Ying Xia Yu

Effect of Ultrasonic Impact Treatment on Corrosion Resistance of Welded Joints of 16MnR Steel

The weld seam and weld toe surface were treated by ultrasonic impact method. The contrast corrosion tests were performed in 3.5% NaCl aqueous solution both for the un-treated and treated joint. The experimental results indicate that the severe plastic deformation on the surface of weld seam and weld toe were formed by ultrasonic impact for different time, the maximum depth of the plastic deformation layer is about 300μm. Residual tensile stress in the surface of weld seam and weld toe can be changed to residual compressive stress by impact treatment, and the grain in the surface of welded joint could be refined. Compared to the un-treated joint, when the impact current is 1.2A and 1.5A, respectively, the corrosion rate of treated joint was reduced by 22.67%, 54.59%, 43.99% and 33.92%, 56.54%, 49.29%, respectively for 10, 20 and 30 min. treating. The corrosion resistance of welded joint has a certain relationship with the residual stress on the surface of welded joint. The ultrasonic impact treatment has distinct effect on the corrosion resistance of 16MnR welded joint.

Review of Status about the Effect of Ultrasonic Impact on Fatigue Properties of Welded Joints of Magnesium Alloy

The study on magnesium alloy has attracted attention at home and abroad. Status and development trend about the fatigue properties of welded joints of magnesium alloy were reviewed. The main problems and deficiencies were pointed out, and the recent developments focus was outlined. The development trend of improving the fatigue propeties and fatigue life was analyzed. The ultrasonic impact method can not only decrease the stress concentration coefficient and tensile residual stress of welded joint, but also refine the grain size of welded joints, even to compressive stress and nanograins. The method has put forward a new way for increasing fatigue properties and life of welded joint of magnesium alloy.

Effect of Air Oxidation Treated Carbon Fiber on Mechanical Properties of Carbon Fiber Reinforced Polyethylene Resin Composite

The composite of carbon fiber reinforced polyethylene resin was prepared by using a twin-screw extruder. The effect of carbon fiber oxidation treating on the mechanical properties of carbon fiber reinforced polyethylene resin composite was researched. The tensile fracture failure mechanism of composite was analyzed for both untreated and air oxidation treated specimen. The experimental results indicate that when carbon fiber content is equal, the tensile strength and the elastic modulus of air oxidation-treated carbon fiber-reinforced polyethylene composite are improved than that of the untreated. When the fraction of adding carbon fiber is 3.99%, compared with the pure polyethylene resin matrix, the tensile strength, elastic modulus is increased by 13.12% and 172.91%, respectively. Compared to the untreated carbon fiber reinforced polyethylene resin composite, the tensile strength and tensile modulus is increased by 4.71% and 13.14%, respectively.

Surface Nanocrystallization of U70 Rail Steel Treated by Ultrasonic Impact

The ultrasonic impact treatment on U70 raill steel was carried out under different technology by using HJ-II ultrasonic impact machine. The electric current was 1.5 A, the amplitude was 24 µm and the impact frequency was 10000 HZ during the treatment, the peening duration was 60 min. The influence of impact on microstructure was observed with the scanning electron microscope of 6360LA type and high resolution transmission electron microscope of JEM-2100 type, and the hardness of impacted surface was also researched before and after impact treatment. The wear resistance was tested by using M-2000 type wearing machine. The experimental results indicate that the surface strength of rail steel can be improved evidently by using ultrasonic impact treatment. The surface microstructure of the rail steel could be refined to nanoscale and the hardness and wear resistance of impact layer were significantly improved through the ultrasonic impact technology. Compared to the specimen without treatment, its surface hardness was increased 26.4%, and the wear resistance was increased 40.63%. The depth of plastic deformation zones of the specimen with 60 min treatment is nearly 100µm. In the plastic deformation zone, ferrite is refined to nanoscale grains so that the matrix is strengthened.

The Effect of QPQ Salt-Bath Nitriding on Microstructure and Wear Resistance of 4Cr5MoSiV1 Steel

In this paper, 4Cr5MoSiV1 steel is dealt with by QPQ salt-bath nitriding at 520°C, 540°C, 560°C and for 2h、4h、6h, respectively. The treated surface microstructure was analyzed by using SEM. The depth of nitriding layer, scratch hardness and wear-resistance were tested for QPQ salt-bath nitriding technology. The corrosion resistance was tested in the 5%NaCl water by using spraying method. The experimental results indicate that with increasing the temperature and the nitriding time, the depth of nitriding layer, scratch hardness and wear-resistance of 4Cr5MoSiV1 steel were increased greatly. Comparing with the untreated specimen, its hardness enhances 196.73%, wear resistance enhances 349.65%, anti-corrosion enhances 943.10%. The die hardness, wear resistance and the corrosion resistance can be greatly improved by using the QPQ salt-bath nitriding technology.

Reliability Calculation of Welded Pressure Pipe with Circumferential Crack Based on 3-D Elastic-Plastic SFEM

In this paper, the reliability of welded pressure pipe with circumferential surface crack was calculated by using three dimensional stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on three dimensional elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as fracture toughness, bending moment and the depth of the circumferential surface crack on the structure reliability were also discussed. The calculation results indicate that the crack depth has great effect on the reliability of the welded pipe. When the mean value of the crack depth is changed from 3mm to 7mm, the failure probability of the welded pipe will change from 10-8 to 10-2. The bending moment also has great effect on the reliability of the welded pipe. When the mean value of moment is changed from10000 N.m to 15000 N.m, the failure probability of the welded pipe increases dramatically for the same circumferential crack depth. Irrespective of the changing of moment, the pipe has higher reliability if the crack depth is less than 5mm(a/t<0.5, t is the thickness of the pipe). The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.

Effects of External Loads on the Reliability of Welded Pipe with Circumferential Crack

The reliability of welded pressure pipe with circumferential surface crack was calculated by using 3-D stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on 3-D elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as bending moment, the inner pressure on the structure reliability were discussed. The calculation results indicate that the bending moment has great effect on the reliability of the welded pipe, and the inner pressure has little effect on the reliability of the welded pipe if the inner pressure is less than 10MPa. If the mean value of the inner pressure changed from 0.5MPa to 30MPa, the failure probability will changes from 10-6 to 10-2. The bending moment also has great effect on the reliability. When the mean value of moment is changed from10000 Nm to 15000 Nm, the failure probability of the welded pipe increases dramatically for the same inner pressure. Irrespective of the changing of moment, the pipe has higher reliability if the inner pressure is less than 6 MPa. The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.

Influential Factors for Very High Cycle Fatigue Behavior of Metallic Materials

In recent years, very high cycle fatigue has become a major concern in design and durability of engineering components and structures such as railway wheels, rails, offshore structures, bridges, load bearings, etc. There are some factors which have been assumed to influence the fatigue behavior for metallic materials in VHCF regime. But most factors influencing the VHCF behavior have not been studied thoroughly. In order to deeply understand the essence of material fatigue, the experimental and theoretical aspects of the factors influencing on very high cycle fatigue for metallic materials should be studied further more. This paper deals with an overview on the effect of factors on the property in very high cycle fatigue regime. Research trends and some conclusions in this field are briefly discussed and obtained.

Research about the Effect of Ultrasonic Impact on the Mechanical Property of Welded Cruciform Joint of P355NL1 Steel

Surface treatment was carried out on the welded cruciform joint of P355NL1 steel by using the HJ-II-type ultrasonic impact machine. The ultrasonic impact current is 1.5A, the impact amplitude is 20 microns and ultrasonic impacting time is 5min. Tensile test was carried out for both treated specimen and un-treated specimen. The fracture observed with the scanning electron microscope of 6360LA type. The experimental results show that although the compressive residual stress can be obtained in the surface of weld toe area, and the grain size in the surface of welded cruciform joint can be refined, but the mechanical property of the welded cruciform joint of P355NL1 steel can not be improved through the ultrasonic impact treatment. The main reason is that the ultrasonic impact layer is only 70um, it is to thin to compared to the thickness of the specimen.

The Effect of Residual Stress on Fatigue Life of Welded Cruciform Joints of 16MnR for Train Bogie

The weld toe surface and its nearby area of welded cruciform joints were treated by ultrasonic impact. Under the same stress concentration and after heat treatment to eliminate residual stress, the effect of residual stress on the fatigue life of joint was researched. The fatigue tests are performed on the joints of 16MnR both for the un-treated and treated joints by using EHF-EM200K2-070-1A type fatigue tester when the load ratio is 0.1, frequency is 10Hz. The experimental results indicate that the severe plastic deformation in the vicinity of weld toe surface was formed by impact treating for 2 minutes, the thickness of the plastic deformation layer is about 60μm. Residual tensile stress in the weld toe surface can be changed to residual compressive stress by impact treatment. The fatigue life of welded joint is 0.260×106 cycle, and the fatigue life of treated joint is 0.499×106 cycle. Compared to the un-treated joint, the fatigue life of treated joint has been increased by 91.92%. The residual stress contributed to fatigue life is about 16%. Residual stress has great effect on the fatigue life of welded cruciform joint.