Advanced Materials Research Vols. 295-297

Abstract: Polishing diamond with hot metal method was hard to get experimental data, which was very important to the process of polishing. The relationship between polishing parameters and polishing quantity cannot be easily deduced with the limited experimental data. This paper uses Rough Set method to process the data and some useful conclusions have been drawn. The load factor in polishing process can be ignored in the polishing process. In the case of engineering application, the load merely ensures the contact between diamond and hot iron metal. Other parameters, such as temperature, polishing speed and time, are important factors to the polishing quality.

Abstract: The control parameters of the removal of Chlorella pyrenoidosa, which was irradiated by low frequency ultrasonic, is optimized by using single factor experiments and response surface methodology (RSM). First of all, the approximate ranges of the ultrasonic frequency, the ultrasonic power and the irradiation time were estimated with single factor experiments for the further experiments. And then the optimized values of the three control parameters were determined, which were analyzed by using central composite design (CCD) and RSM. The results showed that the removal rate of chlorophyll-a could reach to 64.1% after the irradiation for 6.34min by using ultrasonic of 77.7 kHz and 250W. Ultrasonic technology can remove Chlorella pyrenoidosa cells in water quickly and effectively, so as to achieve the purpose of water purification.

Abstract: Experiments were conducted for the impact force and erosion volume of the continuous jet, the self-excited aspirated pulse jet, the self-excited oscillation pulse jet on different hydraulic pressure in this paper. The rules of the three kinds of jet impact force and erosion effect with the change of hydraulic pressure were analyzed. The result shows the center impact force of the continuous jet is bigger than the other impact force. The self-excited aspirated pulse jet is obviously superior to the continuous jet and its erosion volume is 1.15~1.3 times as big as the continuous jet.

Abstract: Cao River aqueduct is the large-scale aqueduct that has been designed and constructed for the first time in China, for the great technical difficulties in structure form, there's no engineering experience or theoretical method for reference in domestic and abroad. Therefore, for mastering the stress characteristics and deformation law of aqueduct structure more overall and deeply, the impounding test of trial span was carried out before formal operation. Deformation characteristics of the aqueduct under impounding condition were analyzed in detail. The maximum deflection at mid-span of longitudinal beam was 0.98mm when three aqueducts all impound to 5.4m, the change range is small and in the allowable range of design and specification , which means the structure of aqueduct was reasonably designed and also provided important reference for the later operation and management.

Abstract: The 1Cr18Ni9Ti stainless steel was brazed in the argon shield and впр7 as the filler metal. The spreadability and clearance fillability of впр7 on 1Cr18Ni9Ti stainless steel was evaluated at different temperatures and the optimum brazing temperature was clearly demonstrated as 1170~1190°C. Scanning electron microscope (SEM) study combined with energy dispersive spectrometer (EDS) showed the presence of many undissolved elements and voids in the joints while the brazing clearance is 0.15mm, which directly caused a low joint shearing strength. Almost no undissolved brittle compounds were observed while the brazing clearance stands in a range of 0.01mm~0.10mm. Therefore, a Ni-based solid solution with good performance was obtained in the joint. Those brazing parameters matching with the holding time 8~10min could bring the joint a typical performance which fully satisfies Russian standard. These conclusions had been proved by joint stress-rupture and low cycle fatigue tests.

Abstract: Butt-joint specimens of Q235B low-strength steel were treated by TIG dressing and ultrasonic peening combined method. The paper presents comparative fatigue test for welded specimens in the as-welded condition and specimens treated by TIG dressing, ultrasonic peening treatment (UPT) and the combined method. When the ratio of stress R=0.1, contrasted with the specimens in as welded condition, the fatigue strength of the specimens treated by TIG dressing is increased by 36%. The fatigue strength of the specimens treated by the combined method and UPT are almost the same, which are increased by 57% and 56% respectively. In the high stress level, weld toe treated by the combined method has smaller stress concentration factor than that of UPT, resulting in less release of residual compressive stress. So it's more effective to improve the fatigue life by the combined method. While in the low stress level, the residual compressive stress of weld toe treated by the combined method and UPT are nearly the same. Besides, the effect of stress concentration factor is smaller, thus the fatigue life of the two methods have little difference.

Abstract: Take series of impact tests on welded joints for steel 09MnNiDR of LPG tank manufacture. And take scanning electron microscopy on impact fracture specimens. The results for the LPG storage tanks at low temperature welding process of steel making and the structure of low temperature storage tank to provide data to support safety analysis.

Abstract: The fatigue property of friction stir welded joints in Ai7075-T651 is crucial adjective in the modern aerospace industry. Treated by the UIP (Ultrasonic impact peening) process using the self-made device, the effects are studied in this paper, and the results show that: under the stress ratio R=0.5, the fatigue life of welded joints treated by ultrasonic peening is prolonged by 8~14 times. The strengthened layer caused by the plastic variation, surface hardening and uniformity of tissue, and transversal residual stress of base metal after UIP becomeing compressive residual stress of 100 Mpa in the surface, which are the main reasons that lead to the improvement of fatigue property.

Abstract: The domestic manufactured CT80, Φ33×3.18 coiled tubing is supplied as heat-treated low-alloy steel. The relationship between thermo cycle, microstructure, tensile properties and hardness were researched for butt welded joint. The results show that CT80 is very sensitive to welding heat input, and the thermo accumulation was obvious for small dimension coiled tubing, varying degrees of softening always exist in HAZ. The reasons include growing of block ferrite, decreasing and isolating of continuous directional bainite. In order to get good properties, the strength of consumable welding wire should be properly matched with base metal, keep uniform strength distribution along welded joint, and avoid the plastic strain concentrate in local area.

Abstract: The welding processes of steel materials are often accompanied by the occurrence of phase transformation. Volume change caused by phase transformation will affect the history of stress and strain. In this article, taking the welding of Q345 as an example, the effects of solid-state phase transformation on the residual stress were investigated by numerical simulation. The values of thermal strain at different temperatures were set to make the volume change caused by phase transformation equivalent as thermal strain. The simulation contained two cases both considering phase transformation and not. The results show that in both two cases the longitudinal stress distribution in the weld zone has almost the same trend. But in the case without considering phase transformation, there is large longitudinal tensile stress concentrating in the weld and HAZ zone and the maximum value is up to 427MPa in the weld. For transverse stress, phase transformation not only changes the value of the stress, but also alters the sign of the stress in the middle of the weld zone. Experiment was also carried out to measure the residual stress by X-ray diffraction. The result considering phase transformation matched much better with the experimental data. It can be concluded that phase transformation in the process of welding has a significant effect on the residual stress and can not be ignored in the numerical simulation of welding.