查看更多>>摘要：This paper investigates the three-dimensional crack propagation and damage evolution process of metallic column shells under internal explosive loading.The calibration of four typical failure parameters for 40CrMnSiB steel was conducted through experiments and subsequently applied to simulations.The numerical simulation results employing the four failure criteria were compared with the differences and similarities observed in freeze-recovery tests and ultra-high-speed tests.This analysis addressed the critical issue of determining failure criteria for the fracture of a metal shell under internal explosive loads.Building upon this foundation,the damage parameter Dc,linked to the cumulative crack density,was defined based on the evolution characteristics of a substantial number of cracks.The relationship be-tween the damage parameter and crack velocity over time was established,and the influence of the internal central pressure on the damage parameter and crack velocity was investigated.Variations in the fracture modes were found under different failure criteria,with the principal strain failure criterion proving to be the most effective for simulating 3D crack propagation in a pure shear fracture mode.Through statistical analysis of the shell penetration fracture radius data,it was determined that the fracture radius remained essentially constant during the crack evolution process and could be considered a constant.The propagation velocity of axial cracks ranged between 5300 m/s and 12600 m/s,surpassing the Rayleigh wave velocity of the shell material and decreasing linearly with time.The increase in shell damage exhibited an initial rapid phase,followed by deceleration,demonstrating accelerated damage during the propagation stage of the blast wave and decelerated damage after the arrival of the rarefaction wave.This study provides an effective approach for investigating crack propagation and damage evo-lution.The derived crack propagation and damage evolution law serves as a valuable reference for the development of crack velocity theory and the construction of shell damage evolution modes.
查看更多>>摘要：Based on the system dynamic model,a full system dynamics estimation method is proposed for a chain shell magazine driven by a permanent magnet synchronous motor(PMSM).An adaptive extended state observer(AESO)is proposed to estimate the unmeasured states and disturbance,in which the model parameters are adjusted in real time.Theoretical analysis shows that the estimation errors of the dis-turbances and unmeasured states converge exponentially to zero,and the parameter estimation error can be obtained from the extended state.Then,based on the extended state of the AESO,a novel parameter estimation law is designed.Due to the convergence of AESO,the novel parameter estimation law is insensitive to controllers and excitation signal.Under persistent excitation(PE)condition,the estimated parameters will converge to a compact set around the actual parameter value.Without PE signal,the estimated parameters will converge to zero for the extended state.Simulation and experi-mental results show that the proposed method can accurately estimate the unmeasured states and disturbance of the chain shell magazine,and the estimated parameters will converge to the actual value without strictly continuous PE signals.
查看更多>>摘要：Boron has been considered a promising powdered metal fuel for enhancing composite propellants'energy output due to its high energy density.However,the high ignition temperature and low com-bustion efficiency limit the application of boron powder due to the high boiling point of the boron oxide layer.Much research is ongoing to overcome these shortcomings,and one potential approach is to introduce a small quantity of metal oxide additives to promote the reaction of boron.This study prepared boron-rich fuels with 10 wt％of eight nano-metal oxide additives by mechanical ball milling.The effect of metal oxides on the thermo-oxidation,ignition,and combustion properties of boron powder was comprehensively studied by the thermogravimetric analysis(TG),the electrically heated filament setup(T-jump),and the laser-induced combustion experiments.TG experiments at 5 K/min found that Bi2O3,MoO3,TiO2,Fe2O3,and CuO can promote thermo-oxidation of boron.Compared to pure boron,Tonset can be reduced from 569 ℃ to a minimum of 449 ℃(B/Bi2O3).Infrared temperature measurement in T-jump tests showed that when heated by an electric heating wire at rates from 1000 K/s to 25000 K/s,the ignition temperatures of B/Bi2O3 are the lowest,even lower than the melting point of boron oxide.Ignition images and SEM for the products further showed that the high heating rate is beneficial to the rapid reaction of boron powder in the single-particle combustion state.Fuels(B/Bi2O3,B/MoO3,and B/CuO)were mixed with the oxidant AP and ignited by laser to study the combustion performance.The results showed that B/CuO/AP has the largest flame area,the highest BO2 characteristic spectral intensity,and the largest burn rate for powder lines.To combine the advantages of CuO and Bi2O3,binary metal oxide(CBO,mass ratio of 3:1)was prepared and the test results showed that CBO can very well improve both ignition and combustion properties of boron.Especially B/CBO/AP has the highest burn rate compared with all fuels containing other additives.It was found that multi-component metal-oxide additive can more synergistically improve the reaction characteristics of boron powder than unary ad-ditive.These findings contribute to the development of boron-rich fuels and their application in propellants.
查看更多>>摘要：Titanium hydride(TiH2),a promising high-energy additive,is doped into PTFE/Al to optimize the energy output structure of the reactive jet and strive for better aftereffect damage ability to the target.Six types of PTFE/Al/TiH2 reactive liners with different TiH2 content are prepared by the molding and sintering method.The energy release characteristics of PTFE/Al/TiH2 reactive jet are tested by the transient ex-plosion energy test,and are characterized from pressure and temperature.The reaction delay time,pressure history,and temperature history of the energy release process are obtained,then the actual value of released energy and reaction efficiency of the reactive jet are calculated.The results show that the peak pressure and temperature of the PTFE/Al/TiH2 jet initially increase and then decrease with increasing TiH2 content.When the TiH2 content is 10％,the actual value of released energy and reaction efficiency increased by 24％and 6.4％,respectively,compared to the PTFE/Al jet.The reaction duration of the reactive material is significantly prolonged as the TiH2 content increased from 0％to 30％.Finally,combined with the energy release behaviors of PAT material and the dynamic deformation process of liner,the enhancement mechanism of TiH2 on energy release of the reactive jet is expounded.
Nehad Abid Allah HamzaFatima Mohammed K.AL-FatlweMuna Ali Talib
177-192页
查看更多>>摘要：The sandwich panel incorporated a honeycomb core,a widely utilized composite structure recognized as a fundamental classification of composite materials.Comprised a core resembling a honeycomb,pos-sessing thickness and softness,and is flank by rigid face sheets that sandwich various shapes and ma-terials.This paper presents an examination of the static and dynamic analysis of lightweight plates made of aluminum honeycomb sandwich composites.Honeycomb sandwich plate samples are 300 mm long,and 300 mm wide,the heights of the core have been varied at four values ranging from 10 to 25 mm.The honeycomb core is manufactured from Aluminum material by using a novel technique namely resistance spot welding(RSW)instead of using adhesive material,which is often used when an industrial flaw is detected.Numerical optimization based on response surface methodology(RSM)and design of experi-ment software(DOE)was used to verify the current work.A theoretical examination of the crashwor-thiness behavior(maximum bending load,maximum deflection)and vibration attributes(natural frequency,damping ratio,transient temporal response)of honeycomb sandwich panels with different design parameters was also carried out.In addition,the finite element method-based ANSYS software was used to confirm the theoretical conclusions.The findings of the present work showed that the relationship between the natural frequency,core height,and cell size is direct.In contrast,the rela-tionship between the natural frequency and the thickness of the cell wall is inverse.Conversely,the damping ratio is inversely proportional to the core height and cell size but directly proportional to the thickness of the cell wall.The study indicates that altering the core height within 10-25 mm leads to a significant increase of 82％in the natural frequency and a notable decrease of 49％in the damping ratio.These findings are based on a specific cell size value of 0.01 m and a cell wall thickness of 0.001 m.Also,the results indicate that for a given set of cell wall thickness and size values,an increase in core height from(0.01-0.025)m,leads to a reduction of the percentage of maximum response approximately 76％.Conversely,the increasing thickness of the wall of cell wall,ranging 0.3-0.7 mm with a constant core height equal to 0.015 m,resulted in a de crease of maximum transient response by 7.8％.
查看更多>>摘要：This paper investigates a new vortex wave imaging approach to improve the imaging quality of small metal targets of size less than 1.5 mm.Antennas with different spiral phase plates are designed to efficiently transmit vortex beams with orbital angular momentums(OAMs).By analyzing the OAM spectrum of the target,it was discovered that the predominant reflection contains a particular OAM mode that carries abundant azimuthal information.This can be explained by the OAM selectivity of the target and the guidance of the vortex transmitting beam.A simple reflection vortex imaging system was designed to capture the phase information.Measurement results show that the high image contrast reaches 14.9％,which is twice as high as that of the imaging without OAM.Both of simulations and experiments demonstrate that the vortex phase imaging approach proposed in this paper can effectively improve the imaging quality at 80 GHz.This approach is suitable for other millimeter wave imaging systems and is helpful to improve the resolution in anti-terrorism security checks.
查看更多>>摘要：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 unde-termined parameters,formulated with incorporating three parallel components to capture the visco-elastic 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.
万方数据
维普