High Velocity Impact Tests Research Articles

A novel dynamic constitutive model for UHPC under projectile impact

Aimed at numerically predicting the impact resistance and damage pattern of ultra-high performance concrete (UHPC) under projectile impact, this study established a novel dynamic constitutive model for UHPC based on an improved Karagozian & Case concrete (KCC) model newly proposed by authors. Firstly, the established model is introduced, which considers the complex dynamic mechanical properties of UHPC, including the Lode-dependence, strain rate effect, compressive strain hardening and softening, tensile strain softening, volumetric compaction, and shear dilation. Particularly, a four-stage strain softening tensile damage model is adopted for UHPC. Then, the established model is embedded in the commercial hydrocode LS-DYNA as a user defined material model. According to the existing test data of UHPC, the failure surface, strain rate effect, equation of state, and damage model parameters are calibrated for the established model. For comparison, the parameters of the KCC model are also calibrated accordingly. To verify the calibrated material model parameters, single element tests are conducted under tensile and compressive loadings. Finally, the high velocity impact tests performed on both the semi-infinite targets and finite-depth panels with varying striking velocity are simulated, where the established model and the KCC model are respectively adopted for UHPC. It demonstrates that the established model reproduced the impact resistance and damage pattern of UHPC under projectile impact accurately, while the KCC model cannot reflect the dynamic response of UHPC satisfactorily.

Ballistic impact study on fibre reinforced polymer composites using FEA

Numerical modeling is one of the essential tools for predicting the ballistic impact strength of hybrid polymer composites without damaging the sample. The purpose of this work is to analyze the ballistic behavior of carbon/glass fibre reinforced epoxy-based composites. To investigate the effect of stacking order, modeled two different laminates containing carbon fibre and glass fibreto predict the impact behavior. High-velocity impact tests were performed with mild steel projectiles with high impact velocities. Finite element modeling was used to analyze the tensile, flexural and ballistic impact behavior of all laminates. The impact strength of laminates is evaluated using various stress plots. The results showed that the ballistic resistance was mainly affected by the fibre stacking order, fibre type, fibre orientation, and laminate thickness.

Assessment of the ballistic response of honeycomb sandwich structures subjected to offset and normal impact

In the present study, experimental and numerical investigations were carried out to examine the behavior of sandwich panels with honeycomb cores. The high velocity impact tests were carried out using a compressed air gun. A sharp conical nosed projectile was impacted normally and with some offset distance (20 mm and 40 mm). The deformation, failure mode and energy dissipation characteristics were obtained for both kinds of loading. Moreover, the explicit solver was run in Abaqus to create the finite element model. The numerically obtained test results were compared with the experimental to check the accuracy of the modelling. The numerical result was further employed to obtain strain energy dissipation in each element by externally running user-defined code in Abaqus. Furthermore, the influence of inscribe circle diameter and cell wall and face sheet thickness on the energy dissipation, deformation and failure mode was examined. The result found that ballistic resistance and deformation were higher against offset impact compared to the normal impact loading. Sandwich panel impacted at 40 mm offset distance required 3 m/s and 1.9 m/s more velocity than 0 and 20 mm offset distance. Also, increasing the face sheet and wall thickness had a positive impact on the ballistic resistance in terms of a higher ballistic limit and energy absorption. However, inscribe circle diameter had a negative influence on the ballistic resistance. Also, the geometrical parameters of the sandwich structure had a significant influence on the energy dissipation in the different deformation directions. The energy dissipation in plastic work was highest for circumferential direction, regardless of impact condition followed by tangential, radial and axial directions.

Modular electromagnetic railgun accelerator for high velocity impact studies.

A modular electromagnetic railgun accelerator facility named "RAFTAR" (i.e., Railgun Accelerator Facility for Technology and Research) has been commissioned and its performance has been characterized for high velocity impact testing on materials in a single-shot mode. In the first tests, RAFTAR demonstrated an acceleration of more than 1000m/s for an 8g solid aluminum-7075 armature projectile. The current fed was 220kA, having a muzzle time of about 1.75ms. It is a single pulse breech-fed rectangular bore (14 × 13mm2) railgun, and its 1.15m long barrel assembly consists of two parallel copper bars with an inter-gap of 13mm that are encased within 50mm thick high strength reinforced fiberglass sheets (Garolite G10-FR4) and bolted from both the sides. RAFTAR is powered by two capacitor bank modules that have a maximum stored energy of 160 kJ each (containing eight 178 μF/15kV capacitors), two high power ignitron switches, and a pulse shaping inductor. To obtain consistent acceleration of the armature inside the barrel, reversal of driving current is prevented, and its pulse duration is stretched by tactical integration of the crowbar switch and bitter coil inductor in the circuit. Armature projectile velocity measurement in-bore and outside in free space was performed by the time-of-flight technique using indigenously made miniature B-dot sensors and a novel shorting-foil arrangement, respectively. The time resolved measurement of the in-bore armature evidenced a velocity-skin-effect in the high acceleration phase. There is good agreement between the experimentally measured and theoretically predicted efficiency, confirming the optimal choice of operating parameters. The conclusion summarizes important experimental findings and analyzes the underlying causes that limit the performance of railguns.

On the Residual Static and Impact Capacity of Shear-Reinforced Concrete Beams Subjected to an Initial Impact

Impact loads in previous research showed to induce brittle responses of statically flexure-critical reinforced concrete (RC) beams designed for ductility. The impact load may produce flexural shear damage modes similar to that observed during quasi-static loads and local shear damage under the impact zone. The occurrence of shear damage modes during impact tests has been investigated extensively, but their effect on the residual quasi-static and dynamic capacity is not fully understood. For this aim, an initial high-velocity impact test initiated severe shear damage to RC beams. The beams were then tested quasi-statically and by sequential impact testing using the same setup as the initial tests. The results indicate a flexure-dominated response during sequential impact tests for beams containing extreme shear reinforcement amounts, favouring the energy-absorption capacity. Significant shear and flexural damage occurred for beams with less shear reinforcement, indicating a hybrid response that varied throughout the tests. The tests for the residual quasi-static capacity indicated severe consequences from initial local shear damage on the capacity, as shown by the brittle response of the beam with the most shear reinforcement. However, wide initial flexural cracks instead showed a favourable effect, as there was an indication of transfer from brittle to ductile failure. For beams showing both global and local shear damage, it was concluded that global shear damage modes were critical for the residual static and dynamic shear capacity.

Microstructural evolution, shielding effectiveness, and the ballistic response of Mg/Al7075/B4C/Pb composite produced by combination of coating and severe plastic deformation (SPD) processes

Light-weight metal matrix composites reinforced by Pb and B4C are of interests in aerospace industry due to high strength to weight ratio and excellent shielding effectiveness. This paper investigates microstructure, shielding effectiveness, tensile properties, and high-velocity impact behavior of Mg/Al/B4C/Pb composite. In this composite, the B4C layer was deposited by electrophoretic deposition (EPD) on aluminum layers, then the sandwich with the stacking sequence of Mg/Al/B4C/Pb was fabricated through accumulative roll bonding (ARB). The optical microscopy (OM) and scanning electron microscopy (SEM) images illustrated that by increasing the cycles, all layers within composite experienced instabilities including necking and fracture. In addition, increasing the number of rolling cycles improved tensile properties, namely Young's modulus, elongation, yield, and ultimate strength. Furthermore, according to the results of the high-velocity impact test, by increasing the rolling cycle, less failure such as cracks and perforation was found on surfaces, indicating the enhanced ballistic resistance of composites. Plus, when composites were subjected to electron radiation, less relative doses of radiation were detected by dosimeter at higher rolling cycles which confirmed the attenuation of transmitted rays and then the enhancement of shielding effectiveness of composites.

Simplified Approach to Verification of Numerical Models for Deformation and Fracture Analysis of Structural Composite Subjected to High-Velocity Impact

Deformation and fracture analysis of the composite elements and structures under high-velocity impact is still associated with many problems. These problems are related not only to the complexity of taking into account the composite layered orthotropic structure and various failure scenarios but also to the problems of instrumented high-velocity impact tests to verify the calculation results. Different requirements for accuracy and numerical efficiency are imposed on the models and their predictive ability depending on the design stage. At the initial design stages, the model should allow one to estimate the energy absorption of the composite structure adequately. At later stages, the size of the damaged area and the fracture pattern also should be predicted with high accuracy. This article describes a simplified approach to the verification of deformation and fracture models of structural composites under high-velocity impact based on low-velocity impact test data. The model with the found parameters makes it possible to predict with satisfactory accuracy the energy absorption of the composite material.

Experimental investigation on high-velocity impact damage and compression after impact behavior of 2D and 3D textile composites

This paper investigates the impact resistance and damage tolerance of 2D triaxially braided composites and 3D angle-interlock woven composites panels using high-velocity impact tests and compression after impact tests. Both materials present equivalent impact resistance with similar ballistic limit and energy absorption ratio. Nevertheless, the damage patterns of the two materials are quite different, among which, 2DTBC is characterized by global response and yarn debonding, while 3DAWC is characterized by localized damage without yarn debonding. However, in compression after impact tests, 3DAWC exhibits higher damage tolerance because the binder yarns resist buckling failure and kink bands formation during compression, resulting in higher residual compressive strength. In addition, how the damage morphology varies spatially due to the different deformation and damage modes caused by high-velocity impact is learned from X-ray CT scanning. Different from the relationship between impact energy and residual compressive strength pointed out by most research, this study also reveals a unique trend of residual compressive strength as a function of impact energy, considering both penetration and rebound conditions.

Impact simulation of composite panels for aerospace applications

The aerospace research community has been working towards the development of a comprehensive framework for the design of composite structures at the component, subassembly, assembly, and system levels. Such a framework requires accurate, efficient and easy-to-use mathematical and computational models that are in sync with physical reality. The research work in this paper is designed to help an aerospace structural engineer move towards this goal by simulating dynamic impact to composite panels. First, the existing orthotropic visco-elastic visco-plastic material model in LS-DYNA commercial finite element program, MAT_COMPOSITE_TABULATED_PLASTICITY_DAMAGE (MAT_213) is enhanced with the development and use of rate-dependent damage data. Using state-of-the-art experimental procedures, impact validation test data are created. Second, the versatility of the constitutive model is examined by its ability to simulate a low velocity (27 ft/s, 8 m/s) impact test, and two high velocity impact tests (385–417 ft/s, 117–127 m/s) that straddle the ballistic limit of the projectile and the composite panels. Third, these impact events are modeled using three different finite element types – under-integrated and fully-integrated solid elements, and fully-integrated thin shell elements. Insight into accuracy versus numerical efficiency is gained by comparing the performance of solid versus thin shell elements. The numerical results show that accurate predictions of these impact events can be obtained with reasonable effort and care.

Perforation studies of concrete panel under high velocity projectile impact based on an improved dynamic constitutive model

The finite-depth concrete panels have been widely applied in the protective structures, and its impact resistance and dynamic fracture failures, especially the scabbing/perforation limits, under high velocity projectile impact, are mainly concerned by protective engineers, which are numerically studied based on an improved dynamic concrete model in this study. Firstly, based on the framework of the KCC (Karagozian & Case concrete) model, a dynamic concrete model is proposed which considers an independent tensile damage model and a continued transition between dynamic tensile and compressive properties. Secondly, the strength surface, equation of state and damage parameters of the proposed model are comprehensively calibrated by a triaxial compressive test with high confinement pressure, the rationality of which is further verified based on the single element tests, e.g., uniaxial and triaxial compression as well as uniaxial, biaxial and triaxial tension. Thirdly, a series of projectile high velocity impact tests on thin and thick concrete panels are simulated, which indicates that the projectile residual velocity and dynamic fracture failures are reproduced satisfactorily, while the KCC model underestimates both the spalling and scabbing dimensions severely. Finally, based on the validated concrete model and finite element analyses approach, the validations of the existing five empirical formulae are evaluated, in terms of the depth of penetration (DOP) and scabbing/perforation limits of concrete panel. Both the Army corps of engineers (ACE) and modified National Defense Research Committee (NDRC) formulae are recommended in the design of the protective structure to avoid scabbing failure.

Analysis of Damage of Typical Composite/Metal Connecting Structure in Aircraft under the Influences of High-Velocity Fragments

A two-stage light gas gun was used to conduct a high-velocity impact test on the aircraft’s typical composite/metal connecting structure (CFRP/AL). The battle damage simulations used for the CFRP/AL connecting structure were carried out under different intersection conditions. Then, the damage morphology and mechanism of high-velocity prefabricated spherical fragments on typical structures, the dynamic process of hyper-velocity impact, and the formation of debris clouds on the secondary damage morphology of different component structures were investigated. Next, based on the X-ray computerized tomography (CT), the typical mode of different damage areas and evolution trends of CFRP under high-velocity impacts were explored. Finally, a simulation model was established for battle damages of typical structures by combining FEM methods, and structural components’ energy dissipation capabilities for fragments under different velocities were analyzed. The study results provide a reference and model support for the rapid repair of battle-damaged aircraft and aircraft survivability design.

High-velocity impact behaviour of curved GFRP composites for rail vehicles: Experimental and numerical study

This study aims to explore the projectile impact behaviour of curved glass fibre reinforced plastics (GFRP) composites for rail vehicles through experimental and numerical methods. Quasi-static material tests were firstly carried out to obtain the tensile, compression, shear and bending properties. Then, high-velocity impact tests under different velocities were conducted for curved GFRP plates, which were cut from hood covers of a rail vehicle. The residual velocity of the projectile, the failure modes and the energy absorption of the composite targets were analysed. The classical Lambert-Jonas equation was used to predict the critical perforation velocity, which was also verified by the following finite element (FE) simulation in LS-DYNA. Based on the validated FE model, the effects of the impact velocity (65.14–152.22 m/s), target thickness (2 mm–8 mm) and impactor shape (flat, blunt, hemisphere and sphere) on the high-velocity impact performance of the target were studied. The results showed that the predicted critical perforation velocity of the curved GFRP plate with thickness of 6 mm was about 101.98 m/s in this study, and only local damages were observed near the trajectory. Increasing the thickness of the GFRP plate can improve its anti-penetration capability, however, the 4-mm plate possesses the highest specific energy absorption among the thickness of 2 mm–8 mm. Compared to the sharp impactors, the flat impactor resulted in the highest peak force of 260.39 kN and the maximum specific energy absorption of 502.65 J in the curved GFRP plates with thickness of 6 mm, due to the shear failure mechanism and the formation of embolism.

Ballistic impact response of flexible and rigid UHMWPE textile composites: Experiments and simulations

This study elaborates on the effects of matrix rigidity on the high-velocity impact behaviour of UHMWPE textile composites using experimental and numerical methods. Textile composite samples were manufactured of a plain-weave fabric (comprising Spectra® 1000 fibres) and four different matrix materials. High-velocity impact tests were conducted by launching a spherical steel projectile to strike on the prepared samples via a gas gun. The experimental results showed that the textile composites gradually changed from a membrane stretching mode to a plate bending mode as the matrix rigidity and thickness increased. The composites deformed in the membrane stretching mode had higher impact resistance and energy absorption capacity, and it was found that the average energy absorption per ply was much higher in this mode, although the number of broken yarns was smaller in the perforated samples. Moreover, the flexible matrix composites always had higher perforation resistance but larger deformation than the rigid matrix counterparts in the tested thickness and velocity range. A novel numerical modelling approach with enhanced computational efficiency was proposed to simulate textile composites in mesoscale resolution. The simulation results revealed that stress and strain development in the more rigid matrix composite was localised in the vicinity of the impact location, leading to larger local deformation and inferior perforation resistance.

High velocity impact behavior of Hybrid composite under hydrostatic preload

The Hybridization concept creates a niche within the composite segment to customize materials for specific applications with reduced cost without sacrificing strength and durability. The composite structures develop strain during continuous operation, and any sudden impact on these preloaded parts might result in catastrophic accidents. Studying impact response during such conditions is essential in designing and developing structures. This study experimentally investigates the high velocity impact response of Hybrid (Carbon-Glass) composite under normal and hydrostatic preload conditions. Mechanical tests involving Tensile, Izod, and Charpy are conducted. High velocity impact testing is carried out with a vertical single-stage gas gun with additional provision for hydrostatic preloading. An oscilloscope with a laser source measures the initial velocity, and Photogrammetry using a high-speed camera measure the residual velocity of a projectile. The mechanical test results suggest that Hybridization resulted in a significant property enhancement. The high velocity impact resistance and energy absorption are higher for Hybrid under both normal and preloaded impact.

Assessment of high-velocity impact effects on carbon fiber reinforced polymer sandwich panel with M-shaped core reinforced by nano-SiO2: Experimental and numerical study

This paper describes the high-velocity impact behavior of composite sandwich panels with different amounts of nano-SiO2. The sandwich panels were manufactured by carbon/fiber epoxy composite face sheets and an M-shaped core using the vacuum-assisted resin transfer molding method. To enhance the mechanical strength of the matrix, especially impact resistance, the nanoparticles were added to the resin epoxy matrix as filler with the ratios of 1%, 2%, and 3% of the composite's total weight. A scanning electron microscope was utilized to observe the microscopic structure of the composites, and it revealed an exceptional homogeneous mixture of nano-SiO2 particles in the resin epoxy matrix. Afterward, high-velocity impact tests were carried out using a single-stage gas gun test machine. A spherical steel projectile with a diameter of 8.7 mm was used for the test with a speed of 235 m/s. The experimental results indicated that adding 1–3 wt% of nano-SiO2 into the matrix remarkably increased the impact resistance of the composite. Moreover, the results showed that when the projectile collides with the core of the sandwich panel, it remains in the sandwich panel and its output velocity becomes zero, while when the projectile does not collide with the core, its output velocity is not zero. In order to validate the results, the experimental data were compared to the finite element models, and good agreement was observed.

Rocket Sled Based High Speed Rail Track Test Facilities

The present study introduces and compares several high-speed track based ground test facilities available all over the world to simulate high-speed dynamic events for selected portions of flight trajectories. The scope of performing high speed flight-testing is addressed, which is followed by the requirements of these track based test facilities. The facilities deliver flight test articles under controlled conditions to achieve high velocity impact, acceleration, aerodynamic and other related testing for small and large test articles depending upon the requirements. Sled is designed in such a way so that it can carry the test articles like aircrafts, payloads, warheads, missiles and many other ballistic systems to achieve high velocities ranging from subsonic to hypersonic by accelerating these sleds using solid rocket motors over the rail track. Such facilities provide instrumentation for large set of trial data acquisition and offline analysis for both recovery and non- recovery (impact) trials, which makes such facilities important for test, research and evaluation purposes.
 Here, the detailed description of test facilities, which are available in many countries such as India, United States (US), Japan, United Kingdom (UK), France, and others countries based on their technical characteristics is presented. Additionally, a brief history and introduction into basic rocket sled test facility aspects, essential technical characteristics and major features to support high speed testing at these facilities as an accurate testing technique based on quality of construction and engineering design are also covered in this paper. Compilation of available or under development facilities is done in one place which provides the information about facilities’ technological gaps. The paper concludes with an explanation of the role, major capabilities and limitations of these test facilities in the present global scenario.

High velocity impact response of corrugated core composite sandwich structures

The mechanisms of projectile penetration of composite sandwich panel with empty, trapezoidal corrugated cores have been experimentally investigated. The panels have been designed to investigate the influences of specific parameters, like the fiber type of corrugated core, the projectile nose shape and the stacking sequence of face-sheets, on the impact performance from the aspects of sequential deformation, failure modes and associated mechanisms. Experimental results demonstrated that usage of Twill glass fiber in corrugated core is attained highest performance in term of energy absorption and residual velocity for the fully perforated specimens. Comparisons of panels with different stacking sequences for face-sheets verify that the corrugated core composite sandwich structures with [Formula: see text] stacking sequence is indicated the highest energy absorption. This panel is displayed a superior resistance over the ones with other stacking sequences. The hemispherical projectile is showed no deviation from the direct line of path flight relative to the conical and blunt projectile in the high velocity impact test. Moreover, the deviation of the projectile decreases the damage area in specimens.

Constitutive model for fibre reinforced composites with progressive damage based on the spectral decomposition of material stiffness tensor

Complex nature of the fibre reinforced composites, their non-homogeneity and anisotropy make their modelling a challenging task. Although the linear – elastic behaviour of the composites is well understood, there is still a significant uncertainty regarding prediction of damage initiation, damage evolution and material failure especially for a general loading case characterised with triaxial state of stress or strain. Consequently, simplifying assumptions are often unavoidable in development of constitutive models capable of accurately predicting damage. The approach used in this work uses decomposition of the strain energy based on spectral decomposition of the material stiffness tensor and an assumption that each strain energy component represent free energy for a characteristic deformation mode. The criteria for damage initiation are based on an assumption that the damage corresponding to a deformation mode is triggered when the strain energy for that mode exceeds a specified critical limit. In the proposed model the deformation modes are not interacting at continuum scale due to orthogonality of the eigenvectors, i.e. the stiffness tensor symmetry. Damage and its evolution are modelled by reduction of the principal material stiffness based on the effective stress concept and the hypothesis of strain energy equivalence. The constitutive model was implemented into Lawrence Livermore National Laboratory (LLNL) Dyna3d explicit hydrocode and coupled with a vector shock Equation of State. The modelling approach was verified and validated in a series of single element tests, plate impact test and high velocity impact of hard projectile impact on an aerospace grade carbon fibre reinforced plastic. The model accurately predicted material response to impact loading including the test cases characterised by presence of shock waves, e.g. the plate impact test. It was also demonstrated that the model was capable of predicting damage and delamination development in the simulation of the high velocity impact tests, where the numerical results were within 5% of the post impact experimental measurements.

High-velocity impact resistance of doubly curved sandwich panels with re-entrant honeycomb and foam core

This work describes the high-velocity impact behavior of doubly curved sandwich panels. The sandwich panels are manufactured using carbon/fiber epoxy composite face sheets, polyurethane foam core and 3D-printed PLA plastic cellular auxetic (re-entrant) honeycombs. High-velocity impact tests are carried out by using a single-stage air gas gun test machine. A spherical steel projectile with the radius of 5 mm is impacted to the center of the specimens with the speed of 100 m/s. The experimental data are used to validate explicit finite element models of the doubly curved structures. An analytical model is also developed for the ballistic limit of the flat and doubly curved sandwich panels, and the analytical results are compared to those obtained from the numerical ones. Parametric numerical analyses of the high-speed impact of the curved sandwich panels are then carried out considering various radii of curvature of the panels. The results show that the energy absorption is increased as the curvature is decreased for the panels with both foam and re-entrant core. In addition, the core configuration provides a key role in the impact resistance of the sandwich panels. Re-entrant models show an increase in specific energy absorption (SEA) compared to the foam core types.

Experimental analysis of corrugated core sandwich panel with smart composite face-sheets under high-velocity impact

The present research work investigated on the behavior of corrugated core composite sandwich panel (CCCS) with composite face-sheets reinforced by pseudo-elastic NiTi shape memory alloy (SMA) wires subjected to high-velocity impact experimentally. The number of SMA wires, their location, and their pre-strain percentage are the parameters studied in this investigation. The sandwich specimens were made by woven glass fibers/epoxy composite face-sheets strengthened by the SMA wires and Aluminum corrugated core and prepared using the wet hand lay-up method. Their behavior is evaluated under high-velocity impact test by a gas gun impactor testing machine. According to the results obtained, a significant change in the amount of energy absorption of the specimens containing SMA wires is observed. By increasing the number of the SMA wires, the energy absorption by the specimen is increased, but by pre-straining the SMA wires, the effect in energy absorption is significant. Also, when the projectile hits the SMA wire in CCCS, better properties in energy absorption can be observed. The results show that the energy absorption increased from 117.247 J for the specimen without the SMA wire to 128.749 J for the six SMA wires specimen. On the other hand, by applying the pre-strain to the SMA wires, the residual stresses in the specimens and hence the energy absorption in the specimen with six SMA wires with 3% pre-strain increased to 142.57 J.