[en] Highlights: • An analytical model is developed based on the maximum entropy production principle. • The model is self-consistent and complete without assuming the response of system. • The model can directly predict the steady state of continuous drive friction welding. • The accuracy and universality of the model are confirmed by the experiment results. -- Abstract: An analytical model was developed based on the thermodynamic theory of Onsager-Ziegler maximum entropy production principle (OZ-MEPP) and the relevant dynamic laws, and used for characterizing the steady-state system of the severe plastic deformation (SPD) produced by continuous drive friction welding (CDFW) without any pre-assumed or measured response parameters. The accuracy and universality of the model were verified by the CDFW experiments of eight kinds of alloys, the results of which indicated that the model could precisely predict the temperature, axial shortening rate, welding power. Moreover, the coefficient of friction, traditionally regarded as an empirical parameter, could be forecasted too.

[en] Highlights: • A parametric reduced order modeling-based discrete velocity method is developed for simulation of steady rarefied flows. • The reduced-order basis for the target parameter value is constructed from the pre-computed bases by interpolation method. • The reduced discrete velocity space and its connection to the original discrete velocity space are established by DEIM. • A marked improvement in computational efficiency and memory load with respect to the full DVM is achieved. In this work, a parametric reduced order modeling-based discrete velocity method (PROM-DVM) is developed for simulation of steady rarefied flows. This method aims to reduce the number of discrete velocity points so as to improve the computational efficiency of DVM. For solving similar problems with different initial parameters, the developed method can generate a sought-after reduced discrete velocity space for the target parameter value from some pre-computed cases and solve the Boltzmann equation directly in the reduced discrete velocity space. At first, the singular-value decomposition (SVD) method is used to find the reduced-order bases for the cases of pre-computed parameter values and the reduced-order basis for the target parameter value is then constructed from the pre-computed bases by the interpolation method based on the Grassmann manifold and its tangent space. The reduced discrete velocity space and its connection to the original discrete velocity space are further established by the discrete empirical interpolation method (DEIM) based on the interpolated reduced-order basis. Since most points in the original discrete velocity space which are of negligible importance are removed in the computation of the present method, a marked improvement in computational efficiency with respect to the DVM in the original discrete velocity space is achieved. Numerical results show that the PROM-DVM can reach 13 times speed-up in CPU time for lid-driven cavity flow.

[en] In this study, the refractory high entropy alloy Al₅(TiZrHfNb)₉₅ was diffusion bonded (DB) with the intermetallic compound (IMC) Ti₂AlNb under 5 MPa at 970–1100 °C in vacuum. The microstructure and element distribution were analyzed using a scanning electron microscope (SEM) and mechanical properties were evaluated by nanoindentation and shear tests. The typical microstructure of DB joint was Ti₂AlNb substrate/solid solution/scattered Al3Zr5/solid solution/Al₅(TiZrHfNb)₉₅ substrate, which the discrete brittle Al₃Zr₅ phase was arranged along a straight line in the bonding surface, and gradually elongated and dissolved as the bonding temperature increased from 970 °C to 1100 °C. The formation of Al₃Zr₅ was attributed to the lowest Gibbs energy of all the possible IMCs in the range of the welding temperature. In the joining region, the IMC Al₃Zr₅ had the highest hardness (9.01 GPa) and modulus (143.37 GPa) but the lowest elastic recovery (20.37%), thus, it tended to cause stress concentration at the phase interface and induced crack initiation, which had a detrimental effect on the shear strength of joints. The shear strength of DB joints improved with the increase of bonding temperature and reached the highest (427 MPa) at 1100 °C owing to is lowest Al₃Zr₅ content. As the bonding temperature increased, the fracture of the joint transformed from intergranular brittle to ductile.

[en] The multi-band observation, from radio to gamma-ray, plays a crucial role in constraining the emission physics and geometrical magnetospheric models of the pulsars. In this paper, We use three-dimensional magnetospheric model, with the joint of the annular gap (AG) and core gap (CG) model, to simulate the radio and gamma-ray light curves for two representative pulsars, a millisecond pulsar J2302+4442 and a young pulsar J0659+1414. It is found that for PSR J2302 + 4442, the simulated magnetic inclination angle α and viewing angle ζ are ${34}^{\circ }$ and ${46}^{\circ }$, and for PSR J0659 + 1414 are ${45}^{\circ }$ and ${33}^{\circ }$. This implies that the radio and gamma-ray pulse emission originates from different magnetospheric regions and the radiation geometry for millisecond and young pulsar is different. The studies show that the joint of the AG and CG model can describe the light curves not only for millisecond pulsars but also for young pulsars, and hence it can be used to explain the multi-wavelength observations of pulsars.