Advanced Materials Research Vols. 1004-1005

Abstract: Transmission casing fatigue fracture is one of the most serious failure of the transmission system in the form of tracked vehicles. This article through the analysis of materials and structural stress analysis of a typical fracture failure mechanism of the tracked vehicle transmission cabinet. And in obtaining the stress on the basis of load spectrum its fatigue life was calculated. The results show that in the structure of the stress concentration and cabinet material number ZL101 cast aluminum defects such as inclusions, porosity are the main cause of fatigue crack initiation and propagation.

Abstract: The fundamental principle of three dimensional Element-free Galerkin has been briefly investigated in this paper, and built forming mode of steel ball cold forging, Element-free Galerkin method successfully applied to the simulation analysis of steel ball cold forging forming process in the LS-DYNA simulation software. In comparison to Finite Element Method and experiment data, Proved Element-free Galerkin method was feasible in metal plastic forming process, and in the large deformation simulation was more accurate than the finite element method, Element-free Galerkin method has more obvious advantages after altering the impact factors.

Abstract: In order to reduce the roundness error of cylindrical grinding of shaft parts for 20CrMnTi alloy steel, the related experiments of high-speed cylindrical grinding are carried out and the influence of grinding parameters on roundness is analyzed. Based on the analysis of experimental data the conclusions are as follows: The influence of grinding wheel speed on work-piece roundness is not apparent, but the influence of work-piece speed and grinding depth on roundness is very significant. Based on high-speed grinding experiments the prediction model of cylindrical grinding for 20CrMnTi alloy steel is established by using of regression analysis method of least square. Based on the analysis of the roundness prediction model of cylindrical grinding the conclusions are as follows: The roundness error of cylindrical grinding parts will become lager with the increase of work-piece speed, grinding depth and grinding wheel speed.

Abstract: The microstructure and mechanical properties of permanent mold low-pressure casting (PMLPC) and sand mold gravity casting (SMGC) of A357 alloy were studied. The grain size of alloys formed by PMLPC is finer than that formed by sand mold gravity casting because of higher freezing rate of the former. The secondary dendrite arm spacing of PMLPC is approximately 15.2 μm (SD=4) while that of SMGC is 33.2 μm (SD=6). The ultimate tensile strength of PMLPC has a wider range from 350 MPa to 299.9 MPa and an elongation from 1.2 to 4.9. In comparison, the ultimate tensile strength of SMGC ranges from 307 MPa to 315 MPa and its elongation ranges from 2.1 to 3.7. These differences may be attributed to various factors, such as filling speed, filling pressure, and cooling rate, that affect the quality of permanent molds during the filling process.

Abstract: Microphases and triangle phase diagrams of cyclic ABCB tetrablock copolymer melts have been investigated by a combinatorial screening algorithm based on self-consistent field theory (SCFT) in two-dimensional space. Eight main stable ordered morphologies have been observed in the intermediate-segregation regime. SCFT simulation experiments reveal that the compositions of block chain in the cyclic polymer are comparable, the cyclic architecture of polymer chain has a strong topological constraint on the geometry of microphases. The morphologies and phase diagrams are helpful to control and design the suitable ordered microstructure of cyclic copolymer systems.

Abstract: Coupling the force flow field with the phase field model for the isothermal growth of dendrite, Sola algorithm is used to calculate the flow speed and pressure of liquid metal, Using double grid numerical method to reduce the calculation amount of computer simulation, The space factor and time factor are introduced to improve the accuracy of double grid numerical calculation, Taking Al-2%-Cu alloy as an example, the dendrite growth process of the binary alloy under forced convection environment is simulated; The simulation results can capture the real dendrite growth and interactions of the liquid metal flow in the process of dendrite growth under forced convection environment: In the incident flow regions, the dendrite morphology is complex, the secondary dendrite is lush and the growth speed is fast due to the influence of liquid metal flow. In the back flow regions, the growth of dendrite changes the flowing pressure among the liquid metals, it causes the regional complex flow patterns and there are two opposite eddy current; the grow speed of the main branch which grows perpendicular to the initial flow direction is the fastest and presents tilt growth phenomenon. When the space coefficient value is appropriate, the dual mesh method can save calculation time effectively.

Abstract: The randomness of structural and material parameters needs to be considered in the reliability analysis of gun barrel ablation life. However, the traditional method, like Stochastic FEM sampling, results in huge computing workload and low efficiency. This paper proposed a modified response surface model for estimating the gun barrel ablation life. In which, the estimation error of the response surface model is the optimization goal. Gauss-Newton method (GNM) is used to get the optimal solution whose initial value is solved by Genetic-algorithm (GA). After that, ablation life can be calculated by the optimized response surface model. GA is effective in global solution space searching, while GNM is effective in local searching. The new method takes full advantages of both GA and GNM in parameters estimation. The simulation result shows that the combination of GA and GNM obtains a higher precision of ablation estimation and greatly improves the computational efficiency.

Abstract: Aiming at the problem of global interference correction that the extrusion tool is entirely contained within the workpiece in 5-axis CNC incremental forming, a method that can avoid interference by correcting only once based on STL (StereoLithography) model is proposed in this paper. The interference critical point is found by using the plane which is paralleled to the extrusion tool and the Z-axis to cut the extrusion tool and the workpiece model, and then the interference correction angle is calculated through the interference cirtical point. The case study shows that this method is simple, effective and it can correct interference only by one step.

Abstract: After precise grinding n-WC/12Co coatings with diamond wheel , there is residual stress on the surface of parts ,the paper drawn conclusions about this study,it Pointed out the contents of further study ,the direction of farther study was prospected in this study too. The interaction between the abrasive grains and the workpiece was approximately regarded as ideal small-scale indentation phenomenon, it was used to evaluate the surface quality in ceramic machined processing that formation of grinding crack and its propagation process, the material removed process and the surface defects of the ceramic grinding, the cutting model proved that although the removed material is usually brittle removal, most of the grinding energy consumption was related with plastic deformation.

Abstract: Flow phenomenon in spot welding nugget of dissimilar materials was studied. Metallographs in the course of welding nugget formation were observed and analyzed, through which it was indicated that: in the early stage of welding nugget formation, spot welding of dissimilar materials made liquid metals in the nugget produce a violent stirring action because the electrodynamic force overcame the medium resistance, causing unevenness of elements and compositions in the welding nugget; and then the unevenness was represented by vortex flow by means of different resistances to corrosion. It was proposed that the formation law of welding nugget could be recognized according to the formation law of vortex flow, and the vortex flow often moved from later-molten metal to former-molten metal. The property of welded joint with vortex flow was poorer than that without vortex flow.