In this work,a Cu-10Ta alloy with a copper to tantalum mass ratio of 9:1 is prepared using powder metallurgy technology.Physical properties of the alloy,including density,microstructure,melting point,and constant-volu...In this work,a Cu-10Ta alloy with a copper to tantalum mass ratio of 9:1 is prepared using powder metallurgy technology.Physical properties of the alloy,including density,microstructure,melting point,and constant-volume specific heat,are tested.Via the split Hopkinson pressure bar(SHPB)and flyerplate impact experiments,the relationship between equivalent stress and equivalent plastic strain of the material is studied at temperatures of 298-823 K and under strain rates of 1×10^(-3)-5.2×10^(3)s^(-1),and the Hugoniot relationship at impact pressures of 1.46-17.25 GPa and impact velocities of 108-942 m/s is obtained.Evolution of the Cu-10Ta microstructure that occurs during high-strain-rate impact is analyzed.Results indicate that the Cu-10Ta alloy possesses good thermal stability,and at ambient temperatures of up to 50%its melting point,stress softening of less than 15%of the initial strength is observed.A modified J-C constitutive model is employed to accurately predict the variation of yield strength with strain rate.Under strong impact,the copper phase is identified as the primary source of plastic deformation in the Cu-10Ta alloy,while significant deformation of the high-strength tantalum particles is less pronounced.Furthermore,the longitudinal wave speed D is found to correlate linearly with the particle velocity u upon strong impact.Analysis reveals that the sound speed and spallation strength of the alloy increase with increasing impact pressure.展开更多
The impact value (AK) measured with classic impact experiment of mechanical properties is a normal index from the five important basic mechanical properties for engineering, but it still has no definite physical meani...The impact value (AK) measured with classic impact experiment of mechanical properties is a normal index from the five important basic mechanical properties for engineering, but it still has no definite physical meaning. By use of the advanced impact experimental machine, the load-deflection signals under impact loading have been measured. According to the load-deflection curve of 30CrMnSiA steel obtained by this method, the AK value could be divided into the elastic deformation work, the plastic deformation work, the crack forming work, the work of crack propagation and the work of unstable crack propagation. Therefore, we can obtain the expression for the continuous changing of stress and strain under impact load. In this experiment, specimens with three different breaches, U type, V type and linear grooving, are used and the dynamic fracture toughness value (KDIC) of 30CrMnSiA steel is treated and calculated which follows the measuring method of material static fracture toughness, as ASTM E399. The experimental results verify that these impact specimens with three different breaches are satisfactory for plane strain relation under impact load. For high strength 30CrMnSiA steel, the maximum load of load-deflection curve under impact load can represent the unstable propagation load of crack. The precision of the calculated fracture toughness (KDIC) meets the engineering requirement of materials.展开更多
This study examines the cultural impact upon the dating scripts, perceptions, and behaviors of college students from the United States and Taiwan in their cross-cultural romantic relationships. Ten same-culture and te...This study examines the cultural impact upon the dating scripts, perceptions, and behaviors of college students from the United States and Taiwan in their cross-cultural romantic relationships. Ten same-culture and ten cross-culture couples participated in the retrospective account interviews. Reconfirming the prevalent quantitative research findings that the American participants tend to begin dating at a younger age and change dating partners more frequently, this qualitative study finds that most of the American and Taiwan Residents participants perceived their dating and cross-cultural romantic relationships seriously by demonstrating a strong sense of responsibility and consistent support in the face of language difficulties, cultural confusions, and social obstacles.展开更多
This study proposed three types of Al—Hf reactive materials with particle size ratios(a),which were almost completely dense(porosity of<5.40%)owing to their preparation using hot-pressing technology.Microstructure...This study proposed three types of Al—Hf reactive materials with particle size ratios(a),which were almost completely dense(porosity of<5.40%)owing to their preparation using hot-pressing technology.Microstructure characteristics and phase composition were analyzed,and the influence of particle size ratios on dynamic mechanical behavior and damage mechanism were investigated.The prepared sample with a=0.1 exhibited continuous wrapping of the Hf phase by the Al phase.Hf—Hf contact(continuous Hf phase)within the sample gradually increased with increasing a,and a small amount of fine Hf appeared for the sample with a=1.The reactive materials exhibited clear strain-rate sensitivity,with flow stressσ0.05and failure strainεfincreasing approximately linearly with increasing strain rate.ε.It is found that the plastic deformation of the material increased with increasing strain rate.As a increased from 0.1 to 1,the flow stress gradually increased.Impact failure of the material was dominated by ductile fracture with a large Al phase plastic deformation band for lower a,while brittle fracture with crushed Hf particles occurred at higher a.Finally,a constitutive model based on BP neural network was proposed to describe the stress-strain relationships of the materials,with an average relative error of 2.22%.展开更多
文摘In this work,a Cu-10Ta alloy with a copper to tantalum mass ratio of 9:1 is prepared using powder metallurgy technology.Physical properties of the alloy,including density,microstructure,melting point,and constant-volume specific heat,are tested.Via the split Hopkinson pressure bar(SHPB)and flyerplate impact experiments,the relationship between equivalent stress and equivalent plastic strain of the material is studied at temperatures of 298-823 K and under strain rates of 1×10^(-3)-5.2×10^(3)s^(-1),and the Hugoniot relationship at impact pressures of 1.46-17.25 GPa and impact velocities of 108-942 m/s is obtained.Evolution of the Cu-10Ta microstructure that occurs during high-strain-rate impact is analyzed.Results indicate that the Cu-10Ta alloy possesses good thermal stability,and at ambient temperatures of up to 50%its melting point,stress softening of less than 15%of the initial strength is observed.A modified J-C constitutive model is employed to accurately predict the variation of yield strength with strain rate.Under strong impact,the copper phase is identified as the primary source of plastic deformation in the Cu-10Ta alloy,while significant deformation of the high-strength tantalum particles is less pronounced.Furthermore,the longitudinal wave speed D is found to correlate linearly with the particle velocity u upon strong impact.Analysis reveals that the sound speed and spallation strength of the alloy increase with increasing impact pressure.
文摘The impact value (AK) measured with classic impact experiment of mechanical properties is a normal index from the five important basic mechanical properties for engineering, but it still has no definite physical meaning. By use of the advanced impact experimental machine, the load-deflection signals under impact loading have been measured. According to the load-deflection curve of 30CrMnSiA steel obtained by this method, the AK value could be divided into the elastic deformation work, the plastic deformation work, the crack forming work, the work of crack propagation and the work of unstable crack propagation. Therefore, we can obtain the expression for the continuous changing of stress and strain under impact load. In this experiment, specimens with three different breaches, U type, V type and linear grooving, are used and the dynamic fracture toughness value (KDIC) of 30CrMnSiA steel is treated and calculated which follows the measuring method of material static fracture toughness, as ASTM E399. The experimental results verify that these impact specimens with three different breaches are satisfactory for plane strain relation under impact load. For high strength 30CrMnSiA steel, the maximum load of load-deflection curve under impact load can represent the unstable propagation load of crack. The precision of the calculated fracture toughness (KDIC) meets the engineering requirement of materials.
文摘This study examines the cultural impact upon the dating scripts, perceptions, and behaviors of college students from the United States and Taiwan in their cross-cultural romantic relationships. Ten same-culture and ten cross-culture couples participated in the retrospective account interviews. Reconfirming the prevalent quantitative research findings that the American participants tend to begin dating at a younger age and change dating partners more frequently, this qualitative study finds that most of the American and Taiwan Residents participants perceived their dating and cross-cultural romantic relationships seriously by demonstrating a strong sense of responsibility and consistent support in the face of language difficulties, cultural confusions, and social obstacles.
基金funded by the National Natural Science Foundation of China(Grant No.12302437)China Postdoctoral Science Foundation(Grant No.2021M701710)。
文摘This study proposed three types of Al—Hf reactive materials with particle size ratios(a),which were almost completely dense(porosity of<5.40%)owing to their preparation using hot-pressing technology.Microstructure characteristics and phase composition were analyzed,and the influence of particle size ratios on dynamic mechanical behavior and damage mechanism were investigated.The prepared sample with a=0.1 exhibited continuous wrapping of the Hf phase by the Al phase.Hf—Hf contact(continuous Hf phase)within the sample gradually increased with increasing a,and a small amount of fine Hf appeared for the sample with a=1.The reactive materials exhibited clear strain-rate sensitivity,with flow stressσ0.05and failure strainεfincreasing approximately linearly with increasing strain rate.ε.It is found that the plastic deformation of the material increased with increasing strain rate.As a increased from 0.1 to 1,the flow stress gradually increased.Impact failure of the material was dominated by ductile fracture with a large Al phase plastic deformation band for lower a,while brittle fracture with crushed Hf particles occurred at higher a.Finally,a constitutive model based on BP neural network was proposed to describe the stress-strain relationships of the materials,with an average relative error of 2.22%.
