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.

Finite Temperature Magnetism in the Triangular Lattice Antiferromagnet KErTe_(2)

After the discovery of the ARECh_(2)(A=alkali or monovalent ions,RE=rare-earth,Ch=chalcogen)triangular lattice quantum spin liquid(QSL)family,a series of its oxide,sulfide,and selenide counterparts has been consistently reported and extensively investigated.While KErTe_(2) represents the initial synthesized telluride member,preserving its triangular spin lattice,it was anticipated that the substantial tellurium ions could impart more pronounced magnetic attributes and electronic structures to this material class.This study delves into the magnetism of KErTe_(2) at finite temperatures through magnetization and electron spin resonance(ESR)measurements.Based on the angular momentum J after spin-orbit coupling(SOC)and symmetry analysis,we obtain the magnetic effective Hamiltonian to describe the magnetism of Er^(3+)in R3m space group.Applying the mean-field approximation to the Hamiltonian,we can simulate the magnetization and magnetic heat capacity of KErTe_(2) in paramagnetic state and determine the crystalline electric field(CEF)parameters and partial exchange interactions.The relatively narrow energy gaps between the CEF ground state and excited states exert a significant influence on the magnetism.For example,small CEF excitations can result in a significant broadening of the ESR linewidth at 2 K.For the fitted exchange interactions,although the values are small,given a large angular momentum J=15/2 after SOC,they still have a noticeable effect at finite temperatures.Notably,the heat capacity data under different magnetic fields along the𝑐axis direction also roughly match our calculated results,further validating the reliability of our analytical approach.These derived parameters serve as crucial tools for future investigations into the ground state magnetism of KErTe_(2).The findings presented herein lay a foundation for exploration of the intricate magnetism within the triangular-lattice delafossite family.

Rare-Earth Chalcogenides:An Inspiring Playground for Exploring Frustrated Magnetism

The rare-earth chalcogenide ARECh_(2) family(A=alkali metal or monovalent ions,RE=rare earth,Ch=chalcogen)has emerged as a paradigmatic platform for studying frustrated magnetism on a triangular lattice.The family members exhibit a variety of ground states,from quantum spin liquid to exotic ordered phases,providing fascinating insight into quantum magnetism.Their simple crystal structure and chemical tunability enable systematic exploration of competing interactions in quantum magnets.Recent neutron scattering and thermodynamic studies have revealed rich phase diagrams and unusual excitations,refining theoretical models of frustrated systems.This review provides a succinct introduction to ARECh_(2)research.It summarizes key findings on crystal structures,single-ion physics,magnetic Hamiltonians,ground states,and low-energy excitations.By highlighting current developments and open questions,we aim to catalyze further exploration and deeper physical understanding on this frontier of quantum magnetism.

Rare-Earth Chalcogenides:A Large Family of Triangular Lattice Spin Liquid Candidates

Frustrated quantum magnets are expected to host many exotic quantum spin states like quantum spin liquid（QSL）, and have attracted numerous interest in modern condensed matter physics. The discovery of the triangular lattice spin liquid candidate YbMgGaO_4 stimulated an increasing attention on the rare-earth-based frustrated magnets with strong spin-orbit coupling. Here we report the synthesis and characterization of a large family of rare-earth chalcogenides AReCh_2（A = alkali or monovalent ions, Re = rare earth, Ch = O,S,Se）. The family compounds share the same structure（R3 m） as YbMgGaO_4,and antiferromagnetically coupled rare-earth ions form perfect triangular layers that are well separated along the c-axis. Specific heat and magnetic susceptibility measurements on NaYbO_2,NaYbS_2 and NaYbSe_2 single crystals and polycrystals, reveal no structural or magnetic transition down to 50 mK. The family, having the simplest structure and chemical formula among the known QSL candidates, removes the issue on possible exchange disorders in YbMgGaO_4. More excitingly, the rich diversity of the family members allows tunable charge gaps, variable exchange coupling, and many other advantages.This makes the family an ideal platform for fundamental research of QSLs and its promising applications.

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.

Crystal growth and magnetic properties of quantum spin liquid candidate KErTe_(2)

Recently rare-earth chalcogenides have been revealed as a family of quantum spin liquid(QSL)candidates hosting a large number of members.In this paper we report the crystal growth and magnetic measurements of KErTe_(2),which is the first member of telluride in the family.Compared to its cousins of oxides,sulfides and selenides,KErTe_(2) retains the high symmetry of R3m and Er3+ions still sit on a perfect triangular lattice.The separation between adjacent magnetic layers is expectedly increased,which further enhances the two dimensionality of the spin system.Specific heat and magnetic susceptibility measurements on KErTe_(2) single crystals reveal no structural and magnetic transition down to 1.8 K.Most interestingly,the absorption spectrum shows that the charge gap of KErTe_(2) is roughly 0.93±0.35 eV,which is the smallest among all the reported members in the family.This immediately invokes the interest towards metallization even superconductivity using the compound.

Rare-Earth Chalcohalides: A Family of van der Waals Layered Kitaev Spin Liquid Candidates

The Kitaev spin liquid(KSL) system has attracted tremendous attention in recent years because of its fundamental significance in condensed matter physics and promising applications in fault-tolerant topological quantum computation.Material realization of such a system remains a major challenge in the field due to the unusual configuration of anisotropic spin interactions,though great effort has been made before.Here we reveal that rare-earth chalcohalides REChX(RE=rare earth;Ch=O,S,Se,Te;X=F,Cl,Br,I) can serve as a family of KSL candidates.Most family members have the typical SmSI-type structure with a high symmetry of R3m,and rare-earth magnetic ions form an undistorted honeycomb lattice.The strong spin-orbit coupling of 4f electrons intrinsically offers anisotropic spin interactions as required by the Kitaev model.We have grown the crystals of YbOCl and synthesized the polycrystals of SmSI,ErOF,HoOF and DyOF,and made careful structural characterizations.We carry out magnetic and heat capacity measurements down to 1.8 K and find no obvious magnetic transition in all the samples but DyOF.The van der Waals interlayer coupling highlights the true two-dimensionality of the family which is vital for the exact realization of Abelian/non-Abelian anyons,and the graphene-like feature will be a prominent advantage for developing miniaturized devices.The family is expected to act as an inspiring material platform for the exploration of KSL physics.

Magnetism of NaYbS_(2):From finite temperatures to ground state

Rare-earth chalcogenide compounds ARECh_(2)(A=alkali or monovalent metal,RE=rare earth,Ch=O,S,Se,Te)are a large family of quantum spin liquid(QSL)candidate materials.NaYbS2is a representative member of the family.Several key issues on NaYbS_(2),particularly how to determine the highly anisotropic spin Hamiltonian and describe the magnetism at finite temperatures and the ground state,remain to be addressed.In this paper,we conducted an in-depth and comprehensive study on the magnetism of NaYbS_(2) from finite temperatures to the ground state.Firstly,we successfully detected three crystalline electric field(CEF)excitation energy levels using low-temperature Raman scattering technique.Combining them with the CEF theory and magnetization data,we worked out the CEF parameters,CEF energy levels,and CEF wavefunctions.We further determined a characteristic temperature of~40 K,above which the magnetism is dominated by CEF excitations while below which the spinexchange interactions play a main role.The characteristic temperature has been confirmed by the temperature-dependent electron spin resonance(ESR)linewidth.Low-temperature ESR experiments on the dilute magnetic doped crystal of NaYb_(0.1)Lu_(0.9)S_(2) further helped us to determine the accurate g-factor.Next,we quantitatively obtained the spin-exchange interactions in the spin Hamiltonian by consistently simulating the magnetization and specific heat data.Finally,the above studies allow us to explore the ground state magnetism of NaYbS_(2) by using the density matrix renormalization group.We combined numerical calculations and experimental results to demonstrate that the ground state of NaYbS_(2) is a Dirac-like QSL.

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.