Crack propagation due to indentation with constant speed

This paper is concerned with the propagation of a surface crack in a brittle solid induced by the indentation of a sharp wedge into the crack under constant speed. The analysis is based on a double-cantilever-beam model. Only the shear deformation of the cantilever is considered. Griffith concept of the balance of energy is used as the fracture criterion. It is found that crack propagation begins when the shear wave front is at the tip of the initial crack. During crack propagation, the crack speed remains constant with finite jumps at those moments when the shear wave front reaches the tip of the running crack. The results obtained by the dynamic analysis agree approximately with those derived from a quasi-static analysis.

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Résumé Le mémoire est relatif à la propagation d'une fissure superficielle dans un corps fragile sous l'effet de la pénétration d'un coin aigu dans la fissure à une vitesse constante. L'analyse du problème est basée sur un modèle en double poutre cantilever, où l'on ne considère que les déformations de cisaillement. Le critère de rupture utilisé est le concept de Griffith d'équilibre des énergies.On trouve que la propagation de la fissure débute lorsque le front d'onde de cisaillement atteint l'extrémité de la fissure initiale. Au cours de sa propagation, la fissure atteint une vitesse qui demeure constante, quoique comportant des ressauts d'amplitude finie chaque fois que le front d'onde de cisaillement atteint l'extrémité de la fissure en mouvement.Les résultats obtenus par une analyse dynamique sont en accord approximatif avec ceux que l'on obtient par une analyse quasistatique.

     

Simulation of particle bed breakage by slow compression and impact using a DEM particle replacement model

The present work introduces a particle replacement model implemented in the commercial software EDEM to describe breakage of particles. Several model parameters were initially estimated on the basis of single-particle breakage tests on iron ore pellets. The model was then used to simulate breakage of particle beds by both slow compression and impact. Model predictions were compared to experiments in terms of compressive force versus packing density, breakage probability of the particles versus compressive force applied to the bed, and the product size distribution in compression and impact. The model showed the expected trends as well as some agreement with the measured product size distributions both from confined and unconfined stressing conditions of the bed of particles, being a simple and effective approach to describe breakage in systems where particles are stressed as assemblies.     

Laws of propagation of an instantaneous heat pulse in a fluidized bed

A function is obtained representing the effect of an instantaneous heat pulse in a fluidized bed in the presence of heat losses by way of the gas flow and through the external walls of the cylindrical apparatus.     

Fast pyrolysis of an ensemble of biomass particles in a fluidized bed

A combined approach to the modeling of fast pyrolysis of biomass particles in a fluidized bed has been used. We used models of different levels: two models of pyrolysis of a single particle — with lumped and distributed parameters — and a model of pyrolysis of an ensemble of biomass particles based on the continuum equations for the gas blown through the bed and the equations of motion for individual particles. We have determined optimal (in terms of the biofuel yield) temperatures of the process for various particle sizes of wood biomass and various values of its moisture.     

The effect of approach direction on damage in MgO due to spherical particle impact

The damage produced by spherical particle impact against {1 0 0} surfaces of MgO has been investigated over a range of impact angles for a fixed particle velocity and over a range of particle velocities for a fixed impact angle. The mass of material removed by each impact was determined gravimetrically, and the crater and surrounding damage were studied by means of surface profilometry and scanning electron microscopy. A numerical computer model of the crater formation process was developed which was able to predict crater geometries in close agreement with those observed experimentally. This same model also provided estimates of the dynamic hardness, the contact time and the energy transmitted to the surface during the impact. The mean dynamic hardness was ~ 25% less than that measured in previous normal impact studies [1] on MgO of similar static hardness. The contact time and energy calculations give some insight into the reasons why the energy balance model, which successfully describes the velocity dependence of mass loss under normal impact conditions, breaks down for oblique impact.     

The effect of cristallographic orientation on damage in MgO due to spherical particle impact

A single stage gas gun has been used to fire spherical chrome steel and WC particles at variously oriented and prepared MgO single crystals at velocities of up to 350 m sec^–1. The resultant damage has been studied by optical and scanning electron microscopy, dislocation etching and surface profilometry, and mass losses have been determined gravimetrically. The measured crater dimensions and the mass loss data have been compared with the predictions of a simple analytical model of the impact event.     

Reduced fracturing of intermetallic particles during crack propagation in age hardening Al-based alloys due to PFZs

Based on a shear lag model approach, a simple analytic model for the stress shielding of intermetallic particles due to the presence of a weakened precipitate free zone (PFZ) is derived. The PFZ desensitises the material to the breaking of particles. For the S and θ phase particles in the 2091 aluminium based alloy, particles with average sizes in the range 3–15 μm receive effective shielding from matrix stresses, which raise the matrix stress required to break the particle, and causes a propensity for larger particles to break at smaller applied macroscopic stress.     

Stripping of surface water from particles in an injected bed

Mechanical water stripping has been observed in an injected bed; measurements have been made on the effects of the water content of the material, the bed depth, particle diameter, and injected gas speed on the stripping rate.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 3, pp. 411–415, March, 1976.     

Modeling of fast pyrolysis of a single biomass particle in an inert boiling bed

We have developed a model of fast pyrolysis of a biomass (wood) particle including the heating of the particle in a boiling bed under regular conditions, the pyrolysis kinetics of the three basic components of the biomass (cellulose, hemicellulose, and lignin), and the destruction kinetics of the intermediate pyrolysis products, as well as a submodel of the particle motion in the free space of the reactor. The numerical optimization of the fast pyrolysis performed by us has shown that the main control parameter of the process determining the yield of liquid biofuel is the temperature of the boiling bed.     

Horizontal particle mixing in a free fluidized bed

Horizontal particle diffusion in free fluidized beds is investigated experimentally.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 42, No. 5, pp. 767–773, May, 1982.     

Estimated incident cost savings in shipping due to inspections

The effectiveness of safety inspections of ships has been analysed from various angles, but until now, relatively little attention has been given to translate risk reduction into incident cost savings. This paper provides a monetary quantification of the cost savings that can be attributed to port state control inspections and industry vetting inspections. The dataset consists of more than half a million ship arrivals between 2002 and 2007 and contains inspections of port state authorities in the USA and Australia and of three industry vetting regimes. The effect of inspections in reducing the risk of total loss accidents is estimated by means of duration models, in terms of the gained probability of survival. The monetary benefit of port state control inspections is estimated to range, on average, from about 70 to 190 thousand dollars, with median values ranging from about 20 to 45 thousand dollars. Industry inspections have even higher benefits, especially for tankers. The savings are in general higher for older and larger vessels, and also for vessels with undefined flag and unknown classification society. As inspection costs are relatively low in comparison to potential cost savings, the results underline the importance of determining ships with relatively high risk of total loss.     

Fine-scale mixing in a gas-fluidized bed of fine particles

The coefficients of diffusion of the particles and gas in the dense phase of a fluidized bed and the mean squares of the components of their pulsation velocity are analyzed with direct particle collisions neglected.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 5, pp. 836–846, May, 1980.     

High speed crack propagation in bi-phase materials: an experimental study

Compliance and strain energy release rate of homogeneous and interleaved end-notched flexure specimens for mode II fracture characterization are investigated with shear deformation beam theory and finite element analysis. Interleaving refers to a thin layer of polymer film being placed at the midplane of the beam. Analytical results are correlated with numerical finite element results for a wide range of interleaf thicknesses. The finite element results revealed that the compliance and energy release rate remained virtually the same whether the crack was within the interlayer or between the interlayer and the composite. Furthermore, within the accuracy of the numerical modeling, the asymmetric crack configuration did not render the specimen mixed mode, (G _I=0). Close agreement was observed between sandwich beam theory and finite element analysis.     

Moisture evaporation in a fluidized bed of inert particles

Results of an experimental study are compared with calculations based on the equations for thermal and material balance.     

Thermal relaxation time of particles in a fluidized bed

Results are given of an experimental investigation of the thermal relaxation time of particles in a fluidized bed. Values of the coefficient of heat transfer from particles to gas are determined.     

Radiation of a bed of coarse alumina particles

Spectral and integral emissivity is calculated of a semiinfinite bed of alumina particles with diameters up to 1 mm which are at high temperatures.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 6, pp. 996–999, December, 1976.     

Effects of phase lags on wave propagation in an infinite solid due to a continuous line heat source

The present work is concerned with the wave propagation in a homogeneous, isotropic and unbounded solid due to a continuous line heat source under the theory of thermoelasticity with three phase-lags (Roychoudhari in J Therm Stress 30:231?C238, 2007). For the solution of the problem, we employ a potential function approach together with Laplace and Hankel transform method. Analytical expressions for the distributions of different fields like temperature, displacement and stresses inside the medium are derived by inverting Laplace transforms in an approximate manner for small values of time. The problem is illustrated by computing numerical values of the field variables for a particular material. The theoretical as well as numerical results are compared with the corresponding results for other theories of thermoelasticity reported earlier.     

The passage of an electrical current through a fluidized bed of electrically conducting particles

The mechanism of the nonlinear relation between the specific resistance of a fluidized bed of graphite particles and the current density when a 50 hertz alternating current is supplied to the bed is discussed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol.18, No.1, pp.64–67, January, 1970.     

Relationships for a fluidized bed of solid particles

A new theory for a fluidized bed is presented and corroborated by experimental data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 6, pp. 1122–1130, June, 1970.     

Modeling the diffuse reflectance due to a narrow beam incident on a turbid medium

We present a model for the diffuse reflectance when a continuous beam is incident normally on a half space composed of a uniform scattering and absorbing medium. This model is the result of an asymptotic analysis of the radiative transport equation for strong scattering, weak absorption, and a narrow beam width. Through comparison with the diffuse reflectance computed using the numerical solution of the radiative transport equation, we show that this diffuse reflectance model gives results that are accurate for small source--detector separation distances.