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1
2024, 39(4): 1-9.
Abstract：
In order to address the issue of sidewall non-fusion during narrow gap welding of TA31 titanium alloy, the wetting mechanism of the sidewall induced by magnetically controlled arc swing is investigated. The successful completion of welding a 42 mm-thick TA31 titanium alloy plate is achieved, followed by microstructure and mechanical properties analysis of the welded joint. The results demonstrate that magnetic-controlled arc swing enhances the wettability of liquid melt towards the sidewall, resulting in the formation of concave groove.This improvement in wettability primarily arises from alterations in temperature gra-dient between the molten pool and sidewall due to arc swing, as well as utilizing arc pressure and shear force to drive molten pool towards the sidewall. Microstructure analysis reveals the equiaxed β grains at the bottom layer is due to low heat input, and that the middle and cap layers exhibit large columnar β grains due to the competitive growth and epitaxial growth mechanisms in the cause of multi-layer welding. The α microstructures inside the β grains exhibit a typical basket weave morphology where the α plates overlap. Influenced by thermal cycle, the α phase coarsens significantly in the bottom layer. The average impact absorption energy of the weld zone is 55 J, approximately 74% of that of the base metal, and the heat affected zone demonstrates an average impact absorption energy value of 62 J, around 84% of that of the base metal. The magnetic control narrow gap welding technology can effectively resolve issues related to sidewall non-fusion and obtain TA31 titanium alloy joint with good microstructure and comprehensive mechanical property.
In order to address the issue of sidewall non-fusion during narrow gap welding of TA31 titanium alloy, the wetting mechanism of the sidewall induced by magnetically controlled arc swing is investigated. The successful completion of welding a 42 mm-thick TA31 titanium alloy plate is achieved, followed by microstructure and mechanical properties analysis of the welded joint. The results demonstrate that magnetic-controlled arc swing enhances the wettability of liquid melt towards the sidewall, resulting in the formation of concave groove.This improvement in wettability primarily arises from alterations in temperature gra-dient between the molten pool and sidewall due to arc swing, as well as utilizing arc pressure and shear force to drive molten pool towards the sidewall. Microstructure analysis reveals the equiaxed β grains at the bottom layer is due to low heat input, and that the middle and cap layers exhibit large columnar β grains due to the competitive growth and epitaxial growth mechanisms in the cause of multi-layer welding. The α microstructures inside the β grains exhibit a typical basket weave morphology where the α plates overlap. Influenced by thermal cycle, the α phase coarsens significantly in the bottom layer. The average impact absorption energy of the weld zone is 55 J, approximately 74% of that of the base metal, and the heat affected zone demonstrates an average impact absorption energy value of 62 J, around 84% of that of the base metal. The magnetic control narrow gap welding technology can effectively resolve issues related to sidewall non-fusion and obtain TA31 titanium alloy joint with good microstructure and comprehensive mechanical property.
2
2023, 38(1): 85-97.
Abstract：
Titanium matrix composites have been widely used in aerospace, automotive and other fields due to their low density and excellent room and high temperature properties. Here are reviewed the common preparation methods, hot working processes and main properties of discontinuous titanium matrix composites, and are summarized the main problems and solutions in the preparation of titanium matrix composites. Finally, the future development of research and application of titanium matrix composites is pointed out.
Titanium matrix composites have been widely used in aerospace, automotive and other fields due to their low density and excellent room and high temperature properties. Here are reviewed the common preparation methods, hot working processes and main properties of discontinuous titanium matrix composites, and are summarized the main problems and solutions in the preparation of titanium matrix composites. Finally, the future development of research and application of titanium matrix composites is pointed out.
3
2023, 38(2): 16-22.
Abstract：
The welding residual stress of two welding steel plates is measured by the impact indentation method, and the residual stress distribution on the butt welding plate is simulated by the finite element method. The residual stress values by measurement and simulation are contrasted and analyzed. The two methods agree well with each other both on the stress value and distribution, The peak value of the residual stress by the actual measurement is 599 MPa, and that by the simulation is 597 MPa, indicating good applicability of the numerical simulation. The longitudinal residual tensile stress near the heat affected zone is larger than that of the horizontal residual compressive stress. In addition, the peak of the equivalent stress (Mises stress) is 792 MPa, higher than the yield stress at room temperature, showing the significant strain-strengthening phenomenon occurs to the material.
The welding residual stress of two welding steel plates is measured by the impact indentation method, and the residual stress distribution on the butt welding plate is simulated by the finite element method. The residual stress values by measurement and simulation are contrasted and analyzed. The two methods agree well with each other both on the stress value and distribution, The peak value of the residual stress by the actual measurement is 599 MPa, and that by the simulation is 597 MPa, indicating good applicability of the numerical simulation. The longitudinal residual tensile stress near the heat affected zone is larger than that of the horizontal residual compressive stress. In addition, the peak of the equivalent stress (Mises stress) is 792 MPa, higher than the yield stress at room temperature, showing the significant strain-strengthening phenomenon occurs to the material.
4
Abstract：
The stress fields at the top of the penetrating notch in the center of the double-tension-plate are analyzed with 350 sets of sizes by elastic finite element method. The functions of the normal stress concentration factor normal to the length-direction Ktσy, the first stress invariant concentration factor KtI1 and the Mises equivalent stress concentration factor i>Ktσ are built. The results indicate that all the elastic stress concentration factors increase with the increase of the ratio 2a/W of the length to the width of the notch as the parabolic function, and reduce exponentially with the decrease of the ratio r/a of the radius to half of the width of the notch.
The stress fields at the top of the penetrating notch in the center of the double-tension-plate are analyzed with 350 sets of sizes by elastic finite element method. The functions of the normal stress concentration factor normal to the length-direction Ktσy, the first stress invariant concentration factor KtI1 and the Mises equivalent stress concentration factor i>Ktσ are built. The results indicate that all the elastic stress concentration factors increase with the increase of the ratio 2a/W of the length to the width of the notch as the parabolic function, and reduce exponentially with the decrease of the ratio r/a of the radius to half of the width of the notch.
5
2021, 36(4): 1-8.
Abstract：
Fatigue crack propagation rate of metallic materials is an important index of mechanical property, which is employed for damage tolerance design and fatigue life assessment in engineering application. Paris model is the most popular expression for fatigue crack propagation rate, and the relation of fatigue crack propagation rate and stress intensity factor range at the crack front is believed to meet a power-function rule in the model. The model involves in two material constants of C and m. In this paper, based on some test data published in some literatures, the relationships between material constants of C and m in Paris model for fatigue crack propagation rate of metallic materials of alloy steels, copper alloy, titanium alloy and aluminum alloy were analyzed. The results indicated that the constants of C and m of different types of metallic materials satisfied good linear relationship, namely m=alnC+b, which was not affected by specimen sampling orientation, weld position, and test environment. Stress ratios had great influence on the linear relationship, especially when the stress ratio value was negative. The slopes of the linear models for different metallic materials were not equivalent and the influencing factors should be further researched systematically. The analyzing results would provide reference for fatigue design and application in engineering.
Fatigue crack propagation rate of metallic materials is an important index of mechanical property, which is employed for damage tolerance design and fatigue life assessment in engineering application. Paris model is the most popular expression for fatigue crack propagation rate, and the relation of fatigue crack propagation rate and stress intensity factor range at the crack front is believed to meet a power-function rule in the model. The model involves in two material constants of C and m. In this paper, based on some test data published in some literatures, the relationships between material constants of C and m in Paris model for fatigue crack propagation rate of metallic materials of alloy steels, copper alloy, titanium alloy and aluminum alloy were analyzed. The results indicated that the constants of C and m of different types of metallic materials satisfied good linear relationship, namely m=alnC+b, which was not affected by specimen sampling orientation, weld position, and test environment. Stress ratios had great influence on the linear relationship, especially when the stress ratio value was negative. The slopes of the linear models for different metallic materials were not equivalent and the influencing factors should be further researched systematically. The analyzing results would provide reference for fatigue design and application in engineering.
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