Search Results (35)

To investigate the energy transfer mechanisms during the micro-explosive initiator-driven flyer process and to guide the performance evaluation of micro-sized charges and the structural design of micro-initiators, a combined approach of numerical simulations and experimental tests was employed to study the detonation process of copper-based azide micro-charges driving a flyer. The output pressure and detonation velocity of the copper-based azide micro-charge were measured using the manganese–copper piezoresistive method and electrical probe technique, and the corresponding JWL equation of the state parameters was subsequently fitted. A simulation model for the micro-charge-driven flyer was established and validated using Photonic Doppler Velocimetry (PDV), and the influence of charge conditions, structural parameters, and other factors on the flyer velocity and morphology was investigated. The results indicate that the flyer velocity decreases as its thickness increases, whereas the specific kinetic energy of the flyer initially increases and then decreases with increasing thickness. The optimal flyer thickness was found to be in the range of 30 to 70 μm. The flyer velocity increases with the density and height of the micro-charge; however, when the micro-charge density exceeds a certain threshold, the flyer velocity decreases. The flyer velocity exhibits an exponential decline as the diameter of the acceleration chamber increases, whereas it shows a slight increase with the increase in the length of the acceleration chamber. The diameter of the acceleration chamber should not exceed the charge diameter and must be no smaller than the critical diameter required for detonation initiation of the underlying charge. The use of a multi-layer accelerating chamber structure leads to a slight reduction in flyer velocity and further increases in the transmission hole diameter while having no significant impact on the flyer velocity. Full article

Small-scale impact welding may have several advantages over rivets: the strength can be higher, it can be applied right at the edges in lap joints, and it can be lighter and more easily installed if simple systems can be developed. Laser Impact Welding (LIW) is compact and simple, adapting the technologies of laser shock peening. It is limited in terms of the energy that can be delivered to the joint. Augmented Laser Impact Welding (ALIW) complements optical energy with a small volume of an exothermic detonable compound and has been shown to be an effective welding approach. The scope of this study is extended to build upon previous work by investigating varied augmentation chemistries and confinement layers, specifically borosilicate glass, sapphire, and water. The evaluation of these compositions involved the use of two aluminum alloys: Al 2024 and Al 6061. Photonic Doppler Velocimetry (PDV) was utilized to measure the flyer velocity and assess the detonation energy. The findings indicated that adding micro-air bubbles (GPN-3 scenario) to the original GPN-1 enhanced the flyer velocity by improving the sensitivity, which promoted gas release during detonation. Hence, employing 1 mm thick Al 2024 as a flyer with GPN-3 enhances the flyer velocity by 36.4% in comparison to GPN-1, thereby improving the feasibility of using 1 mm thick material as a flyer and ensuring a successful welded joint with the thickest flyer ever welded with laser impact welding. When comparing the confinement layers, sapphire provided slightly lower flyer velocities compared to borosilicate glass. However, due to its higher resistance to damage and fracture, sapphire is likely more suitable for industrial applications from an economic perspective. Furthermore, the lap shear tests and microstructural evaluations confirmed that GPN-3 provided higher detonation energy, as emphasized by the tendency of the interfacial waves to have a higher amplitude than the less pronounced waves of the original GPN-1. Consequently, this approach demonstrates the key characteristics of a practical process, being simple, cost-effective, and efficient. Full article

As a main component of the magnetic pulse welding (MPW) system, the working coil exerts a great influence on the electromagnetic force and its distribution, which, in turn, affects the quality of the MPW joints. This study proposes a structural parameter optimization of the MPW coil, with the objective of achieving a higher induced current density on the flyer plate. The optimal Latin hypercube sampling technique (OLHS), Kriging approximate model, and the Non-Linear Programming by Quadratic Lagrangian (NLPQL) algorithm were employed in the optimization procedure, based on the finite element model built in LS-DYNA. The results of the sensitivity analysis indicated that all the selected parameters of the coil had a specific influence on the induced current density in the flyer plate. The optimized coil structure serves to refine the pulse current flowing path within the coil, effectively reducing the current loss within the coil. Additionally, the structure reduces the adverse effect of the current within the coil on the induced current within the flyer plate. Numerical results show the peak-induced current of the flyer plate increasing by 25.72% and the maximum Lorentz force rising by 58.10% at 25 kJ with the optimized coil structure. The experimental results show that with the same 25 kJ discharge energy, the optimized coil could increase the collision velocity from 359.92 m/s to 458.93 m/s. Moreover, 30 kJ of discharge energy should be needed to achieve the failure mode of base material failure with the original coil, while only 15 kJ should be applied to the optimized coil. These findings verify the optimization model and give some outline for coil design. Full article

Information on the flyer deformation during laser impact welding (LIW) is an important aspect to consider when high reliability of the welded components is required. For this reason, accurate numerical models simulating thermal and mechanical aspects are needed. In the present work, the cross-section morphology during LIW of Ti/Brass joints at varying laser pulse energies is modeled by a 2D finite element (FE) model. A hydrodynamic plasma pressure model able to describe the evolution of the pressure load step by step, taking into account the progressive deformation of the flyer, was implemented. Hence, this paper proposes an alternative method to the conventional node concentrated forces or predefined velocity as flyer boundary conditions. The levels of the equivalent plastic strain (PEEQ), shear stress, and critical flyer velocity at the collision point were used as reference parameters to predict the success of the welding bond, distinguishing the welded area from the unwelded area. The model was validated by comparison with the experimental data, which showed the effectiveness of the proposed FE code in predicting the cross-section morphology of the welded materials. Moreover, practical industrial information such as variation in the flyer impact velocity, collision angle, and process temperatures was predicted by varying the process laser pulse energy according to the basic principle of the process. Full article

To enhance the energy efficiency of exploding foil initiator systems (EFIs) and mitigate energy loss due to ablation in the bridge-wing regions, a low-energy bridge-wing-thickened EFI chip was designed and fabricated. Computational analysis revealed that increasing the thickness of the bridge flanks significantly reduces ablation within the bridge region during the electrical explosion. The refinement of the design led to the adoption of a bridge flank thickness of 19 μm, with the bridge area dimensions specified as 0.25 mm × 0.25 mm × 4 μm. This bridge-wing-thickened EFI chip was produced by employing micro-electro-mechanical systems (MEMS) technology and underwent rigorous performance evaluations. The empirical results closely matched the computational predictions, thereby corroborating the precision of the proposed model in simulating the temperature distribution seen during the explosion process. Notably, this enhanced EFI design achieves a flyer velocity of 3800 m/s at a condition of 900 V/0.22 μF, signifying a significant advancement in EFI system efficiency and performance. Full article

Current progress in numerical simulations and machine learning allows one to apply complex loading conditions for the identification of parameters in plasticity models. This possibility expands the spectrum of examined deformed states and makes the identified model more consistent with engineering practice. A combined experimental-numerical approach to identify the model parameters and study the dynamic plasticity of metals is developed and applied to the case of cold-rolled OFHC copper. In the experimental part, profiled projectiles (reduced cylinders or cones in the head part) are proposed for the Taylor impact problem for the first time for material characterization. These projectiles allow us to reach large plastic deformations with true strains up to 1.3 at strain rates up to 10⁵ s⁻¹ at impact velocities below 130 m/s. The experimental results are used for the optimization of parameters of the dislocation plasticity model implemented in 3D with the numerical scheme of smoothed particle hydrodynamics (SPH). A Bayesian statistical method in combination with a trained artificial neural network as an SPH emulator is applied to optimize the parameters of the dislocation plasticity model. It is shown that classical Taylor cylinders are not enough for a univocal selection of the model parameters, while the profiled cylinders provide better optimization even if used separately. The combination of different shapes and an increase in the number of experiments increase the quality of optimization. The optimized numerical model is successfully validated by the experimental data about the shock wave profiles in flyer plate experiments from the literature. In total, a cheap, simple, but efficient route for optimizing a dynamic plasticity model is proposed. The dislocation plasticity model is extended to estimate grain refinement and volume fractions of weakened areas in comparison with experimental observations. Full article

Miniaturized laser-initiated pyrotechnic devices have great application prospects in aerospace and modern weapon systems due to their excellent energy output performance and reliability. In order to develop a low-energy insensitive laser detonation technology based on a two-stage charge structure, it is important to deeply analyze the motion law of a titanium flyer plate driven by the deflagration of the first-stage charge (RDX). The effects of the charge mass of RDX, flyer plate mass, and barrel length on the motion law of flyer plates were studied through a numerical simulation method based on the Powder Burn deflagration model. The consistency between the numerical simulation and the experimental results was analyzed using the paired t confidence interval estimation method. The results show that the Powder Burn deflagration model can effectively describe the motion process of the RDX deflagration-driven flyer plate with a 90% confidence level, and its velocity error is ≤6.7%. The speed of the flyer plate is proportional to the mass of the RDX charge, inversely proportional to the mass of the flyer plate, and exponentially related to its moving distance. As the moving distance of the flyer plate increases, the RDX deflagration products and air in front of the flyer plate are compressed, which inhibits the motion of the flyer plate. In the optimum state (the mass of the RDX charge is 60 mg, the mass of the flyer is 85 mg, and the length of the barrel is 3 mm), the speed of the titanium flyer reaches 583 m/s, and the peak pressure of the RDX deflagration reaches 2182 MPa. This work will provide a theoretical basis for the refined design of a new generation of miniaturized high-performance laser-initiated pyrotechnic devices. Full article

In this study, two sheets of AA5052 are joined with the high-strain-rate multi-spot joining process using an electromagnetic system. While producing a single spot joint by electromagnetic joining (EMJ) is common, the distribution and application of the pressure can be modified by the design of the coil and spacers to make multiple joints at once. When a preformed dimple is used to provide the standoff distance, it can eliminate the need for spacers and provide good aesthetics for the final product. In the current study, a joint design is developed to provide three spot joints coincidentally by a single discharge of a capacitor bank. For the experiment, four distinctive discharge energies were used for joining: 7, 8, 9, and 10 kJ. The most successful joint sample was made by 8 kJ and was tested for mechanical properties. The cross-section was observed in order for us to understand the joint quality produced by the process. It was found that the ”I”-shaped rectangular coil produces a variable magnetic flux, leading to different flyer deformation variations in the joint geometry. At the centre of the ”I” coil, the minimum flux was predicted, leading to lesser sheet forming, hence a weaker centre-spot joint strength. Further, a numerical study is performed to find the Von Mises stresses, equivalent plastic strain, impact velocity, and impact pressure on the sheets. This manuscript provides new information regarding coil designing and the changes that could be further made to improve the electromagnetic sheet multi-spot joining process. Full article

Flyers driven by various technologies have been widely used as effective shock loading techniques in the ignition of energetic materials, space debris impact modeling, equation of state measurement, etc. However, their flying characteristics have the greatest influence on application reliability. The flying velocity, as well as the flyer’s planarity and integrity, are crucial characteristics. Therefore, mainstream flyer-driving technologies are examined in this study, and research progress in investigation approaches on flyer velocity and morphology are reviewed. Furthermore, for each flyer-driving technique, the affecting factors of flyer velocity and morphology are summarized. Current research deficiencies are highlighted, and future research directions are discussed, including the parallel coupling of various driving principles, quantitative characterizations of the flyer’s planarity and integrity, and the physical model matching the flying process. Full article

In order to study the performance of ultra-fine 2,2′, 4,4′, 6,6′–hexanitrostilbene (HNS-IV) explosives initiated by a microflyer driven by microsized lead azide (Pb(N₃)₂), a corresponding simulation model was established in Autodyn software, and the accuracy of the simulation model was verified with a photonic Doppler velocimeter (PDV). Various influencing factors were studied in combination with the power flux–action time (Π-τ) initiation criterion. The results showed that the exponential growth rate of the flyer velocity decreased with an increase in the diameter and height of the lead azide and that the influence of the charge diameter was more obvious than that of the charge height. The flyer velocity increased linearly with the density of the lead azide. The velocity of the flyer also increased linearly with an increase in the shock wave impedance of the restraint materials, and the velocities of the flyer that corresponded to silicon and organic glass were lower than those of the metal materials. The flyer’s velocity and power flux increased with a decrease in the flyer’s density; when considering the flyer’s velocity, power flux, and actual shear effect, titanium was the best material for the flyer. As the thickness of the flyer was decreased, the velocity and power flux of the flyer increased; under the premise of satisfying the forming effect, the thinner flyer was selected. When used as the material for the acceleration chamber, silicon showed a lower flyer velocity and power flux than sapphire, nickel, stainless steel, and other materials. With the increase in the acceleration chamber aperture, the exponentially declining trend in the flyer’s velocity increased; when the aperture of the accelerating chamber was consistent with the diameter of the primary explosive, the power flux was the largest. Finally, the ability of the microflyer to initiate the HNS-IV was verified by a steel dent test. Full article

Insect RoboFlyers are interesting and active focuses of study but producing high-quality flapping robots that replicate insect flight is challenging., due to the dual requirement of both a sophisticated transmission mechanism with light weight and minimal intervening connections. This innovative mechanism was created to address the need for a producible structure that is small in size, small in mass, and has reduced design linkages. The proposed Single Crank-Slotted Dual Lever (SC-SDL) mechanism transforms rotational motion into specific angular motion at different velocities for each of its two strokes, i.e., the forward stroke and the return stroke. The discovery of a lag between the left and right lever motions in our design mechanism-I leads us to the conclusion that the flapping is asymmetric. To eliminate the position lag, the design has been altered, and a new design mechanism-II has been developed. Comparative kinematic analysis of both design systems is performed using simulations. Two-dimensional analysis of the base ornithopter configuration using ANSYS FLUENT yielded deeper insights regarding the influence of varying flapping frequency on critical flow metrics regarding adequate lift and thrust. For a flapping frequency of 24 Hz, adequate lift generation was achieved with minimal flow disturbances and wake interactions. Averaged dual wing estimations were made as part of the CFD study, which showed similar agreements. To validate the estimations, experimental tests were performed over the design mechanism-II configuration. Full article

Magnetic pulse welding of overlapping dissimilar metallic sheets is an emerging technique and usually employs flat electromagnetic coils with rectangular-, H-, I-, and E-shaped cross-sections. The asymmetric cross-section of these coils results in a non-uniform electromagnetic field and in a non-uniform connection in the interface between the overlapping sheets. In this article, the use of a novel O-shaped flat coil is proposed to join an aluminium flyer sheet with a target steel sheet. A finite element-based numerical model is developed to calculate the electromagnetic field, flyer velocity, and its gradual impact onto the target, and the deformations of the sheet assembly. The calculated results with the O-shaped coil show a high-intensity electromagnetic field, the concentration of which decreases radially outwards in a uniform manner. The numerically computed and experimentally measured flyer velocity are found to be in fair agreement. The calculated results show a regularly decreasing impact behaviour between the flyer and target and their resulting deformation. The measured results show the formation of an annular ring-shaped joint profile that is generally found to be stronger compared to that obtained with flat coils with a rectangular cross-section. Full article

The exploding foil initiator (EFI) system has been extensively used in ignition and detonation sequences and proved to be of high safety and reliability. Polyimide is considered the ideal flyer material for EFI due to its excellent performance, including thermal stability, outstanding mechanical properties, high radiation resistance, and excellent dielectric properties. In this study, we prepared the EFI based on a polyimide (ODPA-ODA) flyer, which is spin-coated and solidified on patterned copper film in situ. The electric explosion test shows that the prepared EFI has good working performance, and the 4000 V working voltage drove the flyer to reach a maximum velocity of 5096 m/s. The polyimide morphology and chemical structure after the electric explosion was observed by microscope, SEM, XPS, and FTIR, which showed that the polyimide flyer underwent thermal deformation and complex chemical reactions during an electric explosion. A large number of polyimide bonds broke to form new carbonyl compounds, and the opening of aromatic rings was accompanied by the formation of aliphatic hydrocarbon chains. The morphology and chemical structure analysis after the electric explosion test will lay a foundation for us to further understand the working principle and evolution process of polyimide (ODPA-ODA) flyer. Full article

In this study, we experimentally investigate the high stain rate and spall behavior of Cantor high-entropy alloy (HEA), CoCrFeMnNi. First, the Hugoniot equations of state (EOS) for the samples are determined using laser-driven CoCrFeMnNi flyers launched into known Lithium Fluoride (LiF) windows. Photon Doppler Velocimetry (PDV) recordings of the velocity profiles find the EOS coefficients using an impedance mismatch technique. Following this set of measurements, laser-driven aluminum flyer plates are accelerated to velocities of 0.5–1.0 km/s using a high-energy pulse laser. Upon impact with CoCrFeMnNi samples, the shock response is found through PDV measurements of the free surface velocities. From this second set of measurements, the spall strength of the alloy is found for pressures up to 5 GPa and strain rates in excess of 10⁶ s⁻¹. Further analysis of the failure mechanisms behind the spallation is conducted using fractography revealing the occurrence of ductile fracture at voids presumed to be caused by chromium oxide deposits created during the manufacturing process. Full article

Magnetic pulse welding involves the joining of two metallic parts in a solid state by the use of a short and intense electromagnetic impulses and the resulting impact between the parts. The coalesced interface undergoes visco-plastic deformation at a high strain rate and exhibits a wavy shape at a microscopic scale. A practical estimation of the electromagnetic pressure, impact velocity and welded joint length as a function of the process conditions and the electromagnetic coil geometry is required but currently not available. Three novel analytical relations for the estimation of the electromagnetic pressure, impact velocity, and welded joint length for magnetic pulse welding of tubes and sheets, are presented. These relations were developed systematically, following a dimensional analysis, and validated for a wide range of conditions from independent literature. The comparison of the analytically computed results and the corresponding values reported in the literature has illustrated that the proposed analytical relations can be used for the estimation of the electromagnetic pressure and impact velocity for the magnetic pulse welding of tubes and sheets with a good level of confidence. The analytically calculated results for the welded joint length show a little discrepancy with the corresponding experimentally measured values. Further investigations and more experimentally measured results are required to arrive at a more comprehensive analytical relation for the prediction of welded joint length. Full article