Explosive Shock Loading Research Articles

Shock Wave Behaviour of Polymeric Materials for Detonation Waveshapers

This paper discusses the experimental determination of explosive shock attenuation parameters of four different polymers viz., Teflon, Phenol formaldehyde, Polyethylene foam and Polypropylene foam. These polymers are candidate materials for waveshapers in shaped charge warheads. Cylindrical specimens of the polymer materials were subjected to explosive shock loading by the detonation of RDX:Wax (95:5). Shock arrival time was measured using piezo-wafers positioned at known spatial intervals in the specimens. Initial shock velocity, stabilised shock velocity and attenuation constant were determined. These parameters are essential for the design of waveshapers. Foams have better shock attenuating properties compared to solids due to their cellular structure. Polypropylene foam has the highest shock attenuating characteristic among the four materials studied.

Deformation and acceleration of Zn and Cu liners under explosive shock loading

Both zinc and copper shaped charge jets (SCJs) generated from conical liners under explosive shock loading were observed using soft flash x-ray radiography. The goal was to ascertain the effect of the liner material melting point on the jet features and density. An analytical method termed in situ mass analysis from x-ray image processing (i-MAX) was utilized to estimate the mass and apparent density of each SCJ in this study. The masses determined for the zinc and copper leading jets were (34 ± 2) mg and (68 ± 3) mg, respectively. The overall mass distributions of both the zinc and copper SCJs showed the same tendency to decrease toward the tip of the jet, with the exception of the leading jet. The density distribution of the zinc SCJ gradually decreased toward the leading jet as it stretched. In contrast, the density distribution of the copper SCJ varied depending on the appearance of a necking region, and the minimum apparent density was observed 30 mm from the leading jet. These results demonstrate that the occurring of cavitation or vacancy avalanches in metal jet depend on the melting point of the liner material.

Nanotwin Formation in High-Manganese Austenitic Steels Under Explosive Shock Loading

The micro-deformation mechanisms active in a high-manganese austenitic steel were investigated upon explosive shock loading. Single system of nanotwins forming within primary twins were shown to govern the deformation despite the elevated temperatures attained during testing. The benefits of nanotwin formation for potential armor materials were demonstrated.

Effect of explosive contact and non-contact shock-processing on structure, microstructure and mechanical characteristics of aluminum

Contact and non-contact techniques are used to obtain monoliths of micro-sized aluminum powder under explosive shock loading. The measurement technique involves instrumented detonics to determine the velocity of detonation and compaction of powder in a single-shot experiment. The compacted specimens were examined for crystallographic, micro-strain, particle size, microstructure, mechanical strength, microhardness and density variations. Results indicate that non-contact technique gives rise to uniform thick compacts with negligible change in particle size, micro-strain, microhardness and microstructure with lower density. Whereas the compacts obtained by contact arrangement are accompanied by a substantial change in these parameters with higher density. Compacts of uniform density greater than 98 % theoretical value have been obtained by using explosive mixture of detonation velocity of 4.2 km/s. The compacted specimens possess micro-strain 2.8×10−3, microhardness (60±2)H v, tensile strength of 112 MPa and compressive strength of 116 MPa with elongation up to 6.4 %. Fracture/void free compacts obtained by contact arrangement have tremendous use in materials science and technology.

Localization of plastic deformation on contacts, determining the formation of a strong joint

It is shown that a strong joint is formed on the contact surface in explosive welding. A band of material on which plastic deformation is localized is formed along the boundary of the surface, this band representing a qualitatively new structure. Use of the laws governing strain localization, obtained from a study of the collapse of thick-walled cylinders that were subjected to explosive shock loading, makes it possible to predict the collision parameters in explosive welding in accordance with the grain size of the materials that are used.

The damage and failure of GRP laminates by underwater explosion shock loading

This paper examines the development of microstructural damage in a glass-reinforced polymer ( grp ) laminate subjected to explosive shock loading in water. GRP is commonly used in small naval vessels, and may be subjected to underwater explosions. In the experiments, the laminates were exposed to increasing amounts of shock loading produced by underwater explosions. The laminates were backed with either water or air to modify the amount of bending experienced under loading, with the air-backed laminates having the higher amount of bending. Examination of the grp microstructure by optical and scanning electron microscopy after shock testing failed to reveal any damage to either the polymer matrix or glass fibres when the laminate was backed with water. In contrast, when the laminate was backed with air, small cracks were produced in the polymer matrix at low shock pressures. Raising the shock pressure above a threshold limit caused complete failure of the laminate by cracking in the polymer matrix, cracking of the glass fibres, and delamination of the glass fibres from the polymer. The differences in the shock resistance of the water- and air-backed grp are discussed. Measurements of the residual tensile fracture strength of the laminates after shock loading are also presented. The fracture strength of the water-backed laminate was not affected by shock, but the fracture strength of the air-backed laminate deteriorated with the onset of glass fibre breakage and delamination in the grp microstructure.

Experimental investigation of the deflection of peripherally restrained plates under explosive shock loading

The article describes a laboratory apparatus for study of the effect of explosive shock loading on plane barriers (plates) and a method for evaluating the delfection of plates with different forms of the restrained periphery. These facilitate investigation of the process of pulse loading due to the energy of explosion of the condensed explosives under laboratory conditions. The apparatus facilitates variation in the explosive shock loading parameters (mass of explosive, distance from charge to tested plates, thickness of plates and multilayer barriers, and form of the restraining periphery) along with recording of the magnitude of the pulse of pressure of explosion products on the plates. Results of a study of deflection of plates with a circular restraining periphery under explosive shock loading are presented

Explosive compaction of superconducting powder

Superconducting powder, YBa2Cu3O7−x , with grains of size varying from 2 to 20μ and superconductivity up to 90°K was compacted to a uniform density of 6.2 g/cc (96% of theoretical maximum density) by explosive-shock loading in cylindrical configuration. A typical size of rod (3.76 mm diameter and 70 mm length) was fabricated using the present technique of explosive compaction. The compacted specimen shows levitation at the liquid nitrogen temperature.

Shock compaction of cubic boron nitride powders

C-BN powders with different grain sizes were dynamically compacted by explosive shock loading using approximate peak pressures from 33 to 77G Pa. The density and the microhardness of the resulting c-BN compacts were strongly dependent upon the grain size of the c-BN powders used as the starting materials. The best c-BN compacts, with 98% of the theoretical density and microhardness of 51.3G Pa, were obtained from the coarse c-BN powder (40 to 60μm). In the compacted fine c-BN powder (2 to 4μm) conversion of the c-BN to low density forms of BN at a residual temperature degraded the interparticle bonding significantly. X-ray line-broadening analysis of the compacted c-BN powders indicated that the residual lattice strain increased with the increase in grain size of the starting powder, while the crystallite size was independent of the grain size.

ChemInform Abstract: Plastic Deformation in Alumina by Explosive Shock Loading.

AbstractBy explosive shock loading with maximum pressures of 13 to 26 GPa and a maximum adiabatic temp. rise of z 400°C spherical alumina powders (a‐AIZO; and transitional alumina phases) have been compacted achieving densities 90% of theoretical.

Plastic Deformation in Alumina by Explosive Shock Loading

Spherical alumina powder, composed of α‐Al2O3 and transitional alumina phases, was compacted by explosive shock loading with maximum pressures of 13 to 26 GPa and a maximum adiabatic temperature rise of ∼400°C. A final density >90% of theoretical was achieved. The powder densified primarily by plastic deformation, with only occasional particle fracture. Transmission electron microscopy showed dislocation densities of at least 1011 cm−2 in all phases and extensive twinning in transitional alumina phases.

Explosive shock loading of alpha-Si3N4 powder

Alpha-Si3N4 powders were explosively shock loaded at levels of 260 and 570 kbar pressure. Specimens exhibited densification without additives into the 93 to 98% dense range as a result of shock-induced consolidation. X-ray line broadening investigations indicated that significant residual, internal strain levels of the order of 0.4% were developed in the densified material. Hardness and indentation fracture toughness values for shock-densified regions were nearly equivalent to those for ultra-high-pressure hot-pressed Si3N4 without densification aids.

Explosive loading of lead hemispherical liners

This paper documents results of a combined analytical/experimental program to study the behavior of lead hemispheres of various thicknesses subjected to explosive shock loading. Previous studies of collapse and jetting of lead structures indicated that, due to the low melting temperature of lead, significant amounts of vapor were present in the jet. However, its high density, ready availability and low cost make lead an attractive material for industrial and military applications. Hemispherical lead liners of three different thicknesses were fabricated into aluminum confined cavity charges using OCTOL high explosive to drive the liners. Analysis of flash radiographs of the formation and jetting process indicated a gradual transition from an apparent liquid-vapor jet for the smallest wall thickness to a liquid-solid jet for the largest thickness. This apparent phase transition of the lead liners through a region of decreasing vapor lead to an analysis of the phenomena with the two-dimensional HULL code, a finite-difference Eulerian code for computations of hydrodynamic and elastic-plastic phenomena. Good correlation (8%) was obtained between experimentally determined and computed jet characteristics, thus permitting inferences to be drawn regarding the effects of material properties and strain rates on the response of lead to shock loading. Additional computations were made with HULL for copper hemispherical liners (for which more extensive experimental data was available) and these were compared with results from HELP, another Eulerian code. The EPIC code was also used to predict the geometric characteristics and velocities of the jets from the lead liners. On the whole, good agreement with experiments was obtained from all codes indicating that existing two- and three-dimensional codes may be valuable tools for the study of explosive forming problems. In addition, the temperature profiles of the jets from the lead liners are in general agreement with the quality of the flash radiographs (i.e. appearance of vapor) and with experimental measurements of the jet surface temperature.

EPR study of shock and thermally induced reaction in solid copper tetramine nitrate

Electron paramagnetic resonance studies of copper tetramine nitrate, subjected to explosive shock loading and analyzed after recovery, indicate that the Cu(NH3)2+4 complex is completely converted to Cu(NH3)2+2. The same reaction could also be induced by isothermal heating of the material for 1 h at +160 °C. The intrinsic linewidth of the Cu(NH3)2+2 complex in the shocked material was larger by a factor of 3 compared to the linewidth of the spectrum produced by isothermal decomposition. The perpendicular g shift was also slightly different. These differences are attributed to shock-induced defects in the material. When a foil flyer plate electric gun is used to shock CTN, the conversion to Cu(NH3)2+2 was not observed, but evidence of a new spectrum was obtained.

Laser-shock-induced microstructural changes and a comparison with explosive-shock-induced phenomena in metals: Field-ion and electron microscopic studies

Annealed etched molybdenum and tungsten wires were field evaporated to perfection in a specially designed field-ion microscope through which a laser beam could be focused onto the perfect metal emission end form or along the wire shank. Irradiation utilizing a Q-switched laser at fluences between 22 and 35 J/cm2 produced residual effects ranging from increasing numbers of lattice vacancies and vacancy clusters to massive deformation, cavitation and spallation, and melting. The results of increasing vacancy concentration with increasing laser fluence for molybdenum and tungsten were compared to similar observations in explosively shock-loaded molybdenum in concluding that laser shocking can produce residual effects approximately up to several hundred kbar peak pressure. Laser irradiation of electron transparent molybdenum foils also confirmed the attendant features of laser irradiation including vaporization, melting, and shock-induced spallation by direct observations in the transmission electron microscope. Dislocation substructures identical to those observed following explosive shock loading of molybdenum were also observed in the laser-irradiated molybdenum foils.

Calculated Transient Response of an A-6 Landing Gear Door

TRANSIENT response to explosive shock loading of aircraft structures must be evaluated with due regard for aerodynamic and structural resonance phenomena. An explosively generated shock front, after normal reflection from a rigid surface, will be at least doubled in amplitude; the exact factor depends on the incident shock amplitude and ambient atmospheric pressure. In addition, a transient load with a short rise time may precipitate a peak response twice that caused by a slowly rising (static) load of the same amplitude. Results of static load tests on aircraft are often extrapolated to give transient loading limits without obvious consideration of the points mentioned above. Exhaustive transient loading tests or detailed calculations are seldom carried out. This paper outlines finite element calculations made with NASTRAN on a model of an aircraft door. Good agreement was found with statically produced displacements of a fullscale sample of a landing gear door from an A-6 fighter bomber. Transient calculations were made, also with NASTRAN, and these showed that accepted transient load limits appear conservative.

Hardening during explosive shock loading of steel 110G13L alloyed with vanadium and modified with titanium

1. The addition of vanadium and titanium favors greater explosive hardening of steel 110G13L. 2. The depth of hardening decreases with increasing alloying of the matrix and with increasing numbers of hard dispersed particles formed after alloying with vanadium and titanium, which is due to greater scattering of the energy and the shock wave as it passes into the depth of the metal.

Shock deformation of k-state in Ni-Cr alloys

Abstract The change of electrical resistivity was used to study the ordering kinetics and the anomalous resistivity behaviour in Ni-22 wt. % Cr and Ni-30 wt. % Cr (Ni-22 Cr and Ni-30 Cr) before and after shock deformation. Ordering was found to occur in two stages: the attainment of an equilibrium domain size, and the increase of long-range order (LRO) within the domains. Specimens of Ni-22 Cr and Ni-30 Cr in the ordered and disorderd states were subjected to explosive shock loading at shock pressures between 90 and 300 kbars. In the pressure range of 200 to 300 kbars, the resistivity of the ordered alloys decreased sharply. The resistivity of the shock-deformed initially quenched alloys decreased continuously between 90 and 300 kbars. The decrease in resistivity with shock deformation for the quenched alloys was related to the destruction of short-range order (SRO).

Comparison of residual defect structures and hardness in Inconel 600 following deformation by explosive shock loading, cylindrical (explosive) expansion, and cold-reduction

The terminal characteristics of Inconel 600 alloy (76% Ni, 16% Cr, 7% Fe) were examined and compared following cold reduction by 5, 10, 20, 30, and 40%, explosive expansion of thin-walled cylinders by 1, 10, 25, and 62%, and explosive shock loading to pressures of 80, 180, 240, and 460 kbar. The hardening behavior and structural characteristics of explosivily formed (expanded) tubes were not significantly different from those resulting for cold reduction. Deformation twins were observed by transmission electron microscopy only in samples shock loaded at 240 kbar and above. The absence of twins in the explosively formed Inconel was attributed to the failure of an adequate number of long jogs on secondary glide systems to activate dislocation pole-twin sources. Dislocations were shown to adequately account for the residual hardening occurring for the three modes of deformation.

Thermal recovery in 304 stainless steel following explosive shock loading and explosive forming

The annealing behavior of type 304 stainless steel sheet samples shock-loaded at pressures between 750 and 1200 kbar, and cylindrical samples explosively expanded between 32 and 62 pct is characterized by rapid (catastrophic) hardness recovery between 750° and 850°C. Apparent aging effects, the occurrence of precipitates and dislocation loops of varying sizes, and a preferential etching at grain boundaries in thin electropolished foils is observed at 750 and 1200 kbar and 32 and 62 pct. Electron transmission microscope observations revealed that the catastrophic recovery and subsequent pseudorecrystallization were essentially synonymous, with no apparent nucleation and growth of new grains. Recovery is characterized mainly by the collapse of deformation twins and the accelerated annihilation of dislocations. Considerably less recovery is observed for lower shock pressures (<750 kbar), and for less explosive expansion (<25 pct) as evidenced by the presence of numerous dislocations at temperatures where complete recovery has occurred for higher pressure samples. It is suggested that a nonequilibrium vacancy concentration exists at the higher shock-pressures and larger degrees of explosive expansion, and that this feature is largely strain-rate dependent.