Dynamic Behavior Of Materials Research Articles

Additive manufacture of ultrasoft bioinspired metamaterials

The dynamic loading behavior of materials plays a vital role in various engineering applications, such as aerospace protective components, armor, marine infrastructures, and automotive crash safety. The advent of additive manufacturing technologies has enabled the design of metamaterials that exhibit exceptional mechanical performance and artificially engineered properties not found in nature. However, fabricating ideal materials that resist dynamic loading is challenging because of the complexity of dynamic mechanical processes and varying requirements across different applications. In this study, a novel hierarchical design is proposed that combines natural fiber-inspired frameworks with graphene-inspired parent structures. This design aims to produce metamaterials, with characteristics such as reduced dynamic compressive strength, high energy absorption, and programmable dynamic loading, via advanced manufacturing technologies. An additive-manufacturing-oriented digital design approach and machine learning techniques were employed to engineer the dynamic loading performance of graphene-inspired metamaterials using the bonding principles inspired by natural fibers, to facilitate the design of next-generation metamaterial for advanced manufacturing. Experimental results illustrate the significant improvements achieved with our metamaterials compared to their existing counterparts. These improvements include a decrease in dynamic compressive strength of up to 86 %, while maintaining a remarkable 682 % enhancement in energy absorption during dynamic compressions, with a 42 % reduction in the energy decay rate. A compositional design strategy and programmable dynamic compression curve methodology is proposed that enable the tailored optimization of dynamic loading behaviors without modifying the base topology of metamaterials. This research offers a promising pathway for the development of next-generation materials, engineered to withstand dynamic loadings with intelligent and programmable performances suitable for aerospace, defense, and other high-value applications. By leveraging the advantages of natural fiber-inspired structures and graphene-inspired metamaterials, this work contributes to the advancement of materials with tailored resistance to dynamic loading and opens new possibilities for intelligent dynamic loading performance.

Impact induced compression and decompression waves in porous meta-materials modeled using a continuum theory of phase transitions

Porous meta-materials with both regular and random microstructure are of intense research interest today due to their interesting dynamical properties, including but not limited to, their acoustic band structure, shock absorption properties, and fracture toughness. Some of these materials can exist in a rarefied or densified state depending on the state of stress, and recover their original configuration after a cycle of loading and unloading. Often, they exhibit a hysteretic stress–strain response under quasistatic uniaxial compression. As such, many aspects of their mechanical behavior can be captured using a continuum theory of phase transitions. In this work, the dynamical behavior of such materials is explored. It is shown that the impact problem for these materials can result in propagating shocks, phase boundaries, and fans. The impact problems admit multiple solutions for the same set of initial and boundary conditions leading to non-uniqueness. This non-uniqueness can be remedied using a nucleation criterion and kinetic laws, as is known from the continuum theory of phase transitions. The fan solutions which arise in decompressive impact problems have not received much attention in the literature and may be regarded as a novel contribution of this work. The analysis presented here may have applications in the dynamic behavior of a broad class of porous materials including architected truss-like metastructures and random fiber networks.

Goufo-Caputo fractional viscoelastic photothermal model of an unbounded semiconductor material with a cylindrical cavity

In order to describe the photothermal dynamic behavior of viscoelastic semiconductor materials, the authors of this work propose a fractional modification of the Kelvin-Voigt type. The generalized Mittag-Leffler function method with two parameters was utilized as the non-local, nonsingular kernel of the Goufo-Caputo fractional operator, which is similar to the AB fractional derivative. Also, a new concept of photovoltaic heat transfer has been developed to describe the process of photothermal heating in semiconductors, in which light energy is converted into thermal energy by absorption. This unique model is grounded in the theoretical framework of the Moore-Gibson-Thompson (MGT) equation, and it offers additional insights into the underlying process of light sensitive heat transfer, as well as the intricate interaction between heating signals, elasticity, and plasma. As a direct application of the proposed model, the photothermal interactions that occur when an infinitely rotating semiconductor material with a cylindrical hole is subjected to a laser thermal flux and immersed in a constant axial magnetic field have been investigated. These findings may have implications for developing optically absorbent nanostructures and their use in photothermal energy generation. For this reason, the comparison of modified photoelasticity models with spherical derivatives and classical models applied to semiconducting materials seems interesting.

Static and dynamic behavior of cemented heat storage materials

Assessing the mechanical and thermal stability of heat storage media is vital in the design and wellbeing of sensible heat storage systems, which are typically designed below ground level or as part of the sub-structure of buildings with load bearing capabilities. Nevertheless, considering the importance that a mechanically sound heat storage media (especially at elevated temperatures) has on the efficiency and performance of heat storage systems, it has not been given adequate attention in past studies. On this basis, the mechanical performance of two commercial cemented heat storage materials at different curing periods, pressure and temperature is studied in this research. The influence of curing period on the mechanical strength of the materials was studied by performing unconfined compression tests, where as to study the effects of pressure and temperature on seismic velocities, and hence mechanical properties of the materials, laboratory tests on P- and S-wave velocities were performed. Ultrasonic wave velocity studies can be used to estimate many geomechanical properties of materials such as density, elastic modulus, Poisson’s ratio etc., thus providing an accurate and reliable estimate of the mechanical properties of rocks and cemented materials. The results presented in this study show a considerable dependence of the mechanical behavior of the investigated materials on curing period, pressure and temperature, which when unaccounted for can result in the inaccurate planning and design of heat storage systems.

A Numerical Study of the Dynamic Crack Behavior of Brittle Material Induced by Blast Waves.

Blast stress waves profoundly impact engineering structures, exciting and affecting the rupture process in brittle construction materials. A novel numerical model was introduced to investigate the initiation and propagation of cracks subjected to blast stress waves within the borehole-crack configuration. Twelve models were established with different crack lengths to simulate sandstone samples. The influence of crack length on crack initiation and propagation was investigated using those models. The linear equation of state was used to express the relationship between the pressure and density of the material. The major principal stress failure criterion was used to evaluate the failure of elements. A triangular pressure curve was adopted to produce the blast stress wave. The results indicated that the pre-crack length critically influenced the crack initiation and propagation mechanism by analyzing the stress history at the crack tip, crack propagation velocity, and distance. The inducement of a P-wave and S-wave is paramount in models with a short pre-crack. For long pre-crack models, Rayleigh waves significantly contribute to crack propagation.

Parameter determination and verification of ZWT viscoelastic dynamic constitutive model of Al/Ep/W material considering strain rate effect

As a new type of energetic structural material, Al/Ep/W(Aluminum/epoxy/tungsten), whether as a fragment or projectile material, should comprehensively consider the impact energy release and structural strength, especially the structural strength is the premise to ensure the material integrity. The dynamic constitutive model of materials is the theoretical basis for describing the strength and dynamic behavior of materials. Therefore, it is great significance to determine the dynamic constitutive model parameters of Al/Ep/W materials considering strain rate effect, and to verify the reliability of the model. In this paper, Al/Ep/W material is prepared, and the stress/strain relationship curve of the material under high strain rate is obtained through Split Hopkinson Pressure Bar (SHPB) test. The ZWT viscoelastic constitutive model is selected based on the composition of the material and the distribution of the internal components, and the simplified ZWT constitutive model with damage under constant strain rate is derived, and the parameters of the constitutive model are fitted by the least square method. By using Kirchhoff stress and Green strain tensor theory, the incremental form of the constitutive model is derived, and the Abaqus user material subroutine is written and embedded in the finite element software. The accuracy of material VUMAT subroutine is verified by comparing the results of SHPB test and numerical simulation under high strain rate. Combined with the verified material model subroutine, the experiment and numerical simulation of Al/Ep/W cylindrical projectile impacting aluminum plate are conducted. The results show that the experimental and numerical simulation results are in good agreement. The proposed model can be used to evaluate the dynamic response characteristics of the new energetic material projectile to the lightweight aluminum armor protective structure.

Combining multiple lattice-topology functional grading strategies for enhancing the dynamic compressive behavior of TPMS-based metamaterials

Recent developments in additive manufacturing technology have enabled the precise fabrication of intricate lattice materials, also known as metamaterials, for various engineering applications, particularly those involving dynamics. Lattice materials, consisting of sheet-based triply periodic minimal surface (TPMS) structures, have been extensively studied for their mechanical performance under quasi-static and dynamic loading conditions. However, less attention has been given to assessing the effect of grading the lattice topological properties for improved compression loading. Consequently, this paper investigates the effect of topology hybridization, periodicity gradation, cell compaction, and combining multiple functional grading strategies on the quasi-static and dynamic compressive behavior of sheet-based TPMS lattice materials. We conducted quasi-static compression tests to evaluate different regular sheet-based TPMS architectures and select the most promising candidates for topology-functional gradation. Subsequently, numerical simulations were performed to analyze the compressive deformation behavior and properties of functionally graded sheet-based TPMS lattice materials alongside the uniform topologies. This test showed that Schwartz Diamond (Du) and Face-centered Rhombic Dodecahedral (FRDu) lattice structures exhibit superior compressive properties in quasi-static conditions. Furthermore, simulations revealed that the lattice topology and grading strategy significantly influence the quasi-static and dynamic compressive behavior of sheet-based TPMS lattice materials. Specifically, the IWPu topology showed a notable increase in compressive strength and energy absorption compared to the other lattice types as the strain rate increased. Hybridizing Du and FRDu topologies produced a strictly layer-wise deformation pattern, resulting in improved quasi-static and dynamic compressive properties compared to the elementary topology. However, a superior uniaxial compressive modulus and strength were achieved by gradually adjusting the periodicity of a single topology (Du) while maintaining the same relative density. The combination of relative density and periodicity gradation led to more desirable deformation behavior while enhancing the overall compressive properties of the metamaterial, regardless of the strain rate.

Block‐Grain Phase Transition in Rock Avalanches: Insights From Large‐Scale Experiments

AbstractKnowledge of the processes and effects of the block‐grain phase transition in a fragmented system is essential for investigating rock avalanches. Several series of experiments are performed with a very large apparatus, using a jointed block, simulated by an assembly of packed breakable subblocks varying in configuration, as an analog for brittle rock. The analog jointed block is released from a hopper, moves on two inclined flumes with different slopes, and finally deposits on a horizontal platform. The block‐grain phase transition occurs, caused by subblock collisions and explosive impacts with the flume bottom. The dynamic behavior, seismic signal, fragment characteristic, and deposit structure of the analog material are determined. Our results demonstrate that fragmentation influences energy dissipation and momentum transfer, as well as subsequent flow and emplacement processes. A nonunified and piecewise relationship between the fragmentation degree and friction coefficients is observed. We ascribe this nonunified relationship to the varying dynamics and runout regimes that different configurations of jointed blocks undergo. The positive or negative feedback on energy generated by fragmentation is closely associated with the energy budget involved in this fragmented system, which depends substantively on the block configuration. Particularly, for flatter or larger jointed blocks, despite increased fragmentation absorbing the available energy for runout, it simultaneously changes the runout regime toward a more energy‐efficient one, thus instigating positive feedback. Our study further highlights the contribution of post‐fragmentation granular flow to the energy system.

Dynamic tensile deformation behavior of AISI 316L stainless steel fabricated by laser-beam directed energy deposition

The dynamic deformation behavior of metallic materials is the key to crash-safe design in many applications, e.g., in the automotive sector. However, in the field of additive manufacturing, dynamic deformation properties have only been scarcely studied. Based on the intrinsic interrelationships of process parameters, post-process heat treatments and the resulting microstructure, the present study seeks to provide a holistic overview of the dynamic tensile deformation properties of AISI 316L stainless steel, fabricated by laser-beam directed energy deposition. Utilizing in situ digital image correlation, the local deformation behavior at varying strain rates from 100 s−1 to 1000 s−1 was unveiled. In combination with pre- and post-mortem microstructure analysis using electron backscatter diffraction and scanning transmission electron microscopy, the microstructural effects on the active deformation mechanisms were studied. The results show that twinning contributes to the overall deformation in the heat-treated condition owing to the weaker crystallographic texture. On the contrary, twinning is less prominent in the non-heat-treated condition due to its pronounced <001> texture. As a result of the differences in terms of active deformation mechanisms, superior fracture elongations are observed in heat-treated condition, which are rationalized by delayed necking due to a more homogeneous strain distribution along the gauge section. Independently from the sample condition, fractography analysis revealed a ductile mode of failure being characterized by equiaxed dimples on the fracture surfaces. Consequently, it can be concluded that AISI 316L stainless steel is excellently suited for dynamic tensile loading, although heat-treatment-depended differences have to be taken into account.

Irreversible Mechanical Deformations Associated with the Formation of Cathode-Electrolyte Interface on Lithium Iron Phosphate Cathodes

The demand for rechargeable batteries for energy storage in electrical automobiles is rising presently due to their key role in reducing carbon emissions. However, the increasing demands require improvement in batteries lifetime. interfacial instabilities associated with the formation of cathode-electrolyte interface and intercalation-induced volumetric expansions are the primary reasons behind the capacity fade. Although there have been great efforts to understand structural stress/strains in cathodes, there is a lack of knowledge about the formation mechanism of cathode-electrolyte interface (CEI) layers. To fill the gap, we investigate the role of electrolyte chemistry on the interfacial deformation of lithium iron phosphate (LFP) cathodes by employing digital image correlation (DIC), spectroscopy, and electrochemical techniques. DIC was utilized to study the dynamic physical behavior of the electrode materials and irreversible strains associated with the electrolyte decomposition on the electrode surface [1]. Therefore, the overall objective of this study is to elucidate the mechanical deformations in the LFP cathodes of battery electrodes by investigating the physical response of the electrode and dynamic changes on the electrode – electrolyte interface.To be able to understand the different effects of the electrolyte solution, electrolytes were made of either LiPF6, LiClO4, or LiTFSI salts dissolved in 1 M EC:DMC. When cycled in the LiClO4 and LiTFSI salts containing electrolytes, the volumetric contraction is observed in the electrode because of the extraction of lithium and associated phase transformations during the first delithiation. However, positive strain generation was observed only during the first cycle in LiPF6 containing electrolyte, although delithiation results in reducing the lattice parameters. Control experiments were conducted where the electrode was cycled in LiClO4-containing electrolyte for one cycle and electrolyte was changed to the LiPF6-containing electrolyte for the subsequent cycles. A similar irreversible mechanical behavior was also observed in the control experiments where positive strain generation is recorded during the subsequent first delithiation cycle in LiPF6-containing electrolyte. To further analysis, electrochemical impedance spectroscopy measurements were performed on each system to identify surface resistance of the electrodes in a voltage range between 3 - 4.4 V. Increasing in the surface resistance of the electrodes were associated with CEI layer formations [2, 3]. Chemical composition of the CEI layers were characterized by using x-ray photoelectron spectroscopy. Our study provides a pathway to investigate the formation of the cathode-electrolyte interface on the cathode electrodes by monitoring irreversible physical behavior of the electrode – electrolyte interface during cycling.This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences (Award numberDE-SC0021251). References Çapraz, Ö. Ö., Rajput, S., Bassett, K. L., Gewirth, A. A., White, S. R., & Sottos, N. R. (2019). Controlling expansion in lithium manganese oxide composite electrodes via surface modification. Journal of The Electrochemical Society, 166(12), A2357.Liu, Y., & Xie, J. (2015). Failure study of commercial LiFePO4 cells in overcharge conditions using electrochemical impedance spectroscopy. Journal of The Electrochemical Society, 162(10), A2208.Bassett, K. L., Çapraz, Ö. Ö., Özdogru, B., Gewirth, A. A., & Sottos, N. R. (2019). Cathode/electrolyte interface-dependent changes in stress and strain in lithium iron phosphate composite cathodes. Journal of the Electrochemical Society, 166(12), A2707.

Dynamic Mechanical Properties and Damage Parameters of Marine Pipelines Based on Johnson–Cook Model

A comprehensive understanding of the dynamic behavior of materials and structures under impact loads is paramount for the design and maintenance of reliable marine pipelines and associated structures. However, there is a lack of comprehensive research on the full characterization of constitutive and failure models of carbon steels, which are commonly used in marine pipelines. In this paper, Q235 steel was subjected to quasi-static tensile tests at room temperature on smooth specimens to obtain the constitutive parameters using the Johnson–Cook (J-C) model. Subsequently, quasi-static tensile tests were conducted on notched specimens, and dynamic tensile tests were performed on smooth round bars to obtain stress triaxiality and failure strain. The acquired data were then utilized to fit the failure parameters using the Johnson–Cook (J-C) damage model, a widely accepted constitutive model employed in high-strain rate applications through the least squares method. Finally, the tensile test is numerically simulated based on the acquired experimental parameters. The obtained results reveal a remarkable agreement between the curve fitted by the J-C constitutive model and the experimental tensile curve. Additionally, a high degree of correlation between the load-displacement curves of the tests and simulations provides robust validation of the accuracy of the dynamic mechanical parameters for Q235 steel. These findings contribute valuable insights into the behavior of carbon steels commonly used in marine pipelines, enhancing the overall understanding of their response to impact loads and informing more reliable design and maintenance practices.

The Shock-Induced Deformation and Spallation Failure of Bicrystal Copper with a Nanoscale Helium Bubble via Molecular Dynamics Simulations.

Both the nanoscale helium (He) bubble and grain boundaries (GBs) play important roles in the dynamic mechanical behavior of irradiated nanocrystalline materials. Using molecular dynamics simulations, we study the shock-induced deformation and spallation failure of bicrystal copper with a nanoscale He bubble. Two extreme loading directions (perpendicular or parallel to the GB plane) and various impact velocities (0.5-2.5 km/s) are considered. Our results reveal that the He bubble shows hindrance to the propagation of shock waves at lower impact velocities but will accelerate shock wave propagation at higher impact velocities due to the local compression wave generated by the collapse of the He bubble. The parallel loading direction is found to have a greater effect on He bubble deformation during shock compression. The He bubble will slightly reduce the spall strength of the material at lower impact velocities but has a limited effect on the spallation process, which is dominated by the evolution of the GB. At lower impact velocities, the mechanism of spall damage is dominated by the cleavage fracture along the GB plane for the perpendicular loading condition but dominated by the He bubble expansion and void growth for the parallel loading condition. At higher impact velocities, micro-spallation occurs for both loading conditions, and the effects of GBs and He bubbles can be ignored.

Experimental and numerical studies on the mechanical behaviors of basic magnesium sulfate cement concrete under dynamic split-tension

Dynamic splitting-tensile tests were conducted on basic magnesium sulfate cement concrete (BMSCC) at three different water-cement ratios using a 75 mm diameter split Hopkinson pressure bar (SHPB). The failure process of BMSCC under dynamic splitting loading was simulated using the finite element software LS-DYNA and a random aggregate mesoscopic model. The results demonstrated the strain rate effect in BMSCC, where the dynamic splitting-tensile strength increased with higher strain rates. Furthermore, the strength grade of the material significantly influenced the growth rate of peak stress, with higher strength grades exhibiting faster rates. The dynamic increase factor (DIF), a parameter characterizing the dynamic behavior of brittle materials, exhibited a linear relationship with the logarithm of strain rate. The LS-DYNA software was employed to numerically simulate the dynamic splitting-tensile process at the meso-scale, yielding satisfactory results with relative errors of 12.7%, 6.3%, and 3.3% for the dynamic splitting-tensile strength at different water-cement ratios, respectively.

Dynamic mechanical behaviour of rock-like materials with a flaw under different orientation and infill conditions

Dynamic mechanical behaviour of rock-like materials with a flaw under different orientation and infill conditions

Bismuth Telluride Nanoplates Hierarchically Confined by Graphene and N-Doped C as Conversion-Alloying Anode Materials for Potassium-Ion Batteries.

Potassium-ion batteries (PIBs) have broad application prospects in the field of electric energy storage systems because of its abundant K reserves, and similar "rocking chair" operating principle as lithium-ion batteries (LIBs). Aiming to the large volume expansion and sluggish dynamic behavior of anode materials for storing large sized K-ion, bismuth telluride (Bi2 Te3 ) nanoplates hierarchically encapsulated by reduced graphene oxide (rGO), and nitrogen-doped carbon (NC) are constructed as anodes for PIBs. The resultant Bi2 Te3 @rGO@NC architecture features robust chemical bond of Bi─O─C, tightly physicochemical confinement effect, typical conductor property, and enhanced K-ion adsorption ability, thereby producing superior electrochemical kinetics and outstanding morphological and structural stability. It is visually elucidated via high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) that conversion-alloying dual-mechanism plays a significant role in K-ion storage, allowing 12 K-ion transport per formular unit employing Bi as redox site. Thus, the high first reversible specific capacity of 322.70mAhg-1 at 50mAg-1 , great rate capability and cyclic stability can be achieved for Bi2 Te3 @rGO@NC. This work lays the foundation for an in-depth understanding of conversion-alloying mechanism in potassium-ion storage.

Goethite Mineral Dissolution to Probe the Chemistry of Radiolytic Water in Liquid-Phase Transmission Electron Microscopy.

Liquid-Phase Transmission Electron Microscopy (LP-TEM) enables in situ observations of the dynamic behavior of materials in liquids at high spatial and temporal resolution. During LP-TEM, incident electrons decompose water molecules into highly reactive species. Consequently, the chemistry of the irradiated aqueous solution is strongly altered, impacting the reactions to be observed. However, the short lifetime of these reactive species prevent their direct study. Here, the morphological changes of goethite during its dissolution are used as a marker system to evaluate the influence of radiation on the changes in solution chemistry. At low electron flux density, the morphological changes are equivalent to those observed under bulk acidic conditions, but the rate of dissolution is higher. On the contrary, at higher electron fluxes, the morphological evolution does not correspond to a unique acidic dissolution process. Combined with kinetic simulations of the steady state concentrations of generated reactive species in the aqueous medium, the results provide a unique insight into the redox and acidity interplay during radiation induced chemical changes in LP-TEM. The results not only reveal beam-induced radiation chemistry via a nanoparticle indicator, but also open up new perspectives in the study of the dissolution process in industrial or natural settings.

Effect of crack angle and concrete strength on the dynamic fracture behavior of rock-based layered material containing a pre-existing crack

Effect of crack angle and concrete strength on the dynamic fracture behavior of rock-based layered material containing a pre-existing crack

Uniaxial dynamic behavior of foam glass aggregate under oedometric (fully side restrained) condition at different compaction ratios

Foam glass aggregate (FGA) is considered as a lightweight and thermal insulation material. It has a wide granular size distribution nature that can influence the material's dynamic response when subjected to moving loads. Therefore, it is crucial to investigate the impact of different compaction ratios on the material's dynamic behavior. This study focused on examining the effects of varying compaction ratios (10%, 20%, 30%, and 40%) on dynamic parameters such as resilient stiffness (Mr) and accumulated plastic strains (ɛacc) of FGA. Uniaxial deviatoric stresses were applied to the material samples in a series to assess their influence on the material's behavior over multiple cycles. The results revealed the significant influence of increasing the compaction ratio to 40% on the material's behavior. At this compaction ratio, the ɛacc decreased to approximately 71%, 69%, and 86% for deviatoric stresses of 25 kPa, 100 kPa, and 200 kPa, respectively, after subjecting the material to 40,000 cycles. The increase in recoverable strains resulting from the material's fragile property under higher compaction energy led to a decrease in the Mr values of FGA samples as the compaction ratios increased. The lower boundary of Mr values for FGA ranged from 102 MPa to 189 MPa, while the upper boundary ranged from 150 MPa to 219 MPa under the selected deviatoric stresses. Although the interpretation of the shakedown criterion limitations yielded varying ranges for the colocation of FGA samples, it was found that FGA samples compacted at 40% exhibited robust characteristics suitable for constructing road embankments. This can be beneficial for infrastructure applications due to their excellent lightweight and thermal insulation properties.

Coherent two-dimensional THz magnetic resonance spectroscopies for molecular magnets: Analysis of Dzyaloshinskii-Moriya interaction.

To investigate the novel quantum dynamic behaviors of magnetic materials that arise from complex spin-spin interactions, it is necessary to probe the magnetic response at a speed greater than the spin-relaxation and dephasing processes. Recently developed two-dimensional (2D) terahertz magnetic resonance (THz-MR) spectroscopy techniques use the magnetic components of laser pulses, and this allows investigation of the details of the ultrafast dynamics of spin systems. For such investigations, quantum treatment-not only of the spin system itself but also of the environment surrounding the spin system-is important. In our method, based on the theory of multidimensional optical spectroscopy, we formulate nonlinear THz-MR spectra using an approach based on the numerically rigorous hierarchical equations of motion. We conduct numerical calculations of both linear (1D) and 2D THz-MR spectra for a linear chiral spin chain. The pitch and direction of chirality (clockwise or anticlockwise) are determined by the strength and signof the Dzyaloshinskii-Moriya interaction (DMI). We show that not only the strength but also the signof the DMI can be evaluated through the use of 2D THz-MR spectroscopic measurements, while 1D measurements allow us to determine only the strength.

Dynamic mechanical properties and failure behaviors of brittle rock materials with a tunnel-shaped opening subjected to impact loads

Since the surrounding rocks of underground tunnels are frequently suffered from the dynamic disturbance of mechanical percussion drilling and explosive blasting, it is significantly meaningful to investigate the mechanical properties and failure behaviors of rock material with a tunnel-shaped opening under dynamic loads. In this work, seven groups of prismatic samples, including the intact samples and the samples with a circular opening of three kinds of diameters, a square opening, a horseshoe-shaped opening and a D-shaped opening, were prepared for dynamic compressive loading. The results show that the prismatic specimens satisfy the stress uniformity condition in impact tests using SHPB testing system with a bar diameter of 50 mm. The weakening effects of the existed openings on the dynamic compressive strength, elastic modulus and peak strain of rocks are closely associated with the size and shape of opening and the loading direction. Based on the energy parameters of the samples, the dissipated energy density of each group of samples can be solved. The failure degree of the samples characterized by dissipated energy density and fractal dimension are in good agreement. Besides, the failure mode of the intact specimen belongs to splitting tensile failure, while that of the pre-holed specimens can be classified as shear-dominated failure due to the coalescence of the openings and the shear cracks occurring along the diagonals of the specimens. The test results provide some insights into the mechanical behavior of rock materials under dynamic loads and lay an important theoretical foundation for support design and rock disaster prevention of underground tunnel.