Effects of projectile parameters on the momentum transfer and projectile melting during hypervelocity impact

The effects of projectile/target impedance matching and projectile shape on energy,momentum transfer and projectile melting during collisions are investigated by numerical simulation.By comparing the computation results with the experimental results,the correctness of the calculation and the statistical method of momentum transfer coefficient is verified.Different shapes of aluminum,copper and heavy tungsten alloy projectiles striking aluminum,basalt,and pumice target for impacts up to 10 km/s are simulated.The influence mechanism of the shape of the projectile and projectile/target density on the momentum transfer was obtained.With an increase in projectile density and length-diameter ratio,the energy transfer time between the projectile and targets is prolonged.The projectile decelerates slowly,resulting in a larger cratering depth.The energy consumed by the projectile in the excavation stage increased,resulting in lower mass-velocity of ejecta and momentum transfer coefficient.The numerical simulation results demonstrated that for different projectile/target combinations,the higher the wave impedance of the projectile,the higher the initial phase transition velocity and the smaller the mass of phase transition.The results can provide theoretical guidance for kinetic impactor design and material selection.

Effective model for rare-earth Kitaev materials and its classical Monte Carlo simulation

Recently,the family of rare-earth chalcohalides were proposed as candidate compounds to realize the Kitaev spin liquid(KSL)[Chin.Phys.Lett.38047502(2021)].In the present work,we firstly propose an effective spin Hamiltonian consistent with the symmetry group of the crystal structure.Then we apply classical Monte Carlo simulations to preliminarily study the model and establish a phase diagram.When approaching to the low temperature limit,several magnetic long range orders are observed,including the stripe,the zigzag,the antiferromagnetic(AFM),the ferromagnetic(FM),the incommensurate spiral(IS),the multi-Q,and the 120°ones.We further calculate the thermodynamic properties of the system,such as the temperature dependence of the magnetic susceptibility and the heat capacity.The ordering transition temperatures reflected in the two quantities agree with each other.For most interaction regions,the system is magnetically more susceptible in the ab-plane than in the c-direction.The stripe phase is special,where the susceptibility is fairly isotropic in the whole temperature region.These features provide useful information to understand the magnetic properties of related materials.

Failure wave motion of 3D-C/SiC composites subjected to shock compression

The response and failure behavior of 3D-C/S軨 composites subjected to shock compression have been experimentally studied. With the help of a one-stage light gas gun, the 3D-C/SiC composite samples, which are subjected to the plane shock compression by LY-12 aluminum flyer sheets with different speeds become available. Based on the analysis of observation for the curve of pressure vs time, which has been measured from the tests as well as from the samples, it is found that when the shock speed is larger than a critical value, the material of 3D-C/SIC will be comminuted and the failure surface will move from the shock plane to its inward direction in the waveform.

Hypervelocity impact induced shock acoustic emission waves for quantitative damage evaluation using in situ miniaturized piezoelectric sensor network

Manmade debris and natural meteoroids, travelling in the Low Earth Orbit at a speed of several kilometers per second, pose a severe safety concern to the spacecraft in service through the HyperVelocity Impact(HVI). To address this issue, an investigation of shock Acoustic Emission(AE) waves induced by HVI to a downscaled two-layer Whipple shielding structure is performed,to realize a quantitative damage evaluation. Firstly a hybrid numerical model integrating smoothparticle hydrodynamics and finite element is built to obtain the wave response. The projectiles, with various impact velocities and directions, are modelled to impact the shielding structure with different thicknesses. Then experimental validation is carried out with built-in miniaturized piezoelectric sensors to in situ sense the HVI-induced AE waves. A quantitative agreement is obtained between numerical and experimental results, demonstrating the correctness of the hybrid model and facilitating the explanation of obtained AE signals in experiment. Based on the understanding of HVI-induced wave components, assessment of the damage severity, i.e., whether the outer shielding layer is perforated or not, is performed using the energy ratio between the regions of ‘‘high frequency" and ‘‘low frequency" in the acquired AE signals. Lastly, the direct-arrival fundamentalsymmetric wave mode is isolated from each sensing signal to be input into an enhanced delay-andsum algorithm, which visualizes HVI spots accurately and instantaneously with different sensor network configuration. All these works demonstrate the potential of quantitative, in situ, and real time HVI monitoring using miniaturized piezoelectric sensor network.

Dynamic Deformation Behaviors and Constitutive Relations of High-Strength Weldox700E Steel

High-strength Weldox700E steel has been increasingly applied to dynamic environment because of its high strength and good toughness. The plastic deformation behaviors of Weldox700E steel at strain rates ranging from 10^-4 to 6200 s^-1 are investigated by the quasistatic and dynamic uniaxial compression tests. The Weldox700E steel exhibits rate-related plastic behavior, work hardening and thermal softening behaviors. Due to the nonlinear strain rate effect of the material and the adiabatic temperature rise caused by high-speed impact compression, the properties of material are greatly affected. By improving the strain rate enhancement term and temperature term in the Johnson-Cook constitutive model, a new constitutive model was proposed to describe the dynamic mechanical behavior of Weldox700E steel. This constitutive equation was implemented into the finite element software, ABAQUS, via an explicit user material subroutine utilizing the stress update algorithm. The simulation results at different strain rates were in good agreement with the experimental data, verifying the validity of the constitutive model.

Dimensional crossover tuned by pressure in layered magnetic NiPS_(3)

The physical properties of most 2D materials are highly dependent on the nature of their interlayer interaction.In-depth studies of the interlayer interaction are beneficial to the understanding of the physical properties of 2D materials and permit the development of related devices.Layered magnetic NiPS_(3)has unique magnetic and electronic properties.The electronic band structure and corresponding magnetic state of NiPS_(3)are expected to be sensitive to the interlayer interaction,which can be tuned by external pressure.Here,we report an insulator-metal transition accompanied by the collapse of magnetic order during the 2D-3D structural crossover induced by hydrostatic pressure.A two-stage phase transition from a monoclinic(C2/m)to a trigonal(P31m)lattice is identified via ab initio simulations and confirmed via high-pressure X-ray diffraction and Raman scattering;this transition corresponds to a layer-by-layer slip mechanism along the a-axis.Temperature-dependent resistance measurements and room temperature infrared spectroscopy under different pressures demonstrate that the insulator-metal transition and the collapse of the magnetic order occur at~20 GPa,which is confirmed by low-temperature Raman scattering measurements and theoretical calculations.These results establish a strong correlation between the structural change,electric transport,and magnetic phase transition and expand our understanding of layered magnetic materials.Moreover,the structural transition caused by the interlayer displacement has significance for designing similar devices at ambient pressure.