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Based on the JH-2 theoretical model, an improved JH-2 discrete model for the finite element simulation of brittle materials is established, which is used to redevelop the client module of DEFORM software as a constitutive model. And the cutting force of engineering ceramics is simulated and analyzed. Through the fluorophlogopite turning test, the simulation effects of the JH-2 discrete model and J-C idealized model are compared. The effects of three process parameters, namely cutting speed, feed speed and cutting depth, on the cutting force simulation are analyzed. And the accuracy and reliability of the JH-2 model are verified. The test results show that the variation trend of the simulation value of cutting force is the same as that of the test value, and the precision is good. Compared with the J-C idealized model, the machining morphology of brittle materials simulated by the JH-2 discrete model is more consistent with the actual situation. Therefore, in the finite element research of engineering ceramics, the improved JH-2 discrete model has significant advantages over the J-C model in theoretical analysis and simulation prediction. [ABSTRACT FROM AUTHOR]

Abstract The lining structures of tunnels are typically constructed using sprayed or cast concrete materials, and their performance and quality during tunnel excavation and blasting are crucial for the stability and safety of tunnels. Therefore, the safe distance between the lining structure and blasting source should be determined to avoid concrete damage caused by blasting vibrations. In this study, taking the subway tunnel of Danshan Station in Qingdao as an example, the JH-2 model is introduced as the constitutive model of the tunnel blasting simulation, and the JH-2 model parameters of the local surrounding rock are obtained by experiments, and finally the numerical simulation and theoretical verification are carried out to study the safety distance of shotcrete under various safety judgment standards. The results indicate that the JH-2 model can effectively simulate the propagation of stress waves under different media conditions, and the closer the strength parameters and pressure constant of the lining structure are to those of the surrounding rock, the safer the concrete–rock bonding interface. During tunnel blasting construction using the ring blasting method, the peak particle velocity (PPV) of the lining structure increases with an increase in the arch angle. Based on the numerical simulation results, we recommend that concrete lining be constructed at a distance of at least 62 m from the blasting source to avoid damage caused by vibrations. The effect of concrete tensile failure caused by longitudinal stress is much smaller than the damage to the bonding interface caused by the PPV and can be neglected.

Tempered glass is a transparent material that can withstand various shocks and constant loads, which is widely used in the field of safety protection. This manuscript presents the determination of Johnson–Holmquist (JH-2) model parameters for tempered glass and investigates the effect of strain rate on its strength through quasi-static and dynamic compression tests. The hydrostatic tensile pressure was indirectly determined via split tensile tests, and literature data were employed to calculate the value of HEL and EOS. The JH-2 model accurately predicted the real shapes of strain waves in the input and output bar of SHPB tests and was capable of describing the mechanical behavior of the brittle material from elasticity to fracture. The determined parameters for tempered glass were validated to represent the response to shock and impact loads. [ABSTRACT FROM AUTHOR]

• The HE-BMG exhibited a negative SRS under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. • Variation of spall strength with impact speed is dominated by strain rate. • The fracture behavior of the HE-BMG under different strain rates and stress states was compared. • The JH-2 model was established and its accuracy was verified by various experiments and simulations. In this work, the mechanical response and fracture characteristics of (Ti 37.31 Zr 22.75 Be 26.39 Al 4.55 Cu 9) 94 Co 6 high-entropy bulk metallic glass (HE-BMG) were investigated in detail over a wide range of strain rates (10−4–105 s−1). The HE-BMG exhibited a negative strain rate sensitivity under uniaxial compression, with the strength showing more significant rate dependence under dynamic conditions. The shear band behavior translated from the dominance of multiple shear bands propagations under quasi-static compression to the rapid propagation of a single shear band to form cracks under dynamic compression. Under dynamic loading, the shearing velocity increased along an arc-shaped displacement path, and the local stress state on the shear fracture surface shifted from compressive-shear to tensile-shear, accompanied by changes in fracture morphologies. The spall strength of HE-BMG decreased as flyer impact speed increased, while the long-term dependence of spall strength on strain rate may be positive. With the increase of impact speed, the main microstructural features of the spalling surface translated from flat regions accompanied by dimples to cup-cone structures. Furthermore, the complete parameters of the Johnson–Holmquist II (JH-2) model for HE-BMG were obtained based on experimental data. Numerical simulations of planar impact, penetration, and hypervelocity impact are in good agreement with experimental results, demonstrating the validity of the JH-2 model parameters. The current work has important guiding value for the application of HE-BMG in space debris protection. [Display omitted] [ABSTRACT FROM AUTHOR]

The dynamic experimental tests were performed on cylindrical zirconium diboride‐silicon carbide ceramic specimens under the uniaxial compression from 519 to 2861 s−1. The effect of the strain rate on the dynamic response of a ZrB2‐SiC ceramic was investigated using experimental and numerical methods. A significant increase on the dynamic compressive strength, elastic modulus, and the dynamic tensile strength was found with the increase of the strain rate. The damage process and fracture pattern of the ZrB2‐SiC ceramic exhibited a significant strain‐rate dependence under the dynamic compression. The strain rate‐dependent elastic modulus and tensile strength were introduced into Johnson–Holmquist (JH‐2) model to predict the dynamic compression behavior of the ZrB2‐SiC ceramic. The simulation results of the dynamic compressive strength, stress–strain relation, and fracture patterns were in good accordance with the dynamic experimental results. [ABSTRACT FROM AUTHOR]

The Al3Ti compound has potential application in the high temperature structure materials due to its low density, high strength and stiffness. The mechanical behaviors of the material under different loading rates were studied using compression tests. The results indicate that Al3Ti is a typical brittle material and its compressive strength is dependent on the strain rate. Therefore, a series of rate-dependent constitutive equations are needed to describe its mechanical behaviors accurately. However, it is still short of professional research on the material model for Al3Ti. In this study, the material model was developed on the basis of JH-2 constitutive equations using the experimental data. The model was then applied in simulating the impact process of Ti/Al3Ti metal-intermetallic laminate composites so as to validate the established model. Good agreement between simulation and experiment results shows the constitutive model predict the material responses under high rate and large deformation accurately. This work provides more support for the theoretical and numerical research on the intermetallic.

In order to investigate the application of JH-2 (Johnson-Holmquist-2) constitutive model in concrete, a series of parameters study have been conducted to evaluate the JH-2 model in C30 concrete. The finite element analysis software ABAQUS is utilized to simulate the compression test of the three-dimensional standard concrete test based on the ALE adaptive mesh and the damage failure criterion of element deletion function. The numerical analysis of 3D concrete pile foundation and simplified shield machine cutter head to simulate shield cutting pile is established. Analyzing the numerical simulation and construction data, the key points of the shield machine cutting pile are illustrated. Research shows that: (1) JH-2 constitutive model can be used to simulate the concrete cutting. (2) The better damage parameters have been represented and verified against the results of experiments, which are D1 = 0.6 and D2 = 0.1 in the JH-2 model of C30 concrete. (3) In the simulation example of concrete compression and cutting pile, the failure form of concrete is brittle failure, and the non-linear characteristics of concrete has been observed. (4) The simulated torque vibration of the cutter head is relatively large than actual pile cutting, and the actual shield machine cutting pile construction should have a low rotation speed and low propulsion speed. [ABSTRACT FROM AUTHOR]

A macroscopic constitutive model is presented herein for ceramic materials subjected to dynamic loadings by closely following a previous study on concrete. The equation of state is described by a polynomial equation and the strength model takes into account various effects such as pressure hardening, Lode angle, strain rate, shear damage and tensile softening. In particular, the strength surface of ceramic materials is characterized by a new function which levels out at very high pressures and strain rate effect is taken into account by dynamic increase factor (DIF) which excludes inertial effect. The present model is verified against some available experimental data for ceramic materials in terms of pressure-volumetric response, quasi-static strength surface and strain rate effect. The model is further verified against the data for triaxial test by single element simulation approach and the test data for depth of penetration in AD99.5/RHA struck by tungsten alloy penetrators. Furthermore, comparisons are also made between numerical results of the present model and the JH-2 model. It is demonstrated that the present model can be employed to describe the mechanical behavior of ceramic materials under different loading conditions with reasonable confidence and is advantageous over the existing model. [ABSTRACT FROM AUTHOR]

The Al3Ti compound has potential application in the high temperature structure materials due to its low density, high strength and stiffness. The mechanical behaviors of the material under different loading rates were studied using compression tests. The results indicate that Al3Ti is a typical brittle material and its compressive strength is dependent on the strain rate. Therefore, a series of rate-dependent constitutive equations are needed to describe its mechanical behaviors accurately. However, it is still short of professional research on the material model for Al3Ti. In this study, the material model was developed on the basis of JH-2 constitutive equations using the experimental data. The model was then applied in simulating the impact process of Ti/Al3Ti metal-intermetallic laminate composites so as to validate the established model. Good agreement between simulation and experiment results shows the constitutive model predict the material responses under high rate and large deformation accurately. This work provides more support for the theoretical and numerical research on the intermetallic. [ABSTRACT FROM AUTHOR]

The present work aims to understand the stress-strain response of a metamorphic rock, and gneiss under high loading rate for different specimen diameters and slenderness ratios through detailed tests. The high strain rate characterisation of gneiss rock is done for two different diameters and five different slenderness ratios of the rock specimens using a 76 mm-diameter split Hopkinson pressure bar (SHPB) device in an effort to understand the standard specimen dimension for gneiss in SHPB test. The stress-strain response of the rock specimens is studied by varying the length of the striker bars and the gas gun pressure values, systematically. The petrological and static characterisation of the gneiss rock is also carried out to assess the response of the rock specimens. Finally, a methodology is proposed to characterize gneiss rock specimens under high loading rate. Furthermore, numerical simulation of SHPB test on gneiss rock is performed using strain rate-dependent Johnson-Holmquist (JH-2) model available in the finite-element software package, LS-DYNA. The simulation results are compared with the experimental data, and thus, the parameters of JH-2 model for gneiss rock are determined. [ABSTRACT FROM AUTHOR]

A series of numerical simulations were performed to investigate the influence of side free surface on the rock fragmentation induced by single TBM disc cutter. The JH-2 model combined with a Rankine tensile cracking softening model was adopted to define the rock constitutive model to simulate the rock dynamic fracture process. The distance that allows for cracks just to extend to side free surface under a given penetration is defined as the critical distance, which distinguishes the rock fragmentation patterns between induced by disc cutter close to side free surface and conventional single cutter. The former rock fragmentation pattern is that rock chips in the form of wedge-shaped block spalling from rock specimen due to tensile cracks intersection. From the mean rolling force and the rock debris mass, the specific energy to reflect cutting efficiency was calculated for different distances to side free surface. The cutting efficiencies of former patterns are far higher that by conventional single cutter. The rock macro-fracture patterns and cutting efficiency were then compared with those obtained from linear cutting experiments. The critical distance for Baiyun granite is about 100 mm obtained from experiments, in good agreement with that deduced from numerical simulations. The height difference between the inner and outer cutterhead of the two-stage cutterhead should be more than 220 mm and the distance from first disc cutter on the inner cutterhead to free surface should be less than 100 mm for granite ground. [ABSTRACT FROM AUTHOR]

To simulate the complete procedure efficiently for the explosively-formed projectile (EFP) being formed, flying in the air and penetrating into alumina ceramic/metal composite target in the condition of high stand-off, the material properties of the 99 alumina ceramic were described by JH-2 constitute model, the moving mesh method was used for the computing flow field and the EFP penetrating into alumina ceramic/steel composite target was simulated with the fluid-structure interaction arithmetic. The computation time decreased greatly with the moving meth method due to the less number of meshes. The residual penetration depths in the A3 steel back plates were acquired. The results indicate that the tip speed of the EFP is consistent with the test result and the rear speed of the EFP is a little higher than the test. Thus the residual penetration depths are a little deeper than the test results. The residual penetration depths acquired both by the tests and by the simulations decrease with the increase of ceramic thickness. There is a nearly linear relationship between the residual penetration depths and the thickness of the ceramics. [ABSTRACT FROM AUTHOR]