOP Publishing Ltd., 2019-06) Sgobba, Stefano; Avilés Santillana, Ignacio; Langeslag, Stefanie A. E.; Fernández Pisón, María del Pilar; Castillo Rivero, S.; Libeyre, P.; Jong, C.; Everitt, D.; Freudenberg, K.
    The ITER Central Solenoid (CS) consists of six independent wound modules. The cooling of the cable-in-conduit conductor is assured by a forced flow of supercritical He at 4.5 K supplied by He inlets located at the innermost radius of the coil. The inlets consist of a racetrack-shaped boss welded to the outer conduit wall through a full penetration Tungsten Inert Gas (TIG) weld. They are critical structural elements submitted to severe cyclic stresses due to the electro-magnetic forces acting on the coils. The weld contour is shape-optimised and locally processed by Ultrasonic Shot Peening (USP), conferring large compressive residual stresses on a subsurface layer of several millimetres thickness to improve fatigue strength. The distribution of the residual stresses and the effect of USP on microstructure and mechanical properties is assessed, with reference to the results of a cryogenic fatigue test campaign, performed on peened and as-welded inlets for comparison.
  • Publication
    Influence of unobservable overstress in a rate-independent inelastic loading curve on dynamic necking of a bar
    (Elsevier Ltd., 2018-01) Rubin, M. B.; Rodríguez-Martínez, José A.
    A nonlinear rate-independent overstress model with a smooth elastic-inelastic transition is used to analyze instabilities during dynamic necking of a bar. In the simplified model the elastic strain epsilone determines the value of stress and the hardening parameter kappa determines the onset of inelasticity. These quantities {epsilone, kappa} are obtained by integrating time evolution equations. The main and perhaps surprising result of this paper is that, based on the critical growth rate omegacr of a perturbation, two rate-independent materials with a smooth elastic-plastic transition due to overstress and nearly the same loading curve (elastic strain or stress versus total strain) can have different susceptibilities to tensile instabilities. Specifically, increase in overstress causes decreased material instability near the onset of the smooth elastic-inelastic transition and increased instability when the elastic strain approaches its saturated value. To the authors' knowledge, this new insight has not been reported in the literature.