Applied Mechanics and Materials Vols. 117-119

Abstract: In this study，tensional mechanical properties of sheet metal with different heating-lines after laser forming are investigated. The basic mechanical properties of material (such as elastic modulus, yield strength, ultimate strength, TEI (total elongation index) and EIU (elongation index of uniform)) with different spacing between neighbored heating-lines and different heating-lines number are presented. The stress-strain curves are complied with a modified Swift law, where the hardening coefficient and strain hardening exponent of material are controlled by strain. The influence of heating-lines number on tensional mechanical properties of material is greater than that of the spacing between neighbored heating-lines. The results show that all mechanical properties are related to the distribution of microstructure in heat-affected zone after laser forming.

Abstract: A coupled constitutive model of viscoplasticity and ductile damage for penetration problems has been deduced. The model proposed by Lemaitre was based on the continuum damage mechanics. In the model, large strain, high strain-rate, thermal softening and damage evolution were taken into account. At the meanwhile, Von Mises yield criterion, Johnson-Cook hardening model and Johnson-Cook fracture strain model were adopted. The model was implemented in the explicit finite element code Abaqus\Explicit through the Vumat subroutine by using an efficient explicit time integration algorithm. Based on the model, the rotating band’s engraving process was simulated, at the same time the influence of the stress state on damage evolution and the thermal softening effect was discussed. An effective way to simulate the fire process of gun was afforded.

Abstract: To study the fire performance of the profiled sheet-light aggregate concrete composite floor subjected to fire load, study of fire response and post-fire bearing capacity of a profiled sheet-lightweight aggregate concrete composite floor subjected to dead load is carried out. Based on the experimental results, the fire performance and post-fire bearing capacity of the floor after exposure to fire are analyzed. It is shown that the failure form of the profiled sheet-ceramsite concrete composite floor after exposure to fire still exhibits higher bearing capacity, and the ultimate value of the equivalent distributed load is up to 35kN/m², which may be used as basis of strengthening and repairing of the profiled sheet-lightweight aggregate concrete composite floor after exposure to fire.

Abstract: There is considerable industrial significance to understand the nature of subsurface deformation under the machined surface for correct prediction of surface properties in machined components based upon the machined conditions and material behaviors that give rise to them. In this study, high speed machining of Inconel 718 was carried with whisker reinforced ceramic cutting tool under different conditions of tool wear, coolant state and cutting parameters. The objective of the present investigation was to determine the effect of both cutting parameters and tool wear on the plastic deformation in the subsurface region of Inconel 718 after the finishing machining with above process conditions. The surface and subsurface region of machined specimens were examined using a high resolution scan electron microscope (HRSEM) and EBSD technique, microhardness measurements were also conducted on the test samples, accordingly plastic strain analysis were carried out.

Abstract: To study the superplasticity of AZ31B magnesium alloy, hot compression tests were performed in forming temperature range from 280°C to 440°C and strain rate range from 0.001s-1 to 0.1s-1. The influence of deformation strain rate and forming temperature on flow stress was also analyzed detailed. It was shown that the flow stress of AZ31B was very sensitive to formpng temperature and stain rate, and was decreased with deformation temperature increasing, and was increased with stain rate increasing. However, no significant change of flow stress was observed at the temperature of 440°C and the strain rate below 0.01s-1. The activation energy of AZ31B in superplastic deformation was 141.6KJ•mol-1 and its constitutive equation was established also.

Abstract: This study aims to clarify the breaking behavior during wedge shearing process of an aluminum worksheet that stacked on to an underlay sheet. One of the problems faced in wedge cutting process is the separation possibility and the quality sheared profile of worksheet, the lower underlay sheet was introduced. To study the breaking behavior of an aluminum sheet with flexible underlays, a 42°center bevel blade indentation test to a 0.39mm thickness aluminum stacked on to several flexible underlays conditions were carried out experimentally and numerically. For discussing the effect of the rigidity of underlay on the breaking behavior of worksheet, an elasto-plastic finite element analysis was applied to. The following were obtained: (i) the initial breaking of worksheet and the sheared profile depends on the underlay rigidity; (ii) the breaking propagation is started from the lower surface of worksheet and grows up to the upper side beneath the tip edge.

Abstract: A new porous nozzles for refining molten aluminum were made from mullite，graphite powder, red mud and sodium silicate. The relationships between graphite content and permeability, sintering parameters and permeability, graphite content and compressive strength were investigated, respectively. The internal structures of the nozzle before and after sintering were observed by SEM. The experimental results show that the permeability of sample can be improved by sintering at temperature of 1000°C for 2 hours. As graphite content increases, the permeability of sample increases, yet the ultimate compressive strength decreases. The compressive strength can be enhanced by using combination of different sizes of mullite particles.

Abstract: A Q550 high strength steel was selected at two different cooling rates through ultra-fast cooling process, and its microstructures and strengthening mechanisms were analyzed. The results show the bainite transformation temperature of the steel decreased with the increasing of cooling rate.The ultra-fast cooling process can improve the performance of Q550 compared with the conventional cooling process, and the yield strength, tensile strength and elongation are 600MPa, 755MPa and 19%, and - 20 °Cimpact energy is 253J, and good strength and toughness are obtained under ultra-fast cooling process. The microstructure of this steel is bainite and good strength and toughness are caused by the refinement of bainite and fine precipitates. Ultra-fast cooling technology improves the strength and toughness of this steel effectively.

Abstract: Propose the grey relation theory for influence of electric milling on machining targets in achieving parameter optimization, when an engine cylinder head milling processing under plane milling tool. The experiment was designed via orthogonal experimental design technique. Some parameters such as machining distortion, surface roughness and machining efficiency were chosen as machining targets, and the milling speed, feed per tooth and milling depth were chosen as milling parameters, calculate and analyze the grey relational degree and relational coefficient between milling parameters and machining targets. The optimized milling parameters including milling speed of 380m/min, feed per tooth of 0.05mm, and milling depth of 1.5mm were obtained in single-object and multi-objects. Experimental results show that the machining distortion of 0.055mm, the surface roughness of 0.7964μm and the machining efficiency of 36.3 mm³/min are excellent according to the optimized designs, and the machining efficiency and the machining quality are improved greatly.

Abstract: Based on the soft of FLOW3D, the numerical simulation was study the effect of runner-reduction ratio on the dispersing uniformity of added powders inside alloy melt. The parameters studied were gating shape and reduction ratio in cross section area. The results revealed that dispersing uniformity of powders, the flat gating system is better than the comb one, and the best dispersing uniformity was achieved when the reduction ratio was up to 50%.