Projectile Impact Loading Research Articles

Dynamic behaviour of multi-layer composite against single and multiple projectile impact loading

In this work, a novel multi-layer composite structure has been proposed for its application in the design of protective shelters. The proposed work investigates the dynamic behaviour of a multi-layer composite under the action of single and multiple projectile impact loading. The target consists of soil, reinforced concrete, steel plate, high-density polyethylene and boulder-mixed cement mortar. It has been subjected to the projectile impact (single and multiple) of a 2.3 kg ogive-nose hard cylindrical projectile having a 50.80 mm diameter. The mechanical performance in terms of the velocity profile of the projectile, residual velocity, penetration depth, ballistic limit velocity, energy absorption and damage of the target has been quantified through a numerical framework. Further, equations have been formulated to determine the fracture material parameters associated with the Riedel–Hiermaier–Thoma (RHT) model to cater for varying strengths of concrete or similar materials. The proposed composite target has demonstrated enhanced penetration resistance and lesser damage compared to its reinforced concrete monolayer counterpart. The interaction between shock waves and the target’s material characteristics lead to projectile ricocheting in multiple projectile impacts. Further, an analytical model has been developed to predict the forces transmitted to the lowest layer, which are essential for design purposes. The model has been proposed from the fundamentals using the concepts of impedance. The result derived from the theoretical formulation is in good agreement with the numerical results. Finally, the damage has been quantified to assess the extent of structural deterioration in multi-layer targets, emphasizing the relationship between energy absorption ratio and damage.

Effects of steel fiber and target thickness on the penetration resistance of UHPC under high velocity small projectile impact loading

Ultra high performance concrete (UHPC) with significant compressive strength and elastic modulus is expected to perform well under high–velocity impact loading. This paper introduces a study on the penetration resistance of UHPC based on variables including the thickness, fiber volume ratio, and striking velocity. The maximum striking velocity reaches approximately 1150 m/s. The results indicate that although the addition of steel fiber insignificantly improves the resistance, its effect on restraining the development of damage is non–negligible when the fiber volume ratio increases from 0.5% to 2%. The target thickness substantially influences the residual velocity and depth of penetration. Through computed tomography (CT) scanning, the damage can be divided into two parts: central damage (cratering, penetration tunnel, and scabbing) and interior cracks (radiate cracks, incomplete spalling cracks, and asymmetrical horn–shaped cracks). According to Forrestal's and the authors' previous models, satisfactory prediction results are obtained based on the suggested penetration resistance and modified cratering height.

Analysis of the Influence of Silty Sands Moisture Content and Impact Velocity in SHPB Testing on Their Compactability and Change in Granulometric Composition

This paper presents the results of a test cycle of two types of silty sand (siSa) with different contents of fine fractions. Fine fractions are understood as soil grains with a grain diameter of less than 63 µm (as the sum of silt and clay fractions). The soils tested had a content of fine fractions of fSi+Cl,1 = 15.14% and fSi+Cl,2 = 20.48%, respectively, before the study. Changes in the content of these fractions after the experiments were analyzed. These experiments consisted of dynamic bar projectile impact loading, and a split Hopkinson pressure bar (SHPB) test stand was used in the study. Changes in the granulometric composition of the silty sands studied were carried out in a laser particle size analyzer, allowing measurement of fractional content in the grain size range from 0.01 µm to 3500 µm. As a result, a summary of changes in soil grain size curves in the range of fine fractions was compiled. Repeated trends were observed in the changes in the granulometric composition of the soil samples as a function of the moisture content of the soil sample (w1 = 0%, w2 = 5%, w3 = 10%, and w4 = 15%) and the impact velocity of the loading bar projectile for SHPB pneumatic launcher pressures (p1 = 1.2 bar → v1 = 12.76 m/s, p2 = 1.8 bar → v2 = 17.69 m/s and p3 = 2.4 bar → v3 = 21.32 m/s). The influence of the initial moisture content of the investigated soil on the value of the optimum moisture content obtained during its dynamic compaction was discussed. The trend in the behavior of the change in the granulometric composition of the tested samples was determined, taking the value of the initial moisture content of the soil in relation to the optimum moisture content of the reference sample as a reference. The largest percentage change in granulometric composition through an increase in the value of the silt and clay fraction relative to the reference sample fSi+Cl for both types of silty sand tested occurs for the same moisture content variant w2 = 5%–for soil fSi+Cl,1 = 15.14% there is an increase in the fine fraction of 11.08% and for soil fSi+Cl,2 = 20.48% there is an increase in the fine fraction of 15.17%. In general, it can be seen that more silty soil is more strongly susceptible to the phenomenon of grain crushing for moisture content w1 = 0% and w2 = 5% less than its optimum moisture content wopt,1 = 8.70%. In contrast, less silty soil is more susceptible to the phenomenon of grain crushing for moisture contents w3 = 10% and w4 = 15% greater than its optimum moisture content wopt,2 = 9.20%. The presented dynamic physical phenomenon of soil behavior is crucial during explosive and impact impacts on structures made of soil, e.g., as ground protection layers.

Dynamic response of fully-clamped steel plate under laboratory-simulated sequential fragment impact and blast loading

Composite projectile (CP) impact, as a new in-laboratory experimental technique, was further developed to simulate sequential fragment impact and blast loading generated by cased charge explosion. New developments include modification of the equivalent relationships between main loading characteristics from the explosion and the CP impact and the improvement of the experimental setup. Then, it was used to study the dynamic response of a fully-clamped steel plate under simulated sequential fragment impact and blast loading. For comparison, a widely used traditional technique, which decoupled the two load types by generating pressure pulse on the structure with pre-formed holes to simulate the sequential loading, was also employed. Deformation processes, deformation/failure modes, and central deflections of the plates tested using the two different techniques were compared and analyzed. It was found that the traditional technique underestimated the damage caused by sequential fragment impact and pressure pulse: the plate subjected to the CP impact was found to be more susceptible to tearing fractures at high impact velocities. Finite element simulations were subsequently performed and the simulation results were validated against experimental data. The validated FE model was then employed to further evaluate the synergetic effects of sequential fragment simulating projectile (FSP) impact and impulsive loading on the ballistic performance and deformation behavior of the fully-clamped steel plate. Results indicate that while pressure pulse in the sequential loading leads to an enhanced ballistic limit of the plate, FSP impact in the sequential loading causes significant local shear and tensile deformation around the perforation, resulting in plate tearing at a lower impact velocity.

Comparative study on performance of UHTCC and RPC thick panels under hard projectile impact loading

This paper presents a comparative study on the perforation resistance of thick panels made of the reactive powder concrete (RPC) and the ultra high toughness cementitious composites (UHTCC). Damage patterns of the target were measured, including the diameter and depth of the cratering and scabbing on the front and rear surfaces. Residual velocities of the projectiles were determined by a high speed camera. The test results showed 46 MPa UHTCC has superior resistance to the tensile damage induced cratering and scabbing while its penetration resistance is comparable to NC with a lower compressive strength (30 MPa). The 123 MPa RPC exhibits much higher penetration resistance than UHTCC and NC, and has improved performance over NC in resisting tensile damage. Besides, based on the framework of the Forrestal formula, a unified semi-analytical model is proposed which can predict the penetration and perforation ballistic parameters of thick concrete panel under projectile impact. Compared to the experimental observations, the proposed model predicts the residual velocity and penetration depth of this test with better results than existing models. Finally, the new model is applied to the available perforation tests of thick concrete panels, and its error used for relatively thin concrete panel is analyzed.

A strain rate dependent nonlinear elastic orthotropic model for SFRC structures

A strain rate dependent orthotropic model for steel fiber reinforced concrete (SFRC) structures subjected to impact or blast loads is proposed in this paper. Based on the previously introduced orthotropic model for plain concrete, an improved strain rate dependent material model for SFRC is developed to account for the effect derived from the addition of steel fibers in the concrete matrix and to cope with the multiaxial strain rate dependent behavior of SFRC. In addition to verification of the constructed multiaxial strength envelope of SFRC through correlations with experimental data, improved failure strains in the uniaxial stress-strain relation are also introduced to minimize the mesh size dependency in the numerical results. Finally, the proposed orthotropic model is incorporated into LS-DYNA as a user defined material model. Numerical analyses were performed for experiments of RC and SFRC slabs under projectile impact and blast loading, and the obtained results show that the addition of the steel fibers provides a considerable improvement in the structural resistance and the proposed model effectively simulates the structural responses of SFRC structures while minimizing the mesh size dependency in the numerical results.

Experimental and mesoscale numerical investigation on the failure behavior of reinforced concrete under projectile-impact loading

<p indent=0mm>Reinforced concrete is widely used and plays important roles in civil engineering and national defense. It also suffers from an obvious scale effect. Conducting a large-scale penetration experiment is necessary to study the dynamic response of reinforced-concrete under impact loading. In this study, experiments were conducted for a 100-mm large-caliber ovoid projectile to penetrate reinforced-concrete targets at high speed. The damage mode, penetration depth, and crater diameter of the target were analyzed in detail. Owing to the reinforcement, concrete exhibits more complex heterogeneity and anisotropy, and the deformation, damage, and interaction of each component indicate an important effect on the mechanical properties of concrete. A fast and parallel modeling method of 3D mesoscale reinforced-concrete model based on the Voronoi technique was proposed, which solved the problems of large-scale arranged aggregates and intersection detections between the reinforcement and aggregates. The mesoscale numerical simulations were conducted in combination with the K&C model, and the effects of the projectile hitting and not hitting the reinforcements on the penetration depth, crater diameter, and ballistic trajectory were analyzed. The damage mode of the slabs and reinforcements, penetration depth of the projectile, and trajectory deflection were obtained. The numerical results show good agreement with the experimental results, which indicate that the mesoscale model can effectively and accurately predict the failure behavior of reinforced-concrete.

Post-impact flexural capacity of UHPFRC plates

This work aims to demonstrate the effective use of fibre reinforcement in thin plate elements made of UHPFRC under projectile impact loading. The use of fibre reinforcement is very efficient in case of ballistic loading, as fibres are evenly distributed over the entire volume of the material body and possible damage to the plate is thus suppressed in all points of the plate element equally. The aim of this study is therefore to provide data on the residual flexural capacity of plates that have been significantly damaged by the impact of the projectile and to demonstrate the benefits of using fibre reinforcement for localized impact loading.

The structural response of the thermoplastic composite joint subjected to out-of-plane loading

This paper presents a study on thermoplastic single-lap double rivet joints (SLDJ) with and without adhesive subjected to out-of-plane projectile impact and quasi-static concentrated loading. The three-dimensional finite element (FE) models considering strain-rate effects and damage evolution were developed and implemented in the commercial code Abaqus/Explicit through a user-defined subroutine VUMAT. The FE models were validated against the experimental results, in terms of the peak load, the maximum displacement and the dissipated energy. It was found that there were three stages in the load-displacement trace up to the failure, i.e. rivet slip, hole failure and laminate break for the rivet joint, and debonding, rivet slip and laminate break for the rivet joint with adhesive. The rivet joint with adhesive has a higher stiffness before debonding occurs; however, its out-of-plane load carrying capacity is slightly lower than the rivet only counterpart. The validated models were used to study the failure mechanisms of SLDJ through the progressive failure simulation, and further to investigate the effects of boundary conditions, ply angle and impact energy on the impact response of the composite joints. The laminates with 45° ply could be used to enhance the impact resistance of composite joint structures with the reduced damaged area.

Experimental and theoretical investigation of the failure behavior of a reinforced concrete target under high-energy penetration

The dynamic mechanical properties of concrete and reinforced concrete targets subjected to high-speed projectile impact loading have a significant influence on the impact resistance of protective structures. In this study, high-speed projectile penetration and perforation of concrete and reinforced concrete structures was carried out to determine the high-energy impact loading. The failure behaviors of projectile penetration and perforation of the concrete and reinforced concrete targets were investigated, and the destruction characteristics of the targets were measured. An analytical model was established using the principle of minimum potential energy. The results show that the theoretical predictions are consistent with the experimental data, indicating that the energy method is effective for predicting the dynamic mechanical properties of concrete and reinforced concrete targets under high-speed projectile penetration.

Weak-shock wave propagation in polymer-based particulate composites

Shock waves are common in polymer-based particulate composites that are subjected to intermediate to high-velocity impact loading. However, quantitative information on the spatial variation of stress, particle velocities, and energy dissipation during the formation and propagation of weak-shock waves is limited. In this paper, a systematic experimental study is conducted to understand the characteristics of weak-shocks in polymer-bonded particulate composites. Specimens made of polymer-bonded sugar are subjected to a projectile impact loading, at varying velocities, using a modified Hopkinson pressure bar apparatus. Full-field displacement and strains of the deformed samples are obtained with the help of an ultrahigh-speed imaging and digital image correlation technique. Using the full-field displacement data, the shock wave velocity, shock front thickness, and the full-field stress fields are calculated. From the spatial stress field and the strain rate data, the spatial energy dissipation profile is also estimated. The effect of impact velocity on the spatial stress profile, shock wave velocity, and energy dissipation are discussed.

Failure mechanism of reinforced concrete subjected to projectile impact loading

Abstract The study of failure mechanism of reinforced concrete subjected to high-energy projectile impact loading has important significance to accurately evaluate the impact resistance of structures and reasonably design and construct engineering structures. In this study, experiments in which high-speed (>1000 m/s) projectiles impact 1000-mm-thick slabs of reinforced concrete were performed and the damage of the reinforced concrete slabs were measured. Then, an analytical model of the characteristics of reinforced concrete subjected to projectile impact loading is constructed. The principles of energy conservation and minimum potential energy are used to formulate explicit equations for the perforation performance of reinforced concrete. These theoretical predictions agree with our experimental results and with similar published studies. Furthermore, in the context of our model, the effects of impact velocity, concrete compressive strength, and reinforcement ratio on the perforation performance of reinforced concrete are discussed.

ULTRA-HIGH-PERFORMANCE FIBRE-REINFORCED CONCRETE UNDER HIGH-VELOCITY PROJECTILE IMPACT. PART I. EXPERIMENTS

A series of cratering experiments were performed where the response of the Ultra-High-Performance Fibre-Reinforced Concretes with various fibre volume fractions to the high- velocity projectile impact loading was investigated. It was found that the increment of the fibre volumetric fraction did not have a significant influence on the depth of the penetration, but it was very effective in reducing the crater area and volume.

Experimental characterization of compaction wave propagation in cellular polymers

A great-deal of literature is available in the study of compaction wave propagation in cellular materials. However, experimental investigations concerning the spatial variation of the deformation features of compaction waves are limited. In this study, the formation and propagation of compaction wave in a low density polymeric foam under intermediate velocity projectile impact loading is investigated experimentally. The results are discussed in terms of the compaction wave characteristic parameters such as compaction wave velocity, axial strain, particle velocity, etc. In addition, spatial distribution of inertia stress during compaction wave propagation, and the critical velocity required to form shock are estimated. The stress jump across the compaction wave is also calculated using an inertia stress analysis and compared with the shock theory. It was observed that an elastic precursor propagates, at a velocity of 740 m/s, along the material upon impact, and it decays as it propagates along the specimen. Whereas, the compaction wave formed following the elastic precursor was propagated at a constant velocity much slower than the elastic precursor. Inertia stress calculations shows that the fast moving elastic precursor is reflected from the distal end and reduces the inertia component of the total stress. On the other hand, the compaction thickness is seen to be approximately constant during the entire duration of the compaction wave propagation after the achievement of the quasi-steady condition.

The Response of Clamped Shallow Sandwich Arches with Metallic Foam Cores to Projectile Impact Loading

THE DYNAMIC RESPONSE AND ENERGY ABSORPTION CAPABILITIES OF CLAMPED SHALLOW SANDWICH ARCHES WITH ALUMINUM FOAM CORE WERE NUMERICALLY INVESTIGATED BY IMPACTING THE ARCHES AT MID-SPAN WITH METALLIC FOAM PROJECTILES. THE TYPICAL DEFORMATION MODES, DEFLECTION RESPONSE, AND CORE COMPRESSION OF SANDWICH ARCHES OBTAINED FROM THE TESTS WERE USED TO VALIDATE THE COMPUTATION MODEL. THE RESISTANCE TO IMPACT LOADING WAS QUANTIFIED BY THE PERMANENT TRANSVERSE DEFLECTION AT MID-SPAN OF THE ARCHES AS A FUNCTION OF PROJECTILE MOMENTUM. THE SANDWICH ARCHES HAVE A HIGHER SHOCK RESISTANCE THAN THE MONOLITHIC ARCHES OF EQUAL MASS, AND SHOCK RESISTANCE COULD BE SIGNIFICANTLY ENHANCED BY OPTIMIZING GEOMETRICAL CONFIGURATIONS. MEANWHILE, DECREASING THE FACE-SHEET THICKNESS AND CURVATURE RADIUS COULD ENHANCE THE ENERGY ABSORPTION CAPABILITY OF THE SANDWICH ARCHES. FINITE ELEMENT CALCULATIONS INDICATED THAT THE RATIO OF LOADING TIME TO STRUCTURAL RESPONSE TIME RANGED FROM 0.1 TO 0.4. THE PROJECTILE MOMENTUM, WHICH WAS SOLELY USED TO QUANTIFY THE STRUCTURAL RESPONSE OF SANDWICH ARCHES, WAS INSUFFICIENT. THESE FINDINGS COULD PROVIDE GUIDANCE IN CONDUCTING FURTHER THEORETICAL STUDIES AND PRODUCING THE OPTIMAL DESIGN OF METALLIC SANDWICH STRUCTURES SUBJECTED TO IMPACT LOADING.

Dynamic delamination in laminated fiber reinforced composites: A continuum damage mechanics approach

Delamination causes a significant reduction in the load carrying capacity of fiber reinforced polymer (FRP) composites, which is a major concern to the aerospace and automotive industries. High performance FRPs are often subjected to dynamic loadings of different energy densities in their service life when strain rate, stress triaxiality, temperature, and mode of fracture can have a significant knock-down effect on the interfacial strength of plies in a laminate. This paper develops a predictive tool, in a continuum damage mechanics (CDM) framework, to assess delamination damage in FRPs under dynamic loading; the model takes into account the effects of dynamic energy density, mixed-mode fractures and temperature. The CDM model is formulated based on the fracture mechanics (FM) of decohesion and an advantage of the proposed model is that nearly all of the material parameters can be obtained directly through calibration to experimental data rather than numerical curve fitting of simulation results. The developed scheme is coded into a commercial FEA package (ABAQUS) through user-defined subroutines and the fidelity of the model is assessed by comparison with existing experimental data in the literature. The validated model is used to investigate delamination damage in a laminated FRP subject to projectile impact loading, where it will be shown that the extent of delamination damage through the thickness of the FRP structure is dependent upon different wave propagation scenarios. The proposed model provides a design platform for damage assessment caused by dynamic delamination and may be a useful tool for designing FRP composites with a greater impact tolerance.

The perforation resistance of sandwich structures subjected to low velocity projectile impact loading

AbstractThis article presents the findings of a study to investigate the impact perforation resistance of sandwich structures. The dynamic response of sandwich panels based on PVC foam cores has been evaluated by determining the energy to perforate the panels. The impact response of the sandwich structures was predicted using the finite element analysis package Abaqus/Explicit. The validated FE models were also used to investigate the effect of oblique loading and to study the impact response of sandwich panels subjected to a pressure differential equivalent to flying at an altitude of 10,000m.Low velocity impact testing has shown that the energy to perforate the sandwich panels is dependent on the properties of the core. It has been shown that increasing the density of the crosslinked PVC foams by a factor of two yielded a 600% increase in the perforation resistance of the sandwich structures. At higher densities, the crosslinked foam sandwich structures offered a superior perforation resistance to the linear PVC structures. The numerical analysis accurately predicted the perforation energies of the sandwich panels, as well as the prevailing failure mechanisms following impact. Finally, it has been shown that sandwich panels impacted at high altitude offer a similar perforation resistance to those tested at sea level.

The mechanical response of metallic sandwich beams under foam projectile impact loading

THE DYNAMIC RESPONSE OF THE CLAMPED SANDWICH BEAMS WAS MEASURED BY IMPACTING THE BEAMS AT MID-SPAN WITH METAL FOAM PROJECTILES. EFFECTS OF APPLIED IMPULSE FACE-SHEET THICKNESS AND CORE THICKNESS ON THE SHOCK RESISTANCE OF SANDWICH BEAMS ARE DISCUSSED. THE RESULTS INDICATE THAT THE STRUCTURAL RESPONSE IS SENSITIVE TO THE CONFIGURATION OF SANDWICH STRUCTURES. BASED ON THE EXPERIMENTS, CORRESPONDING FINITE ELEMENT SIMULATIONS HAVE BEEN UNDERTAKEN USING THE LS-DYNA SOFTWARE. A GOOD AGREEMENT HAS BEEN OBTAINED BETWEEN THE NUMERICAL AND EXPERIMENTAL RESULTS. THE DEFORMATION AND FAILURE MODES OF SANDWICH BEAMS UNDER IMPACT LOADING ARE PRESENTED, I.E. LARGE INELASTIC DEFORMATION, CORE COMPRESSION AND CORE SHEAR WITH INTERFACIAL FAILURE. NUMERICAL RESULTS ALSO SHOW THAT THE VELOCITY-TIME HISTORIES OF THE MID-SPAN OF THE FRONT AND BACK SHEET OF SANDWICH BEAMS ARE RELATED TO NOT ONLY CORE STRENGTH BUT ALSO CORE THICKNESS. THE RESEARCH RESULTS ARE OF WORTH TO THE THEORETICAL PREDICTION OF THE DYNAMIC RESPONSE OF METALLIC SANDWICH BEAM.

Finite-element Simulation of Kevlar Yarns and Fabrics in Assessing its Mechanical Protective Performance under Projectile Impact Loading

With the increasing concern on occupational safety, people pay more and more attention to mechanical protection. At present, the focus of relevant researches is on the mechanical protection performance of high-performance fibres and high-strength fabrics. The influences that mechanical properties of fabrics have on the mechanical protective performance of clothing are discussed in this paper. Woven fabrics made of high-performance fibres have been widely used as mechanical protective clothing in the form of flexible armour such as bullet-proof vests, stab-resistant garments and so on. The mechanical response and energy absorption characteristics of fabrics under high-speed projectile impact are dependent upon intrinsic constitutive relations, construction parameters such as fabric type, fabric construction, areal density, projectile shape, and impact conditions such as impact velocity and boundary conditions.This project involves the study of Kevlar fibre which is a poly-p-phenylene terephthamide (PPTA) fibre. The Kevlar fabric studied in this paper is plain woven. Experiments about construction parameters of Kevlar yarns are proposed to obtain the mechanical properties of woven fabrics. This paper also investigates the finite-element simulation of huge impact on Kevlar fabric by proposing a material model, which incorporates stretch and elasticity restoring property and failure criteria. A non-linear, explicit, three- dimensional finite-element program ANSYS is used to simulate the response of fabric to high-speed projectile impact with two Hookean springs and a Newtonian dashpot.

Energy-absorption performance of porous materials in sandwich composites under hypervelocity impact loading

This study presents the results of an experimental investigation concerning composite structure models for hypervelocity impact-resistant composites. Sandwich models were investigated for their abilities to prevent perforation subjected to 1–7 km/s projectile hypervelocity impact loading. The models involve several material systems, dual-wall configurations, fabric-reinforced silicon carbide ceramic-matrix composite as impact-facing sheet, hollow sphere energy-absorption materials, carbon fabric and Kevlar fabric reinforced epoxy matrix composites as pressure walls. Hypervelocity impact energy decline patterns are related to impact velocity, impact-facing sheet materials, the initial porosity and the pore radius of porous energy-absorption materials, sandwich structure, pressure wall composite configurations and multi-wall structure. Stainless metal fiber reinforced silica carbon matrix composites showed much better performance than polymer matrix composites in absorbing energy and translating energy when they were used as impact-facing sheets under hypervelocity impact. The main mechanism is that stainless metal fiber reinforced silica carbon matrix composites could disintegrate bigger projectile in the first debris cloud into smaller particles and translate super high point-energy into lower facing-energy that was called the second debris cloud. The hollow sphere materials showed excellent performance in reducing impact energy in which the impact pressure dropped to “zero” when they were impacted and collapsed. Porous silicon carbide materials showed a greater ability to reduce impacting energy than hollow silica sphere and carbon sphere. The fabrication processes for composite specimens designed by theoretical number simulations and predictions were also studied. The results of hypervelocity impact tests reveals that different pressure wall composite configurations have different abilities to prevent the perforation. The sandwich composite models in 18 mm thickness designed and manufactured by the author were not perforated by a 5.4 mm diameter aluminum projectile impacted at 4.2–7.4 km/s.