Gas Gun Research Articles

The dynamic response of composite auxetic re-entrant honeycomb structure subjected to underwater impulsive loading

The researches on dynamic responses of underwater impulsive loading have been conducted. However, the previous study mainly concentrated on metal sandwich structure and fixed supported boundary. The relative research on composite auxetic re-entrant honeycomb structure and simply supported boundary are rarely. In this paper, the effect of the gradient form and relative density on impact resistance performance of composite auxetic re-entrant honeycomb structure was experimentally and numerically investigated. The one-stage light gas gun was applied to provide initial kinetic energy of the fly plate, and the diffuser-type shock tube was utilized to generate and propagate exponential decaying shock wave. The pressure–time curve was respectively amplified and recorded by the charge amplifier and oscilloscope. The response speed, final deflection of rear panel and failure mode of cores and panels were used to evaluate impact resistance of composite auxetic re-entrant honeycomb structures. Moreover, acoustic-structure interaction algorithm was applied to simulate impact course of specimens in Abaqus/Explicit. The results between experiment and numerical simulation exhibited good consistency. The results indicated that the positive gradient form could excessively slow down response speed of rear panel by dissipating energy of shock wave, and the average gradient demonstrated smaller final displacement of rear panel and less failure compared with graded structures.

Study on transverse high-velocity impact resistance of carbon nanotube films and their based composites

This paper investigates the resistance of Carbon nanotube (CNT) films and their based composites to transverse high-speed impact and explores the effect of resin content on the impact properties. The study utilizes light gas gun experiments and employs numerical simulation to determine the critical penetration velocities for pure CNT films and those films impregnated with 20 %, 50 %, and 80 % epoxy resin solutions. The results demonstrate that including epoxy resin can enhance CNT films' impact-resisting ability, with a noticeable improvement as the resin content increases The observed strengthening mechanism in CNT resin composite films subjected to high-speed impacts primarily is energy absorption. Based on the above results, CNT films were added to the interlayer of composite laminates. It was found that CNTs could help materials resist impact and ensure the integrity of the laminate structure.

Raman spectra of naphthalene under shock compression

The Hugoniot data of naphthalene under shock compression were measured by using a two-stage gas gun, and the D-u line was obtained at an impact pressure of 13.7 GPa: D = 2.102 (±0.09) + 1.865 (±0.066) up. Furthermore, the Raman spectra of naphthalene were acquired under impact pressures of 2.33 GPa and 3.55 GPa by utilizing a transient Raman spectroscopy system. Seven intramolecular vibration modes were observed, and the corresponding Raman peaks shifted blue with the increase of impact pressure. However, no anomalous phenomena such as peak splitting or disappearance were detected, indicating that the stability of naphthalene within the applied pressure range and the frequency shift of shock-compressed naphthalene obviously depend on the density rather than the pressure.

Development and validation of large-scale gas gun experiment and its simulation for evaluating impact resistance of electronic equipment

This study aimed to develop a structural analysis method to replace and validate large-scale gas gun tests for evaluating the impact resistance of electronic equipment. By measuring projectile's deceleration through experiments and simulations, stress and strain during collisions were quantified. It was demonstrated that optimizing projectile and electronic equipment designs could enhance impact resistance. Simulation results indicated that changes in projectile velocity and head angle led to variations in maximum deceleration and penetration depth, with decreasing the head angle proving more effective in reducing maximum deceleration. Comparisons between experimental and simulation results showed good agreement, particularly in plots between maximum deceleration and target collision depth. As the head angle increased, there was a tendency for maximum deceleration to increase and target penetration depth to decrease. Comparing peak deceleration curves from gas gun tests and simulations revealed similar trends, indicating consistent results. This research provides important information for evaluating the impact resistance of electronic equipment and demonstrates that combining experiments with simulations can yield more reliable results.

Mechanical properties and impact behavior of frozen clay: Insights from static mechanical tests, fly-plate tests, and split-Hopkinson pressure bar analysis

The presence of frozen clay as a natural protective material makes it a crucial layer of defense against potential impacts in various engineering projects. Studying the strength and deformation characteristics of frozen clay is, therefore, particularly important. In this study, static mechanical tests, the Hopkinson impact test, and fly-plate tests were conducted on frozen clay to identify its mechanical properties under an impact load. The uniaxial compression strength, flexural strength, and elastic modulus displayed a linear increase with the change in temperature. The fractal dimension was used to describe the failure characteristics of frozen clay, yielding values ranging from 1.5691 to 1.8785. At the same temperature, the fractal dimension exhibited a strain rate effect as the strain rate increased. A light gas gun system was then used to conduct fly-plate tests on frozen clay at varying temperatures (−3, −20 °C, and ordinary temperature). The impact process was meticulously analyzed, considering factors such as shock wave velocity, particle velocity behind the shock wave, impact pressure, and volume strain. Moreover, our investigation plotted the D–u (volume strain–particle velocity) and P–μ shock (impact pressure–shock wave velocity) adiabatic curves. Notably, we observed that samples with a higher initial strength exhibited an increased resistance to compression under an identical initial density and moisture content, resulting in a discernible leftward shift of the P–μ curve. The results provide a theoretical basis and technical support for similar projects in the future.

Thermomechanical constitutive behaviour of 3D printed biomimetic polymer material under high strain rates

With the continuous technical breakthroughs of flexible electronics, materials with outstanding application potential are constantly being designed and optimized. Biomimetic polymer materials are particularly appealing due to their versatility and ease of fabrication, but their mechanical reliability, particularly their thermomechanical constitutive behaviour under extreme working loads, remains unclear. In this paper, the impact responses of a 3D printed biomimetic polymer material named “Tangoblack” are investigated under thermomechanical, focusing on the effect of strain rate. By adjusting the pressure of the gas gun in the split Hopkinson pressure bar, different strain rates are achieved, while the high temperature of the tested sample can be controlled using a heating furnace integrated into the experiment system. Materials for pulse shapers are carefully selected to ensure longer durations at nearly constant strain rates. The constitutive behaviour of the biomimetic polymer material is further investigated under a wide strain rate range from 958 s−1 to 2158 s−1 and three different temperatures (20 °C, 70 °C and 120 °C). The results demonstrate a significant dependence of the polymer material on both strain rate and temperature. A rapid increase in forming strain rate enhances the strain hardening process, while simultaneously revealing a substantial temperature softening effect. Then, an improved nonlinear thermoviscoelastic ZWT constitutive model is proposed utilizing the Vogel-Fulcher-Tammann equation and implemented as a user-defined material model in ABAQUS/Explicit. The proposed constitutive model is demonstrated to be distinctly advantageous, which suggests a novel pathway for describing the mechanical reliability of biomimetic polymer materials under extreme working conditions.

Effect of Target Layering in Gravity‐Dominated Cratering in Nature, Experiments, and Numerical Simulations

AbstractImpacts into layered targets may generate “concentric craters” where a wider outer crater in the top layer surrounds a smaller, nested crater in the basement, which itself may be complex or simple. The influence of target on cratering depends on the ratio of target strength to lithostatic stress, which, in turn, is affected by gravity, target density, and crater diameter. When this ratio is large, the crater size is primarily determined by target strength, whereas gravitational forces dominate when the ratio is small. In two‐layer targets, strength may dominate in one or both layers, whereby the outer crater develops in the weaker top layer and the nested crater in the stronger substrate. However, large natural craters that should be gravity‐dominated in both cover strata and substrate may be concentric, the reasons for which are not yet fully understood. We performed qualitative impact experiments at 10–502 G and 1.8 km/s with the Boeing Corp. Hypervelocity centrifuge gun, and at 1 G and 0.4 km/s with the CAB CSIC‐INTA gas gun into layered sand targets of different compositions and grain densities but similar granulometry to analyze gravity‐dominated cratering. The results are compared with iSALE‐2D numerical simulations and natural craters on Earth and Mars. We show that target layering also affects the excavation process and concentric crater formation in gravity‐dominated impacts. The most important factors are the density and internal friction of each target layer, respectively. We propose that this is also valid for natural craters of sizes that should make their formation gravity‐dominated.

An exploration of anomalous electrical noise in shocked cyclotrimethylenetrinitramine (RDX)-based explosives

Gas gun shock experiments on cyclotrimethylenetrinitramine (RDX)-based explosive compositions that employ embedded gauge particle velocity tracers have noted a significant amount of electrical noise when compared to other explosive formulations. This paper reexamines previously published embedded gauge data on Cyclotols (60–80 wt. % RDX) to quantify the electromagnetic behavior of these materials. The primary observation is a fourfold increase in the electrical noise when Cyclotols are shocked above 4.22 ± 0.08 GPa. Electromagnetic gauge noise is also observed within particle velocity traces in reactive growth and off-Hugoniot shocks, although at higher pressures than the direct shock case, suggesting a temperature- or kinetically dependent transition. In all cases, the electrical noise disappears upon detonation. By comparing with the static high-pressure phase diagram of RDX, we interpret this change in electromagnetic behavior to be a change in the RDX crystal structure to a piezoelectric phase, although it is uncertain whether the γ or ε phase is responsible for the observed behavior.

Anti-penetration response and response mechanism of laminated structures made of different composite materials under impact load

Composite laminated structures are often subjected to high-speed impact from external objects in high impact environments, resulting in unpredictable forms of damage and even uncontrollable damage modes. To ensure the safety and reliability of these structures, research was conducted on the anti-penetration response and response mechanism of laminated structures made of different composite materials. Using carbon fiber reinforced plastic (CFRP) laminated structures and glass fiber/epoxy resin composite aluminum alloy (GLARE) laminated structures as research objects, a high-impact experimental setup was constructed based on a first-stage light gas gun to explore the relationship between the energy absorption characteristics and impact energy of composite laminates. Combined with the ballistic limit equations, the ballistic limit values of the composite laminated structures were determined, and the ballistic limits of the 2 mm thick CFRP laminated structure and the 2 mm thick GLARE laminated structure were 138.3 m/s and 215.6 m/s, respectively. The damage modes of CFRP laminated structure are mainly fiber fracture on the impact surface and fiber delamination, fiber tensile fracture and fiber bundle splitting on the back surface, while the damage modes of GLARE laminated structure are mainly plastic deformation, internal fiber fracture and crack extension at the penetration. At the same time, the cohesion unit is introduced to carry out numerical simulation research, which shows that the damage pore morphology of the cohesion unit between layers of composite laminated structures are closely related to their fiber layups, and the damage mode of cohesion unit between layers of composite laminated structures have been investigated, which reveals the damage mechanism in high-impact environments. The research results provide theoretical basis and common technical support for reverse design of composite laminated structures suitable for high impact environments.

Shakedown of metallic sandwich beams when subjected to repeated impact loadings

When a monolithic metallic beam/plate subjected to repeated dynamic loadings with fixed impact level experiences elastoplastic deformation, its measurable deformations may cease to develop for further repetitions of the same dynamic load: this phenomenon was referred to as “pseudo-shakedown” in previous studies (Jones, 2014; Shen and Jones, 1992). Would pseudo-shakedown occur in a metallic sandwich structure under repeated shock loadings remains elusive. A combined experimental and numerical study was carried out to explore whether dynamic shakedown could occur in all-metallic ultralightweight corrugated core sandwich beams. For repeated impact tests, the sandwich beams were fabricated via the sequential process of cutting-stamping-vacuum brazing. When subjected to repeated impact loads (achieved via aluminum foam projectiles launched from a light gas gun), the dynamic responses of each sandwich specimen - including structural evolutions, beam deflections, and deformation/failure modes - were measured. Experimental results revealed that, depending upon the level of impact momentum applied to the sandwich beam, either dynamic shakedown or progressive failure could occur. The method of finite elements (FE) was subsequently employed to simulate the repeated shock tests, which was validated against experimental measurements, with good agreement achieved. To explore the physical mechanisms underlying the observed dynamic shakedown, the FE results of final plastic energy and effective plastic strain distribution in the sandwich beam were extracted and analyzed. When shakedown occurred, the measurable permanent deformation of the sandwich beam kept a relatively stable state, but its plastic energy remained positive, which is different from its monolithic beam/plate counterpart (i.e., plastic energy dropping to zero during dynamic shakedown). Such difference is mainly attributed to stress concentration occurring at the connecting joint points between the corrugated core and face sheets of sandwich and clamped endings, which produces plastic deformations that are difficult to reflect in overall large deformations of the beam. Consequently, the dynamic shakedown of metallic corrugated core sandwich beam captured in this study appears to be inexhaustive and hence may be termed as the “apparent pseudo-shakedown” (with danger lurking in the welding joints as well as clamped endings). Finally, based on a simplified bi-linear hardening constitutive law, the mechanisms underlying the dynamic shakedown of sandwich beam were further discussed from a purely base material point of view.

Comprehensive effect of simulated centrifugal force on characteristics of different extent notch-type foreign object damages

To systematically reveal effects of the centrifugal force on macro and micro characteristics and residual stress distributions of notch-type foreign object damages (FODs) on the leading edge of rotating titanium alloy fan/compressor blades, four series of notch-type damages with different depths were obtained under the same impact condition but four kinds of preloading conditions by using a light gas gun equipped with a 4-axial adjustable fixture. Macro and micro characteristics, stress concentrations and predicted numerical residual stress distributions of the notch-type damage impacted under the different preloading conditions were observed, calculated and compared. Finally, a qualitative analysis of fatigue crack initiation locations of FOD specimens was conducted by the comprehensive comparison of locations of stress concentrations, maximum residual stresses, micro damages such as micro cracks.

Study on projectile impact resistance of carbon-glass hybrid bioinspired helical composite laminate

Mantis shrimp dactyl clubs have excellent impact resistance due to their special helical structure. Meanwhile, hybrid fibre has become increasingly popular to improve the mechanical properties of composite materials. Based on the helical structure of the periodic region of mantis shrimp dactyl clubs and hybrid fibres, in this study, a hybrid fibre helical lay-up laminate (HHL) is designed. The laminates are prepared using unidirectional carbon fibre prepregs and unidirectional glass fibre prepregs. To study the protective performance and damage process of HHL, a light gas gun impact test and numerical simulation calculations were carried out on the specimens. The harvested protective capability of the HHL specimen was then compared with those of carbon fibre unidirectional lay-up laminate (CUL), carbon fibre helical lay-up laminate (CHL), and hybrid fibre unidirectional lay-up laminate (HUL) specimens. The ballistic protection capability of HHL at different helical lay-up angles was also explored. The testing results show that HHL has the best ballistic protection performance. HHL’s ballistic limiting velocity is 228.5 m/s, which is 49.5%, 30.8%, and 19.9% higher than those of CUL (152.8 m/s), CHL (174.7 m/s), and HUL (190.5 m/s), respectively. Finally, hybrid fibres with a 90° interlaminar helix angle were found to have the highest ballistic limiting velocity. The reason is that the larger interlaminar angle allowed more fibres to be involved in the protection, increasing the energy loss of the projectile and enhancing the protection of the laminate.

Experimental and numerical study on projectile impact damage of EBC-SiC/SiC

The ingested particles or debris will cause high-speed & low-energy impact to the hot end components of aeroengine. Few literature focus on the projectile impact of SiC/SiC with Environmental Barrier Coating(EBC). The impact of 2 mm projectile was specially studied for Si/Yb2Si2O7/Yb2SiO5-SiC/SiC. Gas gun system was used to conduct impact testing at the speed of 3 m/s∼353m/s. The optical microscope, Scanning Electronic Microscope(SEM), micro CT were used to observe the impact and tension after impact(TAI) damage. For TAI, Digital Image Correlation (DIC) was used to conduct the full-field strain detection around the impact point. Meanwhile, the Smoothed Particle Hydrodynamics (SPH) methodology was programmed in C++ and developed to simulate SiC/SiC impact problem by introducing modified Hashin-Rotem criteria, extending interface method to 3D and adding GPU accelerated algorithm. The results indicate that threshold velocities of EBC huge peeling and SiC/SiC penetration are different, TAI residual strength also has extinct threshold at the velocity of 246 m/s with 37.1% declining extent, and the impact pit depth of SPH simulation is in good agreement with the experiment.

Using graded density impactor to achieve quasi-isentropic loading with stress and strain-rate controlled

In gas gun experiments, a graded density impactor (GDI) is used to achieve quasi-isentropic loading. However, inconsistency between the designed and experimental loading profiles, mainly caused by by-products during preparation, limits the application of GDI for a long time. In this work, a kind of W/Ti GDI with advantages of a wide density range of 4.5–19.3 g/cm3 and high structural designability was designed and synthesized. Each of mid-layers of the W/Ti GDI was composed of W and Ti without the formation of an intermetallic compound, and had good parallelism and flatness. This provides a prerequisite for good agreement between the designed and experimental loading profiles. Due to the high designability of the GDI, quasi-isentropic loading with different stress-paths was achieved by controlling the structure of the GDI. Then, independently controlling peak stress and strain rates of loading was successfully achieved by changing the flyer velocity and the type of the W/Ti GDI. The W/Ti GDI has enormous application potential in studying the dynamic response of materials under quasi-isentropic loading with stress and strain rate controlled.

High-velocity oblique impact experiments on ice and snow spheres: Implications for the collisional evolution of icy planetesimals at different thermal evolution stages

In order to determine the effect of impact angle on the impact strength of icy planetesimals, we conducted a range of oblique impact experiments for spherical ice and snow targets simulating icy planetesimals at different thermal evolution stages. The ice targets had no porosity and the snow targets had a porosity of 0.5. A polycarbonate or glass sphere impacted the ice targets at 744–1747 m s−1 and the snow targets at 938–5085 m s−1 over a range of impact angles from grazing to head-on collisions. All experiments were conducted using a two-stage light gas gun and a target chamber set in a cold room of −15 °C at Kobe University, Japan. The impact strength, which is a specific energy, Q, when the largest fragment mass is a half of the original target mass, for the ice and snow targets in a head-on collision was determined to be 12 and 520 J kg−1, respectively, whereas it was found that the impact strength depended on the impact velocity. Thus, the normalized largest fragment mass, ml/Mt, could well scale with the velocity dependent Q, that is, Qviγ (where ml and Mt are the masses of largest fragment and target, respectively, and vi is the impact velocity). At high Q, ml/Mt increased drastically with the decrease of impact angle when the impact angle was smaller than a critical angle, θc, and θc~30° for the ice targets and θc~45° for the snow targets. At small Q, ml/Mt continued to increase as the impact angle became smaller for both types of targets. The ml/Mt for oblique impacts had a good correlation with the effective specific energy, Qeff=Qsin2θ, where θ is the impact angle, and the effective impact strength was determined to be 16 J kg−1 and 499 J kg−1 for the ice and snow targets, irrespective of the impact angle. Furthermore, the scaling parameter, Πs_eff, which was proposed by Housen and Holsapple (1990) but includes Qeff instead of Q, multiplied by 1−ϕλ, where ϕ is the porosity, showed even better correlation with ml/Mt, and all ml/Mt data of ice and snow targets could be merged, irrespective of impact velocity and ϕ. Based on our experimental results and a theory on the oblique impact of solar system bodies proposed by Shoemaker (1962), we could estimate the degree of disruption (ml/Mt) at any impact energy and any impact angle for icy planetesimals. Our findings demonstrate that the degree of disruption for icy planetesimals that have experienced sufficient thermal evolution was larger than that for those that did not experience significant thermal evolution.

Study on the enhancement mechanism of ballistic properties of shear thickening fluid impregnated aramid fabric composite plates

AbstractThis study proposes a process for the preparation of composite laminates using the shear thickening fluid (STF) impregnated aramid fabric and presents some fabric panel configuration strategies. Firstly, this study prepared two kinds of STF using 20 nm and 500 nm silica particles. Then, the STF‐impregnated Kevlar fabrics were laminated and hot‐pressed to form the fabric panels. After that, the ballistic performance of the fabric panels was evaluated by firing the 9 mm steel core projectile using a gas gun. The ballistic tests showed that the ballistic performance of the hybridized configuration panels using STF‐20 treated fabrics as the front panels and STF‐500 treated fabrics as the backing panels was superior, with a reduction of 36.1%–37.6% in the number of perforated layers (4.7–5 layers) compared to a single STF‐treated panel. This study provides a new idea and method for applying STF in protective equipment.Highlights Shear thickening fluid (STF) and aramid fabric are better combined by hot pressing lamination process; The ballistic properties of fabric panels are significantly improved by hybrid configuration; The ballistic performance enhancement mechanism of composite bulletproof plate was revealed.

Experimental and numerical investigations of damage and ballistic limit velocity of CFRP laminates subject to harpoon impact

The harpoon is a space debris capture mechanism with strong adaptability to targets. In this paper, experiments and finite element models are used to study the harpoon impact on carbon fiber laminate. Firstly, a harpoon penetration gas gun experiment was designed to obtain the damage and ballistic limit velocity of carbon fiber laminates. Then finite element modeling and numerical simulation of the impact on the laminate were carried out using the user–defined VUMAT subroutine in ABAQUS, focusing on the ballistic limit velocity change, damage evolution of the laminate and energy absorption of the laminate when the harpoon penetrates the laminate obliquely at a specific angle. The results showed that compared with vertical penetration, the ballistic limit velocity of harpoon increased by 3.2 %, 9.6 % and 24.3 % respectively under 15°, 30° and 45° oblique penetration conditions; and with the increase of harpoon impact angle, the damage of laminates gradually tended to occur on one side of the projection of harpoon on laminates; while in terms of energy absorption, the energy absorption of laminates for the same angle tended to a constant value as the launch velocity increased.

Dynamic measurement of ballistic impact using an optical fibre sensor

An optical fibre-based sensor is developed for measuring the dynamics of the back face deformation of soft body armor. The measurement system consists of embedding an optical fibre into a thin silicone mat to increase survivability. The silicone sensor mat is placed between the soft body armor and the backing material. The optical fibre experiences times of sticking and slipping. The portions of the impact with the optical fibre stuck are reconstructed into slipping-equivalent strain using exponential extrapolation from adjacent slipping portions. The strain on the optical fibre is related to the projectile acceleration when the optical fibre is slipping. The strain is measured with the optical fibre sensor using a fibre Bragg grating. The system is characterized using a gas gun in combination with high-speed imaging. The system is experimentally demonstrated at the Army Test Center in Aberdeen, MD. Of the 23 shots 17 had an error less than 10%.

Study on impact resistance of sandwich glass based on CT scan-3D reconstruction

Utilizing the light gas gun system, impact tests on sandwich glass specimens with various structural configurations were performed at high-speed, medium-speed, and low-speed to evaluate the impact resistance of polyvinyl butyral (PVB) sandwich glass. An impact damage test method that incorporates stress data and three-dimensional fracture data was proposed in conjunction with the CT scan-3D reconstruction technique. The experimental findings demonstrated that as glass thickness grew, sandwich glass’ rigidity increased noticeably, and impact resistance of sandwich glass was significantly improved. On the other hand, under the action of elastic deformation energy absorption and horizontal cohesion of the PVB interlayer, the thicker interlayer could consume and disperse more impact energy, making the veins radially distributed and reducing the flying of debris. The conclusion that thin glass-thick interlayer could equivalently replace thick glass-thin interlayer to a certain extent was obtained. The study offers crucial technological backing for sandwich glass’s industrial applicability.

Life-cycle performance of aluminium cladding panels in resisting hailstorms

This paper delves into cumulative damage on aluminium cladding panels attributed to hailstorms throughout the lifespan of the installations. 40 gas gun tests subjecting the cladding panel to repeated impact were undertaken for the purpose of studying cumulative damage behaviour. Insights from these tests were integrated into a hail size distribution model to characterise the probabilistic distribution of permanent indentation resulted from multiple hailstorm events. A life-cycle analysis framework was subsequently introduced, incorporating the natural variability of hailstone sizes and dynamic response of claddings to repeated ice impact. Intervention criterion can be established based on knowledge of the accumulation of permanent indentation into the cladding panels. Proactive actions are recommended should the indentations become visible to prevent worsening damage. Randomness of hailstorm occurrences was considered using hazard function which can be inferred from historical observations. Practical application of the proposed model is illustrated through case studies of two Australian states, coupled with comparative analyses highlighting key factors influencing cladding performance. The ability to account for stochasticity distinguishes the presented framework from existing deterministic approaches.