Explosive Compaction Technique Research Articles

Explosive compaction technology for loess embankment settlement control: numerical simulation and field implementation

Loess covers about one-tenth of the world’s land area. While it is often used as embankment fill, loess is not an ideal construction material due to its wet collapsible nature, as it may cause significant embankment settlement and other related problems. Although explosive compaction (EC) technology has been used for many years, the challenges in experimental testing and theoretical analysis hinder its wider application. This paper contributes to the development of a design construction scheme of EC technology for loess embankment improvement through an integrated approach that involves finite element modeling, small-scale experiments, full-scale simulation and field implementation. In this study, a reliable finite element model is developed and validated through a small-scale experiment. The model is developed based on the software ANSYS/LS-DYNA®14.5 and takes into account the coupling between different materials (including soil, explosives, air and pavement). Critical performance factors such as the volume of the explosion cavity, the density of the compacted soil and the soil pressure can be obtained directly from the model. The model is then extended to simulate full-scale embankments. A sensitivity study is conducted to establish the correlations between the design parameters and the abovementioned performance factors. The relationships served as design guidelines for the successful implementation of the EC technique in an embankment section on the Cheng-Chao highway in China. The results demonstrated the feasibility of the EC technique as a ground improvement method for loess embankments, and it illustrated the effectiveness of the numerical method as a tool in design.

Production of Wire Mesh Reinforced Aluminium Composites through Explosive Compaction

In this study, aluminum based composites with stainless steel wire-mesh as reinforcement is fabricated by explosive compaction technique. Stacks containing four layers of alternatively positioned aluminum sheets and stainless steel wire-meshes are explosively compacted at varied explosive masses and the results are reported. Microstructure of explosive compacted aluminum composite reveal a smooth interface at lower explosive mass, while formation of reacted products are observed at higher energetic conditions. Though the hardness of the post clad composite is higher than pre-clad materials, the maximum hardness is observed at the first interface.

Special Features of the Mechanical Characteristics of Al–Al2O3 Composites Produced By Explosive Compaction of Powders Under Shock-Wave Deformation

The results obtained from investigations into the special features inherent in the mechanical characteristics (Hugoniot elastic limit and spall strength) observed under shock-wave loading of Al–Al2O3 composite samples produced by an explosive powder compaction technique are presented. Embedding 10 wt.% of aluminum oxide in the aluminum matrix has been found to increase the Hugoniot elastic limit as opposed to the commercialgrade AD1(Al 1013) aluminum alloy.

Shock-consolidated TiO 2 bulk with pure anatase phases fabricated by explosive compaction using underwater shockwave

Titanium dioxide (TiO 2) bulk with pure anatase phases was fabricated by an explosive compaction technique using an underwater shockwave. Dynamic shock pressure of 6 GPa was used to consolidate anatase TiO 2 powders. Its microstructural, crystalline structural and photocatalytic characteristics were observed and measured by various techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and photocatalytic activity measurement system. It was confirmed that the relative density of anatase TiO 2 compact is about 96% (3.73 g/cm 3) of the theoretical density (3.89 g/cm 3) and a strong surface bonding between particles is formed by a shock energy. In X-ray diffraction analysis, high purity anatase phases, broadened peaks due to lattice defects and decreased crystallite size were found. For the photocatalytic activities, the anatase TiO 2 compact was quite excellent compared to the commercial sintered TiO 2 bulk.

Numerical Simulation of Explosively Compacted Powder-in-Tube MgB<sub>2</sub> Superconductor

High Tc MgB2 superconductors were fabricated using the ex-situ and in-situ powder in tube (PIT) technique. During treatment, the precursor materials were shock consolidated under high strain-rates using PETN as the explosive medium. After compaction, the superconducting properties of the steel-sheathed MgB2 samples were examined by means of magnetization measurements using a SQUID magnetometer. Bean’s critical state model was applied to investigate the critical current density characteristics of the samples at fields up to 5T. The superconducting transition temperature of the specimens was determined by examining the material temperature dependence of magnetisation in zero field cooled (ZFC) and field cooled (FC) states. An assessment of the explosive compaction technique was carried out by simulating the procedure using the LS-DYNA explicit finite element code. The sample is modelled as a porous soil-like material with a customised yield surface. The numerically estimated final product dimensions, porosity and hardness are compared to the experimental results; furthermore, the numerically obtained pressure, temperature and strain rate profiles are used to assess the efficiency of the compaction process for different explosive quantities and powder compositions.

Low Temperature Failure of Fe<sub>76</sub>Ni<sub>2</sub>Si<sub>9</sub>B<sub>13</sub> Compacted from Amorphous Glass Powder

The fracture surface morphology of Fe76Ni2Si9B13 bulk amorphous alloys failed in compression at temperatures from 4.2 to 300 K was investigated. The samples were prepared by the explosive compaction technique from amorphous powder. It has been found that fracture stress decreases with temperature from 300 to 4.2 K. In this temperature range, the brittle failure prevails. The failure propagates across particles and along particle boundaries too. The fracture micromorphology is riverlike pattern with fine dimples.

Hot explosive compaction of diamond powder using cylindrical geometry

Diamond powders were attempted to be consolidated at elevated temperature using an explosive compaction technique employing a cylindrical configuration. A compacted diamond sample recovered from the center of a cylinder, close to the end plug made of stainless steel showed high hardness and tight interparticle bonding between the diamond powders. The sample was characterized on the basis of X-ray diffraction patterns. No graphitization was observed due to heating or compaction, and the hot compacted sample was highly strained by intensive deformation at elevated temperature.

WC/Co Coating on a Mild Steel Substrate through Underwater Shock Compaction Using a Self Combustible Material Layer (WC/Co Coating through Underwater Shock Compaction)

The explosive compaction technique has been applied to consolidate WC/Co powder to make a coating layer on a steel substrate, and the microstructure and some properties are investigated. Explosive compaction was performed using an improved method through underwater shock compression. Two types of assemblies, open and closed types were used for the experiments for generating relatively low and high pressure respectively. The effect of a thin nitrocellulose layer placed above the powders and the effect of the following heat treatment were investigated. In most of the experiments, the WC/Co layer was successfully recovered without cracks. The effects of applying higher underwater shock pressure, role of nitrocellulose as self combustible material and the following heat treatment showed positive effect to improve the properties by the increase of hardness as well as wear resistance of the coating layer.

Development of numerical modelling to simulate the explosive compaction/cladding of YBCO ceramic powders

Since explosive compaction constitutes a tool for producing superconducting materials with unique properties for advanced structural applications, the calculation of the optimal compaction parameters is of great importance. In this paper, a methodology of numerical finite element modelling in the explosive compaction technique of the YBCO superconducting powder of various geometries is reported. The information stemming from this implementation may constitute some basic conditions for the creation of numerical models of explosive loading of superconducting materials, resulting in the prediction of parameters that are difficult to measure experimentally. The evolution of the deformed shapes, the pressure, density and temperature distributions during the entire compaction process is predicted. The mechanical response of the superconducting powder was described by the modified Drucker–Prager/cap elastoplastic constitutive model, which was implemented by using explicit finite element techniques. The computational results obtained are presented and discussed, showing good agreement with the experimental work.

Numerical Simulation of Explosive Consolidation of Superconducting Bulk Components

The explosive compaction technique has been used for manufacturing bulk superconducting components, e.g. three dimensional plates and axisymmetric billets, rods, discs and tubes, with high density and good electrical and magnetic characteristics. The high pressures and temperatures developed in a very short time result in sintering and in fracturing of the original grains, inducing primarily line defects that would provide flux pinning centers in Type II superconductors. Densified superconducting ceramic YBCO bulk components of various geometries were produced by this dynamic technique and the whole process was simulated by the explicit finite element code LS-DYNA3D. In this paper, experimental and numerical results of the fabricated superconducting bulks are reported and discussed. Applications are also briefly outlined.

Hot explosive compaction of Mo-Ti alloys

The hot explosive compaction (HEC) technique developed for tungsten-titanium (W-Ti) alloys has been applied to molybdenum-titanium (Mo-Ti) alloys as well. The Mo+Ti powders were mixed and surrounded by an exothermic Ti+C mixture. The TiC reaction, when ignited, released a large amount of heat via a self-propagating high-temperature synthesis (SHS) reaction. Heat from the SHS reaction diffused into the Mo+Ti powder bed, causing the interior temperature to rise above 1500 °C. When the powder bed became isothermal, it was consolidated to high density by pressure waves generated by the detonation of an explosive. The amount of explosive charge and the molar ratio of exothermic mixture to sample were adjusted to produce full-density Mo-Ti alloy billets. The billets were sectioned and examined with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), and microhardness measurements. In the context of the original fabrication process, the evolution of the resultant microstructure of the Mo-Ti product is described.

Hot Explosive Consolidation of Mo-Ti and W-Ti Alloys

A novel hot explosive compaction (HEC) technique has been applied to molybdenum (Mo) and tungsten (W)-based titanium (Ti) alloys. The precursor powders of the alloy billet were surrounded by an exothermic mixture, which, when ignited, released a large amount of heat via a self-propagating high-temperature synthesis (SHS) reaction. Heat from the SHS reaction diffused into the precursor powder bed, causing the interior temperature to rise above 1,500°C. When the powder bed became isothermal, it was consolidated to high density by pressure waves generated by the detonation of an explosive. The amount of explosive charge and the molar ratio of exothermic mixture to sample were adjusted to produce full-density Mo-Ti and W-Ti alloys. The billets were sectioned and examined with scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), x-ray diffraction analysis (XRD), and microhardness measurements. In context of the fabrication process the similarities and differences of the resultant product microstructures are discussed.

Explosive compaction of Nd-Fe-B powder

The explosive compaction technique has been applied to consolidate Nd-Fe-B amorphous powder, and the microstructure and magnetic properties of the compacts have been investigated. Explosive compaction was performed using an improved direct method. Nd-Fe-B amorphous powder was filled in the upper part of a metal sleeve and SiC powder was filled up to a lower part of the powder to suppress a reflection of the shock wave. This sleeve was set at the center of a steel base and shock consolidation was carried out using plastic explosive (SEP) which was set at the top of the amorphous powder. Highly dense compact (>95% relative density) without cracks was obtained by this technique under an optimum condition. A very thin melted layer was observed at the interface of powder particles. The magnetic properties of the compact are Br=8.5 kG, iHc=9.7 kOe, (BH)max=13.2 MOe, and these values are same as those before shock consolidation. Transmission electron microscopy observation reveals that small Nd2Fe14B particles exist inside the powder particle. These results indicate that the microstructure of the original powder is kept after explosive compaction. Since the microstructure inside grain was not changed even after shock consolidation, such excellent magnetic properties were obtained.

Highly-efficient shock-wave diamond synthesis from fullerenes

Shock-wave synthesis of micron-size diamonds from fullerenes C 60–C 150 was performed using the explosive compaction technique with plane shock-wave loading at pressures in the range of 24–40 GPa. The coarsest diamond crystallites were of size up to 6 μm. A modified explosive compaction technique was found with a very high efficiency of diamond synthesis from fullerenes due to intensive shear deformation of samples at shockcompaction. The quantity of recovered diamonds approached 90%. By supplementary modification of the explosive compaction technique, the fullerene constituent was transformed into coarse-grained (up to a few hundred of microns) amorphous diamond which had a hardness which was estimated directly and was found to be higher than that of crystallite diamond.

The effect of heat treatment on explosively compacted (YBaKCuO) superconductive powders

A ceramic powder mixture corresponding to the stoichiometric ratio of YBa 1.95K 0.05Cu 3O y superconducting ceramic with 10% w/w Ag was heat treated at 950°C for 3 h in flowing oxygen. The resultant superconducting powder was consolidated in a silver tube by the explosive compaction technique (pre-heat treated ceramic). The same fabrication technique, i.e. explosive compaction, was employed to the initial stoichiometric powder mixture, without prior heat treatment and the green product was subsequently subjected to a series of heat-treating cycles (920°C, 70 h), in order to obtain the required superconducting properties (post-heat treated ceramic). The microstructure and physical properties of the pre- and post-heat treated ceramics were analyzed and compared using various characterization techniques. X-ray diffraction performed on the pre-heat and post-heat treated ceramics indicated that maximum 123-phase content retained in the former case (pre-heat treated ceramic), whilst DC magnetic susceptibility measurements have shown the characteristic Meissner shielding effect at 99 and 92 K, respectively. Furthermore, the pre-heat treated compacted billet was characterized by a critical current density, J c equal to 2800 A/cm 2 at 77 K after suitable annealing at 850°C for 10 h in oxygen stream.

Shock-wave synthesis of diamonds from fullerenes C60?C100

Shock-wave synthesis of diamond from C60−C100-fullerene powder was first accomplished by using the explosive compaction technique with plane wave loading in the pressure range of 24–40 GPa. The compacts of various initial composition comprised diamond, FCC C60-fullerite, graphite, and amorphous carbon. The largest diamonds of 0.1–1.0 μm were obtained under shock loading of pellets consisting of copper powder with 5 wt. % fullerite at 24 and 38 GPa, and pellets consisting of copper powder with 10 wt. % fullerite at 40 GPa. The end product consists of diamond without intermediate diamondlike phases such as n-diamond and hexagonal diamond (lonsdaleite).

Structural analysis of a TiAl 3 + ZrO 2 particulate composite

The mechanical properties, microstructure and crystallographic structure of TiAl 3 + ZrO 2 particulate composites as well as TiAl 3 without ZrO 2, consolidated by explosive-induced pressuring, were studied. The compacts prepared by the explosive compaction technique were crack free, highly dense and structurally sound. Slight improvements in fracture toughness values of compacts were obtained with ZrO 2 addition and attributed to the presence of the tetragonal form of ZrO 2. Post-shock annealing at 850°C for 4 h retained approximately 12% of the ZrO 2 in the tetragonal form. TiAl 3 exhibited DO 22 structure both in rapidly solidified powder and in the consolidated form.