a 00 -Fe 16 N 2 has been suggested as a promising candidate for future rare-earth-free magnets. In this paper, a unique technical route including a ball milling approach and shock compaction is experimentally demonstrated as a promising way to produce an a 00 -Fe 16 N 2 magnet. Firstly, a 00 -Fe 16 N 2 powder is prepared by ball milling, in which ammonium nitrate (NH 4 NO 3 ) is adopted as a solid nitrogen source. The volume ratio of the a 00 -Fe 16 N 2 phase reaches 70% after 60 h of milling with a ball mill rotation speed of 600 rpm in planetary mode. Its saturation magnetization (M s ) is 210 emu g -1 and the coercivity is 854 Oe at room temperature. After ball milling, shock compaction is used to compact the milled powder sample into a bulk magnet. Its magnetic properties and crystalline structure are characterized. Overall, the ball milling-based approach can be used to prepare a 00 -Fe 16 N 2 magnets at an industrial production level.
Exchange-coupled R 2 Fe 14 B/␣-Fe (RϭNd or Pr͒ nanocomposite bulk magnets with nearly full density have been successfully produced by shock compaction of melt-spun powders. X-ray diffraction and transmission electronic microscopy analyses of the shock-consolidated compacts showed no grain growth upon compaction, in fact, a decrease in the crystallite size of both the hard and soft phases was observed. As a consequence, magnetic properties were retained and even improved after compaction. Hysteresis loops of the shock-consolidated powder compacts showed a smooth single-phaselike behavior, indicating effective exchange coupling between hard and soft magnetic phases.
The spall properties of rolled Al 5083-H116 plate are investigated using symmetric plate impact experiments over the stress range 1.5–6.2 GPa. Rear free surface velocity measurements made employing Velocity Interferometer System for Any Reflector interferometry reveal velocity profiles with clear signals of the Hugoniot elastic limit (HEL) and velocity pullback, indicative of a transition from elastic to plastic behavior and spalling. Experiments were performed on samples obtained both through the thickness and along all of the three principal axes of the rolled plate. For impact through the thickness, the average values of the HEL and spall strength are 0.43 GPa and 0.81 GPa, respectively. Decreasing the flyer plate and sample thicknesses resulted in an increased spall strength value of 0.95 GPa, while the HEL remained the same. The spall strength along the longitudinal (rolling) direction was 1.06 GPa versus 0.95 GPa for impact along either transverse direction. Spall damage for this impact direction often propagated away from the spall plane in the direction of impact and along the grain boundaries. For impact through the thickness, the fracture surface revealed a mixed mode of ductile and intergranular fracture that was not present for the fracture surface in the other two directions. This mixed fracture mode seems to correspond to a shoulder observed in the free surface velocity traces after the pullback. In all cases, cracked brittle inclusions were observed near the spall damage regions, indicating their role in nucleating voids during spall failure.
The chiral auxetic cellular structures are fabricated using SEBM (selective electron beam melting) method and tested under compressive loading. The results of experimental testing are used for validation of the computational model in LS-DYNA. Furthermore, ballistic velocity and deformation behaviour of monolithic aluminium (Al 7075-T651) and titanium (Ti-Gr.37) cover plates of composite sandwich panels are experimentally evaluated using a gas gun setup and fragment simulating projectile (FSP). The experimental results are used for validation of computational model of cover plates, which is further used for development of computational model of auxetic composite sandwich panel. It is shown that by using the auxetic sandwich panel, the ballistic performance is enhanced in comparison to the monolithic cover plates.
The effect of grain size and moisture content on the dynamic macroscopic response of granular geological materials was explored by performing uniaxial planar impact experiments on high purity, Oklahoma #1, sand samples composed of either fine (75–150 μm) or coarse (425–500 μm) grain sizes in either dry or fully water-saturated conditions. Oklahoma #1 sand was chosen for its smooth, quasi-spherical grain shapes, narrow grain size distributions, and nearly pure SiO2 composition (99.8 wt. %). The water-saturated samples were completely saturated ensuring a two-phase mixture with roughly 65% sand and 35% water. Sand samples were dynamically loaded to pressures between 1 and 11 GPa. Three-dimensional meso-scale simulations using an Eulerian hydrocode, CTH, were created to model the response of each sand sample. Multi-phase equations of state were used for both silicon dioxide, which comprised individual sand grains, and water, which surrounded individual grains. Particle velocity profiles measured from the rear surface of the sand, both experimentally and computationally, reveal that fine grain samples have steeper rise characteristics than coarse grain samples and water-saturated samples have an overall much stiffer response than dry samples. The experimentally determined particle velocity vs. shock velocity response of dry sand was linear over this pressure range, with little difference between the two grain sizes investigated. The experimental response for the water saturated sand exhibited a piecewise continuous response with a transition region between particle velocities of 0.6 km s−1 and 0.8 km s−1 and a pressure of 4.5–6 GPa. Hypotheses for the cause of this transition region are drawn based on results of the meso-scale simulations.
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