Applied Mechanics and Materials Vols. 633-634

Abstract: In the process of plastic forming of metals, ductile fracture is an important factor influencing the improvement of forming limit of metals, while ductile fracture criteria can predict when and where ductile fracture occurs. Some conventional ductile fracture criteria based on mesoscopic void-damage and their application in different plastic forming of metals are introduced in this paper. And the ductile fracture criteria will be summarized into two categories: based on triaxial stress degree and based on maximum tensile stress. Because the triaxial stress degree and maximum tensile stress are a main factor deciding the occurrence of the ductile fracture.

Abstract: Aspheric lens of Zinc sulfide is widely used in infrared, but it is always formed by polishing with low efficiency, ductile regime grinding aspheric surface of hot-pressed zinc sulfide is studied to reduce time-consuming of polishing. The results of orthogonal grinding experiments demonstrate that the depth of grinding is the main influencing factor on ductile regime removal mechanisms and surface roughness Ra values which decrease with decreasing depth of grinding, and the optimal value is 7.6nm, the steady ductile regime removal mechanisms appears when depth of grinding is below 0.4μm. With diamond wheel by grain size of D20/30, machining parameters on the basis of orthogonal grinding experiments, the aspheric surface cross grinding experiments show that ductile regime removal is obtained only in little center areas of aspheric surface, most of aspheric surface is in brittle regime. Then, the ductile regime aspheric surface with roughness of 20.1nm is observed by cross grinding of diamond wheel with grain size of D4/8.

Abstract: The free forging process of medium scale specimen was carried out to study the effects of the die temperature on the microstructure evolution of 7A85 aluminum forging. The results show that with the increase of die temperature, the size of the grains and the distribution of dislocations and precipitates of free forging tend to have a high degree of uniformity. Considering the effects of die temperature, the isothermal forging process was applied for the deformation of complex aviation forging. The metal flows smoothly during the isothermal forging process and thus there is little possibility of forming unfill, crack and other defects. The dislocations are evenly distributed during the isothermal forging process. Consequently, there is a relatively uniform distribution of precipitated phases of the aviation forging.

Abstract: This paper proposed a method on accurate phase matching control between the pulse laser and the AC TIG arc in real time, and a pulse laser-arc hybrid heat source phase matching control system is developed as well. With the utilization of this system in two typical matching cases that the pulse laser acts on the peak and the trough of the arc welding current waveform, effect regulations on weld formation, weld penetration depth and hybrid plasma shape are studied during welding on magnesium alloy AZ61. Results indicate that, when the pulse laser acting on the peak of arc welding current waveform, the weld formation is better than that of on the trough. However, when pulse laser act on the arc trough the weld penetration depth is deeper than that of on the peak.

Abstract: The ever-increasing demands of very high precision components have forced manufacturers to improve equipment to meet the demand. The main factor is the identification and compensation of errors in machine tools. In this paper, a new real-time method is presented to identify and compensate the error with space gauge, by use of which the composition of errors is directly compensated by measuring the deformation of the points in machine bed. Then, a simple single-axis machine tool is used to determine the relationship of deformation between gauging point and control point to verify the feasibility of the method. Furthermore, due to the simplicity of the implement and, the method can be easily used in an industrial production with minimal investment. Consequently, the result shows the method can be widely applied.

Abstract: The machinability of Nickel-based superalloy GH4169 is poor. The traditional method to machining is to apply cutting fluids with the active additives, which, however, cause environmental pollution and health problems. In this paper, the MQL using organic alcohols, instead of cutting fluids, was applied on turning for the aim of green cutting GH4169. The effects of MQL, wet and dry cutting on cutting force and the chip deformation have been examined with coats carbide tools YBC251. The results of experiments indicated that the application of MQL produced lower cutting force with about 20 percent reduction compared to dry cutting, and it is advantageous in chip curl. The research results show that clean production was achieved in metal cutting associated with MQL using alcohols for cooling and lubricating.

Abstract: The accuracy of tool setting has a great influence on the machining accuracy of micro structures. In this paper, electric breakdown in micro gap is used for tool setting and the accuracy of this method is ±0.2μm. Experimental studies have been done to prove the feasibility of this method. Experimental results show that the breakdown voltage is about 30V when the gap between the tool and the tool setting probe is 2μm, and tool diameter has little effect on this phenomenon. With the increase of the tool wear the breakdown voltage shows ascendant trend, so this method can be used to monitor tool wear.

Abstract: The friction and wear characteristics of different cemented carbides YG6 with Ti6Al4V alloys in different loads and speeds are revealed by pin-on-disc rotation, and analyses the wear mechanism, when the system is designed with the tribology theory to guide the development of titanium machining tool material and rational use.

Abstract: This paper focus on fatigue problem of submarine pipelines, four points bending full scale fatigue experiment were conducted on X65 pipelines butt joints specimens, utilizing pipeline full scale fatigue test machine developed by CNPC. Meanwhile contrast test was also carried out on small specimens. The results show that the fatigue strength of full scale welded joints is lower than the small scale joints. Owing to having no regard for the influence of residual stress and size effect, the small test would provide dangerous results. The fatigue property of full scale welded joints only meets the requirement of DNV C203 W3 curve, and meets the needs of DNV C203 F3 curve basically while not meet BS 7608 F2 curve’s requirements which relatively demand higher. Weld toe and geometric discontinuous near weld root is the weak point for the whole welded joints.

Abstract: This paper presents a theoretical and experimental investigation into the ablation threshold of nickel template by femtosecond laser in air at atmospheric pressure. The laser pulses used for the study are 800 nm in wavelength, 100fs in pulse duration, and 1KHz in repetition rate. The two-temperature model is used to predict the single-pulse ablation threshold for nickel theoretically. Micro-hole ablation experiments are carried out in air by focusing the femtosecond laser beam on the nickel target surface at normal incidence with the long-focus objective lens of enlargement factor 50 and NA=0.7 to determine the single-pulse and multi-pulse ablation thresholds for nickel by setting up the relationship between the measured hole diameters and the pulse energies. The single pulse ablation threshold of 4132.98 Jm^-2 obtained experimentally is very close to that of 3907.99 Jm^-2 predicted by two-temperature model. The incubation factor ξ, which describes the changes of the multi-pulse ablation thresholds with the number of pulses, is determined to be 0.812 for nickel.