Papers by Author: Xiao Ping Zhang

Abstract: Edge rolling in roughing area of continuous hot strip rolling is a basic method of controlling slab width. Edge rolling will induce dog-bone, width loss and fish tail at head and tail ends of slabs in unsteady deformation zone. A 3D elastic-plastic FEM model for roughing stage of continuous hot strip rolling was established and research on the influences of those technical parameters such as slab width, thickness and reduction of edging roll on unsteady deformation of metal was carried out. The research work provides a scientific basis for the optimization of edge rolling schedule.

Abstract: Monel K-500 alloy is an important nickel-based corrosion resistant material with excellent corrosion resistant ability in various corrosion circumstances (include electrochemical and chemical corrosion) and good mechanical properties. However, Monel K-500 alloy is also a sensitive material to high temperature. Hot working process has significant effect on its working character and quality. In view of existing problems in domestic manufacturing enterprises, some experiments were carried out in different working temperature, deformation degree and strain rate to investigate the performance of Monel K-500 alloy in hot working process. The research results show that moderate temperature, higher strain rate and deformation degree will be favorable to improve crystal structure and mechanical property of Monel K-500 Alloy.

Abstract: Monel K-500 alloy is an important nickel-based corrosion resistant material with increasingly wide range of application in the areas of aviation, navigation and petroleum engineering. Comparing to other corrosion resistant metal material and nonmetal material, Monel K-500 alloy has excellent corrosion resistant ability in different corrosion circumstances (include electrochemical and chemical corrosion) and good mechanical properties. However, Monel K-500 alloy is also a sensitive material to high temperature. Its heating schedule has significant effect on heating quality and subsequent hot-working character. In view of existing heating problems of Monel K-500 alloy such as over-burning or non-uniform heating in domestic manufacturing enterprises, different heating velocities have been used to investigate its performance in heating process. The research results can provide more scientific basis for the setting up of reasonable heating schedule.

Abstract: Due to the coupled function of shape and gauge control in rolling process, mutual effects must be considered when shape control or gauge control is carried out. Traditional shape and gauge control theories are of independent and the control systems are also separated, so it is difficult to ensure the quality of shape and gauge simultaneously. Based on the updated shape theory and a single parameter model of load distribution method, a combined shape and gauge control method was developed, which can adjust rolling regulations on-line according to the deviation of strip crown measured at the exit of the rolling mill. The method can ensure gauge precision while strip crown is adjusted and the purpose of combined shape and gauge control is reached.

Abstract: Bar straightening is an important work before the bar is applied as qualified products. In this paper, the mechanics of the straightening process is analyzed in detail on the base of conjugate quadric theory. A simulation program is developed with the investigation of straightening process as well. The equations, which describe roll contour curve and the longitudinal section, are given and simulated in computer. And a brief method of designing and drawing the straightening roll contour curve is introduced.

Abstract: Asymmetrical rolling is usually used on some special rolling produce. It offers lower rolling pressure, more reduction and better crystallographic textures. In recent years asymmetrical rolling has become more important due to realization of improved properties of the strip. In this paper, a elasto-plastic finite element method code has been developed to simulate the asymmetrical rolling of strip, considering unequal roll radii, unequal speed ratio between the upper roll and lower roll, different exit thickness and different reduction. Meanwhile, The profile, crown and edge drop of strip, as well distribution of front tensile stress were discussed in different rolling process. It makes better preset values for the online control system and good results was obtained.

Abstract: Thermal fatigue performance and creep resistance of soldered connections are crucial to the integrity and reliability of microelectronics, optoelectronics and photonics packaging systems. In this work, creep and thermal fatigue behaviours of lap shear joints soldered by a tin-based nanocomposite solder were characterized at different temperatures, with a comparison to a traditional Sn60Pb40 solder. The results show that the nano-composite solder has much better creep resistance and thermal creep fatigue property than the Sn60Pb40 solder. This is mainly due to the uniformly dispersed nano-sized Ag particles that have provided effective impediment to dislocation movement and grain boundary sliding, in addition to the alloying effect. The creep fractography analysis by SEM shows that a progressive shear deformation occurred as the main creep fracture mechanism. Sn60Pb solder joints deform dominantly by transgranular sliding, while the nano-composite solder joints creep by intergranular mechanism through grain boundary sliding and voids growth.

Abstract: How a crack initiates from the smooth surface of single crystals subjected to uniaxial cyclic loading is unclear. Experiments were conducted to observe in detail the dislocation microstructures during the saturation stage of cyclic deformation in a copper single crystal using scanning electron microscopy and the electron channeling contrast (SEM–ECC) technique. Some dark zones were found in the dislocation microstructures, which were located either at the edge region of the specimen or within the persistent slip bands (PSBs) at the matrix/PSB interfaces. Hence, fatigue cracks will initiate at these sites with high stress concentrations, i.e., the dark zones. Also, dislocation dynamics (DD) simulation was adopted to calculate internal stress distributions induced by dislocations, and finite element analysis (FEA) used to obtain stress distribution at the matrix/PSB interfaces and neighboring micro-regions caused by an externally applied load. Simulation results show that the external shear stresses distribute uniformly in all specimens; while near the free-surface regions, the maximum value of internal stresses not only occurs at interfaces between PSBs and dislocation matrix, but also at locations where these interfaces cross the freesurface. Consequently, the interfaces are most probable sites for nucleated cracks. Finally, the simulation results agree well with experimental observations.