The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Ferhun C Caner - One of the best experts on this subject based on the ideXlab platform.
-
impact Comminution of solids due to local kinetic energy of high shear strain rate i continuum theory and turbulence analogy
Journal of The Mechanics and Physics of Solids, 2014Co-Authors: Zdeněk P Bažant, Ferhun C CanerAbstract:The modeling of high velocity impact into brittle or quasibrittle solids is hampered by the unavailability of a constitutive model capturing the effects of material Comminution into very fine particles. The present objective is to develop such a model, usable in finite element programs. The Comminution at very high strain rates can dissipate a large portion of the kinetic energy Of an impacting missile. The spatial derivative of the energy dissipated by Comminution gives a force resisting the penetration, which is superposed on the nodal forces obtained from the static constitutive model in a finite element program. The present theory is inspired partly by Grady's model for expansive Comminution due to explosion inside a hollow sphere, and partly by analogy with turbulence. In high velocity turbulent flow, the energy dissipation rate gets enhanced by the formation of micro-vortices (eddies) which dissipate energy by viscous shear stress. Similarly, here it is assumed that the energy dissipation at fast deformation of a confined solid gets enhanced by the release of kinetic energy of the motion associated with a high-rate shear strain of forming particles. For simplicity, the shape of these particles in the plane of maximum shear rate is considered to be regular hexagons. The particle sizes are assumed to be distributed according to the Schuhmann power law. The condition that the rate of release of the local kinetic energy must be equal to the interface fracture energy yields a relation between the particle size, the shear strain rate, the fracture energy and the mass density. As one experimental justification, the present theory agrees with Grady's empirical observation that, in impact events, the average particle size is proportional to the (-2/3) power of the shear strain rate. The main characteristic of the Comminution process is a dimensionless number B-a (Eq. (37)) representing the ratio of the local kinetic energy of shear strain rate to the maximum possible strain energy that can be stored in the same volume of material. It is shown that the kinetic energy release is proportional to the (2/3)-power of the shear strain rate, and that the dynamic Comminution creates an apparent material viscosity inversely proportional to the (1/3)-power of that rate. After Comminution, the interface fracture energy takes the role of interface friction, and it is pointed out that if the friction depends on the slip rate the aforementioned exponents would change. The effect of dynamic Comminution can simply be taken into account by introducing the apparent viscosity into the material constitutive model, which is what is implemented in the paper that follows. (C) 2013 Elsevier Ltd. All rights reserved.
-
Comminution of solids caused by kinetic energy of high shear strain rate with implications for impact shock and shale fracturing
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Zdeněk P Bažant, Ferhun C CanerAbstract:Although there exists a vast literature on the dynamic Comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of Comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the −2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the Comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the −1/3 power of this rate. A dimensionless indicator of the Comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow.
Zdeněk P Bažant - One of the best experts on this subject based on the ideXlab platform.
-
impact Comminution of solids due to local kinetic energy of high shear strain rate i continuum theory and turbulence analogy
Journal of The Mechanics and Physics of Solids, 2014Co-Authors: Zdeněk P Bažant, Ferhun C CanerAbstract:The modeling of high velocity impact into brittle or quasibrittle solids is hampered by the unavailability of a constitutive model capturing the effects of material Comminution into very fine particles. The present objective is to develop such a model, usable in finite element programs. The Comminution at very high strain rates can dissipate a large portion of the kinetic energy Of an impacting missile. The spatial derivative of the energy dissipated by Comminution gives a force resisting the penetration, which is superposed on the nodal forces obtained from the static constitutive model in a finite element program. The present theory is inspired partly by Grady's model for expansive Comminution due to explosion inside a hollow sphere, and partly by analogy with turbulence. In high velocity turbulent flow, the energy dissipation rate gets enhanced by the formation of micro-vortices (eddies) which dissipate energy by viscous shear stress. Similarly, here it is assumed that the energy dissipation at fast deformation of a confined solid gets enhanced by the release of kinetic energy of the motion associated with a high-rate shear strain of forming particles. For simplicity, the shape of these particles in the plane of maximum shear rate is considered to be regular hexagons. The particle sizes are assumed to be distributed according to the Schuhmann power law. The condition that the rate of release of the local kinetic energy must be equal to the interface fracture energy yields a relation between the particle size, the shear strain rate, the fracture energy and the mass density. As one experimental justification, the present theory agrees with Grady's empirical observation that, in impact events, the average particle size is proportional to the (-2/3) power of the shear strain rate. The main characteristic of the Comminution process is a dimensionless number B-a (Eq. (37)) representing the ratio of the local kinetic energy of shear strain rate to the maximum possible strain energy that can be stored in the same volume of material. It is shown that the kinetic energy release is proportional to the (2/3)-power of the shear strain rate, and that the dynamic Comminution creates an apparent material viscosity inversely proportional to the (1/3)-power of that rate. After Comminution, the interface fracture energy takes the role of interface friction, and it is pointed out that if the friction depends on the slip rate the aforementioned exponents would change. The effect of dynamic Comminution can simply be taken into account by introducing the apparent viscosity into the material constitutive model, which is what is implemented in the paper that follows. (C) 2013 Elsevier Ltd. All rights reserved.
-
Comminution of solids caused by kinetic energy of high shear strain rate with implications for impact shock and shale fracturing
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Zdeněk P Bažant, Ferhun C CanerAbstract:Although there exists a vast literature on the dynamic Comminution or fragmentation of rocks, concrete, metals, and ceramics, none of the known models suffices for macroscopic dynamic finite element analysis. This paper outlines the basic idea of the macroscopic model. Unlike static fracture, in which the driving force is the release of strain energy, here the essential idea is that the driving force of Comminution under high-rate compression is the release of the local kinetic energy of shear strain rate. The density of this energy at strain rates >1,000/s is found to exceed the maximum possible strain energy density by orders of magnitude, making the strain energy irrelevant. It is shown that particle size is proportional to the −2/3 power of the shear strain rate and the 2/3 power of the interface fracture energy or interface shear stress, and that the Comminution process is macroscopically equivalent to an apparent shear viscosity that is proportional (at constant interface stress) to the −1/3 power of this rate. A dimensionless indicator of the Comminution intensity is formulated. The theory was inspired by noting that the local kinetic energy of shear strain rate plays a role analogous to the local kinetic energy of eddies in turbulent flow.
Pei Zhong - One of the best experts on this subject based on the ideXlab platform.
-
the effect of treatment strategy on stone Comminution efficiency in shock wave lithotripsy
The Journal of Urology, 2004Co-Authors: Yufeng Zhou, F H Cocks, Glenn M Preminger, Pei ZhongAbstract:Purpose: The Comminution of kidney stones in shock wave lithotripsy (SWL) is a dose dependent process caused primarily by the combination of 2 fundamental mechanisms, namely stress waves and cavitation. The effect of treatment strategy with emphasis on enhancing the effect of stress waves or cavitation on stone Comminution in SWL was investigated. Because vascular injury in SWL is also dose dependent, optimization of the treatment strategy may produce improved stone Comminution with decreased tissue injury in SWL. Materials and Methods: Using an in vitro experiment system that mimics stone fragmentation in the renal pelvis spherical BegoStone (Bego USA, Smithfield, Rhode Island) phantoms (diameter 10 mm) were exposed to 1,500 shocks at a pulse repetition rate of 1 Hz in an unmodified HM-3 lithotripter (Dornier Medical Systems, Kennesaw, Georgia). The 3 treatment strategies used were increasing output voltage from 18 to 20 and then to 22 kV every 500 shocks with emphasis on enhancing the effect of cavitation on medium fragments (2 to 4 mm) at the final treatment stage, decreasing output voltage from 22 to 20 and then to 18 kV every 500 shocks with emphasis on enhancing the effect of stress waves on large fragments (greater than 4 mm) at the initial treatment stage and maintaining a constant output voltage at 20 kV, as typically used in SWL procedures. Following shock wave exposure the size distribution of fragments was determined by the sequential sieving method. In addition, pressure waveforms at lithotripter focus (F2) produced at different output settings were measured using a fiber optic probe hydrophone. Results: The rate of stone Comminution in SWL varied significantly in a dose dependent manner depending on the treatment strategies used. Specifically the Comminution efficiencies produced by the 3 strategies after the initial 500 shocks were 30.7%, 59% and 41.9%, respectively. After 1,000 shocks the corresponding Comminution efficiencies became similar (60.2%, 68.1% and 66.4%, respectively) with no statistically significant differences (p 0.08). After 1,500 shocks the final Comminution efficiency produced by the first strategy was 88.7%, which was better than the corresponding values of 81.2% and 83.5%, respectively, for the other 2 strategies. The difference between the final Comminution efficiency of the first and second strategies was statistically significant (p 0.005). Conclusions: Progressive increase in lithotripter output voltage can produce the best overall stone Comminution in vitro.
Glenn M Preminger - One of the best experts on this subject based on the ideXlab platform.
-
variable pulse duration from a new holmium yag laser the effect on stone Comminution fiber tip degradation and retropulsion in a dusting model
Urology, 2017Co-Authors: Daniel A Wollin, Glenn M Preminger, Anika Ackerman, Chen Yang, Tony Chen, Walter Neal Simmons, Michael E LipkinAbstract:Objective To more clearly define the efficiency and potential benefits of variable pulse-width laser technology for ureteroscopic lithotripsy, we performed comparative in vitro evaluations assessing stone Comminution, laser fiber tip degradation, and stone retropulsion. Methods All experiments were conducted using a Swiss LaserClast Holmium:YAG laser (Electro Medical Systems, Nyon, Switzerland) with adjustable pulse duration (300 µs-1500 µs). To assess Comminution efficiency and fiber tip degradation, a “dusting” model was employed; the laser fiber tip was moved by a 3-dimensional positioning system in a spiral motion across a flat BegoStone surface submerged in water. Comminution efficiency was measured as the loss of stone mass while fiber tip degradation was measured simultaneously. The same laser and fiber were used in a pendulum model to measure stone retropulsion with a high-speed resolution camera. Results In our dusting model, Comminution was significantly greater at high energy (2 J/5 Hz). At the high energy setting, Comminution was significantly greater with long pulse duration than short pulse, although this difference was not seen at the high frequency setting (1 J/10 Hz). Tip degradation was increased at high energy settings and was even more pronounced with short pulse duration than long pulse. Short pulse duration caused far more retropulsion than the long pulse setting. Conclusion In an in vitro dusting model, a longer laser pulse duration provides effective stone Comminution with the advantage of reducing laser fiber tip degradation and stone retropulsion.
-
the effect of treatment strategy on stone Comminution efficiency in shock wave lithotripsy
The Journal of Urology, 2004Co-Authors: Yufeng Zhou, F H Cocks, Glenn M Preminger, Pei ZhongAbstract:Purpose: The Comminution of kidney stones in shock wave lithotripsy (SWL) is a dose dependent process caused primarily by the combination of 2 fundamental mechanisms, namely stress waves and cavitation. The effect of treatment strategy with emphasis on enhancing the effect of stress waves or cavitation on stone Comminution in SWL was investigated. Because vascular injury in SWL is also dose dependent, optimization of the treatment strategy may produce improved stone Comminution with decreased tissue injury in SWL. Materials and Methods: Using an in vitro experiment system that mimics stone fragmentation in the renal pelvis spherical BegoStone (Bego USA, Smithfield, Rhode Island) phantoms (diameter 10 mm) were exposed to 1,500 shocks at a pulse repetition rate of 1 Hz in an unmodified HM-3 lithotripter (Dornier Medical Systems, Kennesaw, Georgia). The 3 treatment strategies used were increasing output voltage from 18 to 20 and then to 22 kV every 500 shocks with emphasis on enhancing the effect of cavitation on medium fragments (2 to 4 mm) at the final treatment stage, decreasing output voltage from 22 to 20 and then to 18 kV every 500 shocks with emphasis on enhancing the effect of stress waves on large fragments (greater than 4 mm) at the initial treatment stage and maintaining a constant output voltage at 20 kV, as typically used in SWL procedures. Following shock wave exposure the size distribution of fragments was determined by the sequential sieving method. In addition, pressure waveforms at lithotripter focus (F2) produced at different output settings were measured using a fiber optic probe hydrophone. Results: The rate of stone Comminution in SWL varied significantly in a dose dependent manner depending on the treatment strategies used. Specifically the Comminution efficiencies produced by the 3 strategies after the initial 500 shocks were 30.7%, 59% and 41.9%, respectively. After 1,000 shocks the corresponding Comminution efficiencies became similar (60.2%, 68.1% and 66.4%, respectively) with no statistically significant differences (p 0.08). After 1,500 shocks the final Comminution efficiency produced by the first strategy was 88.7%, which was better than the corresponding values of 81.2% and 83.5%, respectively, for the other 2 strategies. The difference between the final Comminution efficiency of the first and second strategies was statistically significant (p 0.005). Conclusions: Progressive increase in lithotripter output voltage can produce the best overall stone Comminution in vitro.
Yufeng Zhou - One of the best experts on this subject based on the ideXlab platform.
-
the effect of treatment strategy on stone Comminution efficiency in shock wave lithotripsy
The Journal of Urology, 2004Co-Authors: Yufeng Zhou, F H Cocks, Glenn M Preminger, Pei ZhongAbstract:Purpose: The Comminution of kidney stones in shock wave lithotripsy (SWL) is a dose dependent process caused primarily by the combination of 2 fundamental mechanisms, namely stress waves and cavitation. The effect of treatment strategy with emphasis on enhancing the effect of stress waves or cavitation on stone Comminution in SWL was investigated. Because vascular injury in SWL is also dose dependent, optimization of the treatment strategy may produce improved stone Comminution with decreased tissue injury in SWL. Materials and Methods: Using an in vitro experiment system that mimics stone fragmentation in the renal pelvis spherical BegoStone (Bego USA, Smithfield, Rhode Island) phantoms (diameter 10 mm) were exposed to 1,500 shocks at a pulse repetition rate of 1 Hz in an unmodified HM-3 lithotripter (Dornier Medical Systems, Kennesaw, Georgia). The 3 treatment strategies used were increasing output voltage from 18 to 20 and then to 22 kV every 500 shocks with emphasis on enhancing the effect of cavitation on medium fragments (2 to 4 mm) at the final treatment stage, decreasing output voltage from 22 to 20 and then to 18 kV every 500 shocks with emphasis on enhancing the effect of stress waves on large fragments (greater than 4 mm) at the initial treatment stage and maintaining a constant output voltage at 20 kV, as typically used in SWL procedures. Following shock wave exposure the size distribution of fragments was determined by the sequential sieving method. In addition, pressure waveforms at lithotripter focus (F2) produced at different output settings were measured using a fiber optic probe hydrophone. Results: The rate of stone Comminution in SWL varied significantly in a dose dependent manner depending on the treatment strategies used. Specifically the Comminution efficiencies produced by the 3 strategies after the initial 500 shocks were 30.7%, 59% and 41.9%, respectively. After 1,000 shocks the corresponding Comminution efficiencies became similar (60.2%, 68.1% and 66.4%, respectively) with no statistically significant differences (p 0.08). After 1,500 shocks the final Comminution efficiency produced by the first strategy was 88.7%, which was better than the corresponding values of 81.2% and 83.5%, respectively, for the other 2 strategies. The difference between the final Comminution efficiency of the first and second strategies was statistically significant (p 0.005). Conclusions: Progressive increase in lithotripter output voltage can produce the best overall stone Comminution in vitro.