Papers by Keyword: Fragmentation

Abstract: This work presents the results of experimental investigations into deformation relief formed at the faces of aluminium single crystals. The aim of the investigations was to define the rules of macro fragmentation and macro localisation processes in plastic deformation. It was established that for the families of maximum loaded planes {111} in the aluminium single crystals, one can differentiate volumes which aren't limited to the specimen's front face. It is assumed that shearing in these volumes is eased during plastic deformation due to the absence of a reverse stress. Moreover, it is suggested that such volumes are called volumes of eased slip (VES). In addition to this, the role played by the volume of eased slip at the macroscopic level during the plastic deformation process was examined.

Abstract: The evolution of the dislocation structure and the ensemble of boundaries during plastic deformation of Zr-Nb alloys studied using electron microscope. The role of the anisotropy of slip in the formation and restructuring of the boundaries, recurrence of dislocation transformation was established. Special emphasis is placed on specific features of geometrically necessary defects evolution. It was found that the geometrically necessary boundaries formation involves an athermal coalescence as a mechanism of relaxation of large accumulated internal stresses, which prevents fracture in an anisotropic polycrystalline material.

Abstract: This paper introduces an innovative solution for devising a robust blasting plan that will present consistently good fragmentation performance under highly uncertain environments. The analysis will be carried out using complexity analysis tools, a model-free approach to complex systems which is particularly well suited to the problem of finding non-deterministic dependencies between multiple variables. The study is backed-up by data from over 2,000 blast records from Brazilian mines and identifies what are the critical aspects of the system and how to manage the blasting plan to reduce their impact on its performance.

Abstract: A new experimental technology based on the Split Hopkinson Pressure Bar (SHPB) is developed for conducting expanding ring tests. The technique is useful for the studies of the dynamic tensile deformation and the fracture (fragmentation) properties of ductile metallic materials. The loading fixture includes a hydraulic cylinder filled with the incompressible fluid, which is pushed by a piston connected to the input bar. As the liquid is driven, it transfers the pressure to the specimen, compressing and expanding the metallic ring specimen in the radial direction. The approximately incompressible property of the liquid makes it possible to transfer a relatively low piston-driving velocity to a very high radial-expansion velocity of the specimen, as the sectional area of the cylinder narrows significantly. Using this experimental technology the ring specimens made of LY12 aluminum alloy were dynamically expanded and fragmentized. Results show apparent increases of the fragment numbers and fracture strain of the specimen with the increase of the impact velocity. The recovered ring fragments were examined and measured to obtain the average fragment sizes (lengths) during each test. These fragment sizes were compared with the estimates from the classical fragmentation theory that was initiated by N.F. Mott and later developed by D.E. Grady. It was found that the Mott-Grady theory provides reasonably good predictions of the fragment sizes for ductile materials. This conclusion agrees with the recent findings of ours based on the numerical simulations and physical arguments.

Abstract: This paper reported the fragmentation behavior of lignite coal particles during coal pyrolysis in fluidized bed reactor at temperature of 300°C,350°C,600°C,650°C. The particles with size of 2-4mm,4-6mm and 7-10mm pyrolyzed under N₂ atmosphere. The fragments were recovered by hopper, cooled to the ambient temperature and sieved in different ranks. Experimental results show that with the increasing of temperature and initial coal size due to internal overpressure induced by volatiles releasing and thermal stress caused by thermal gradient of coal intra-particles the intensity of fragmentation was enhanced monotonously, the number of fragments increased sharply and the average size of fragments declined.

Abstract: In the frame of ESA-MAP (Microgravity Application Promotion) project entitled XRMON (In situ X-Ray MONitoring of advanced metallurgical processes under microgravity and terrestrial conditions), a microgravity (μg) experiment in the XRMON-GF (Gradient Furnace) setup was successfully launched in 2012 on board MASER 12 sounding rocket. During this experiment, in situ and real time observations of the formation of the solidification microstructures in diffusive conditions were carried out for the first time by using X-ray radiography. In addition, two reference experiments with the same control parameters but in ground-based conditions were performed to enable us a direct comparison with the μg experiment and therefore to enlighten the effects of gravity upon microstructure formation. This communication reports on fragmentation phenomenon observed during those experiments. For 1g upward solidification, fragmentations mainly take place in the upper part of the mushy zone. After their detachments, dendrite fragments are carried away by buoyancy force in the bulk liquid where they are gradually remelted. For μg experiment and horizontal solidification, this type of fragmentation is not observed. However, a great number of fragmentations are surprisingly revealed by in situ observation in the deep part of the mushy zone, when the liquid fraction is very small. Moreover, as soon as they are detached, the dendrite fragments move toward the cold part of the mushy zone, even in the case of μg experiment. The observations suggest that sample shrinkage may be at the origin of this fragment motion.

Abstract: Replication in distributed database is the process of copying and maintaining database objects in multiple databases that make up a distributed database system. In this paper, we will manage fragmented database replication and transaction management for Malaysian Greater Research Network (MyGRANTS) using a new proposed algorithm called Binary Vote Assignment on Cloud Quorum (BVACQ). This technique will combine replication and fragmentation. Fragmentation in distributed database is very useful in terms of usage, efficiency, parallelism and also for security. This strategy will partition the database into disjoint fragments. The result shows that managing replication and transaction through proposed BVACQ able to preserve data consistency. It also increases the degrees of parallelism. This is because by using fragmentation, replication and transaction can be divided into several subqueries that operate on the fragments.

Abstract: Copper single crystals grown according to the Bridgman method and having their axes [] or [11 aligned with the normal load axis were processed by dry sliding. As shown, sliding-induced severe plastic deformation occurred in the subsurface of single crystals and caused formation of a lip by mechanism of texture formation. The SEM structure of this lip was found to be composed of fragments with their shapes dependent on the single crystal orientation with respect to normal load and friction force.

Abstract: We study the impact fragmentation of two-and three-dimensional disordered solids in a discrete element model of heterogeneous brittle materials focusing on the spatial distribution and mass-velocity correlation of fragments. Our calculations revealed that depending on the energy of impact the breakup process can have two different outcomes: at low impact energy the sample gets damaged, however, to achieve fragmentation the imparted energy has to surpass a critical value. Based on large scale computer simulations we show that the position of fragments inside the original body with respect to the impact site determines their mass and velocity in the final state. A novel relation of the mass and velocity of fragments is revealed: In the damage phase the mass and velocity of fragments are strongly correlated, however, in the fragmented phase correlation emerge solely for large fragments. The correlation function decays as a power law with a universal exponent in an excellent agreement with recent experimental findings.

Abstract: We present a theoretical study of the fracture of two-dimensional disc-shaped samples due to projectile penetration focusing on the geometrical structure of the crack pattern. The penetration of a cone is simulated into a plate of circular shape using a discrete element model of heterogeneous brittle materials varying the speed of penetration in a broad range. As the cone penetrates a destroyed zone is created from which cracks run to the external boundary of the plate. Computer simulations revealed that in the low speed limit of loading two cracks are generated with nearly straight shape. Increasing the penetration speed the crack pattern remains regular, however, both the number of cracks and their fractal dimension increases. High speed penetration gives rise to a crack network such that the sample gets fragmented into a large number of pieces. We give a quantitative analysis of the evolution of the system from simple cracking through fractal cracks to fragmentation with a connected crack network.