The article deals with the motion of the breech block carrier and the weapon casing of an automatic weapon mounted on a flexible carriage and the base of the weapon.Earlier works,which did not consider the dynamic pro...The article deals with the motion of the breech block carrier and the weapon casing of an automatic weapon mounted on a flexible carriage and the base of the weapon.Earlier works,which did not consider the dynamic properties of the base of the weapon,did not allow to reconcile the calculated and experimental results of the weapon casing displacement when shooting from firing rests.For the analysis of the motion of individual parts,the methods of mathematical modelling and firing experiments using a high-speed camera were chosen.Calculations show the best accord with experiment when modelling the system with 4 degrees of freedom.The oscillation of the system regarding the movement of the breech block carrier and the weapon casing was investigated under changed conditions of rate of fire,the use of a muzzle brake and different types of shock absorbers.The velocities and displacements of the weapon casing and the breech block carrier at different values of the impulse of the gases to the breech block carrier were determined.展开更多
In order to investigate the mechanical response behavior of the gas obturator of the breech mechanism,made of polychloroprene rubber(PCR), uniaxial compression experiments were carried out by using a universal testing...In order to investigate the mechanical response behavior of the gas obturator of the breech mechanism,made of polychloroprene rubber(PCR), uniaxial compression experiments were carried out by using a universal testing machine and a split Hopkinson pressure bar(SHPB), obtaining stress-strain responses at different temperatures and strain rates. The results revealed that, in comparison to other polymers, the gas obturator material exhibited inconspicuous strain softening and hardening effects;meanwhile, the mechanical response was more affected by the strain rate than by temperature. Subsequently, a succinct viscoelastic damage constitutive model was developed based on the ZWT model, including ten undetermined parameters, formulated with incorporating three parallel components to capture the viscoelastic response at high strain rate and further enhanced by integrating a three-parameter Weibull function to describe the damage. Compared to the ZWT model, the modified model could effectively describe the mechanical response behavior of the gas obturator material at high strain rates. This research laid a theoretical foundation for further investigation into the influence of chamber sealing issues on artillery firing.展开更多
目的:探讨足月臀位外倒转术成功的相关因素。方法:以2014年4月至2017年4月在首都医科大学附属北京妇产医院定期产检的≥孕37周单胎臀位行外倒转术(均行椎管内麻醉)的孕妇149例为研究对象,按照倒转成功与否分为成功组和失败组,将相关因素...目的:探讨足月臀位外倒转术成功的相关因素。方法:以2014年4月至2017年4月在首都医科大学附属北京妇产医院定期产检的≥孕37周单胎臀位行外倒转术(均行椎管内麻醉)的孕妇149例为研究对象,按照倒转成功与否分为成功组和失败组,将相关因素(产妇年龄、产次、孕周、体质量指数、脐带长度、羊水指数、新生儿体质量、臀先露类型、绕颈与否、胎盘位置、是否使用宫缩抑制剂)行单因素分析和Logistic回归多因素分析。结果:149例行足月臀位外倒转术的孕妇中,成功59例,成功率39.60%。单因素分析结果提示:成功组(59例)与失败组(90例)脐带长度(54.00±5.92 cm vs 49.89±9.95 cm)和产次(初产妇与经产妇)差异有统计学意义(P<0.05)。多因素分析结果提示:产次、宫缩抑制剂、脐带长度是足月臀位外倒转手术成功的影响因素(P<0.05)。结论:多学科联合下进行足月臀位外倒转术是安全可行的,其成功的相关因素可能与产次、使用宫缩抑制剂和脐带长度有关。选择合适的病例,术前使用宫缩抑制剂,建议行椎管内麻醉,术中及术后加强观察和母儿监护,以达到安全分娩的目的。展开更多
基金supported by the Research project VAROPS(Military autonomous and robotic assets)of the Ministry of Defence of The Czech Republicby the Specific Research Support Project(Grant No.SV22-201)financed from funds of the Ministry of Education,Youth and Sports of The Czech Republic。
文摘The article deals with the motion of the breech block carrier and the weapon casing of an automatic weapon mounted on a flexible carriage and the base of the weapon.Earlier works,which did not consider the dynamic properties of the base of the weapon,did not allow to reconcile the calculated and experimental results of the weapon casing displacement when shooting from firing rests.For the analysis of the motion of individual parts,the methods of mathematical modelling and firing experiments using a high-speed camera were chosen.Calculations show the best accord with experiment when modelling the system with 4 degrees of freedom.The oscillation of the system regarding the movement of the breech block carrier and the weapon casing was investigated under changed conditions of rate of fire,the use of a muzzle brake and different types of shock absorbers.The velocities and displacements of the weapon casing and the breech block carrier at different values of the impulse of the gases to the breech block carrier were determined.
基金National Natural Science Foundation of China (Grant No. U2141246)。
文摘In order to investigate the mechanical response behavior of the gas obturator of the breech mechanism,made of polychloroprene rubber(PCR), uniaxial compression experiments were carried out by using a universal testing machine and a split Hopkinson pressure bar(SHPB), obtaining stress-strain responses at different temperatures and strain rates. The results revealed that, in comparison to other polymers, the gas obturator material exhibited inconspicuous strain softening and hardening effects;meanwhile, the mechanical response was more affected by the strain rate than by temperature. Subsequently, a succinct viscoelastic damage constitutive model was developed based on the ZWT model, including ten undetermined parameters, formulated with incorporating three parallel components to capture the viscoelastic response at high strain rate and further enhanced by integrating a three-parameter Weibull function to describe the damage. Compared to the ZWT model, the modified model could effectively describe the mechanical response behavior of the gas obturator material at high strain rates. This research laid a theoretical foundation for further investigation into the influence of chamber sealing issues on artillery firing.
文摘目的:探讨足月臀位外倒转术成功的相关因素。方法:以2014年4月至2017年4月在首都医科大学附属北京妇产医院定期产检的≥孕37周单胎臀位行外倒转术(均行椎管内麻醉)的孕妇149例为研究对象,按照倒转成功与否分为成功组和失败组,将相关因素(产妇年龄、产次、孕周、体质量指数、脐带长度、羊水指数、新生儿体质量、臀先露类型、绕颈与否、胎盘位置、是否使用宫缩抑制剂)行单因素分析和Logistic回归多因素分析。结果:149例行足月臀位外倒转术的孕妇中,成功59例,成功率39.60%。单因素分析结果提示:成功组(59例)与失败组(90例)脐带长度(54.00±5.92 cm vs 49.89±9.95 cm)和产次(初产妇与经产妇)差异有统计学意义(P<0.05)。多因素分析结果提示:产次、宫缩抑制剂、脐带长度是足月臀位外倒转手术成功的影响因素(P<0.05)。结论:多学科联合下进行足月臀位外倒转术是安全可行的,其成功的相关因素可能与产次、使用宫缩抑制剂和脐带长度有关。选择合适的病例,术前使用宫缩抑制剂,建议行椎管内麻醉,术中及术后加强观察和母儿监护,以达到安全分娩的目的。
