Explosive Forming Research Articles

Novel Aerospace Architectures Made Possible by Forming Simulation

In the aerospace industry lightweight design in combination with fast and reliable manufacturing processes are key components to defend the leading position in the worldwide competition. In this frame it is an overall goal to reduce the number of process steps in order to produce parts for an aircraft to its minimum. Integral design is one way to cope with this goal but on the other hand raises a lot of problems that may occur in manufacturing or final assembly. To be able to predict potential bottlenecks or drawbacks in certain designs, finite element simulation can be helpful. Especially if it’s an early design phase and new material concepts are taking into account, the virtual manufacturing, done by finite element simulations is the only way to predict real life behavior. In this paper we will focus on the use and benefit of finite element simulations in the early design phase of very huge integral parts of a next generation aircraft. The parts do belong to the nose fuselage structure and will be manufactured from a 100-150mm thick AlMgSc plate. Two different manufacturing routes will be covered by simulation. 1. Hot forming the plates at around 300°C and machining 2. Explosive forming of the plates and machining For both routes, a complete simulation chain from forming over springback to final machining is developed and presented in detail. Special care is taken on a fully automated workflow from one step to the other to allow an easy adaptation to other part geometries in the future. To ensure a high quality of the simulation results all process steps of the hot forming route are simulated with ABAQUS implicit and approved constitutive laws. The explosive forming manufacturing route is simulated using an Eulerian-Lagrange approach taken into account the various possibilities of detonation loading. To validate the simulation results to real measurements, a scaled down version of one of the parts is manufactured in reality and each process step is compared with the simulation result.

Explosively Formed Projectile Soft-recovery Force Analysis

The design of a soft-recovery system is critical to a researcher's ability to analyze hypervelocity projectiles. The researcher may decide to use one method over another based on several criteria, including whether or not non-deformed projectile measurements are required. This report analyzes the forces two different soft-recovery methods impart on the projectiles collected. Method 1 utilized three polyethylene water barrels placed “end-to-end” horizontally, providing 2.6 meters (9 feet) of water to stop the projectile. Method 2 is a modification of the soft-recovery method utilized in “Soft-Recovery of Explosively Formed Penetrators” by Lambert and Pope [1]. This method utilizes a series of several materials with an increasing density gradient, placed end-to-end over 14.3 meters (47 feet) to stop the projectile. Despite the fact that explosively formed projectiles (EFPs) of the same design were fired into each recovery method, the projectiles collected using the two methods differed in shape, size, weight, and the number of pieces collected. Since the EFP designs were identical to begin with, the physical differences are most likely due to the different magnitudes of the forces exerted on the projectile during deceleration. Drag force calculations will be performed for both recovery methods in an attempt to determine the differences in the drag forces exerted on the projectile during its deceleration. The results of the calculations will assist in determining to what extent the physical deformation of the projectile is due to the material selection of each recovery method. The consistency of the shapes and weights of the recovered projectiles will also be briefly addressed to assist the researcher in choosing the most useful recovery method for a given objective.

Black limit. Part 11

New limitation is introduced – no body can be accelerated to the mass exceeding the mass of a black hole, in addition to the light velocity limitation. Based on this limitation, new formulae for the theory of relativity and extension of classical equations for mass, length, time can be obtained. Charge relativity has been shown. Formulae for charge and gravitation have been extended. The paper considers the extension of the theory of relativity based on the ether theory development, where crypton (strong wave) functions as a discrete element of super-fluid ether, elementary particles are represented as flat whirlpools, gravitation - as varying density of crypton (strong wave) created by flat whirlpools. The charge is presented as a sinusoid tail stretched by a whirlpool, not coiled and created by a dipole offset of the crypton (ether). The energy of particles is presented in the form of transformation of progressive wave energy into rotational whirlpool energy. It is shown that the gravitation of the black hole has flat form. It is shown that spherical form of stellar explosion with further formation of a black hole transforms into conical one. The equation of gravitation can be written as follows

Theoretical and experimental study on the effects of explosive forming parameters on plastic wrinkling of annular plates

Wrinkling is increasingly becoming one of the most common and troublesome modes of unacceptable deformation in sheet metal-forming prediction that is very important on the design of die geometry and processing parameters. In an effort to provide a reliable and efficient tool to predict the critical blank holding force for prevention of wrinkling, an analytical model for flange wrinkling in high-velocity forming processes, such as explosive forming, is presented here. With consideration of constant blank holder force and using a combination of energy method and plastic bending theory, the critical radial displacement and number of wrinkling waves are obtained. For validation, some experimental tests have been performed that their results have adequate agreements with the analytical ones. Moreover, the effects of process parameters such as blank holding force, radii ratio, and material mechanical properties on wrinkling behavior has been discussed.

Experimental analysis and simulation of effective factors on explosive forming of spherical vessel using prefabricated four cones vessel structures

Abstract Construction of spherical vessel in various dimensions is known as one of the frequent problems for construction and production engineers, since conventional methods of shell construction require mold and press which leads to higher costs of production. Therefore, current work has tried to investigate a new method based on explosive forming without using molds. In this technique, final shape of the shell can be achieved by explosion inside a prefabricated structure called four cones. This structure is produced from combination and welding of four truncated cones two of which are paired in each side. Initial shape of the tank is then used to transform this structure into a more complete sphere using explosives at its center. This paper aims to study the amount of explosives needed for this process in terms of vessel’s diameter and thickness. In this regard, simulation was run by LS-DYNA software and the resultant outputs were evaluated with those of experimental tests. The results shows that the required charge of forming varies exponentially with thickness.

Hydrocode Simulation with Modified Johnson-Cook Model and Experimental Analysis of Explosively Formed Projectiles

The formation of mild steel (MS) and copper (Cu) explosively formed projectiles (EFPs) was simulated in AUTODYN using both the Johnson-Cook (JC) and modified Johnson-Cook (JCM) constitutive models. The JC model was modified by increasing the hardening constant by 10%. The previously established semi-empirical equations for diameter, length, velocity, and depth of penetration were used to verify the design of the EFP. The length-to-diameter (L/D) ratio of the warhead used in the simulation varied between 1 < L/D < 2. To avoid projectile distortion or breakup for large standoff applications, the design of the EFP warhead was modified to obtain a lower L/D ratio. Simulations from the JC model underestimated the EFP diameter, resulting in an unrealistically elongated projectile. This shortcoming was resolved by employing the JCM model, giving good agreement with the experimental results. The projectile velocity and hole characteristics in 10-mm-thick aluminum target plates were studied for both models. The semi-empirical equations and the JC model overestimated the projectile velocity, whereas the JCM model underestimated the velocity slightly when compared to the experimental results. The depths of penetration calculated by the semi-empirical equations in the aluminum (Al) target plate were 55 and 52 mm for Cu and MS EFPs, respectively.

The Explosively Formed Projectile (EFP) as a Standoff Sea Mine Neutralization Device

There are many methods that can be used for the clearance of underwater ammunition; for example, sea mines. In all such techniques, the primary aim is to defuse underwater ammunition without detonation. Explosively formed projectiles (EFPs) have great potential to cleanly and safely defuse underwater ammunition. Underwater simulations and experiments were conducted to highlight the use of EFPs for safe destruction of sea mines. The copper liner configuration was used to study the penetration performance of the EFPs in water. ANSYS AUTODYN-2D hydrocode was used to simulate copper EFP penetration, passage, and impact with a target immersed in water. Simulation results were obtained by making use of Lagrangian and Euler formulations. The results indicated that the velocity of an EFP reduces sharply as it enters the water. However, the velocity of an EFP is stable in the later part of its flight through the water. The results further indicated that after covering five cone diameters (CDs) in water, the velocity of the EFP was reduced below critical and it failed to perforate an aluminum target plate of 5 mm thickness. Nevertheless, it perforated the target plate at 4 CDs in water. A known quantity of high explosive sandwiched between two plates, just like explosive reactive armor (ERA), was used as a target to simulate the sea mine. Flash X-ray was also used to record the flight and penetration of the EFP through the target plate. Simulation results matched reasonably well with the experimental results.

Evaluation of recombinant E2 protein-based and whole-virus inactivated candidate vaccines against chikungunya virus

ObjectivesWith the re-emergence of chikungunya virus (CHIKV) in an explosive form and in the absence of a commercially available vaccine, we aimed to develop candidate vaccines employing recombinant E2 protein or chemically inactivated whole virus. Design and methodsE2 gene of CHIKV isolate of ECSA genotype was cloned in pET15b vector, expressed and purified (rE2p). The virus was propagated in Vero cell line, purified and inactivated with formalin and BPL individually. Six to eight weeks old female BALB/c mice were immunized intramuscularly with two doses of 10μg, 20μg and 50μg of vaccine formulations with or without adjuvants, 2 weeks apart. The adjuvants evaluated were alum, Mw, CadB (rE2p), alum/Mw (formalin inactivated CHIKV) and alum (BPL-inactivated CHIKV). Humoral immunity was assessed by ELISA and in vitro neutralization test using homologous and heterologous (Asian genotype) strains of CHIKV. Two cohorts of vaccinated mice were challenged separately via intranasal route with homologous virus two and 20 weeks after the 2nd dose. Viral load (CHIKV RNA by real time PCR) was determined in the serum and tissues (muscle, brain, spleen) of the mice challenged with the homologous virus. ResultsAnti-CHIK-antibody titres were dose dependent for all the immunogen formulations. BPL-inactivated vaccines led to the highest ELISA/neutralizing antibody (nAb) titres while alum was the most effective adjuvant. Asian genotype strain could be neutralized by the nAbs. In an adult mouse model, complete protection was offered by the alum-adjuvanted rE2p and both the inactivated vaccines as no virus was detected in the tissues and blood after challenge 2 weeks or 20 weeks-post-2nd dose. However, with rE2p-CadB, very low viremia was recorded on the 2nd day-post-challenge. ConclusionBoth rE2p and BPL/formalin-inactivated virus are promising candidate vaccines deserving further evaluation.

The Use of Explosive Energy for Joining Advanced High Strength Low Alloy Steels

This article deals with an alternative method of joining advanced steels for frame structures. These steels cannot be joined by a conventional process due to the impact of temperature on the base material. Therefore, a simple and cost-effective method of forming a high-strength joint, intended for advanced high-strength materials, was designed using explosive forming. One of its key advantages is that it preserves the microstructure of the high-strength material being joined. At the same time, the design of the joint allows it to undergo further plastic deformation if the yield stress is exceeded, thus preventing the step change in load-carrying capacity and the instability of the structure. The alternative joint was intended for materials with yield stress above 1000 MPa and elongation of 10%, under quasi-static conditions. However, the design is also suitable for materials with ultimate tensile strength higher than 2000 MPa. Testing of the load-carrying capacity of the joint in a mechanical testing shop showed that the larger the flow stress of the material, the higher the load-carrying capacity of the joint. The selected joint designs with good load-bearing capacity values were manufactured by forming using products of detonation of the SEMTEX industrial blasting explosive. In a compression test, the demonstration joints showed the axial load-bearing capacity of 200 kN with up to 20-mm displacement to failure.

Explosive Evaporating Phenomena of Cryogenic Fluids by Direct Contacting Normal Temperature Fluids

Cryogenic fluids have characteristics such as thermal stratification and flashing by pressure release in storage vessel. The mixture of the extreme low temperature fluid and the normal temperature fluid becomes the cause which causes pressure vessel and piping system crush due to explosive boiling and rapid freezing. In recent years in Japan, the demand of cryogenic fluids like a LH2, LNG is increasing because of the advance of fuel cell device technology, hydrogen of engine, and stream of consciousness for environmental agreement. These fuel liquids are cryogenic fluids. On the other hand, as for fisheries as well, the use of a source of energy that environment load is small has been being a pressing need. And, the need of the ice is high, as before, for keeping freshness of marine products in fisheries. Therefore, we carried out the experiments related to promotion of evaporating cryogenic fluids and generation of ice, in the contact directly of the water and liquid nitrogen. From the results of visualization, phenomena of explosive evaporating and ice forming were observed by using video camera.

Numerical Simulation of Linear Explosive Formed Penetrator by Endpoint Initiating Manner

The formation of linear explosion formed penetrator(LEFP) from linear shaped charge detonated from one end point was studied both theoretically and experimentally, and a numerical simulation was also carried out. By decomposing the detonation velocity vector into spherical and slide components, the theoretical model described the tip velocity change of LEFP. The numerical model illustrated the formation of LEFP and the tip velocity agreed with the theoretical model. The validation of the theoretical and numerical models was verified by experiment, in which steel targets were used to show the effect of LEFP. The results showed that average tip velocity was 2658.4 m/s at 100 mm to the charge mouth. The theoretical and numerical velocity values and distribution curve were very close to the experimental ones. This work may further develop the theory of LEFP and linear shaped charge.

Liner Material's Output Characteristics of Explosively Formed Projectiles (EFPs)

The output considerations: velocity, pressure, density, internal energy, temperature and L/D ratio of explosively formed projectiles (EFPs) were investigated. The internal energy of the EFPs was inversely proportional to the density of the liner material. The shock pressure generated and its fluctuations were highest for Fe and Ta liner materials respectively. The least pressure variations were observed for Cu along its axial direction with highest length to diameter (L/D) ratio to supports deeper penetration. The maximum difference between numerical simulation and experiment was 9.7 % for Cu EFP.

산업용 폭약을 이용한 폭발용접, 폭발성형과 충격분말고화에 관한 실험 및 수치해석적 연구

본 논문은 폭약의 폭발현상을 이용한 폭발용접, 폭발성형과 충격분말고화기술의 기본적 원리와 실험방법, 실험결과에 대하여 기술한다. 타이타늄(Ti)과 스테인레스 강(Stainless steel, SUS 304) 판재의 폭발용접 실험결과, 두 재료 접촉면의 단면에서는 연속적인 젯(jet)모양의 파형이 관찰되었고, 두 금속판재의 설치 경사각도가 <TEX>$15{\sim}20^{\circ}$</TEX> 이고 접착속도가 2,100~2,800 m/s인 경우에 최적의 접합조건을 보였다. 알루미늄(Al) 판재를 이용한 폭발성형 실험과 전형적인 가압성형 실험 결과를 비교분석하여, 폭발성형의 경우가 큰 곡률변형을 보여 가공성이 우수한 것으로 확인되었다. 끝으로 금속과 세라믹의 혼합분말(<TEX>$Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$</TEX>)에 대한 충격고화 실험법을 제안하고 실험을 수행한 결과, 고화체의 표면과 내부에 균열이 확인되지 않았으며 세라믹입자와 금속입자들의 강한 미세조직 결합이 형성되었다. 또한 충격분말고화실험에서 발생되는 폭약의 폭발에 의한 폭굉파와 수중 충격파의 전파 및 간섭현상을 분석하기 위하여 LS-Dyna 3D를 이용한 동적해석을 수행하였다. 그 결과, 물용기 내 벽면에서 반사된 수중충격파가 중앙부에서 중첩되어 폭약의 폭발압력보다 높은 20 GPa의 수중 충격압을 보여, 물용기 내부형상의 중요성을 입증하였다. Theoretical backgrounds on the experimental methods of explosive welding, explosive forming and shock consolidation of powders are introduced. Explosive welding experiments of titanium (Ti) and stainless steel (SUS 304) plate were carried out. It was revealed that a series of waves of metal jet are generated in the contact surface between both materials; and that the optimal collision velocity and collision angle is about 2,100~2,800 m/s and <TEX>$15{\sim}20^{\circ}$</TEX>, respectively. Also, explosive forming experiments of Al plate were performed and compared to a conventional press forming method. The results confirmed that the shock-loaded Al plate has a larger curvature deformation than those made using conventional press forming. For shock consolidation of powders, the propagation behaviors of a detonation wave and underwater shock wave generated by explosion of an explosive are investigated by means of numerical calculation. The results revealed that the generation and convergence of reflected waves occur at the wall and center position of water column, and also the peak pressure of the converged reflected waves was 20 GPa which exceeds the detonation pressure. As results from the consolidation experiments of metal/ceramic powders (<TEX>$Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$</TEX>), shock-consolidated <TEX>$Fe_{11.2}La_2O_3Co_{0.7}Si_{1.1}$</TEX> bulk without cracks was successfully obtained by adapting the suggested water container and strong bonding between powder particles was confirmed through microscopic observations.

Numerical Simulation on Bifurcate Fracture of Linear Red Copper Penetrator

The Red copper has been widely used in shaped charge liner because of good ductility. Red copper penetrator is a Linear Explosively Formed Penetrator (LEFP) when linear red copper shaped charge liner overturned under the effect of detonation production. Compared with ordinary jet swords, red copper penetrator has a wider range of stand-off, bigger cratering and significant aftereffect, which can meet the requirements in various environments. It was observed that bifurcate fracturing of red copper penetrator occurred in the performance testing of LEFP initiated on edge midpoint as the stand-off increased, which resulted in the separate craters on the target and the cratering effect was weakened. The Propagation of detonation wave and the interaction with red copper shaped charge liner were theoretically and experimentally studied, also numerical simulations were conducted. The results showed that velocities of charge liner elements were directly proportional to those of detonation waves, which caused different velocity directions and values of different elements, and great velocity gradient formed in the penetrator. The penetrator fractured as the elongations both on the vertical and horizontal directions were greater than the dynamic elongation of red copper. It was concluded that the main factor which resulted in the bifurcate fracture phenomenon was velocity gradient in the penetrator.

Simulation and experimental work on manufacturing torispherical heads in explosive hydro-forming process

This study presents a numerical investigation on the deformation of the circular blanket against a male die under impulsive loading to form a torispherical heads shape. A finite element model was developed and verified with experimental tests for the explosive forming of the torispherical heads made of AA5083 aluminum alloy in the framework of LS-DYNA crash simulator software. The nature of the deformation was turned from the stretching to the buckling and compression of the specimen by using a male die, which is a novel concept in the high speed forming processes. Johnson-Cook (JC) and Modified Zerilli-Armstrong (MZA) constitutive equations were used to describe the behavior of the specimen in a high strain rate forming process with different stress status. Most of the experimentally observed material behaviors simulated well in pure tension or compression tests, while the transient zone was not adequately described. The predicted width for the transient rim is considerably smaller than experimental measurements. The blast loading process including the underwater detonation and the interaction with the specimen simulated using Arbitrary Lagrangian-Eulerian formulation as well as cavitations and reloading effect. The simulation results for blast loading verified base on Cole’s relation for the underwater detonation of small charges, show a good agreement of 95% accuracy. Key words: Explosive hydro-forming, male die, arbitrary Lagrangian-Eulerian formulation, torispherical head, Johnson-Cook, Zerilli-Armstrong.

Experimental, numerical, and theoretical analyses of simultaneous forming–welding of inhomogeneous plates

Experimental tests for simultaneous explosive forming–welding for two inhomogeneous plates have been carried out. Sheets of copper, aluminium, and steel were used for simultaneous forming and welding. Also, analytical and numerical analyses were conducted. Given analytic model, is based on energy method, and considering support conditions, deformation, and critical amount of impacts. Two metal plates are converted to their equivalent homogeneous plate by a method similar to the analysis of combined beams. On the other hand, finite-element analysis has been done wherein the work plates have been modelled by Johnson–Cook material model. The maximum deformation of plates and the possibility of rupture have been predicted with respect to mechanical properties of the plates. Also, to measure the velocity of flyer plate, which is necessary to compute impact, an innovative method is presented. Then, the amounts of experimental deformation, stresses, and strains were compared with analytical and numerical results and rather good similarities have been observed.

Theoretical calculation of the maximum radial deformation of a cylindrical shell under explosive forming by a new energy approach

Due to different influential parameters that affect an explosive forming process, this classic method of metal forming can potentially be considered as one the most complicated practical approaches to forming metallic shells and plates. Focusing on the importance of the energetic efficiency during an explosive forming procedure, the explosion phenomenon and relating formulation will be reviewed in this article. Furthermore, influential differences between air and water as the media of explosion and their effects on explosive forming process will be discussed. On the other hand, a new theory, called ‘the energy method’ that can be used for calculation of the maximum radial deflection of cylindrical shells under explosive loading will be introduced in this article. Besides, the selected results of hundreds of experiments that have been conducted on different tubular shells by the use of water and air as media of explosive forming process will be presented and the maximum transverse displacements of the shells that have been experimentally tested will then be compared to the results of the proposed energy method. Comparison between the maximum radial deformation of cylindrical specimens that were used in this research and theoretical results shows that the accuracy of the new theory is approximately 84%.

Research of the performance of pulse electrohydrodynamics in blockage removal

In line with contemporary trends and seeking to develop new methods and technologies, a new, original technology was explored and designed based on a non-conventional process of electrical pulse discharge in a water chamber, referred to as 'Pulse Electrohydrodynamic Technology' (PELHYDT). The application of the PELHYDT in sewer blockage removal is presented in this paper. Existing machinery can remove two blockages of gully pot connections per hour. Three blockages of pipe conduits are generally removed during an 8-h working day. Applying PELHYDT technology, which allows for high rates of removal of mechanical obstructions, it is possible to achieve operating fluid pressures in the order of 10(3)-10(4) bars, a velocity of 100 m/s, a deformation acceleration of the model material structure of 10(6)-10(7) m/s2, and high-frequency hydraulic shock waves with a frequency of 10(3)-10(4) Hz. The applicability of this efficient technology in sewer blockage removal was proven under laboratory conditions at operating fluid pressures from 50 to 160 bars, which are standard for sewer maintenance. Water velocities generally achieved in sewers using existing flushing technologies range between 1 and 3 m/s and usually do not exceed 9 m/s. PELHYDT creates waves whose velocity is at least 100 m/s, and is therefore about ten times more efficient than existing technologies. PELHYDT generates an electrohydrodynamic wave very quickly, virtually in the form of an explosion. It was proven under laboratory conditions that the application of this technology for blockage removal in practice will not result in any sewer damage.

Formation Mechanism of Linear Explosive Formed Penetrator by Midpoint Initiating Manner

Linear explosively formed penetrator (LEFP) is an optimal combination of linear cutting sword and conical shaped charge but is completely different with those two above. Initiating manner of LEFP is one of the most important factors that can affect its performance obviously. LEFP forming mechanisms of linear shaped charge initiated from the mid-point were studied with combined method of theoretical analysis, experiments and numerical simulation. Liner movement driven by the detonation wave action was analyzed as a three-dimensional issue and a synthetical model of liner movement was established. The model were verified by the penetrating experiments with the LEFP initiated from midpoint under stand-off which is 5 times distance of the LEFP caliber size. Formation processes of LEFP were described through numerical simulation and the simulation results were in concordance with those of experiments.

Research on Initiation Sensitivity of Solid Explosive and Planer Initiation System

Firstly, recently, there are a lot of techniques being demanded for complex process, various explosive initiation method and highly accurate control of detonation are needed. In this research, the metal foil explosion using high current is focused attention on the method to obtain linear or planate initiation easily, and the main evaluation of metal foil explosion to initiate explosive was conducted. The explosion power was evaluated by observing optically the underwater shock wave generated from the metal foil explosion. Secondly, in high energy explosive processing, there are several applications, such as shock compaction, explosive welding, food processing and explosive forming. In these explosive applications, a high sensitive explosive has been mainly used. The high sensitive explosive is so dangerous, since it can lead to explosion suddenly. So, for developing explosives, the safety is the most important thing as well as low manufacturing cost and explosive characteristics. In this work, we have focused on the initiation sensitivity of a solid explosive and performed numerical analysis of sympathetic detonation. The numerical analysis is calculated by LS-DYNA 3D (commercial code). To understand the initiation reaction of an explosive, Lee-Tarver equation was used and impact detonation process was analyzed by ALE code. Configuration of simulation model is a quarter of circular cylinder. The donor type of explosive (SEP) was used as initiation explosive. When the donor explosive is exploded, a shock wave is generated and it propagates into PMMA, air and metallic layers in order. During passing through the layers, the shock wave is attenuated and finally, it has influence on the acceptor explosive, Comp. B. Here, we evaluate the initiation of acceptor explosive and discuss about detonation pressure, reactive rate of acceptor explosive and attenuation of impact pressure.