Shock Loading Research Articles

High strain-rate deformation analysis of open-cell aluminium foam

This study investigated the high-strain rate mechanical properties of open-cell aluminium foam M-pore®. While previous research has examined the response of this type of foam under quasi-static and transitional dynamic loading conditions, there is a lack of knowledge about its behaviour under higher strain rates (transitional and shock loading regimes). To address this gap in understanding, cylindrical open-cell foam specimens were tested using a modified Direct Impact Hopkinson Bar (DIHB) apparatus over a wide range of strain rates, up to 93 m/s. The results showed a strong dependency of the foam's behaviour on the loading rate, with increased plateau stress and changes in deformation front formation and propagation at higher strain rates. The internal structure of the specimens was examined using X-ray micro-computed tomography (mCT). The mCT images were used to build simplified 3D numerical models of analysed aluminium foam specimens that were used in computational simulations of their behaviour under all experimentally tested loading regimes using LS-DYNA software. The overall agreement between the experimental and computational results was good enough to validate the built numerical models capable of correctly simulating the mechanical response of analysed aluminium foam at different loading rates.

A unified method for studying impact particle relation and spallation under shock loading

Spallation is the phenomenon that under impact loading, the material interior reaches the tensile failure limit instantaneously due to the tensile effect of two sparse waves moving in opposite directions, and cracks are formed in the interior. The specimen of a certain alloy was taken as the research object, and the planar impact experiment was carried out by a 20mm caliber one-stage light gas gun. The free surface particle velocity curve of the alloy specimen was obtained. The Hugoniot state parameters, spallation strength, unloading strain rate and other experimental data were obtained through theoretical analysis. The results show that: The spall strength of the alloy is proportional to the tensile strain rate in the loading range: σs = 0.37 × 10-4 (GPa); the alloy has higher wave impedance and spallation strength compared with C10100. The experimental parameters of Hugoniot state are smaller than those calculated by the mass average method because of the special internal structure of the alloy. The state parameters of the sample can be obtained at the same time by using the material with known Hugoniot state parameters as the flyer.

Structural and flow field analysis of an airfoil subjected to blast-impacted

The shock wave from the explosion of the munition can cause severe damage to the aircraft structure, thereby affecting the aerodynamic performance of the aircraft. This paper aims to propose a Computational Fluid Dynamics (CFD) analysis for the aerodynamic behaviour of the wing after the damage and deformation caused by the impact load. To obtain the damaged deformed wing model for CFD analysis, the explosion damage process was calculated using LS-DYNA software, and the obtained structural deformed wing model was imported into the CFD solver for flow field calculation to obtain lift, drag, and moment coefficients and lift-to-drag ratio. The lift of the damage-deformed wing model decreases due to the destruction of the pressure distribution of the damage-deformed wing model. The lift-to-drag ratio is also affected by shock loading, with smaller values at all considered angles of attack. Similarly, the damage deformed wing model has larger moment coefficients at angles of attack less than 19.5°.

Effect of explosive shock on the mechanical property and energy release characteristics of an Al/Ni reactive material

Reactive materials applied to warhead fragments or charge liner will be driven by strong detonation, so their mechanical behavior and energy release characteristics will be affected to a certain extent. In this paper, dynamic and static mechanical tests and impact initiation experiment were carried out on the detonation-loaded Al/Ni reactive material. Compared with materials that have not subjected to explosive shock, it is found that Al/Ni materials have better mechanical strength after explosive shock. Meanwhile, the impact-initiated energy release efficiency of the material is lower, when loaded with 14.76GPa, 21.79GPa and 28.84GPa, the reaction degree decreased by 26.6%, 78.8% and 80.5% respectively. Due to the incompatibility of elastic modulus and melting point between aluminum and nickel particles, the nickel particles move and aggregate in the aluminum matrix during shock loading. The pores appear at the particle boundaries, and gradually expand into cracks. The research results show that the original material parameters cannot be used to judge the working conditions of the reactive materials, and the explosive conditions of the loading are external factors that requires additional consideration.

The reaction mechanism and interfacial crystallization of Al nanoparticle-embedded Ni under shock loading

The shock-induced reaction mechanism and characteristics of Ni/Al system, considering an Al nanoparticle-embedded Ni single crystal, are investigated through molecular dynamics simulation. For the shock melting of Al nanoparticle, interfacial crystallization and dissolution are the main characteristics. The reaction degree of Al particle first increases linearly and then logarithmically with time driven by rapid mechanical mixing and following dissolution. The reaction rate increases with the decrease of particle diameter, however, the reaction is seriously hindered by interfacial crystallization when the diameter is lower than 9 nm in our simulations. Meanwhile, we found a negative exponential growth in the fraction of crystallized Al atoms, and the crystallinity of B2–NiAl (up to 20%) is positively correlated with the specific surface area of Al particle. This can be attributed to the formation mechanism of B2–NiAl by structural evolution of finite mixing layer near the collapsed interface. For shock melting of both Al particle and Ni matrix, the liquid-liquid phase inter-diffusion is the main reaction mechanism that can be enhanced by the formation of internal jet. In addition, the enhanced diffusion is manifested in the logarithmic growth law of mean square displacement, which results in an almost constant reaction rate similar to the mechanical mixing process.

Evaluation of Accelerator Pedal Strength under Critical Loads Using the Finite Element Method

The core idea of the research consists in a formulation of boundary conditions of a mechanical accelerator pedal’s strength in an Ansys environment, whose conditions are equivalent to full-scale tests under the critical loads defined by the UNECE’s Regulation No. 13. The lack of regulatory requirements for the strength of pedal types other than brake pedals is a major gap in vehicle certification, especially when it comes to agricultural machinery. In such cases, the authors suggest being guided by UNECE R 13 regarding the strength of the accelerator and other types of pedals and checking their behavior under loads of at least 1000 N. The real value of the yield strength of the material (Silumin 4000) is very important, both in the physical real-life experiments and in FEA simulation. The critical case of a short-term shock loading of the pedal in its extreme position has been considered separately. With the help of the Ansys Explicit Dynamics module, results of a pedal’s behavior were obtained; it lost its integrity and suffered destruction. It is also necessary to check the intermediate stress values depending on the loads for direct and hybrid tasks using the Transient Structural module in order to estimate other critical cases of the pedal behavior.

Anisotropic orientation dependent shock wave responses of monocrystalline molybdenum

Molybdenum (Mo) demonstrates excellent industrial application potentials in micro-nano devices, which are inevitably subjected to shock loads during their application under harsh service environments. This study employs molecular dynamics (MD) simulations to investigate the shock responses of Mo under high-strain loading conditions with respect to the effects of crystal orientations. The findings reveal that monocrystalline Mo, along the shock direction of [111], exhibits inhomogeneous microstructure features characterized by significantly high-density and high-temperature localized regions. Once the rarefaction wave is produced, the physical parameters, including density and lateral pressure, will gradually decrease while normal pressure retains a residual value. The us-up, Pzz-up, and Pzz-V/V0 relations along the shock loading direction of [111] show deviations from those of [001] and [110] directions, with this difference being more pronounced for Pzz-V/V0. The formation of dislocations and the magnitude of shear stress experienced within the post-shock region are strongly dependent on crystal orientations. Specifically, an elevated probability of dislocation formation was observed along the [110] direction. Moreover, the magnitude of shear stress induced by shock loading along the [001] and [110] directions can exceed that of the [111] direction when the shock velocity is 1.5 km/s. The MD simulation results can serve as a valuable supplement to the investigations of mechanical properties pertaining to Mo.

Application of residence time distribution (RTD) to enhance the performance of perforated baffled constructed wetland under unsteady flow

The perforated baffle can significantly enhance the performance of the constructed wetland. In the present study, the effects of perforation shape, number of baffles, baffle position and perforation location on the flow pattern of wetlands were investigated using NaCl impulse-response tracer test, and perforated baffles were used to improve the nitrogen removal rate of the constructed wetland. The perforated baffle optimizes the flow pattern by reducing the peak height of the RTD curve and delaying the peak occurrence time. Triangle perforation exhibits better flow pattern optimization due to its smaller area. When the inlet flow rate is 100 mL/min, the mean residence time (Tm) increases by 0.25 h. The position of the perforated baffle has a more significant effect on the flow pattern, being able to better extend hydraulic residence time (HRT) when located at the height of H/2 substrate. In addition, the perforation locations of two adjacent baffles are not on the same vertical line, which can increase the horizontal water flow velocity and improve the space utilization of the wetland. Compared to the control check constructed wetland (CKCW) without baffles, the perforated baffled constructed wetland (PBCW) exhibited a higher NH4+-N removal rate of 84.53 ± 7.48 % during stable operation. This is mainly because the perforated baffle improves the utilization of dissolved oxygen (DO) while improving the water flow distribution and extending the HRT. In conclusion, perforated baffles have considerable potential to alleviate shock loading and enhance the performance of constructed wetlands.

Effect of Cd(II) shock loading on performance, microbial enzymatic activity and microbial community in a sequencing batch reactor

The performance, microbial enzymatic activity and microbial community of a sequencing batch reactor (SBR) were explored under instantaneous Cd(II) shock loading. After a 24-h Cd(II) shock loading of 100 mg/L, the chemical oxygen demand and NH4+-N removal efficiencies decreased significantly from 92.73% and 99.56% on day 22 to 32.73% and 43% on day 24, respectively, and then recovered to the normal values gradually. The specific oxygen utilization rate (SOUR), specific ammonia oxidation rate (SAOR), specific nitrite oxidation rate (SNOR), specific nitrite reduction rate (SNIRR) and specific nitrate reduction rate (SNRR) decreased by 64.81%, 73.28%, 77.77%, 56.84% and 52.46% on day 23 in comparison with the absence of Cd(II) shock loading, respectively, and they gradually returned to the normal levels. The changing trends of their associated microbial enzymatic activities including dehydrogenase, ammonia monooxygenase, nitrite oxidoreductase, nitrite reductase and nitrate reductase were in accordance with SOUR, SAOR, SNOR, SNIRR and SNRR, respectively. Cd(II) shock loading promoted the microbial reactive oxygen species production and lactate dehydrogenase release, indicating that instantaneous shock caused oxidative stress and damaged to cell membranes of the activated sludge. The microbial richness and diversity, and the relative abundance of Nitrosomonas and Thauera obviously decreased under the stress of Cd(II) shock loading. PICRUSt prediction showed that Cd (II) shock loading significantly affected Amino acid biosynthesis, Nucleoside and nucleotide biosynthesis. The present results are conducive to take adequate precautions to reduce the adverse effect on bioreactor performance in wastewater treatment systems.

Blast failure and energy analysis of rubber-modified carbon-fiber vinyl-ester composite laminates

Modifications in vinyl ester resins, a popular matrix resin choice in naval applications through rubber additives, are being experimentally investigated in the current study. Toughening of the composite matrix resin using additives has been a popular choice, where it has been postulated that the inherent modifications to the base resin polymer would enhance the overall response of the composite structure to dynamic loadings. This work intends to understand the effect of such matrix modifications on the shock response of composite panels and the failure mechanism of a composite plate subjected to air shock loading. The study comprises material fabrication, resin and composite material characterization, and analysis of composite panels' response and damage evaluation under a range of shock loadings. A shock tube apparatus is used to generate controlled shock on composite laminates with fixed-fixed boundary conditions. In conjuncture, a high-speed 3-D DIC camera system is used to obtain full-field deformation and strain fields on the specimen's back face (furthest from the loading face). Based on the structural response and energy analysis, the effect of rubber modification is quantified and compared with non-modified resin composites, where the change is shown to improve the structural damping and energy dissipation under below-failure shock loadings and further shows relatively limited crack growth under high-intensity shock loadings.

Atomistic simulation of the effect of porosity on shock response of nanoporous gold.

Nanoporous metals (NPMs) have a three-dimensional bicontinuous porous network structure that consists of interconnected nanoligaments. NPMs have the potential to effectively attenuate and dissipate the effects of impacts and blasts. Previous studies do not provide data on the possible effects of porosity at the nanoscale. Molecular dynamics simulations based on the embedded-atom method potential were performed using the open-source code LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator). Nanoporous gold (NPG) absorbs shock energy first through the elastic-plastic deformation of ligaments and then through the collapse of ligaments. After the shock loading is relaxed, NPG with lower porosity has a higher amount of springback, and new voids tend to nucleate and grow at collapsed ligaments where the packing is looser. NPG with higher porosity has a better ability to resist the propagation of a shock wave and is subjected to a smaller stress effect.

Molecular Dynamics Simulation of Shock Wave Propagation in Aluminum Single Crystal

The characteristics of shock wave propagation in aluminum single crystal are simulated by using the molecular dynamics (MD) method based on the embedded atom method (EAM) potential function. The structure of the shock front and the Hugonoit relation are obtained. The simulated results show that a two-wave structure exists in the aluminum single crystal for the particle velocity bellower than 2 km/s and the velocity of the elastic wave increases slightly with the shock loading. While only plastic wave exists in the aluminum single crystal for the particle velocity higher than 2 km/s and the width of the shock front decreases by exponent with the normal stress. The MD simulation results are basically consistent with the experimental results.

Transition in helium bubble strengthening of copper from quasi-static to dynamic deformation

Damage from low-temperature irradiation and the subsequent degradation of materials performance pose significant challenges for the storage of radioactive materials and for peripheral components in some nuclear reactor designs. Fully understanding the mechanical behavior of such materials requires test data for strain rates in both the quasi-static (< 10/s) and dynamic (≫ 10/s) regimes. While dynamic testing has generally been avoided in the past for neutron irradiated (contamination concerns) and ion irradiated (insufficient volume) materials, surface-sensitive Richtmyer-Meshkov instability (RMI) tests were used in the present work to overcome these limitations. Here, nanopillar compression, nanoindentation, and RMI testing data from a helium implanted surface layer (∼10 µm thick) were compiled to explore the effects of helium bubbles on the materials strength of high-purity copper at strain rates of 0.001/s – 108/s. While nano-mechanical testing revealed increases in yield strength and hardness with increasing helium dose from 1000 to 4000 appm He, RMI indicated no significant changes in strength as compared to unimplanted copper. This discrepancy in behavior was rationalized through a combination of recent literature and follow-on molecular dynamics (MD) simulations, leading to the conclusion that the nanoscale helium bubbles acting as dispersed barriers to dislocation motion at quasi-static strain rates collapse under shock loading and cease to be effective barriers at high strain rates.

Deformation and failure of the CrCoNi medium-entropy alloy subjected to extreme shock loading.

The extraordinary work hardening ability and fracture toughness of the face-centered cubic (fcc) high-entropy alloys render them ideal candidates for many structural applications. Here, the deformation and failure mechanisms of an equiatomic CrCoNi medium-entropyalloy (MEA) were investigated by powerful laser-driven shock experiments. Multiscale characterization demonstrates that profuse planar defects including stacking faults, nanotwins, and hexagonal nanolamella were generated during shock compression, forming a three-dimensional network. During shock release, the MEA fractured by strong tensile deformation and numerous voids was observed in the vicinity of the fracture plane. High defect populations, nanorecrystallization, and amorphization were found adjacent to these areas of localized deformation. Molecular dynamics simulations corroborate the experimental results and suggest that deformation-induced defects formed before void nucleation govern the geometry of void growth and delay their coalescence. Our results indicate that the CrCoNi-based alloys are impact resistant, damage tolerant, and potentially suitable in applications under extreme conditions.

Molecular dynamics simulation of mechanical response of Cu50Zr50 metallic glass under double shock loading

In real applications, materials are often subjected to multiple shock loadings, under which the mechanical response is rather complicated and needs in-depth studies. In this paper, molecular dynamics simulations of Cu50Zr50 metallic glass (MG) that has broad application prospects in various fields under double-shock loading have been carried out in order to uncover the deformation mechanism of MG in the dynamic process. By varying the velocity and the time interval from the first shock, we found that the double shock can lead to different phenomena such as recompaction, second spallation, uncompaction, or non-spallation. We further investigated the characteristics of these different phenomena through analyzing the damage area, stress distribution, density, and temperature in the shock processes. It was found that the void collapse caused high local stress and high temperature. We also found that the shear deformation resistance of the recompaction region cannot be recovered after recompaction through the quantitative statistics of the icosahedral clusters. Moreover, the material softening caused by high temperature in the recompaction region was the main reason for second spallation. In addition, a small second shock velocity could not induce the recompaction and a small interval time between two shocks inhibited the occurrence of the first spallation. The insights gained in this study contribute to a better understanding of the dynamic response of MGs under double-shock loadings.

Tests on the incline rectification of suction bucket foundation installation under local cyclic shock loading

ABSTRACT There are many problems with the vertical installation of suction buckets due to the complex ocean wave current and seabed geological conditions. In this paper, a set of tests were developed to study the mechanism of incline rectification of the suction bucket foundation based on resistance-reduced vibration on local side walls (RRV-LSW). In this experiment, the dynamic evolution process of pore water pressure around the suction barrel foundation was monitored from three angles of vibration frequency, initial inclination angle and load, and the influence of local cyclic vibration parameters on the slope velocity of the suction barrel foundation was quantified. The results indicate that a tilted suction caisson foundation can be effectively corrected through lateral wall vibration, and the correction effect is closely related to the vibration frequency, initial tilt angle, and static pressure load.

Sandwich Structures With Bio-Inspired Viscoelastic Optimized Suture Face Sheets for Blast Mitigation

In this paper, the performance of a novel bio-inspired face sheet in mitigating the effects of blast loading is investigated. The new design of the face sheet consists of an optimized bio-inspired suture structure sandwiched between two aluminium plates. The suture profile is obtained by performing structural optimization using Genetic Algorithm, wherein the dynamic responses obtained using a novel viscoelastic finite element formulation are used. The performance of this optimized suture-based face sheet is experimentally tested in a vertical shock tube which validates the results obtained using commercial finite element software Abaqus. The hybrid sandwich structure composed of an aluminium honeycomb core sandwiched between the developed face sheets is evaluated numerically for its blast resistance performance. The study shows that the proposed face sheet design, not only reduces the stresses in the face sheets significantly, but also reduces the core stresses compared to conventional aluminium face sheet–based sandwich structures. Several parametric studies are presented for axial and transverse shock loading on this hybrid sandwich structures that give more insight into their wave propagation characteristics.

Differences in Automated External Defibrillator Types in Out-of-Hospital Cardiac Arrest Treated by Police First Responders

Background: Police first responder systems also including automated external defibrillation (AED) has in the past shown considerable impact on favourable outcomes after out-of-hospital cardiac arrest (OHCA). While short hands-off times in chest compressions are known to be beneficial, various AED models use different algorithms, inducing longer or shorter durations of crucial timeframes along basic life support (BLS). Yet, data on details of these differences, and also of their potential impact on clinical outcomes are scarce. Methods: For this retrospective observational study, patients with OHCA of presumed cardiac origin and initially shockable rhythm treated by police first responders in Vienna, Austria, between 01/2013 and 12/2021 were included. Data from the Viennese Cardiac Arrest Registry and AED files were extracted, and exact timeframes were analyzed. Results: There were no significant differences in the 350 eligible cases in demographics, return of spontaneous circulation, 30-day survival, or favourable neurological outcome between the used AED types. However, the Philips HS1 and -FrX AEDs showed immediate rhythm analysis after electrode placement (0 [0-1] s) and almost no shock loading time (0 [0-1] s), as opposed to the LP CR Plus (3 [0-4] and 6 [6-6] s, respectively) and LP 1000 (3 [2-10] and 6 [5-7] s, respectively). On the other hand, the HS1 and -FrX had longer analysis times of 12 [12-16] and 12 [11-18] s than the LP CR Plus (5 [5-6] s) and LP 1000 (6 [5-8] s). The duration from when the AED was turned on until the first defibrillation were 45 [28-61] s (Philips FrX), 59 [28-81] s (LP 1000), 59 [50-97] s (HS1), and 69 [55-85] s (LP CR Plus). Conclusion: In a retrospective analysis of OHCA-cases treated by police first responders, we could not find significant differences in clinical patient outcomes concerning the respective used AED model. However, various differences in time durations (e.g., electrode placement to rhythm analysis, analysis duration, or AED turned on until first defibrillation) along the BLS algorithm were seen. This opens up the question of AED-adaptations and tailored training methods for professional first responders.

Dynamic shock response of high-entropy alloy with elemental anomaly distribution

Elemental inhomogeneities formed during the actual preparation or heat treatment of high entropy alloys (HEAs) have a profound effect on the mechanical properties of HEAs. In this work, molecular dynamics (MD) was used to simulate the plastic response of CoCrFeNiMn HEAs with Mn element as the concentration fluctuation variable under shock loading. The results show that the unique physical shock properties, including shock wave propagation, dislocation evolution, defect collapse, and energy dissipation, are related to the anomaly arrangement of Mn elements. Compared to the uniform distribution of Mn elements, the gradient distribution of Mn leads to lattice mismatch between heterogeneous tissues, increasing the energy barriers of the dislocation mediated slip and reducing the probability of generating disordered atoms (from 27.9 to 11.5%), which results in anomalous shock strength in the Hugoniot elastic limit (HEL) (from 69.1 Gpa to about 72.9 Gpa). As the main product of shock energy conversion, energy dissipation is subjected to the complex interaction between the shock compression and the reflection unloading, and the gradient distribution of Mn element can significantly reduce the efficiency of shock energy conversion due to dislocation activity and crystal phase changes caused by lattice mismatch. Finally, when defective structures are introduced, the gradient dislocation nucleation and energy conversion fluctuations of the microstructure were observed during shock loading. This work can provide a new perspective for further understanding the influence of solid solutions with non-uniform element distribution on the plastic deformation mechanism of high entropy alloys subjected to extreme dynamic shock.

Rapid activation of non-oriented mechanophores via shock loading and spallation

Rapid activation of non-oriented mechanophores via shock loading and spallation