A superposing principle, by suitably adding the strain waves from a number of concentrated explosive charges to approximate the waves generated by a cylindrical charge based on the strain wave of a point or small sphe...A superposing principle, by suitably adding the strain waves from a number of concentrated explosive charges to approximate the waves generated by a cylindrical charge based on the strain wave of a point or small spherical explosive charge generated in rock, is used to further study the triggering time of strain gauges installed in radial direction at same distances but different positions surrounding a cylindrical explosive charge in rock. The duration of the first compression phase and peak value of strain wave, and furthermore, their differences are analyzed and some explanations are given. Besides that, the gauge orientation in which the maximum peak value occurs is also discussed. At last, the effect of velocity of detonation(V.O.D.) of a cylindrical explosive charge on the strain waves generated in the surrounding rock is taken as key research and the pattern of peak amplitude of a strain wave varies with the V.O.D. is likely to have been found.展开更多
Compression ratio is significant for cellular structures on energy absorption. In the present work, theoretical formulas to determine the initial densification strain of honeycomb structure were put forward by means o...Compression ratio is significant for cellular structures on energy absorption. In the present work, theoretical formulas to determine the initial densification strain of honeycomb structure were put forward by means of minimum energy principle. Detailed densification strain points were identified, with full fold model for kinds of specimens. To validate, corresponding numerical simulations were carried out with explicit finite element method. Excellent agreement in terms of initial densification stain point has been observed between the theoretical calculation and numerical simulation. The results show that: (1) a different honeycomb structure has different initial densification strain point, and its geometric configuration of cells plays an evident role on densification; (2) half-wave length of the wrinkle of honeycomb in folding process significantly influences on the densification strain point; (3) the initial densification point is an decreasing power function of the ratio of foil thickness to cell length, with the exponent 2/3. These achievements provide important references for design in cellular energy absorption devices.展开更多
Metal sheet plastic deformation or forming is gener at ed through a mechanical pressure or a thermal variation. These pressure variatio ns or thermal variations can be created by a variety of means such as press form ...Metal sheet plastic deformation or forming is gener at ed through a mechanical pressure or a thermal variation. These pressure variatio ns or thermal variations can be created by a variety of means such as press form ing, hydroforming, imploding detonation and so on. According to the magnitude of the strain rates all these forming methods can be divided into quasi-static fo rming and dynamical forming. Up to now there are no reports of forming methods w ith the strain rates above 10 5sec -1, even though the exploding forming. In this article, we work on a dynamic super-speed forming method driven by lase r shock waves and advanced a novel concept of laser shock forming. The initial o bservation of the laser shock forming is done through a bugle testing with speci mens of SUS430 sheet metal, using a neodymium-glass laser of pulse energy 10J～ 3 0J and duration of 20 ns (FWHM). The investigation revealed that the plastic de formation during the laser shock forming is characterized as ultrahigh strain ra te up to 10 7sec -1. We indicate that plastic deformation increases nonlin early when the energy density of the laser varies. By investigating the hardness and residual stress of the surfaces, we conclude that laser shock forming is a combination technique of laser shock strengthening and metal forming for introdu cing a strain harden and a compressive residual stress on the surface of the wor k-piece, and the treated surface by laser shock forming has good properties in fatigue and corrosion resistance. This technique can achieve forming wit h or without mould.展开更多
为探究固体介质中爆炸应变波信号特征,采用Hilbert-Huang Transform(HHT)方法对爆炸应变波信号进行时频分析;讨论爆炸应变波信号EMD分解及时频能分布特征,并将HHT分析结果与Short Time Fourier Transform(STFT)对比;通过分析爆炸波在空...为探究固体介质中爆炸应变波信号特征,采用Hilbert-Huang Transform(HHT)方法对爆炸应变波信号进行时频分析;讨论爆炸应变波信号EMD分解及时频能分布特征,并将HHT分析结果与Short Time Fourier Transform(STFT)对比;通过分析爆炸波在空气、岩石介质中传播的数值模拟结果与爆炸应变波在有机玻璃中传播的动光弹实验结果,探讨爆炸波信号多频率作用特征。结果表明,爆源近中区爆炸应变波主频率在几百千赫兹到几兆赫兹范围内;HHT方法明显表现出爆炸应变波传播的细节特征;固体介质中爆炸应变波信号波形为由不同频率波动共同作用结果。展开更多
基金Projects(51304239,51374243)supported by the National Natural Science Foundation of China
文摘A superposing principle, by suitably adding the strain waves from a number of concentrated explosive charges to approximate the waves generated by a cylindrical charge based on the strain wave of a point or small spherical explosive charge generated in rock, is used to further study the triggering time of strain gauges installed in radial direction at same distances but different positions surrounding a cylindrical explosive charge in rock. The duration of the first compression phase and peak value of strain wave, and furthermore, their differences are analyzed and some explanations are given. Besides that, the gauge orientation in which the maximum peak value occurs is also discussed. At last, the effect of velocity of detonation(V.O.D.) of a cylindrical explosive charge on the strain waves generated in the surrounding rock is taken as key research and the pattern of peak amplitude of a strain wave varies with the V.O.D. is likely to have been found.
基金Project(51505502)supported by the National Natural Science Foundation of ChinaProject(2015BAG13B01)supported by the National Key Technology Support Program,China+1 种基金Project(ZZYJKT2017-09)supported by the State Key Laboratory of High Performance Complex Manufacturing,ChinaProject supported by the Open End Fund for the Valuable and Precision Instrument of Central Sonth University,China
文摘Compression ratio is significant for cellular structures on energy absorption. In the present work, theoretical formulas to determine the initial densification strain of honeycomb structure were put forward by means of minimum energy principle. Detailed densification strain points were identified, with full fold model for kinds of specimens. To validate, corresponding numerical simulations were carried out with explicit finite element method. Excellent agreement in terms of initial densification stain point has been observed between the theoretical calculation and numerical simulation. The results show that: (1) a different honeycomb structure has different initial densification strain point, and its geometric configuration of cells plays an evident role on densification; (2) half-wave length of the wrinkle of honeycomb in folding process significantly influences on the densification strain point; (3) the initial densification point is an decreasing power function of the ratio of foil thickness to cell length, with the exponent 2/3. These achievements provide important references for design in cellular energy absorption devices.
文摘Metal sheet plastic deformation or forming is gener at ed through a mechanical pressure or a thermal variation. These pressure variatio ns or thermal variations can be created by a variety of means such as press form ing, hydroforming, imploding detonation and so on. According to the magnitude of the strain rates all these forming methods can be divided into quasi-static fo rming and dynamical forming. Up to now there are no reports of forming methods w ith the strain rates above 10 5sec -1, even though the exploding forming. In this article, we work on a dynamic super-speed forming method driven by lase r shock waves and advanced a novel concept of laser shock forming. The initial o bservation of the laser shock forming is done through a bugle testing with speci mens of SUS430 sheet metal, using a neodymium-glass laser of pulse energy 10J～ 3 0J and duration of 20 ns (FWHM). The investigation revealed that the plastic de formation during the laser shock forming is characterized as ultrahigh strain ra te up to 10 7sec -1. We indicate that plastic deformation increases nonlin early when the energy density of the laser varies. By investigating the hardness and residual stress of the surfaces, we conclude that laser shock forming is a combination technique of laser shock strengthening and metal forming for introdu cing a strain harden and a compressive residual stress on the surface of the wor k-piece, and the treated surface by laser shock forming has good properties in fatigue and corrosion resistance. This technique can achieve forming wit h or without mould.
文摘为探究固体介质中爆炸应变波信号特征,采用Hilbert-Huang Transform(HHT)方法对爆炸应变波信号进行时频分析;讨论爆炸应变波信号EMD分解及时频能分布特征,并将HHT分析结果与Short Time Fourier Transform(STFT)对比;通过分析爆炸波在空气、岩石介质中传播的数值模拟结果与爆炸应变波在有机玻璃中传播的动光弹实验结果,探讨爆炸波信号多频率作用特征。结果表明,爆源近中区爆炸应变波主频率在几百千赫兹到几兆赫兹范围内;HHT方法明显表现出爆炸应变波传播的细节特征;固体介质中爆炸应变波信号波形为由不同频率波动共同作用结果。
