Explosive Forming Research Articles

Unique spatial methane distribution caused by spontaneous coal combustion in coal mine goafs: An experimental study

Abstract A new type of incident in the form of a methane explosion caused by spontaneous combustion of coal is receiving more and more attention due to the high ground temperature and high methane content in coal mines. To investigate the formation process of this type of incidents and advance the research on methane explosion risk caused by spontaneous coal combustion, a self-designed experimental platform was used to determine the influence of spontaneous coal combustion on methane migration in the goaf. Additionally, the effect of different ventilation velocities at the mining face on methane migration in the goaf was studied. The results reveal that air leakage plays a key role in methane migration in the goaf. The bigger the ventilation velocity, the larger the area affected by air leakage. In addition, the superposition of the air leakage and the horizontal and vertical movement of hot gases creates the entrainment effect in the spontaneous combustion area. Eventually, the methane concentration at the location of spontaneous combustion is the lowest and it gradually increases outside the spontaneous combustion area because of the superposition of air leakage, ‘fire pressure’ and the entrainment effect.

Numerical Simulation of Explosive Forming Using Detonating Fuse

The explosive forming is a characteristic method. An underwater shock wave is generated by underwater explosion of an explosive. A metal plate is affected high strain rate by the shock loading and is formed along a metal die. Although this method has the advantage of mirroring the shape of the die, a free forming was used in this paper. An expensive metal die is not necessary for this free forming. It is possible that a metal plate is formed with simple supporting parts. However, the forming shape is depend on the shock pressure distribution act on the metal plate. This pressure distribution is able to change by the shape of explosive, a mass of explosive and a shape of pressure vessel. On the other hand, we need the pressure vessel for food processing by the underwater shock wave. Therefore, we propose making the pressure vessel by this explosive forming. One design suggestion of pressure vessel made of stainless steel was considered. However, we cannot decide suitable conditions, the mass of the explosive and the distance between the explosive and the metal plate to make the pressure vessel. In order to decide these conditions, we have tried the numerical simulation on this explosive forming. The basic simulation method was ALE (Arbitrary Laglangian Eulerian) method including with Mie-Grumeisen EOS (equation of state), JWL EOS, Johnson-Cook constitutive equation for a material model. In this paper, the underwater pressure contours to clear the propagations of the underwater shock wave, forming processes and deformation velocity of the metal plate is shown and it will be discussed about those results.

Investigation on Interaction of Explosively Formed Projectile with Multi-layer Medium Targets

To investigate the influence of liner material, charge diameter and standoff on explosively formed projectile (EFP) penetrating into multi-layer targets, a large number of experiments were performed and the experimental data on crater diameter, hole diameter, crater depth and penetration depth were obtained. Meanwhile, the numerical simulation have been done to study the formation and penetration processes of all the EFP with AUTODYN software. The numerical results of penetration depth are in good agreement with the experimental ones. The results indicate that the optimal liner material of EFP to achieve a larger penetration hole diameter and depth are aluminum and copper, respectively.

Exploring the analysis and differentiation of plastic explosives by comprehensive multidimensional gas chromatography-mass spectrometry (GC × GC–MS) with a statistical approach

Plastic explosives (PE) are a relatively insensitive form of explosives that are composed of several different types of chemicals. Differentiation of such a complex mixture is of interest to law enforcement agencies. In this work, we explored the possibility of utilizing a mass spectrometric method with statistical processing for PE analysis. Comprehensive two-dimensional gas chromatography coupled with a time-of-flight mass spectrometer (GC×GC–MS) was implemented for the analysis of PE extracts. The resulting chromatographic peaks were aligned using mass spectra and retention time data. The aligned peaks were then subjected to statistical analysis using scores generated via principal component analysis (PCA), followed by a k nearest neighbor classification with Euclidean distance. Using appropriate data treatment steps, a 0% error rate and a 0% unidentified rate in the classification of PE to production lots was achieved in cross validation classification of training samples and classification of test samples. This demonstrates accurate classification of PE samples into production lots using these data treatment steps.

ENSURING SAFETY AT PNEUMOTEST OF THE PIPELINE

The work considers the fundamentals of human life during pneumatic testing of pipeline. Invalid strength pipe and high pressure destruction occurs in the form of explosion of the object, accompanied by the appearance of a shock wave. The shock wave is a transient process is very quick conversion of substances with the release of large amounts of energy in a small volume and is one of the most dangerous effects on humans. The typical width of the shock wave in the air – 10-4 mm (several lengths of free path of molecules). Small thickness of such waves gives possibility in many problems to consider it as a discontinuity surface. But in some cases, it is the structure of the shock wave. This task is of theoretical interest. For weak shock waves, a good agreement of experiment and theory gives a model taking into account viscosity and conductivity of the environment. For shock waves of sufficiently high intensity structure should take into account (consistently) the stage of establishment of thermodynamic equilibrium, the translational, rotational, for molecular gases even and vibrational degrees of freedom, in certain conditions, the dissociation and recombination of molecules, chemical reactions, the processes involving electrons (ionization, electronic excitation). In this paper we have investigated the dependence of the conditional probability of defeat of a man from a change in the overpressure of the shock wave of the explosion. On the basis of the conducted researches the measures to prevent the occurrence of the shock wave pneumatic tests: strict adherence to safety standards and conditions for the maintenance of pressure in the pipeline, ensure an acceptable working range of conditions of the pneumatic tests, the availability of required serviceable equipment and fittings.

Simulation of an Armoured Vehicle for Blast Loading

Occupant safety in an armoured vehicle is of paramount importance. Most serious threat to armoured vehicles comes in the form of explosion of buried charge or an improvised explosive device. The use of numerical methods in the validation process of light armoured vehicles reduces the number of prototypes required and decreases the design time. This paper elucidates the process by which one such validation using numerical methods was done. The process of finite element method used for simulation of blast is a prominent method of numerical method of simulation. The finite element model (FEM) process starts with discretisation. By discretisation or meshing, Shell (Quad/Tria) and solid (Tetra/Hexa) elements are generated. The FEM thus created is provided with relevant material model / properties and loading and boundary conditions. The loading conditions are adopted from STANAG 4569 Level II standards. Local deformation, global displacement, stresses and time history of displacement of particular areas of interest are obtained as results. Comparison results include the effect of with and without thermal softening under blast. Based on the results and comparison, suggestions regarding re-engineering the vehicle are presented.

Fuse Selection for the Two-Stage Explosive Type Switches

In the two-level explosive switch destruction of a delay happens in the form of electric explosion. Criteria of similarity of electric explosion in transformer oil are defined. The challenge of protecting the power electrical equipment from short circuit currents is still urgent, especially with the growth of unit capacity. Is required to reduce the tripping time as much as possible, and limit the amplitude of the fault current, that is very important for saving of working capacity of life-support systems. This is particularly important when operating in remote stand-alone power supply systems with a high share of renewable energy, working through the inverter transducers, as well as inverter-type diesel generators. The explosive breakers copes well with these requirements. High-speed flow of transformer oil and high pressure provides formation rate of a contact gap of 20 - 100 m/s. In these conditions there is as a rapid increase in voltage on the discontinuity, and recovery of electric strength (Ures) after current interruption.

Numerical and Experimental Study on the Formation and Dispersion Patterns of Multiple Explosively Formed Penetrators

THREE-DIMENSIONAL NUMERICAL SIMULATIONS AND EXPERIMENTS WERE PERFORMED TO EXAMINE THE FORMATION AND SPATIAL DISPERSION PAT-TERNS OF INTEGRAL MULTIPLE EXPLOSIVELY FORMED PENETRATORS (MEFP) WARHEAD WITH SEVEN HEMISPHERICAL LINERS. NUMERICAL RESULTS HAD SUCCESSFULLY DESCRIBED THE FORMATION PROCESS AND DISTRIBUTION PAT-TERN OF MEFP. A GROUP OF PENETRATORS CONSISTING OF A CENTRAL PE-NETRATOR SURROUNDED BY 6 PENETRATORS IS FORMED DURING THE FORMA-TION PROCESS OF MEFP AND MOVES IN THE DIRECTION OF AIMING POSITION. THE MAXIMUM DIVERGENCE ANGLE OF THE SURROUNDING PENETRATOR GROUP WAS 7.8°, AND THE DAMAGE AREA COULD REACH 0.16 M2 AT 1.2 M. THE LAWS OF PERFORATION DISPERSION PATTERNS OF MEFP WERE ALSO OBTAINED THROUGH A NONLINEAR FITTING OF THE PERFORATION INFORMATION ON THE TARGET AT DIFFERENT STANDOFFS. THE TERMINAL EFFECTS OF THE MEFP WARHEAD WERE PERFORMED ON THREE #45 STEEL TARGETS WITH A DIMENSION OF 160CM  160CM  1.5CM AT VARIOUS STANDOFFS (60, 80, AND 120 CM). THE SIMULATION RESULTS WERE VALIDATED THROUGH PENETRATION EXPERIMENTS AT DIFFERENT STANDS. IT HAS SHOWN EXCELLENT AGREEMENT BETWEEN SIMULATION AND EXPERIMENT RESULTS.

Analitička i numerička metoda polja brzine za eksplozivno formirane projektile

The current paper presents analytical and numerical approaches of velocity performances estimations for the EFP (Explosively Formed Projectiles). The proposed analytical methods mathematically develop velocities parameters of a particular segment for EFP liner propelled by explosive process. This model is based on the well-known theoretical approaches of energy distribution on plastic body in dynamical conditions providing integral solution for projectile final velocity. The redundant to analytical, the numerical method is also developed, to provides estimations about behavior of projectile vs. time in the EFP forming process powered by explosion. Both models are valid for performances estimations of EFP warheads and design data for optimal EFP configuration. Simulations are supported by the software Matlab and Autodyn for analytical and numerical modeling respectively. The obtained numerical and analytical results are compared with the available experimental data.

Dynamic Response and Microstructure Evolution of Oxygen-Free High-Conductivity Copper Liner in Explosively Formed Projectile

THE DYNAMIC RESPONSE AND MICROSTRUCTURE EVOLUTION OF OXYGEN-FREE HIGH-CONDUCTIVITY COPPER IN A SHAPED CHARGE LINER OF AN EXPLOSIVELY FORMED PROJECTILE ARE INVESTIGATED THROUGH MICROSTRUCTURAL EXAMINATION OF A SOFT-RECOVERED EFP. THEORETICAL CALCULATION RESULTS INDICATE THAT THE HIGHEST TEMPERATURE INCREASE OF EFP CAUSED BY SHOCK WAVE AND PLASTIC DEFORMATION CAN REACH 673K, WHICH IS 0.5TM (WHERE TM IS THE MELTING TEMPERATURE OF COPPER), AND THE FORMATION PROCESS OF COPPER EFP IS PRIMARILY CAUSED BY EXTREME PLASTIC FLOW, WHICH IS POSSIBLY A TYPE OF SUPERPLASTIC FLOW IN A SOLID STATE. THE MAIN BODY OF THE EFP UNDERGOES COMPLETELY DYNAMIC RECRYSTALLISATION, AND THE AVERAGE SIZE OF THE REFINED GRAINS SIGNIFICANTLY DECREASES TO APPROXIMATELY 10ΜM. A SLIGHT INCREASE IN GRAIN SIZE OCCURS MAINLY AWAY FROM THE CENTER AND EXTENDS TOWARDS THE HEAD AND REAR SECTIONS OF THE EFP. DURING THE DRX PROCESS, THE DISLOCATION MOVEMENTS ARE BELIEVED TO BE THE CONTROLLING MECHANISMS SIGNIFICANTLY REFINING THE MICROSTRUCTURE AND HELPING IN THE FURTHER FLOW OF THE MATERIAL.

Characterizing In-Flight Temperature of Explosively Formed Projectiles in CTH

Code validation against experimental data is vital in building confidence for the use of simulation software in modeling and system design. Temperature data is of particular interest in the study of hypervelocity impact, however the experimental measurement of temperature in such a regime is difficult. Novel developments in measurement techniques have enabled the measurement of in-flight hypervelocity projectile temperature. This is done by saturating the projectile with a magnetic field, in flight, and tracking its decay, which is related to material conductivity and therefore temperature. This study seeks to use CTH to computationally model experiments conducted by Uhlig and Hummer in which in-flight temperature of an explosively formed projectile (EFP) was measured. Comparing CTH results to physical observations serves as a benchmark for the accuracy of internal temperature calculations. Transient temperature results were shown to vary greatly with chosen strength model, with highest accuracy (3.4%) being attained with the Johnson Cook model. These results were on the same order as previously done ALEGRA simulations, though with differing variations between strength models, and EFP structure matches well with experimental x-ray. SAND2017-3687C.

Penetration Research of Dual-mode Penetrator Formed by Shaped Charge with Wave Shaper

The objective is to match the penetration capability of dual-mode penetrator. Finite element software LS-DYNA is used to acquire four types of dual-mode penetrators EFP (Explosively Formed Projectile) and JPC (Jetting Projectile Charge). Considering the process of dual-mode penetrator flight and penetration, including the effects of velocity attenuation for stand-off and length change of EFP & JPC, also the differences between mechanisms of EFP into armor steel and JPC into concrete, an analytical model for predicting the final penetration of dual-mode penetrator is presented. We use the analytic model, to estimate the penetration of dissimilar modes and then a series of field tests are provided to demonstrate the reliability of the approach. Moreover, in application of the analytic method, along with the penetration restrictions of different modes, the work in this paper describes the optimal matching zone and extreme points of penetration capability of dual-mode penetrator.

Modelling the plastic deformation of Ti6Al4V under dynamic loading

In this paper, a multiscale numerical method is presented with the aim to model the response of a Ti6Al4V sheet under explosive forming. The numerical modelling focuses on the accurate definition of the plastic deformation of the Ti6Al4V specimens based on the texture of the material. The viscoplastic self-consistent polycrystal model code (VPSC) is used as a link between macroscopic response and the underlying microstructure taking into account the viscoplastic deformation of the specimen. Comparison is made with experimental results. The Cazacu–Barlat (CB06) material model is used because of its capability to describe the yielding asymmetry between tension and compression and to take into account the anisotropic behaviour of the sheet. The study focuses on the evaluation of the material model parameters and on how these affect the structural response of the Ti6Al4V specimens under explosive loading.This paper is part of a Themed Issue on Euromech 570: Interface-dominated materials.

Investigation on Strength Model of Metal Plastic Deformation under High Strain Rate

In the fields of explosive forming, aerospace industry, military industry etc. metallic materials will withstand a high strain rate in the process of deformation. It is very instructive to put forward an accurate strength model which can be used to describe the process of deformation reasonably. In this paper, several strength models are introduced which are mainly based on the macroscopic mechanical behavior of materials and the mechanisms of deformation of material, and their sphere of application, shortcomings and advantages were introduced and reviewed.

Syndrome d’entérocolite induite par les protéines alimentaires

A little known pathology, increasingly diagnosed. Late vomiting after food intake predominate. An insidious chronic form, an explosive acute form. A clinical diagnosis of a typical story, reproducible. Milk and soy often involved, sometimes unusual foods.

Strain Rate Dependant Material Model for Orthotropic Metals

In manufacturing processes anisotropic metals are often exposed to the loading with high strain rates in the range from 102 s-1 to 106 s-1 (e.g. stamping, cold spraying and explosive forming). These types of loading often involve generation and propagation of shock waves within the material. The material behaviour under such a complex loading needs to be accurately modelled, in order to optimise the manufacturing process and achieve appropriate properties of the manufactured component.The presented research is related to development and validation of a thermodynamically consistent physically based constitutive model for metals under high rate loading. The model is capable of modelling damage, failure and formation and propagation of shock waves in anisotropic metals. The model has two main parts: the strength part which defines the material response to shear deformation and an equation of state (EOS) which defines the material response to isotropic volumetric deformation [1]. The constitutive model was implemented into the transient nonlinear finite element code DYNA3D [2] and our in house SPH code. Limited model validation was performed by simulating a number of high velocity material characterisation and validation impact tests.The new damage model was developed in the framework of configurational continuum mechanics and irreversible thermodynamics with internal state variables. The use of the multiplicative decomposition of deformation gradient makes the model applicable to arbitrary plastic and damage deformations.To account for the physical mechanisms of failure, the concept of thermally activated damage initially proposed by Tuller and Bucher [3], Klepaczko [4] was adopted as the basis for the new damage evolution model. This makes the proposed damage/failure model compatible with the Mechanical Threshold Strength (MTS) model Follansbee and Kocks [5], 1988; Chen and Gray [6] which was used to control evolution of flow stress during plastic deformation. In addition the constitutive model is coupled with a vector shock equation of state which allows for modelling of shock wave propagation in orthotropic the material.Parameters for the new constitutive model are typically derived on the basis of the tensile tests (performed over a range of temperatures and strain rates), plate impact tests and Taylor anvil tests.The model was applied to simulate explosively driven fragmentation, blast loading and cold spraying impacts.

Numerical modelling of the effect of using multi-explosives on the explosive forming of steel cones

Modelling and analysis of underwater explosive forming process by using FEM and SPH formulation is presented in this work. The explosive forming of a steel cone is studied. The model setup includes a low carbon steel plate, plate holder, forming die as well as water and C4 explosive.The effect of multiple explosives on rate of targets deformation has been studied. Four different multi-explosives models have been developed and compared to the single explosive model. The formability of the steel plate based on forming limit failure criteria has been investigated. Aspects such as shape of plates deformation and thickness of the plate during the forming process have been examined.The model results indicate that a multi-explosives model does not always guarantee a faster rate of target deformation without central explosive. On the other hand the model results indicate that the multi-explosives setup is capable of preventing crack failure of the steel plate during the forming process which would occur if a single explosive model was used.

Role of Metal Oxide Nanomaterials on Thermal Stability of 1,3,6‐Trinitrocarbazole

AbstractThe thermal behaviour of 1,3,6‐trinitrocarbazole (TENT) in the form of pure and nanocomposite explosives was examined by differential scanning calorimetry (DSC) and thermogravimetry (TG). Thermoanalytical data revealed that thermal decomposition of pure TENT is significantly different from the investigated nanocomposites. The results confirmed that pure TENT decomposed completely in a single stage in the temperature range 400–450 °C. Though, addition of the nanoparticles to the TENT powder leads to higher thermal stability in comparison with the pure TENT. Decomposition kinetics of the pure TENT and the nanocomposites were studied by non‐isothermal DSC at diverse heating rates. The resulted thermokinetic and thermodynamic parameters for the thermal decomposition of pure TENT were compared with the nanocomposites.

Ghost particles in the universe: Neutrinos in astrophysics and cosmology

Neutrinos are nearly massless and very difficult to detect because they interact so very weakly. Sixty years after seeing the first of these «ghost particles» we know a lot about their properties. Today, observing them in nuclear reactors, the Sun, the Earth’s crust and atmosphere, and at high energies from distant cosmic sources is almost a routine task – they have become unique astrophysical messengers. They are important for a number of aspects: neutrinos shape some of the most dramatic astrophysical phenomena in the form of stellar-collapse supernova explosions, they may have created the excess of matter over antimatter in the universe, and neutrino-like «weakly interacting massive particles» may well account for the dark matter of the universe.

Analysis of cavitation time effect on elastoplastic response of underwater rectangular plate subjected to impulsive loading

This paper focuses on the cavitation effect on nonlinear elastoplastic deformation rectangular aluminum plate subjected to underwater explosion loading. Cavitation is a phenomenon that may be occurred for plates in the process of underwater explosion forming. The total pressure of the explosion becomes zero at the cavitation time, so that the governing equations of motion will be different before and after the cavitation. As a result, in terms of analysis and design, the cavitation time is significant in studying the behavior of a rectangular plate at underwater explosive loading. Based on Hamilton principle and variation method the nonlinear equations of motion of an underwater rectangular plate subjected to explosive loading are obtained. Exact linear dynamic response of plate is derived by employing the eigen function and nonlinear dynamic response of plate is derived by employing the finite difference method (FDM). The linear and nonlinear work hardening material modeling is considered to define the elastoplastic stress–strain relations. Return mapping algorithm is applied to calculate the stress and strain in any steps of loading. Then, the displacement, velocity and generated stress of plate during cavitation time are calculated. Using von Mises yield criterion, one can distinguishes the cavitation with in elastic or plastic regimes. By recognizing the time of cavitation in the range of elastic or plastic, the displacement and velocity field of plate are determined in duration of explosive loading. Results show that the cavitation time is on the order of 5–10 μs. Depending on amount of charge mass and stand-off, the cavitation time may occur in elastic or plastic regime. The results obtained of linear exact solution considering the linear work hardening material modeling are compared to results obtained of FDM considering the linear and nonlinear work hardening material modeling.