Dynamic Breakage Research Articles

Ionic supramolecular bonds preserve mechanical properties and enable synergetic performance at high humidity in water-borne, self-assembled nacre-mimetics

Although tremendous effort has been focused on enhancing the mechanical properties of nacre-mimetic materials, conservation of high stiffness and strength against hydration-induced decay of mechanical properties at high humidity remains a fundamental challenge in such water-borne high-performance materials. Herein, we demonstrate that ionic supramolecular bonds, introduced by infiltration of divalent Cu(2+) ions, allow efficient stabilization of the mechanical properties of self-assembled water-borne nacre-mimetics based on sustainable sodium carboxymethylcellulose (Na(+)CMC) and natural sodium montmorillonite nanoclay (Na(+)MTM) against high humidity (95% RH). The mechanical properties in the highly hydrated state (Young's modulus up to 13.5 GPa and tensile strength up to 125 MPa) are in fact comparable to a range of non-crosslinked nacre-mimetic materials in the dry state. Moreover, the Cu(2+)-treated nacre-inspired materials display synergetic mechanical properties as found in a simultaneous improvement of stiffness, strength and toughness, as compared to the pristine material. Significant inelastic deformation takes place considering the highly reinforced state. This contrasts the typical behaviour of tight, covalent crosslinks and is suggested to originate from a sacrificial, dynamic breakage and rebinding of transient supramolecular ionic bonds. Considering easy access to a large range of ionic interactions and alteration of counter-ion charge via external stimuli, we foresee responsive and adaptive mechanical properties in highly reinforced and stiff bio-inspired bulk nanocomposites and in other bio-inspired materials, e.g. nanocellulose papers and peptide-based materials.

Dynamic gap generation in graphene monolayer

The possible development of instability in the gapless state of graphene monolayer due to the dynamic breakage of symmetry as a result of the electron-phonon interaction is considered.

Sertoli cell vacuolization and abnormal germ cell adhesion in mice deficient in an inositol polyphosphate 5-phosphatase.

The dynamic nature of cellular interactions during differentiation of germ cells and their translocation from the basement membrane to the lumen of the seminiferous tubules requires the existence of complex and well-regulated cellular adhesion mechanisms in the testis. Successful migration of the developing germ cells is characterized by dynamic breakage and reformation of cadherin-containing adherens junctions between the germ cells and Sertoli cells, the polarized somatic cells of the testis that support and nourish the developing gametes. Here, we demonstrate the accumulation of abnormally swollen, actin-coated, endosome-like structures that contain intact adherens junctions and stain positive for N-cadherin and beta-catenin in the Sertoli cell cytosol of mice deficient in Inpp5b, an inositol polyphosphate 5-phosphatase. Simultaneous to the formation of these abnormal structures, developing germ cells are prematurely released from the seminiferous epithelium and sloughed into the epididymis. Our results demonstrate a role for Inpp5b in the regulation of cell adhesion in the testis and in the formation of junctional complexes with neighboring cells, and they emphasize the important and essential role of phosphoinositides in spermatogenesis.

Theoretical analysis of the steady state particle size distribution in limited breakage processes

The steady state particle size distribution is examined, resulting from a breakage process with a maximum stable size and a homogeneous continuous kernel. The dynamic breakage problem is transformed into one that allows direct solutions for the steady state distribution. The latter depends on the breakage kernel and on the ratio of critical to initial size. As this ratio goes to zero the steady state distribution approaches its limiting form obtained by the authors previously [7]. A general theoretical analysis concerning the steady state distribution is presented herein. The asymptotic behaviour is determined with regard to various limits. Perturbation analysis for nearly uniform kernels reveals several interesting features of the problem. For the general continuous kernel, the problem can be cast in a matrix form amenable to a conventional theoretical treatment. Finally, comparisons of the new results with existing solutions of the dynamic problem, for large times, confirm their validity.

Probabilistic-kinetic model of dynamic deformation and breakage of fissured hard rocks. part 3: computer implementation

Probabilistic-kinetic model of dynamic deformation and breakage of fissured hard rocks. part 3: computer implementation

Extraction operations in the “Oktyabr” mine

The bed of continuous ores has a benchlike structure due to the development of shearfault tectonics. The faulting consists of level and straight or slightly curved planes of slip. In some parts there are zones of increased jointing. Their thickness is 1-5 m. The azimuths of the strike of the faulting are 110-190 = , and the dips 60-90 = . Within the worked field of the Oktyabr' mine, except in the zones of intensive jointing, the continuous sulfide ores are regarded as only slightly faulted: The mean block dimension is 25 cm. During the construction of the Oktyabr' mine there were cases of dynamic breakage of the rock in workings driven near the periphery in metamorphosed argillites and marls. In the continuous ores during the first stage of development of the mine, the operations were accompanied by large-scale dynamic falls of the roof and sides in the form of flaking, intensive slip, bursts, and sudden caving, due to the high state of stress of the rocks. Using the method of complete stress relaxation, we investigated the state of stress of the rock: We found that the horizontal stresses average 400-600 kg/cm 2 and the vertical ones 200-300 kg/cm 2. The o~ientation of the stress components agrees with the tectonic deformations of the rocks. The minimum horizontal components are parallel to the tectonic faulting, and the maximum ones are normal to it. The nonuniformity of the stress field is due to the tectonics and to the mechanical properties of the rocks. We investigated the variation of the state of stress of the rock round a working, using complete load relaxation, insertion of an indentor into the face and walls of a borehole, electrometry, disk cores, and drillholes; we found that the zone of maximum stresses lies 0.5 to 3-4 m from the periphery of the working. The cause of dynamic breakage in the potentially shock-prone rocks is that near the periphery of the workings there are zones of high stress which reach or exceed the strength under uniaxial compression.

Continuous grinding in a small wet rod mill Part II. Breakage of some common ore minerals

A study has been made of the breakage of galena, marmatite, chalcopyrite and quartz, separately, in a calcite environment in a rod mill. The behaviour of all may be described by the same basic dynamic breakage model, which involves a breakage function, a rate function and a distribution of residence time function. The same breakage and distribution of residence time functions applied to all the minerals but the mean residence times decreased in the order galena > marmatite > chalcopyrite > quartz. Size for size, the values of the rate of breakage constants followed the same sequence.

Mechanism of Rock Breakage under Pressure of Gas Explosion

It is believed that rock breakage by blasting is normally completed both by the dynamic breakage under intense stress waves, and by the quasi-static breakage under the pressure of gas explosion. First in this study the stress condition caused by the time dependent pressure in an elastic medium was computed from time to time as it worked on the spherical cavity, and thereby were inferred what were the stresses in the medium that were affected by the variation of the rise time of the pressure in the cavity. It is concluded that the values of the dynamic stresses in the medium caused by the stress wave decrease with increase of the rise time of the pressure, and that the stress condition in the medium is controlled by the quasi-static stress caused by the pressure in the cavity. It is considered therefore that the breakage of rocks caused by the explosion of the explosives having low velocity of defragration is completed chiefly by the quasi-static pressure of the gas explosion.Next the stress condition caused by the quasi-static pressure was analyzed by using the finite element method as it worked on the circular boreholes, assuming the cases in which the boreholes ranged linearly with constant spacing of 10a, where a was the radius of the hole. At first pressure was applied to every other borehole, and the stress condition around the hole where no pressure was applied was carefully observed, and then the pressure was applied to every hole, and probable change in the stress distribution was studied upon the assumed growth of four radial cracks that would be originated from the inner surfaces of the holes, as two cracks grew along the line which connected the centre of each hole, and two other cracks grew along the line perpendicular to the above. These cracks are supposed to have been produced from the inner surface of each hole when the value of the pressure exceeds the tensile strength of the material. It is clarified as the result that the cracks along the line which connects the centre of each hole will grow further while those which grow perpendicular to the above are repressed. By comparing the results of these stress analyses with the strain measured in the material and the pattern of the crack produced actually by the pressure of the gas explosion, it is concluded finally that the quasi-static gas pressure contributes very much to the completion of smooth wall in the smooth blasting operation.

Measurement of Dynamic Stress and Strain in Tensile Test Specimens

Abstract In the investigation detailed in this paper, the tensile strength, the yield strength, and the breakage energy of test specimens (cold-rolled steel and dural) were measured while the specimens were being broken by a force applied at a high rate of speed in a commercial high-velocity impact-testing machine. The dynamic tensile strength, the dynamic yield strength and the dynamic breakage energy were found to be higher than the static values up to the maximum impact velocities of these tests (100 fps). The paper contains: (1) A presentation of some results of these tests. (2) A description of the technique used. (3) A description of the analysis used.