Study of the axial density/impedance gradient composite long rod hypervelocity penetration into a four-layer Q345 target

Based on the dynamic shock response of the material and structure,the hypervelocity impact processes and mechanisms of long composite rods with axial density/impedance gradients penetration into fourlayer targets were studied through experiments and numerical simulation methods.The propagation law of the shock waves,together with the structural responses of the projectiles and targets,the formation and evolution of the fragment groups formed during the processes and their distributions were described.The damage of each target plate was quantitatively analysed by comparing the results of the experiment and numerical simulation.The results showed that the axial density/impedance gradient projectiles could decrease the impact pressure to a certain extent,and the degree of damage to the target plate decreased layer by layer when the head density/impedance of the projectile was high.When the head density/impedance of the projectile was low,the degree of target damage first increased layer by layer until the projectile was completely eroded and then it decreased.The results can provide a reference for the design and application of long rods with axial composite structure for velocities ranging from 6 to 10 Ma or greater.

Investigation of the Mechanism of Grout Penetration in Intersected Fractures

To study the penetration mechanism of cement-based slurry in intersected fractures during grouting and the related pressure distribution,we have used two different variants of cement,namely,basic cement slurry and fast-setting cement slurry.The influence of a retarder,time-varying viscosity,fracture width and location of injection hole is also considered.A finite element software is used to implement two and three-dimensional numerical models for grouting of intersected fractures in hydrostatic conditions.Results show that there are significant differences in the diffusion morphology and pressure distribution depending on the considered cement slurry.Retarder can effectively slow down the rising rate of injection pressure and extend the diffusion distance of grout.The influence of the branch fracture is more important when basic cement slurry is considered,indicating that the change of grout pressure is correlated with the slurry viscosity.The faster the viscosity increases,the less evident is the effect.

STUDY ON THE MECHANISM OF CHATTER VIBRATION OF INITIAL PENETRATION IN DRILLING

Using time domain data, orbital plots, and spectrum analysis of drill point displacement, cutting force and torque signals, the initial penetration in drilling is experimentally investigated. The mechanisms of drill wandering motion are analyzed by means of three principles of selfexcited vibration, i.e. the regenerative principle, velocity component principle and mode coupling principle.

Resistance of grid steel-tube-confined concrete targets against projectile impact: Experimental investigation and analytical engineering model

Steel-tube-confined concrete(STCC) targets are provided with excellent anti-penetration performance over semi-infinite concrete(SIC) targets since the steel tube imposes passive restraint on the in-filled concrete during the penetration process. Grid STCC system with square steel tubes is a potential solution to protective structures. In this paper, experiments of 9-cell grid STCC targets penetrated by 12.7 mm Armor Piercing Projectile(APP) were performed. The influence of side length and thickness of steel tube,steel ratio and impact velocity on anti-penetration performance were taken into account. Additionally,single-cell square STCC targets were also designed and tested for comparison with the 9-cell grid STCC targets. Damage modes and parameters of the tested targets were measured and discussed. Moreover,the stiffness of radial confinement of grid STCC targets is achieved according to the elastic solution of infinite cylindrical shell in Winkler medium. Furthermore, the penetration resistance and depth of penetration(DOP) for grid STCC targets are obtained on the basis of the dynamic finite spherical cavityexpansion(FSCE) models including radial confinement effect. It is shown that the 9-cell grid STCC targets with optimal dimension match of thickness and side length of steel tube can reduce the DOP by about17 % and 23 % in comparison with the SIC targets and single-cell square STCC targets, respectively, due to both the confinement of square steel tube to concrete in the impacted cell and the additional confinement of the surrounding cells to the impacted cell;the penetration resistance and DOP of the grid and cellular STCC targets with similar steel ratio is close, and thus the grid STCC targets with simpler manufacturing process and excellent in-plane expandability are preferred in engineering practice;moreover, the predicted results of DOP model based on the FSCE models agree well with the tested results with the maximum disparity less than 12 % and the proposed model is more applicable to the grid and cellular STCC targets with high radial confinement.

Fragmentation behavior of large-caliber PELE impacting RHA plate at low velocity

Impact experiments of large-caliber PELE with various inner-outer diameter ratio perforating RHA plate at low velocity were performed.Experimental results showed the size of perforated holes on plate,average diameter of damage area on witness plate,and number of behind-armor fragments will increase as d/D increasing from 0.72 to 0.84.Expansion and fragmentation of large-caliber PELE in this condition were also numerically studied with ANSYS Autodyn.Then,an analytical model accounting for an additional radial shock wave was presented to predict radial expansion velocity and fragmentation of jacket,as well as an empirical approach to estimate diameter of damage area.Calculation results by these approaches were in good agreement with experiments and numerical simulations.Further discussion revealed that Shock/rarefaction wave interactions behavior varying with inner-outer diameter ratio is an important mechanism resulting in different lateral effect by PELE projectiles with various configurations.

Investigation of active vibration drilling using acoustic emission and cutting size analysis

This paper describes an investigation of active bit vibration on the penetration mechanisms and bit-rock interaction for drilling with a diamond impregnated coring bit. A series of drill-off tests(DOTs) were conducted where the drilling rate-of-penetration(ROP) was measured at a series of step-wise increasing static bit thrusts or weight-on-bits(WOBs). Two active DOTs were conducted by applying 60 Hz axial vibration at the bit-rock interface using an electromagnetic vibrating table mounted underneath the drilling samples, and a passive DOT was conducted where the bit was allowed to vibrate naturally with lower amplitude due to the compliance of the drilling sample mountings. During drilling, an acoustic emission(AE) system was used to record the AE signals generated by the diamond cutter penetration and the cuttings were collected for grain size analysis. The instrumented drilling system recorded the dynamic motions of the bit-rock interface using a laser displacement sensor, a load cell, and an LVDT(linear variable differential transformer) recorded the dynamic WOB and the ROP, respectively. Calibration with the drilling system showed that rotary speed was approximately the same at any given WOB, facilitating comparison of the results at the same WOB. Analysis of the experimental results shows that the ROP of the bit at any given WOB increased with higher amplitude of axial bit-rock vibration, and the drill cuttings increased in size with a higher ROP. Spectral analysis of the AEs indicated that the higher ROP and larger cutting size were correlated with a higher AE energy and a lower AE frequency. This indicated that larger fractures were being created to generate larger cutting size. Overall, these results indicate that a greater magnitude of axial bit-rock vibration produces larger fractures and generates larger cuttings which, at the same rotary speed, results in a higher ROP.

Petal Failure Characteristics of a Conical Projectile Penetrating a Thin Plate at High Oblique Angle

<Abstract>In order to determine the impact depth of a conical projectile impacting a thin plate at high oblique angle,the residual velocity of the projectile after penetrating must be known.Based on the petal failure mode of the conical projectile impacting the thin plate at high oblique angle,the energy consumption mode of the target was determined.During the perforation process,the energy consumption of the target was completed by the saucerization,the power work of the petals,the propagation of radial cracks and petal bending.The energy formula was deduced for each energy dissipation mode and the energy consumed in the impact process was determined.The residual velocity and the ballistic limit velocity of the projectile were deduced by energy conservation principle.Comparison of the analytical results of the residual velocity to the numerical results demonstrates the accuracy and reliability of the analytical formula.