In this paper Liapunov's second method is used to analyze the plastic dynamic stability of a column under nonconservative forces. The column is in a viscous medium, and under the action of uniformly distributed ta...In this paper Liapunov's second method is used to analyze the plastic dynamic stability of a column under nonconservative forces. The column is in a viscous medium, and under the action of uniformly distributed tangential follower forces. The strain-rate effect on the stress-strain relation of materials is included in the analysis. A condition of stability is derived, and the critical buckling load is obtained. The strain-rate effect on the stability of the column is discussed.展开更多
Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kin...Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kinetic simulation results showed that both Ni and Co did not obtain enough time to get the equilibrium content in this system. The Ni content in austenite layers decreased significantly, and Co content increased slightly with the decrease of Ni content in overall composition. The austenite stability was estimated by Olson-Cohen model, in which both chemical and mechanical driving force could be calculated by equilibrium thermodynamic and Mohr＇s circle methods, respectively. Simulation and mechanical test results showed that The decrease of Ni content in austenite layers would cause the change of austenite stability and decrease the fracture toughness of the steels. When the Ni content in the overall composition was lower than 7 wt. %, the Ni content in y phase would be lower than 20 wt.%. And the simulation value of M; （stress induced critical martensite transformation temperature） would be up to 80 ℃, which was about 60℃ higher than room temperature. Based on the analysis, the Ni content in the overall composition of high Co Ni secondary hardening steels should be higher than 8 wt. % in order to obtain a good fracture toughness.展开更多
文摘In this paper Liapunov's second method is used to analyze the plastic dynamic stability of a column under nonconservative forces. The column is in a viscous medium, and under the action of uniformly distributed tangential follower forces. The strain-rate effect on the stress-strain relation of materials is included in the analysis. A condition of stability is derived, and the critical buckling load is obtained. The strain-rate effect on the stability of the column is discussed.
基金financially supported by National Basic Research Programs of China (No.2015CB654802 and No.2015GB118001)National Natural Science Foundation of China(Grant No.51471094)
文摘Three kinds of high Co Ni secondary hardening steels with different Ni contents were studied. The nanoscale austenite layers formed at the interface of matensite laths were observed. Both observation and diffusion kinetic simulation results showed that both Ni and Co did not obtain enough time to get the equilibrium content in this system. The Ni content in austenite layers decreased significantly, and Co content increased slightly with the decrease of Ni content in overall composition. The austenite stability was estimated by Olson-Cohen model, in which both chemical and mechanical driving force could be calculated by equilibrium thermodynamic and Mohr＇s circle methods, respectively. Simulation and mechanical test results showed that The decrease of Ni content in austenite layers would cause the change of austenite stability and decrease the fracture toughness of the steels. When the Ni content in the overall composition was lower than 7 wt. %, the Ni content in y phase would be lower than 20 wt.%. And the simulation value of M; （stress induced critical martensite transformation temperature） would be up to 80 ℃, which was about 60℃ higher than room temperature. Based on the analysis, the Ni content in the overall composition of high Co Ni secondary hardening steels should be higher than 8 wt. % in order to obtain a good fracture toughness.
