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We present a dynamic theoretical viscoplastic model of voids subjected to external dynamic tensile loadings. The material viscosity and temperature are factors that are considered in the dynamic evolution of voids in viscoplastic materials. We focus on the thermal effect; the temperature affects the thermal softening of the material strength and also the material viscosity. Viscous flow is the dominant growth mechanism under high stresses and rates based on the results of the calculations for dynamic void growth predictions. The factors are independently studied, and the correlations are systematically analyzed. [ABSTRACT FROM AUTHOR]

Surface effect, inertia and thermal softening are important factors affecting the elasto-plastic evolution of voids. In this study, we theoretically examine the dynamic evolution of a nano-void in an elasto-plastic medium, particularly focusing on influences of surface energy, inertia and thermal softening. A two-stage strategy of analyzing surface effect is adopted, i.e. the first stage which is a quasi-static stage from a fictitious stress-free configuration to the actual initial configuration, and the second one which is the dynamic process of deformation under both surface stress and external dynamic loadings. The void will grow dynamically and quickly under high external loading, and the accelerations of material points in the neighborhood of the void are extremely high, resulting in a profound inertia effect. Under impact-like loading conditions, the plastic work done during the elasto-plastic growing process of the void is mainly transformed into heat, leading to thermal softening of material. Furthermore, heat transfer can be well neglected due to the transient characteristic of the problem studied. Tendencies related to all above influence factors are systematically analyzed. [ABSTRACT FROM AUTHOR]

Using the classical molecular dynamic method, we investigated the evolution of spall damage through a series of stretching simulations for solid–liquid mixed aluminum at several initial temperatures. The results show that a turning point appears before void nucleation when the initial temperature is higher than 940 K in mixed Al at a strain rate of 3 × 108 s−1. The formation mechanism of the turning point is due to the local liquid phase nucleation. The growth of the local liquid phase gradually destroys the consecutive solid phases. The lower tensile strength of liquid Al than solid Al leads to the formation of the turning point. The voids tend to nucleate in the liquid phase in mixed Al at different initial temperatures except at 940 K. The time of void nucleation will be delayed due to the melting process before void nucleation in mixed Al. A nucleation and growth (NAG) model can describe the nucleation and growth of voids very well in mixed Al at 900, 920, 960, and 980 K. By adding the criterion of liquid phase proportion, the NAG model can also well describe the void volume fraction history of mixed Al at 940 K. We clarified the micro-mechanisms of spall damage evolution in mixed Al through tension simulation. The relevant results can provide a reference for future work on spall damage studies in solid–liquid mixed metals. [ABSTRACT FROM AUTHOR]

Researchers in cryogenic magnetic refrigeration have never stopped pursuing magnetic refrigerants with lower ordering temperatures and larger magnetocaloric effects. Rare earth borates have been found to be potential cryogenic magnetocaloric materials due to their low phase transition temperatures and considerable magnetic entropy changes. Here, two rare earth borates RE8.66(BO3)2(B2O5)O8 (RE = Er, Tm) were successfully fabricated, and the crystallographic and magnetic parameters as well as cryogenic magnetocaloric effects were systematically evaluated. The compounds are deemed to crystalize in a monoclinic structure belonging to space group C2/m. They are both second-order phase transition materials without any long-range order above 2 K. These monoclinic rare earth borates, especially for Er8.66(BO3)2(B2O5)O8, show more considerable low-field magnetocaloric effects than rare earth orthoborates. For ΔH = 1 and 2 T, the values of −Δ S M max are 5.1 and 11.2 J/(kg K) for Er8.66(BO3)2(B2O5)O8, 3.0 and 5.3 J/(kg K) for Tm8.66(BO3)2(B2O5)O8, respectively. Therefore, they are regarded as potential candidates for cryogenic magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In order to reduce the beam impedance and refrigeration power dramatically, we have designed a high temperature superconductor (HTS) coated beam screen to screen the cold chamber walls of the super proton-proton collider bending magnets from beam-induced heat loads. It employs an absorber, inspired by the future circular collider studies, to absorb the immense synchrotron radiation power of 12.8 W/m emitted from the 37.5 TeV proton beams. Such a structure has the advantage of decreasing the electron cloud effect and improving the beam vacuum. We have compared the critical magnetic field and current density and accessibility of two potential HTS materials for the beam screen, TlBa2Ca2Cu3O9−δ (Tl-1223) and Yttrium Barium Copper Oxide (YBCO) and finally chose YBCO for coating. The beam screen is tentatively designed to work at 55-70 K because of the limited development of the YBCO material. The thermal analysis with oxygen cooling fluid indicates that the YBCO conductor can maintain its superconductivity even if the synchrotron radiation hits the YBCO-coated surface and the mechanical analysis shows that the structure has the ability to resist the Lorenz force during magnet quenches. [ABSTRACT FROM AUTHOR]

In order to reduce the beam impedance and refrigeration power dramatically, we have designed a high temperature superconductor (HTS) coated beam screen to screen the cold chamber walls of the super proton-proton collider bending magnets from beam-induced heat loads. It employs an absorber, inspired by the future circular collider studies, to absorb the immense synchrotron radiation power of 12.8 W/m emitted from the 37.5 TeV proton beams. Such a structure has the advantage of decreasing the electron cloud effect and improving the beam vacuum. We have compared the critical magnetic field and current density and accessibility of two potential HTS materials for the beam screen, TlBa2Ca2Cu3O9−δ (Tl-1223) and Yttrium Barium Copper Oxide (YBCO) and finally chose YBCO for coating. The beam screen is tentatively designed to work at 55-70 K because of the limited development of the YBCO material. The thermal analysis with oxygen cooling fluid indicates that the YBCO conductor can maintain its superconductivity even if the synchrotron radiation hits the YBCO-coated surface and the mechanical analysis shows that the structure has the ability to resist the Lorenz force during magnet quenches. [ABSTRACT FROM AUTHOR]