Currently,Mg-Gd-Y-Zn-Zr alloys face the issue of a long aging duration.To establish a short-time aging treatment route,the precipitation characteristics and their effects on mechanical properties during elevated-tempe...Currently,Mg-Gd-Y-Zn-Zr alloys face the issue of a long aging duration.To establish a short-time aging treatment route,the precipitation characteristics and their effects on mechanical properties during elevated-temperature heat treatment prior to low-temperature aging treatment,low-temperature single-stage aging treatment,and low-temperature two-stage aging treatment were studied.The following results were obtained:Wider intragranular lamellar phases,including 14-LPSO andγphases,are more easily obtained during long-term holding at heat treatment temperatures of 400℃and 450℃.Although these lamellar phases do not contribute to strengthening,they enhance ductility by hindering crack propagation.Micro-sizedβphases precipitate more readily at heat treatment temperatures of 300℃and 350℃.Intragranular needle-likeβphases are not effective strengthening phases,andβphase precipitating along grain boundaries form a networked distribution,which reduces ductility.The nano-sizedβ’phase,as the main strengthening phase,is more likely to precipitate during single-stage aging at temperatures of 200℃and 250℃.Theβ’phase formed at 200℃is denser,leading to higher strength,but requiring a longer aging time.For two-stage aging,which involves a primary-stage at 200℃for 8 to 12 h followed by a second-stage at 250℃for 10 h,the aging time is reduced to at least one-quarter of that required for single-stage aging at 200℃,ensuring strength while improving ductility.The formation of very dense nano-sizedβ’phases during the primary-stage aging facilitates the densification ofβ’phases during the subsequent second-stage aging.Additionally,the shortened aging time hinders the precipitation ofβphase along the grain boundaries,thus improving ductility.展开更多
In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether(NEPE)propellant,uniaxial tensile tests were conducted using the selfmade c...In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether(NEPE)propellant,uniaxial tensile tests were conducted using the selfmade confining pressure system and material testing machine.The stress-strain responses of the NEPE propellant under different confining pressure conditions and strain rates were obtained and analyzed.The results show that confining pressure and strain rate have a remarkably influence on the mechanical responses of the NEPE propellant.As confining pressure increases(from 0 to 5.4 MPa),the maximum tensile stress and ultimate strain increase gradually.With the coupled effects of confining pressure and strain rate,the value of the maximum tensile stress and ultimate strain at 5.4 MPa and 0.0667 s^(-1)is 2.03 times and 2.19 times of their values under 0 MPa and 0.00333 s^(-1),respectively.Afterwards,the influence mechanism of confining pressure on the NEPE propellant was analyzed.Finally,based on the viscoelastic theory and continuous damage theory,a nonlinear constitutive model considering confining pressure and strain rate was developed.The damage was considered to be rate-dependent and pressuredependent.The constitutive model was validated by comparing experimental data with predictions of the constitutive model.The whole maximum stress errors of the model predictions are lower than 4%and the corresponding strain errors are lower than 7%.The results show that confining pressure can suppress the damage initiation and evolution of the NEPE propellant and the nonlinear constitutive model can describe the mechanical responses of the NEPE propellant under various confining pressure conditions and strain rates.This research can lay a theoretical foundation for analyzing the structural integrity of propellant grain accurately under working pressure loading.展开更多
To further explore the damage characteristics and impact response of the shaped charge to the solid rocket engine(SRE) in storage or transportation, protective armor was designed and the shelled charges model(SCM)/SRE...To further explore the damage characteristics and impact response of the shaped charge to the solid rocket engine(SRE) in storage or transportation, protective armor was designed and the shelled charges model(SCM)/SRE with protective armor impacting by shaped charge tests were conducted. Air overpressures at 5 locations and axial acceleration caused by the explosion were measured, and the experimental results were compared with two air overpressure curves of propellant detonation obtained by related scholars. Afterwards, the finite element software AUTODYN was used to simulate the SCM impacted process and SRE detonation results. The penetration process and the formation cause of damage were analyzed. The detonation performance of TNT, reference propellant, and the propellant used in this experiment was compared. The axial acceleration caused by the explosion was also analyzed.By comprehensive comparison, the energy released by the detonation of this propellant is larger, and the HMX or Al particles contained in this propellant are more than the reference propellant, with a TNT equivalent of 1.168-1.196. Finally, advanced protection armor suggestions were proposed based on the theory of woven fabric rubber composite armor(WFRCA).展开更多
In this paper we present a highly pathogenic Avian influenza epidemic model with saturated contact rate. According to study of the dynamics, we calculated the basic reproduction number of the model. Through the analys...In this paper we present a highly pathogenic Avian influenza epidemic model with saturated contact rate. According to study of the dynamics, we calculated the basic reproduction number of the model. Through the analysis of this model, we have the following conclusion: if R0 ≤ 1, there is only one disease-free equilibrium which is globally stable, the disease will die;if R0 > 1, there is only one endemic equilibrium which is globally stable, disease will be popular.展开更多
基金supported by the special fund for Science and Technology Innovation Team of Shanxi Province,Central Guiding Local Science and Technology Development Fund Projects(No.YDZJSX20231A029)National Natural Science Foundation of China(No.52205428)Fundamental Research Program of Shanxi Province(No.20210302124206).
文摘Currently,Mg-Gd-Y-Zn-Zr alloys face the issue of a long aging duration.To establish a short-time aging treatment route,the precipitation characteristics and their effects on mechanical properties during elevated-temperature heat treatment prior to low-temperature aging treatment,low-temperature single-stage aging treatment,and low-temperature two-stage aging treatment were studied.The following results were obtained:Wider intragranular lamellar phases,including 14-LPSO andγphases,are more easily obtained during long-term holding at heat treatment temperatures of 400℃and 450℃.Although these lamellar phases do not contribute to strengthening,they enhance ductility by hindering crack propagation.Micro-sizedβphases precipitate more readily at heat treatment temperatures of 300℃and 350℃.Intragranular needle-likeβphases are not effective strengthening phases,andβphase precipitating along grain boundaries form a networked distribution,which reduces ductility.The nano-sizedβ’phase,as the main strengthening phase,is more likely to precipitate during single-stage aging at temperatures of 200℃and 250℃.Theβ’phase formed at 200℃is denser,leading to higher strength,but requiring a longer aging time.For two-stage aging,which involves a primary-stage at 200℃for 8 to 12 h followed by a second-stage at 250℃for 10 h,the aging time is reduced to at least one-quarter of that required for single-stage aging at 200℃,ensuring strength while improving ductility.The formation of very dense nano-sizedβ’phases during the primary-stage aging facilitates the densification ofβ’phases during the subsequent second-stage aging.Additionally,the shortened aging time hinders the precipitation ofβphase along the grain boundaries,thus improving ductility.
基金the National Natural Science Foundation of China(Grant No.51606098)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX20_0303).
文摘In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether(NEPE)propellant,uniaxial tensile tests were conducted using the selfmade confining pressure system and material testing machine.The stress-strain responses of the NEPE propellant under different confining pressure conditions and strain rates were obtained and analyzed.The results show that confining pressure and strain rate have a remarkably influence on the mechanical responses of the NEPE propellant.As confining pressure increases(from 0 to 5.4 MPa),the maximum tensile stress and ultimate strain increase gradually.With the coupled effects of confining pressure and strain rate,the value of the maximum tensile stress and ultimate strain at 5.4 MPa and 0.0667 s^(-1)is 2.03 times and 2.19 times of their values under 0 MPa and 0.00333 s^(-1),respectively.Afterwards,the influence mechanism of confining pressure on the NEPE propellant was analyzed.Finally,based on the viscoelastic theory and continuous damage theory,a nonlinear constitutive model considering confining pressure and strain rate was developed.The damage was considered to be rate-dependent and pressuredependent.The constitutive model was validated by comparing experimental data with predictions of the constitutive model.The whole maximum stress errors of the model predictions are lower than 4%and the corresponding strain errors are lower than 7%.The results show that confining pressure can suppress the damage initiation and evolution of the NEPE propellant and the nonlinear constitutive model can describe the mechanical responses of the NEPE propellant under various confining pressure conditions and strain rates.This research can lay a theoretical foundation for analyzing the structural integrity of propellant grain accurately under working pressure loading.
文摘To further explore the damage characteristics and impact response of the shaped charge to the solid rocket engine(SRE) in storage or transportation, protective armor was designed and the shelled charges model(SCM)/SRE with protective armor impacting by shaped charge tests were conducted. Air overpressures at 5 locations and axial acceleration caused by the explosion were measured, and the experimental results were compared with two air overpressure curves of propellant detonation obtained by related scholars. Afterwards, the finite element software AUTODYN was used to simulate the SCM impacted process and SRE detonation results. The penetration process and the formation cause of damage were analyzed. The detonation performance of TNT, reference propellant, and the propellant used in this experiment was compared. The axial acceleration caused by the explosion was also analyzed.By comprehensive comparison, the energy released by the detonation of this propellant is larger, and the HMX or Al particles contained in this propellant are more than the reference propellant, with a TNT equivalent of 1.168-1.196. Finally, advanced protection armor suggestions were proposed based on the theory of woven fabric rubber composite armor(WFRCA).
文摘In this paper we present a highly pathogenic Avian influenza epidemic model with saturated contact rate. According to study of the dynamics, we calculated the basic reproduction number of the model. Through the analysis of this model, we have the following conclusion: if R0 ≤ 1, there is only one disease-free equilibrium which is globally stable, the disease will die;if R0 > 1, there is only one endemic equilibrium which is globally stable, disease will be popular.
