Effect of explosive contact and non-contact shock-processing on structure, microstructure and mechanical characteristics of aluminum (original) (raw)
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Fracture of explosively compacted aluminum particles in a cylinder
SHOCK COMPRESSION OF CONDENSED MATTER - 2015: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter, 2017
The explosive compaction, fracture and dispersal of aluminum particles contained within a cylinder were investigated experimentally and computationally. The aluminum particles surrounded a central, cylindrical high explosive burster charge and were weakly confined in a cardboard tube. The compaction and fracture of the particles were visualized with flash radiography and the subsequent fragment dispersal was recorded with high-speed photography. The aluminum fragments produced were much larger than the original aluminum particles and similar in shape to those generated from the explosive fracture of a solid ductile metal cylinder, suggesting that the shock transmitted into the aluminum compacted the powder to near solid density. The presence of a casing on the burster explosive had little influence on the fragmentation behavior. The effect of an air gap between the burster and the aluminum particles was also investigated. The expansion and fracture of the aluminum were compared with the predictions of a multi-material hydrocode which indicated that the first appearance of cracks through the compacted aluminum layer occurred approximately when the release wave reached the inner surface of the compacted powder.
Study of the conditions of fracture at explosive compaction of powders
Frattura ed Integrita Strutturale, 2013
Joint theoretical and experimental investigations have allowed to realize an approach with use of mathematical and physical modeling of processes of a shock wave loading of powder materials. In order to gain a better insight into the effect of loading conditions and, in particular, to study the effect of detonation velocity, explosive thickness, and explosion pressure on the properties of the final sample, we numerically solved the problem about powder compaction in the axisymmetric case. The performed analysis shows that an increase in the decay time of the pressure applied to the sample due to an increase of the explosive thickness or the external loading causes no shrinkage of the destructed region at a fixed propagation velocity of the detonation wave. Simultaneously, a decrease in the propagation velocity of the detonation wave results in an appreciable shrinkage of this region.
Study of the conditions of fracture at explosive compaction of powders.PDF
Joint theoretical and experimental investigations have allowed to realize an approach with use of mathematical and physical modeling of processes of a shock wave loading of powder materials. In order to gain a better insight into the effect of loading conditions and, in particular, to study the effect of detonation velocity, explosive thickness, and explosion pressure on the properties of the final sample, we numerically solved the problem about powder compaction in the axisymmetric case. The performed analysis shows that an increase in the decay time of the pressure applied to the sample due to an increase of the explosive thickness or the external loading causes no shrinkage of the destructed region at a fixed propagation velocity of the detonation wave. Simultaneously, a decrease in the propagation velocity of the detonation wave results in an appreciable shrinkage of this region.
The Fragmentation of Al-W Granular Composites Under Explosive Loading
MRS Proceedings, 2013
ABSTRACTSmall scale explosively driven fragmentation experiments have been performed on Aluminum (Al)-Tungsten (W) granular composite rings processed using cold isostatic compression of Al and W powders with a particle size of 4-30 microns. Fragments collected from the experiments had a maximum size of the order of a few hundred micrometers. This is a dramatic reduction in the fragment size when compared to the 1-10 mm typical for a homogeneous material such as solid aluminum under similar loading conditions. Numerical simulations of the experiment were performed to elucidate the mechanisms of fragmentation that were responsible for this shift in fragmentation size scales. Simulations were performed with a significantly stronger explosive driver to examine how the mechanisms of fragmentation change when the detonation pressure increases.
2017
Flammable gases or vapors air mixtures generally tend to occupy the entire available volume being quasi stable systems. In contrast, the suspension of dust in air is a heterogenous unstable system, wherein the dust solid particles are deposited in time, depending on their weight. The explosive behavior which is represented by a mixture of air and flammable substances is influenced by many factors of which the most important parameters are the chemical composition and concentration of flammable and explosive mixture with air. In particular, for the combustible powders, additional factors are intervening, related to the physico-chemical properties of combustible solids, the shape and size of dust particles, as well as the environmental conditions under which dust exist in suspension. For this work were performed experimental determination of the explosion and combustible parameters specific for aluminum powder derived from technological processes, as waste, being analyzed both influen...
Aps Shock Compression of Condensed Matter Meeting Abstracts, 2009
A double-tube implosion geometry is used to explosively shock consolidate Ni-Al, Ta-Al, Nb-Al, Mo-Al and W-Al powder mixtures for fabricating bulk structure energetic materials, with both mechanical strength and the ability to undergo impact-initiated exothermic reactions. The shock consolidated compacts are characterized based on the uniformity of the microstructure including degree of densification and variation in constituent volume fraction as a function of the axial and longitudinal dimensions of the compacts. Near full density compacts are achieved with minor variations in mixing of constituents, and no evidence of intermetallic reaction taking place during compaction. Differential thermal analysis was performed to determine the thermal reactivity of the compacts and compare with that of unshocked statically-pressed powder compacts. The dynamic mechanical properties of the compacts are characterized using the split-Hopkinson bar, and the reactivity under impact loading was determine using rod-on-anvil experiments.
Metallurgical Transactions A, 1992
Different approaches to compact cylinders of titanium aluminide powders by explosively generated shock waves were explored. Two basic compositions of the titanium aluminide powders produced by the rapid solidification rate (RSR) technique were used: Ti-21 wt pct Nb-14 wt pct A1 and Ti-30.9 wt pct A1-14.2 wt pct Nb. A double-tube design utilizing a flyer tube was used in all experiments. Experimental parameters that were varied were initial temperature, explosive quantity, and explosive detonation velocity. The major problem encountered with shock consolidation of titanium aluminides was cracking. Titanium aluminide powders were also mechanically blended with niobium powders in one case and elemental mixtures of aluminum and titanium powders in the other case. Enhanced bonding and decreased cracking were observed in both cases. In the former case, the addition of niobium powder provided a ductile binder medium which assisted in consolidation. In the latter case, due to the additional heat generated and melting produced by the shock-induced reactions between Ti and A1, significant improvements in bonding of the titanium aluminide powders were observed.
Dynamic stress-strain response of high-energy ball milled aluminium powder compacts
Mechanics of Materials, 2020
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Fragmentation and constitutive response of tailored mesostructured aluminum compacts
Journal of Applied Physics, 2016
The fragmentation and constitutive response of aluminum-based compacts was examined under dynamic conditions using mesostructured powder compacts in which the interfaces between the powders (sizes of 40, 100, and 400 μm) were tailored during the swaging fabrication process. Fragmentation was induced in ring samples of this material through explosive loading and was examined through high speed photography, laser interferometry and soft capture of fragments. Fragment velocities of around 100 m/s were recorded. The fragment mass distributions obtained correlated in general with the interfacial strength of the compacts as well as with powder size. Experimental results are compared with fragmentation theories to characterize the behavior of reactive powders based on the material's mesostructure by introducing the fracture toughness of the compacts. The mean fragment size is calculated using a modified form of Mott's theory and successfully compared with experimental results.
Effect of stress state and microstructural parameters on impact damage of alumina-based ceramics
Journal of Materials Science, 1989
Alumina discs of two grain sizes (4 and 24#m), and three compositions (99.4% purity, 85% purity, alumina + partially stabilized zirconia) were subjected to planar normal impact in a gas gun at a nominal pressure of 4.6 GPa. The alumina discs were confined in copper and aluminium capsules, which provided solely compressive and compressive plus tensile pulses in the ceramic, respectively. These experiments were conducted at different pulse durations (controlled by the thickness of the flyer plates). The surface area of cracks per unit volume was measured in order to estimate the impact damage. Compression followed by tension produced significantly more damage than compression alone. The small grain-sized discs exhibited more damage than the large grain-sized discs. The amount of damage increased with the duration of the tensile stress pulse. The addition of partially stabilized zirconia (~ 14%) did not enhance the resistance to fragmentation of the discs; X-ray diffraction did not reveal an impact-induced phase transformation. Although the pressures generated were below the Hugoniot elastic limit of alumina, considerable fracturing of the specimens took place. Scanning electron microscopy revealed that the fracture was intercrystalline in regions away from the spall plane. In the spall plane energy was sufficient to comminute the grains, producing considerable grain debris and transgranular fracture. Transmission electron microscopy revealed the onset of damage to the structure, in the form of dislocations (present in only a small fraction of grains), microcracks nucleating at voids, and intergranular microcracks.