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(color online) Patterns of fragmentation in the granular composite rings at 50% radial expansion. A previous stage of expansion was presented in Fig. 2 (a), (b), (c), and (d) corresponding to Cases 1-4 respectively. Detailed views of the radial velocity in the granular composite are plotted to show the equilibration of the velocities between the Al and W constituents at this stage of expansion.
Source publication
Numerical simulations of Aluminum (Al) and Tungsten (W) granular composite
rings under various dynamic loading conditions caused by explosive loading were
examined. Three competing mechanisms of fragmentation were observed: a
continuum level mechanism generating large macrocracks described by the
Grady-Kipp fragmentation mechanism, a mesoscale mech...
Context in source publication
Context 1
... initial mesostructure of the Al-W composite used in the simulations is presented in detonation products such that the detonation products directly contacted the Al-W granular composite. Due to the variations in the initial detonation pressures and differences in the subsequent expansion rates, all samples depicted in Fig. 2 and Fig. 3 are compared at the same radial expansion (10% and 50% increase in the initial ...
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Citations
... Si等人 [31] 研究了Zr-Ti-图 3 (网络版彩色)锆基BMG的破碎及反应过程示意图 [17] Figure 3 (Color online) Schematic diagram of the fragmentation and reaction process of Zr-based BMG [17] 评 述 Nb反应合金在高速冲击下的能量释放特性, 证明了该 材料的碎裂行为高度依赖于冲击速度. Olney等人 [32] 对 Al和W颗粒复合环在各种动态加载条件下的爆炸加载 进行了数值模拟, 观察到3种相互竞争的碎裂机制. ...
... [10] discovered that the compressive gas voids generated during the pressing process caused the internal stress to be greater than the crystal cohesive force and formed defects. From 2006 to 2012, Cai and Nesterenko conducted a series of studies on the mechanical properties of Al/PTFE materials and Al/W/PTFE materials, including mechanical and microstructural properties, high strain, strain rate behavior, and failure properties [11][12][13][14], and the effects of the metal particle size on the mechanical properties, strength, failure, and impact of the materials [15][16][17][18]. ...
Metal/polymer reactive materials have been studied and applied in a wide range of ways in recent years. This type of material is insensitive under normal conditions but reacts violently and releases a large amount of chemical energy under high-speed impact or high strain rate loading conditions. Compared with conventional explosives, it has better mechanical properties, and its unit mass energy is several times that of TNT. In this paper, PTFE/Al/CuO reactive materials are the main research objects, and we assess the impact energy release abilities of this type of reactive material through experimental research. To this end, eight sets of material formulations are designed, and the effects of particle size, the ratio of PTFE/Al and Al/CuO materials, and sintering on the energy release ability of the reactive materials are investigated. All experiments are carried out based on a self-designed new energy release testing device. The experimental device can measure the pressure time history curve generated by the reactive materials, and the rationality of the pressure time history curve can also be verified by the displacement time curve of the piston. The results show that with an increase in the Al/CuO thermite content, the energy release rate of the reactive material clearly increases, which is attributed to the reaction threshold of Al/CuO being low and because the heat generated can promote the reaction of PTFE/Al. The energy release rate of the nano-scale reactive materials is higher than that of the micron-scale reactive materials because the reduction in particle size results in a larger specific surface area. Thus, the energy required for ignition is lower. The energy release rate of sintered reactive materials is higher than that of unsintered reactive materials, which can be explained by the interfacial area between Al particles and PTFE particles in sintered reactive materials being larger, which makes the reaction more sufficient. The self-designed energy release testing device for the reactive materials and the conclusions obtained in this paper have clear significance for guiding engineering applications.
... Powder metallurgy methods have shown the potential to provide reactive materials with structural properties that are similar to traditional engineering materials. Recent research has focused on understanding links between composition, microstructure, fragmentation response, and initiation sensitivity [e.g., 1,2,3,4]. The overall goal of the work presented here was to further elucidate links between the dynamic fragmentation response and the specimen composition and processing parameters using novel diagnostics. ...
The dynamic failure and fragmentation response of pressed metallic composites is investigated experimentally using a Kolsky bar and explosive loading. The composites are made of nominally brittle (tungsten) and ductile (aluminum) metal phases, in varying ratios, to explore the effect of composition on the material fragmentation behavior. Dynamic compression experiments at strain rates ∼2000 s⁻¹ are conducted on a Kolsky bar to apply controlled uniaxial deformation. High-speed images captured during the dynamic loading provide insight to the nature of the failure mechanisms activated (e.g. brittle vs. ductile fragmentation). Explosively-driven fragmentation experiments are conducted in a shock tunnel to investigate the fragmentation behavior under shock loading which produces higher rates and induces spall failure. These experiments incorporate high-speed schlieren imaging to track the explosively driven shock and resulting fragments as they travel down range. The high-speed images from both experimental setups are correlated with postmortem measurements of the resulting fragment size distributions, providing connections between the composition and fragmentation behavior.
... The most studied of these reactive materials are Al-based composite such as Al/Ni and Al/W owing to their high strength, high energy density, easy processing characteristics and rapid energy release properties. [5][6][7][8][9][10][11][12] To improve their intercept efficiency, some high density reactive fragments have been proposed as alternatives to traditional steel fragments of anti-air warheads. For instance, tungsten/zirconium (W/Zr) composites have enough mechanical strength to maintain stability under overload during warhead detonation, and can penetrate targets and rapidly react. ...
The dynamic compressive behavior of a hot pressed tungsten/zirconium (W/Zr) composite with a mass proportion of 34:64 (W:Zr) was experimentally investigated using a split Hopkinson pressure bar and a high-speed camera. The W/Zr composite has high strength but some brittle characteristics; when subjected to a strong enough impact loading, the sample is crushed, rapidly releasing high amounts of energy as a result. This impact-initiated reaction depends on the loading conditions, where a higher loading strain rate resulting a smaller fragment size. The Zr phase is involved in the reaction as the active component of the composite, and these fragments can be divided into small, medium, and large fragments with their reactions labeled as “fire ball,” “spark,” and “no react” respectively. A simple model is constructed to analyze the heat generated during plastic deformation based on yield stress, crack speed and the thermal properties of the brittle material. Our proposed model’s prediction of temperature increase at initiation may reach several hundred degrees Celsius.
... W particles and fibers reinforced AMCs were cold pressed and their dynamic behavior was investigated numerically and experimentally. [20][21][22][23] Because of the large difference in strength between Al and W, Al particles can be heavily deformed by the W reinforcement in the high strain, high strain rate plastic flow. A unique fracture pattern in Al/W composites characterized by Al pulverization was presented in numerical calculations due to the difference of strength and inertial properties of W and Al. ...
... A unique fracture pattern in Al/W composites characterized by Al pulverization was presented in numerical calculations due to the difference of strength and inertial properties of W and Al. 22,23 In this article, high density and high strength Al-W fiber composites in the tubular shape with highly ordered W fiber in axial and hoop directions were processed in the solid state. The combined cold isostatic pressing (CIPing)/hot isostatic pressing (HIPing) processing procedure allowed achieving the solid density and high strength of composites, preventing the fragmentation of W fibers, preserving the periodic arrangement of W fibers in tubular shapes, and preventing significant reactions between W and Al. ...
Novel high-density aluminum (Al)-tungsten (W) fiber composites in the tubular shape with highly ordered tungsten fibers in axial and hoop directions were processed in the solid state using the combination of cold isostatic pressing and hot isostatic pressing. Half of the specimens were additionally heat treated after hot isostatic pressing to regain the properties of aluminum 6061-T6. The strength of both types of samples was investigated under quasistatic compression. Samples after additional heat treatment had the higher microhardness of matrix and compressive strength. No significant reaction between tungsten fibers and aluminum matrix was detected. The micromechanism of samples failure under compression was revealed by removing the aluminum matrix after tests with acid-etching demonstrating that tungsten fibers oriented in the axial direction were deformed by microbuckling and kinking. The sample bulging due to plastic flow of aluminum matrix resulted in the cooperative fracture of tungsten fibers in the hoop direction.
... Explosively loaded homogeneous materials (such as standard engineering metals like aluminum and steels) demonstrate that the characteristic size of the fragments is much larger (of the order 1-10 mm) due to the nature of the fragmentation mechanisms of homogeneous materials [4,5]. Using a highly heterogeneous material composed of components with drastically different densities and shock impedances (e.g., Al and W) can provide enhanced pulverization due to the addition of mesoscale fragmentation mechanisms [6,7]. In this research, Al-W granular/porous composite rings with different mesostructures were prepared and tested in explosively driven expanding ring experiments. ...
... Since the experimental samples showed no bonding (particles in the samples were held together due to bonding was introduced in numerical simulations and the Cook constitutive model [9] parameters were taken from the that the detonation was instantaneous in than the velocity of expansion. The initial pressures/energies of the similar to [6]. The the free surface velocity of the expanding ring from Differences in the initial 3 microseconds due to the geometry of the experimental setup allowing additional ...
Highly heterogeneous materials comprised of elements with drastically different densities and shock impedances (e.g., Al and W) may provide additional mesoscale fragmentation mechanisms reducing the characteristic fragment size in comparison with solid materials with similar density (e.g., Stainless Steel 304). Explosively driven expanding ring experiments were conducted with Al-W granular composite rings, processed using hot and cold isostatic pressing, with different morphologies (W polyhedral particles or W rods with high aspect ratio and bonded/unbonded Al spherical particles with different sizes). In comparison to homogeneous samples with a similar density, these granular/porous composites generated fragments with a significantly smaller characteristic size. Scanning Electron Microscopy revealed that fragments had a propensity to be composed of clustered Al and W particles. Finite element simulations were conducted to gain an insight into the mesoscale fragmentation mechanisms and the clustering behavior observed in the experiments. Understanding the mesoscale mechanisms of explosively driven pulverization is important for tailoring the size of the fragments through the alteration of mesostructural properties.
Architected lattices are gaining prominence for structural applications as additive manufacturing technologies mature. Emergent behavior, such as material jetting and wave propagation, arising from the open architecture has been observed under dynamic loading conditions. The origin of the observed jetting and how it might come about across a broad spectrum of lattice types, material compositions, length scales, and dynamic loading conditions is still an open question. The jetting behavior due to lattice structures was studied through a series of dynamic compression plate impact experiments with in situ x-ray imaging. The role of the impact conditions, the lattice spacing, the lattice architecture, and the lattice base material is explored in the context of promoting or suppressing jet formation. A transition from lattice-led to impactor-led jetting is observed above a certain impact threshold. Complementary direct numerical simulations were also performed to compare with the experiments, to study the underlying stress state giving rise to jetting, and to provide insight into conditions not accessed experimentally. We present a geometric argument on the competitive process leading to lattice and/or impactor jetting which incorporates base material properties, the periodicity of the lattice, and basic tunable length scales of the lattice. Using two-dimensional calculations, we further look at how tuning of a single parameter of the studied systems changes the observed jetting transition.
Three different batches of tungsten-zirconium (W-Zr) reactive material were prepared by hot-pressing elemental powder mixtures. The first sample had a Zr:W mass ratio of 66:34. The second used zirconium hydride (ZrH2) with a (ZrH2):W mass ratio of 66:34. The third had a Zr:W mass ratio 43:57. These batches were numbered #1 to #3. To investigate the mechanical properties of the W-Zr reactive materials, samples were subjected to different strain rates using a materials testing machine and a modified split Hopkinson pressure bar (SHPB). The quasi-static compressive strengths of the three sample batches all exceeded 1022 MPa, with batch #1 sample having the highest value at about 1880 MPa. This could be ascribed to the sample exhibiting a more transgranular and dimpled fracture in the W2Zr intermetallic phase, as demonstrated by the microstructure of the fracture surface, observed by scanning electron microscopy (SEM) using an energy-dispersive spectrometer (EDS). To perform a constant strain rate experiment on this high-strength but brittle material, ramp loading using copper sheet was adopted in this study. All of the samples produced strong, bright flames when subjected to shock loading and exhibited a high compressive strength of approximately 1060 to 2690 MPa. High-resolution X-ray diffraction (XRD) was performed on the original samples and residues after the SHPB test, showing that the Zr and ZrC phases of the batch #1 and batch #3 samples, and the ZrC0.32H1.2 phase of the batch #2 sample are the active components in the reaction with air. Some small balls of ZrO2 reaction product were found not to exhibit any crystalline tungsten oxide on the residue surface. These results suggest that the batch #1 reactive material has huge potential to take the place of inert steel because of its high strength and high energy level, as well as having a density close to that of steel.
