Plain Concrete Targets Research Articles

Analytical and experimental study on elliptical cross-section double-ogive-nose projectile penetration into plain concrete target

Analytical and experimental study on elliptical cross-section double-ogive-nose projectile penetration into plain concrete target

A new material model for concrete subjected to high rate of loading

This study presents a modified HJC model for simulating the constitutive behaviour of concrete under large strains, high strain rate and high pressure. The original HJC model has been modified by introducing the shear cracking, pore crushing, tensile cracking, and hydrostatic expansion damage models to the yield surface for reproducing the crushing, spalling (crater formed at the front surface), scabbing (crater formed at the rear surface), and radial cracking in the concrete target. The Lode-Angle model has been introduced to describe the yield surface to account for the substantial difference in the shear strength between the tensile and compressive meridians. The strain rate effect has been considered to suitably model the dynamic compressive and tensile strengths. Single element simulations have been performed to substantiate the effect of modifications introduced in the constitutive model. The results of the single element simulation obtained by using the proposed model (MHJC_K&I) have been compared with the results of the two latest modified (MHJC_Kong [1] and MHJC_Liu [2]) models available in the literature. The MHJC_K&I model has described more realistic strength softening under uniaxial compression when compared with the experiment results. Further, the MHJC_K&I model has described accurately the magnitude of tensile strength under uniaxial tension in comparison to the other two models. Under hydrostatic tension, the MHJC_K&I model described the exponential strength softening and the MHJC_Kong model described the linear softening while the MHJC_Liu model had limitation in describing the softening behaviour. The ballistic experiments have also been performed on 100 and 60 mm thick plain concrete targets against 0.4 kg steel projectile at incidence velocities in the range 103–220 m/s. The damage induced in the concrete targets as well as the residual projectile velocities have been obtained. The MHJC_K&I model has been found to effectively reproduce the damage with respect to the size and depth of the crater as well as the radial cracking at the front and rear surfaces of the plain concrete target. The MHJC_Kong and MHJC_Liu models underestimated the size and depth of the crater and described limitations in reproducing the radial cracking. The residual velocities obtained by using the proposed model (MHJC_K&I) have been found to have a good agreement with the actual results.

The composite damage effects of explosion after penetration in plain concrete targets

To investigate the composite damage effects of explosion based on initial damage caused by penetration, a series of penetration and explosion tests were conducted on plain concrete at different impact velocities, charge masses, and charge locations. Before that, a dimensional analysis of explosion effects after penetration in a concrete slab was undertaken, in which the composite damage effects can be characterized by a dimensionless explosion coefficient and a dimensionless impact coefficient. In addition, the initial damage caused by penetration can be characterized by the dimensionless impact coefficient. Based on the experimental data and theoretical analysis, the physical relationships between the composite damage effects of explosion and the initial damage effects of penetration were revealed, and the regression equation of the final crater depth and radius caused by explosion was obtained, which is described by the dimensionless impact coefficient and the dimensionless explosion coefficient.

Effect of grooves on the double-nosed projectile penetrating into plain concrete target

At present, it is one of the important ways to improve the penetration performance by changing and optimizing the projectile shape. In order to study the effect of grooved surface on projectile penetrating plain concrete target, a double-conical-nosed projectile with different grooves was proposed in this paper. Specifically, three types of projectile, including straight groove (STG), spiral groove (SPG) and no groove (NOG), were compared and analyzed respectively by using DEM-FEM numerical simulation and field experiment. The results show that during penetration, the role of grooved surface is mainly reflected in two aspects. One is that the interface pressure between the projectile head and concrete is reduced, and other is that the grooves of projectile afterbody can hold a part of the broken particles, which balance the transverse load of the projectile and stabilized the terminal trajectory. For plain concrete target, both straight and spiral grooved surface are beneficial to improve the penetration ability of the projectile. Compared with the spiral groove structure, the straight groove type is more beneficial to improve the penetration depth of trajectory.

Thick plain concrete targets subjected to high speed penetration of 30CrMnSiNi2A steel projectiles: Tests and analyses

In this work, 2 sets of thick plain concrete target penetration tests are carried out with high strength steel alloy projectiles made of 30CrMnSiNi2A whereby the striking velocity ranges from 841 m/s to 1872 m/s. For test 1, 7 shots of ogival nose projectiles with 3.0 calibre radius head as well as 2 shots of double-ogival nose projectiles are comparatively conducted to study the effect of nose shape effect. We adopt 30-mm-diameter projectiles for test 2 to study the higher velocity penetration in concrete. Two penetration regimes including rigid projectile penetration and eroding projectile penetration are observed for this work which are divided by 1402 m/s striking velocity. The target impact surface damage indicates that the crater diameter maintains 0.804 m while the crater depth increases linearly with the striking velocity. Rigid penetration simulations for test 1 are then performed via the recently developed Lattice Discrete Particles Model (LDPM) which is featured with mesoscale constitutive laws governing the interaction between adjacent particles to account for cohesive fracture, strain hardening in compression and compaction due to pore collapse. The penetration numerical model is validated by matching the projectile deceleration curve of shot N1 and predicting the depth of penetration (DOP). By constant velocity penetration simulations, the target resistance R = 406 MPa (Forrestal et al. 2003) is achieved for concrete penetration test 1 scenario. Finally, the equivalent CRH value 3.8 is approximated for the double-ogival nose projectile in this study.

Discrete element modelling of concrete structures under hard impact by ogive-nose steel projectiles

Concrete structures are widely used as shielding barriers to protect sensitive infrastructures. Accidental conditions such as aircraft impacts on nuclear containments lead to a designing demand under extreme loadings. A discrete element method (DEM) model is presented, able to predict damage of concrete structures under severe impacts. The original developments of Cundall and Strack for granular materials were extended in the proposed DEM model for cohesive materials such as concrete by introducing cohesive interactions in addition to contact ones. Spring-like interactions between discrete elements are based on phenomenological models inspired by observations at the macroscopic scale. Constitutive parameters are calibrated thanks to simulations of experiments performed under different states of loading (unconfined quasi-static tests, high confined compression, high strain rates). The DEM approach is validated with the simulation of three hard impact tests where numerical and experimental results are discussed. CEA Gramat performed the experiments on plain concrete targets with a passive confinement given by a steel jacket surrounding the cylindrical specimen and submitted to the impact of ogive-nosed steel projectiles.

Experimental and numerical studies of ultra-high performance concrete targets against high-velocity projectile impacts

Ultra-high performance concrete (UHPC) which is known for high strength, high toughness, excellent ductility and good energy absorption capacity can be adopted as an ideal material in the impact resistant design of structures. In the present study, impact responses of UHPC targets with 3 vol-% ultra-high molecular weight polyethylene (UHMWPE) fibres and UHPC targets with 3 vol-% steel fibres are experimentally investigated subjected to high-velocity projectile penetration, and plain concrete targets under the same loading scenarios are also tested as control specimens for comparative purpose. In addition, numerical studies are conducted to simulate the projectile penetration process into UHPC targets with the assistance of a computer program LS-DYNA. The numerical results in terms of the depth of penetration (DOP) and crater diameter as well as projectile abrasions and damages are compared with the experimental results. Moreover, DOPs of these two types of UHPC targets obtained from tests are compared with the previously proposed empirical model.

Effect of free water content on the penetration of concrete

A numerical study is presented herein on the effect of free water content on the penetration of concrete targets subjected to projectile impact. The paper consists of two parts: the first part proposes a material law that considers the influence of free water content by modifying a recently developed computational constitutive model for concrete; the second part performs the numerical simulations of the penetration of plain concrete targets struck by an ogival-nosed projectile using the material law. The present material law takes into account pressure dependency, strain rate sensitivity, shear damage and tensile softening, loading path dependency (Lode angle) and free water content. Various equations are obtained and the values of relevant parameters are estimated. It is demonstrated that the modified constitutive model correlates well with available test data for concrete. It is also demonstrated that the present model predictions are in good agreement with the experimental observations for wet plain concrete targets struck transversely by an ogival-nosed projectile in terms of sizes of both impact and scabbing craters, time-histories of load, penetration and velocity and that the impact resistance increases with increasing free water content which results in smaller penetration depth in wet concrete target than that in dry one in the case of penetration and smaller residual velocity for wet concrete slab than that for dry one in the case of perforation.

Prestressed concrete targets under high rate of loading

Prestressed concrete is highly being preferred as material for construction in the case of strategic and relevant structures such as, for instance, nuclear containments, armor deposits, shelters, bridges, and military bunkers. It is highly durable, fire and corrosion resistant, and non-porous. In order to study the influence of prestressing on the mechanics of deformation, energy absorption capacity, and failure modes of concrete targets, finite element simulations have been carried out using hard steel bullets and compared with the experiments carried out by the authors earlier. Prestressed concrete targets of plan size 450 mm × 450 mm and thickness of 80 mm were impacted by 0.5-kg hard steel projectiles. The concrete was designed to obtain an unconfined compressive strength of 48 MPa. An initial stress of 10% magnitude of compressive strength was induced by 4-mm-diameter high-tensile-strength (1700 MPa) steel wires in prestressed concrete targets. A grid of 8-mm-diameter steel bars was inserted in the reinforced and prestressed concrete targets to enable the straight comparison between these concretes. The prestressing in concrete has been found to be effective in reducing the volume of scabbed material as well as the ballistic resistance of prestressed concrete targets. The ballistic limit of prestressed concrete with 10% induced stress was found to be, respectively, 14% higher than that of the plain concrete target and 10.2% higher than the reinforced concrete. Failure modes predicted through finite element simulations were found in agreement with that of the actual results.

Numerical predictions of the behaviour of plain concrete targets subjected to impact

One widely used model implemented in the hydrocode ANSYS Autodyn is the Riedel–Hiermaier–Thoma material model, which is used for the prediction of concrete behaviour under severe loading, such as blast and impact. In the Riedel–Hiermaier–Thoma model, parameters are adjusted to be a function of the compressive strength of specific concrete. This advantage enables occasional users (and those who cannot conduct experiments to determine all the required concrete parameters) to input only this parameter, while the rest is automatically calculated by default settings. This study is an attempt to calibrate (not modify) this model, with the least number of possible changes, to better predict the performance of concrete targets, particularly spalling and scabbing phenomena, impacted by hard projectiles. It is shown that the present calibration of the Riedel–Hiermaier–Thoma material model performed well when compared to the default settings currently available in the model.

Ballistic performance of plain, reinforced and pre-stressed concrete slabs under normal impact by an ogival-nosed projectile

The ballistic performance of plain, reinforced and prestressed concrete targets of unconfined compressive strength 48MPa was studied experimentally against long rod steel projectiles. The square targets (450mm×450mm) of thicknesses 60, 80 and 100mm were subjected to normal impact by 1kg ogive nosed hardened steel projectiles of diameter 19mm and length 450mm. The reinforcement in the reinforced and prestressed concrete targets was provided with respect to φ8mm @80mm c/c both ways. An initial prestress of approximately 4–5MPa (10% of unconfined compressive strength) was also induced in the prestressed concrete targets with the help of 4mm diameter steel wires of ultimate tensile strength 1646MPa. The experiments were carried out at varying incidence velocities, 65 - 220m/s, and the results thus obtained with respect to extent and vicinity of damage, volume of spalling and scabbing as well as ballistic resistance for three distinct concretes have been compared and discussed. The reinforcement in the concrete has been found to be effective in minimizing the scabbing and spalling of material. The initial prestressing in the concrete, stimulated the globalization effect in the deformation process and thus improved the ballistic performance. The ballistic limit of reinforced concrete target was 11, 16 and 26% higher than plain concrete target for 60, 80 and 100mm thicknesses respectively. On the other hand, the ballistic limit of prestressed concrete targets was found to be 19, 25 and 35% higher than reinforced concrete, and 32, 45 and 70% higher than plain concrete target for 60, 80 and 100mm thicknesses respectively.

Response of initially stressed concrete targets under high rate of loading

Prestressed concrete is a highly being used material in the construction of strategic and important structures such as nuclear containments, bridges, storage structures and military bunkers. It is highly durable, fire and corrosion resistant and nonporous. In order to study the influence of prestresing on the ballistic characteristics of concrete targets ballistic experiments have been carried out against ogival nosed (3 CRH) hard steel projectiles. The projectile of 0.5 kg mass were normally impacted on 80 mm thick presstressed concrete targets of plan size 450 mm x 450 mm. The unconfined compressive target strength of concrete was designed 48 MPa. An initial stress of 10% magnitude of compressive strength was induced by 4 mm diameter high tensile strength (1700 MPa) steel wires in prestressed concrete targets. A grid of 8 mm diameter steel bars were inserted in the reinforced and prestressed concrete targets to enable the straight comparison between these concretes. The prestressing in concrete has been found to be effective in reducing the volume of scabbed material as well as the ballistic resistance of prestressed concrete targets. The ballistic limit of prestressed concrete with 10% induced stress was found to be 10.2 % higher than that of the reinforced concrete and 14% higher than the plain concrete target, respectively.

Experimental and Numerical Study of Concrete Targets under High Rate of Loading

In order to examine the ballistic resistance of plain concrete and reinforced concrete targets the perforation tests conducted in the laboratory, on square concrete targets size (450 mm x 450 mm x 80 mm) of plain concrete and reinforced concrete and to validate the experimentally obtained results Numerical simulations were carried out in Abaqus/Explicit finite element code. The unconfined target compressive strength of concrete was 48 MPa. A grid of steel bars having 8 mm diameter has been incorporated in reinforced concrete plates. The plates were subjected to normal impact of 0.5 kg ogive nosed hard steel cylindrical projectile having diameter of shaft 19 mm. The projectiles were accelerated by the laboratory pneumatic gun to velocities range between 53m/s to 220m/s. impact and residual velocities were measured with the help of Phantom-V411 high speed digital camera system. Ballistic limit of plain concrete and reinforced concrete targets had been obtained in the experiments as well as in the Numerical simulations in Finite element code Abaqus\\explicit. Also calculated spalling and scabbing volume of plain and reinforced concrete targets after perforation experiments, the reinforcement in the concrete has been found to be effective in minimizing the scabbing and spalling of material. The ballistic limit of reinforced concrete target was experimentally found 16.9% higher than plain concrete target, However Numerical simulations predicted the ballistic limit of plain concrete target within 8% and that of reinforced concrete target within 3% deviation in comparison to experimentally obtained ballistic limits.

Plain and Reinforced Concrete Targets Subjected to Projectile Impact

The ballistic performance of plain concrete and reinforced concrete targets of unconfined compressive strength 40 MPa was studied against projectile impact. The squarer plates of (450 mm x 450 mm) and thickness 60 mm with and without (8 mm@100 mmc/c) reinforcement were subjected to normal impact of hardened steel ogive nosed projectiles with diameter 19 mm and mass 0.5 kg. The incident velocities of the projectiles were varied between 28 to 102 m/s. The amount and area of damage, volume of spalling and scabbing as well as the ballistic limit of plain and reinforced concrete have been obtained and their results have been compared and discussed. The influence of reinforcement is clearly visible in minimizing the scabbing and spalling of material. The magnitude of scabbing decreased with increase in the projectile incidence velocity while the spalling of material remained unaffected. The ballistic limit of reinforced concrete target was 20% higher than plain concrete target for 60 mm thickness.

A numerical study on the influence of free water content on the ballistic performances of plain concrete targets

During the impact of a kinetic penetrator against a plain–concrete target severe damage modes are observed such as spalling on the front face, radial cracking in the whole target and, in the case of perforation, scabbing on the rear face. These damage mechanisms are substantially decreasing the penetration resistance of the concrete structure. Moreover, high confining pressures are observed in front of the projectile that involve mechanisms such as micro-cracking and collapse due to porosity. Both confined compressive and tensile behaviors are influenced by the concrete’s moisture content. Therefore, the constitutive model used for numerical calculation for describing the confined behavior and tensile resistance of the concrete has to take into account the amount of free water in the concrete. In the present work, a series of numerical simulations of impact tests have been conducted considering two saturation ratios (dry and water-saturated) plus two target thicknesses. The confined behavior of the concrete material is modeled using the KST (Krieg–Swenson–Taylor) plasticity model and the so-called DFH (Denoual–Forquin–Hild) anisotropic damage model which allows the description of the tensile strength and softening behavior of concrete in tension. These calculations are used to investigate the influence of the concrete’s free water content through its confined behavior and tensile strength and the influence of friction at the projectile–target interface on the ballistic performance of concrete slabs.

Impact Tests On Steel Fibre ReinforcedConcrete Panels

Impact tests have been conducted to examine the influence of quantity as well as types of steel fibre on the penetration resistance of, and damage to, 50mm thick steel fibre reinforced (SFR) concrete panels. Two fibre volume fractions and three types of steel fibres were used in this study. Results of the relative damage and penetration are compared for each panel. Penetration was accurately estimated for the plain concrete target. It is concluded that normal reinforcement, adequate fibre content and fibre configuration are necessary ingredients to increase damage tolerance and survivability of thin concrete targets.