The Experts below are selected from a list of 42267 Experts worldwide ranked by ideXlab platform
Andrew P Evan - One of the best experts on this subject based on the ideXlab platform.
-
a cumulative shear mechanism for tissue Damage Initiation in shock wave lithotripsy
Ultrasound in Medicine and Biology, 2007Co-Authors: Jonathan B Freund, Tim Colonius, Andrew P EvanAbstract:Abstract Evidence suggests that inertial cavitation plays an important role in the renal injury incurred during shock-wave lithotripsy. However, it is unclear how tissue Damage is initiated, and significant injury typically occurs only after a sufficient dose of shock waves. Although it has been suggested that shock-induced shearing might initiate injury, estimates indicate that individual shocks do not produce sufficient shear to do so. In this paper, we hypothesize that the cumulative shear of the many shocks is damaging. This mechanism depends on whether there is sufficient time between shocks for tissue to relax to its unstrained state. We investigate the mechanism with a physics-based simulation model, wherein the basement membranes that define the tubules and vessels in the inner medulla are represented as elastic shells surrounded by viscous fluid. Material properties are estimated from in-vitro tests of renal basement membranes and documented mechanical properties of cells and extracellular gels. Estimates for the net shear deformation from a typical lithotripter shock (∼0.1%) are found from a separate dynamic shock simulation. The results suggest that the larger interstitial volume (∼40%) near the papilla tip gives the tissue there a relaxation time comparable to clinical shock delivery rates (∼1 Hz), thus allowing shear to accumulate. Away from the papilla tip, where the interstitial volume is smaller (∼20%), the model tissue relaxes completely before the next shock would be delivered. Implications of the model are that slower delivery rates and broader focal zones should both decrease injury, consistent with some recent observations. (E-mail: jbfreund@uiuc.edu )
-
a cumulative shear mechanism for tissue Damage Initiation in shock wave lithotripsy
Ultrasound in Medicine and Biology, 2007Co-Authors: Jonathan B Freund, Tim Colonius, Andrew P EvanAbstract:Evidence suggests that inertial cavitation plays an important role in the renal injury incurred during shock-wave lithotripsy. However, it is unclear how tissue Damage is initiated, and significant injury typically occurs only after a sufficient dose of shock waves. Although it has been suggested that shock-induced shearing might initiate injury, estimates indicate that individual shocks do not produce sufficient shear to do so. In this paper, we hypothesize that the cumulative shear of the many shocks is damaging. This mechanism depends on whether there is sufficient time between shocks for tissue to relax to its unstrained state. We investigate the mechanism with a physics-based simulation model, wherein the basement membranes that define the tubules and vessels in the inner medulla are represented as elastic shells surrounded by viscous fluid. Material properties are estimated from in-vitro tests of renal basement membranes and documented mechanical properties of cells and extracellular gels. Estimates for the net shear deformation from a typical lithotripter shock (approximately 0.1%) are found from a separate dynamic shock simulation. The results suggest that the larger interstitial volume (approximately 40%) near the papilla tip gives the tissue there a relaxation time comparable to clinical shock delivery rates (approximately 1 Hz), thus allowing shear to accumulate. Away from the papilla tip, where the interstitial volume is smaller (approximately 20%), the model tissue relaxes completely before the next shock would be delivered. Implications of the model are that slower delivery rates and broader focal zones should both decrease injury, consistent with some recent observations.
Stefan Zaefferer - One of the best experts on this subject based on the ideXlab platform.
-
micro Damage Initiation in ferrite martensite dp microstructures a statistical characterization of crystallographic and chemical parameters
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Fady Mamdouh Fawzy Archie, Stefan ZaeffererAbstract:Abstract Damage mechanisms occurring in a DP-steel microstructure at low strains, under monotonic and cyclic deformation modes have been studied by a comprehensive statistical analysis of scanning electron microscopy observations. The study aims to define local microstructural configurations of high Damage susceptibility. In particular, the role of grain and interphase boundaries at triggering micro-Damage features was investigated. SEM-based electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) were utilized. Focused ion beam (FIB) milling was additionally applied for a 3-dimensional investigation of the crack morphology and corresponding arrangement of phases. Microstructural configurations of high Damage susceptibility were deduced and confirmed through a quasi in-situ deformation experiment. Damage Initiation is shown to be highly dependent on the distribution and morphology of the martensitic islands. Voids are most likely to nucleate at interphase boundaries under monotonic loading, particularly at triple junctions between ferritic grain boundaries and martensite. On the other hand, decohesion cracks are frequently observed inside of martensite where they are remarkably restricted to prior austenite grain boundaries (PAGbs). The low fracture strength of martensitic PAGbs is discussed in the light of local chemical analysis of different types of interfaces using atom probe tomography (APT).
-
micro Damage Initiation in ferrite martensite dp microstructures a statistical characterization of crystallographic and chemical parameters
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Fady Mamdouh Fawzy Archie, Xiao Long Li, Stefan ZaeffererAbstract:Abstract Damage mechanisms occurring in a DP-steel microstructure at low strains, under monotonic and cyclic deformation modes have been studied by a comprehensive statistical analysis of scanning electron microscopy observations. The study aims to define local microstructural configurations of high Damage susceptibility. In particular, the role of grain and interphase boundaries at triggering micro-Damage features was investigated. SEM-based electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) were utilized. Focused ion beam (FIB) milling was additionally applied for a 3-dimensional investigation of the crack morphology and corresponding arrangement of phases. Microstructural configurations of high Damage susceptibility were deduced and confirmed through a quasi in-situ deformation experiment. Damage Initiation is shown to be highly dependent on the distribution and morphology of the martensitic islands. Voids are most likely to nucleate at interphase boundaries under monotonic loading, particularly at triple junctions between ferritic grain boundaries and martensite. On the other hand, decohesion cracks are frequently observed inside of martensite where they are remarkably restricted to prior austenite grain boundaries (PAGbs). The low fracture strength of martensitic PAGbs is discussed in the light of local chemical analysis of different types of interfaces using atom probe tomography (APT).
-
Damage Initiation in dual phase steels influence of crystallographic and morphological parameters
Materials Science Forum, 2016Co-Authors: Fady Mamdouh Fawzy Archie, Stefan ZaeffererAbstract:Typical microstructures of dual-phase (DP) steels consist of hard martensite particles dispersed within a ductile ferritic matrix. These microstructures possess a complex network of grain and interphase boundaries, which, together with the mechanical contrast of their phase composition, control micro-Damage Initiation mechanisms, induced by deformation. Accordingly, in this study we analyze the influence of individual microstructural features and interfaces on Damage nucleation and progression in DP steels with respect to applied tensile strain. Prominent micro-Damage mechanisms include cracking of martensite and Damage Initiation at interphase boundaries. Influence of martensite morphology is discussed based on a statistical analysis of the Damage features as observed by electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) maps. Prior austenite grain boundaries (PAGbs) in martensite show a brittle behavior and are highly susceptible to crack propagation.
Jonathan B Freund - One of the best experts on this subject based on the ideXlab platform.
-
a cumulative shear mechanism for tissue Damage Initiation in shock wave lithotripsy
Ultrasound in Medicine and Biology, 2007Co-Authors: Jonathan B Freund, Tim Colonius, Andrew P EvanAbstract:Abstract Evidence suggests that inertial cavitation plays an important role in the renal injury incurred during shock-wave lithotripsy. However, it is unclear how tissue Damage is initiated, and significant injury typically occurs only after a sufficient dose of shock waves. Although it has been suggested that shock-induced shearing might initiate injury, estimates indicate that individual shocks do not produce sufficient shear to do so. In this paper, we hypothesize that the cumulative shear of the many shocks is damaging. This mechanism depends on whether there is sufficient time between shocks for tissue to relax to its unstrained state. We investigate the mechanism with a physics-based simulation model, wherein the basement membranes that define the tubules and vessels in the inner medulla are represented as elastic shells surrounded by viscous fluid. Material properties are estimated from in-vitro tests of renal basement membranes and documented mechanical properties of cells and extracellular gels. Estimates for the net shear deformation from a typical lithotripter shock (∼0.1%) are found from a separate dynamic shock simulation. The results suggest that the larger interstitial volume (∼40%) near the papilla tip gives the tissue there a relaxation time comparable to clinical shock delivery rates (∼1 Hz), thus allowing shear to accumulate. Away from the papilla tip, where the interstitial volume is smaller (∼20%), the model tissue relaxes completely before the next shock would be delivered. Implications of the model are that slower delivery rates and broader focal zones should both decrease injury, consistent with some recent observations. (E-mail: jbfreund@uiuc.edu )
-
a cumulative shear mechanism for tissue Damage Initiation in shock wave lithotripsy
Ultrasound in Medicine and Biology, 2007Co-Authors: Jonathan B Freund, Tim Colonius, Andrew P EvanAbstract:Evidence suggests that inertial cavitation plays an important role in the renal injury incurred during shock-wave lithotripsy. However, it is unclear how tissue Damage is initiated, and significant injury typically occurs only after a sufficient dose of shock waves. Although it has been suggested that shock-induced shearing might initiate injury, estimates indicate that individual shocks do not produce sufficient shear to do so. In this paper, we hypothesize that the cumulative shear of the many shocks is damaging. This mechanism depends on whether there is sufficient time between shocks for tissue to relax to its unstrained state. We investigate the mechanism with a physics-based simulation model, wherein the basement membranes that define the tubules and vessels in the inner medulla are represented as elastic shells surrounded by viscous fluid. Material properties are estimated from in-vitro tests of renal basement membranes and documented mechanical properties of cells and extracellular gels. Estimates for the net shear deformation from a typical lithotripter shock (approximately 0.1%) are found from a separate dynamic shock simulation. The results suggest that the larger interstitial volume (approximately 40%) near the papilla tip gives the tissue there a relaxation time comparable to clinical shock delivery rates (approximately 1 Hz), thus allowing shear to accumulate. Away from the papilla tip, where the interstitial volume is smaller (approximately 20%), the model tissue relaxes completely before the next shock would be delivered. Implications of the model are that slower delivery rates and broader focal zones should both decrease injury, consistent with some recent observations.
Fady Mamdouh Fawzy Archie - One of the best experts on this subject based on the ideXlab platform.
-
micro Damage Initiation in ferrite martensite dp microstructures a statistical characterization of crystallographic and chemical parameters
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Fady Mamdouh Fawzy Archie, Stefan ZaeffererAbstract:Abstract Damage mechanisms occurring in a DP-steel microstructure at low strains, under monotonic and cyclic deformation modes have been studied by a comprehensive statistical analysis of scanning electron microscopy observations. The study aims to define local microstructural configurations of high Damage susceptibility. In particular, the role of grain and interphase boundaries at triggering micro-Damage features was investigated. SEM-based electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) were utilized. Focused ion beam (FIB) milling was additionally applied for a 3-dimensional investigation of the crack morphology and corresponding arrangement of phases. Microstructural configurations of high Damage susceptibility were deduced and confirmed through a quasi in-situ deformation experiment. Damage Initiation is shown to be highly dependent on the distribution and morphology of the martensitic islands. Voids are most likely to nucleate at interphase boundaries under monotonic loading, particularly at triple junctions between ferritic grain boundaries and martensite. On the other hand, decohesion cracks are frequently observed inside of martensite where they are remarkably restricted to prior austenite grain boundaries (PAGbs). The low fracture strength of martensitic PAGbs is discussed in the light of local chemical analysis of different types of interfaces using atom probe tomography (APT).
-
micro Damage Initiation in ferrite martensite dp microstructures a statistical characterization of crystallographic and chemical parameters
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Fady Mamdouh Fawzy Archie, Xiao Long Li, Stefan ZaeffererAbstract:Abstract Damage mechanisms occurring in a DP-steel microstructure at low strains, under monotonic and cyclic deformation modes have been studied by a comprehensive statistical analysis of scanning electron microscopy observations. The study aims to define local microstructural configurations of high Damage susceptibility. In particular, the role of grain and interphase boundaries at triggering micro-Damage features was investigated. SEM-based electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI) were utilized. Focused ion beam (FIB) milling was additionally applied for a 3-dimensional investigation of the crack morphology and corresponding arrangement of phases. Microstructural configurations of high Damage susceptibility were deduced and confirmed through a quasi in-situ deformation experiment. Damage Initiation is shown to be highly dependent on the distribution and morphology of the martensitic islands. Voids are most likely to nucleate at interphase boundaries under monotonic loading, particularly at triple junctions between ferritic grain boundaries and martensite. On the other hand, decohesion cracks are frequently observed inside of martensite where they are remarkably restricted to prior austenite grain boundaries (PAGbs). The low fracture strength of martensitic PAGbs is discussed in the light of local chemical analysis of different types of interfaces using atom probe tomography (APT).
-
Damage Initiation in dual phase steels influence of crystallographic and morphological parameters
Materials Science Forum, 2016Co-Authors: Fady Mamdouh Fawzy Archie, Stefan ZaeffererAbstract:Typical microstructures of dual-phase (DP) steels consist of hard martensite particles dispersed within a ductile ferritic matrix. These microstructures possess a complex network of grain and interphase boundaries, which, together with the mechanical contrast of their phase composition, control micro-Damage Initiation mechanisms, induced by deformation. Accordingly, in this study we analyze the influence of individual microstructural features and interfaces on Damage nucleation and progression in DP steels with respect to applied tensile strain. Prominent micro-Damage mechanisms include cracking of martensite and Damage Initiation at interphase boundaries. Influence of martensite morphology is discussed based on a statistical analysis of the Damage features as observed by electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) maps. Prior austenite grain boundaries (PAGbs) in martensite show a brittle behavior and are highly susceptible to crack propagation.
Philippe Bompard - One of the best experts on this subject based on the ideXlab platform.
-
mechanical behaviour of 55 filament wound glass fibre epoxy resin tubes ii micromechanical model of Damage Initiation and the competition between different mechanisms
Composites Science and Technology, 1997Co-Authors: Jinbo Bai, Philippe BompardAbstract:Abstract This series of papers on ± 55 ° filament-wound glass-fibre/epoxy-resin tubes consists of three parts. In the present paper (Part II), micromechanical modelling of the Damage Initiation is conducted in order to determine (1) the mechanical conditions under which different microcracking mechanisms occur and (2) the critical σ zz /σ θθ ratios which correspond to the change from interfacial failure to microcracking at porosity. Emphasis is placed on assessing the influence of microstructural defects and the competition between the different mechanisms. The general tendency of Damage-envelope prediction by means of micromechanical modelling fits the microscopy observations quite well. The sensitivity of local criteria is also discussed. The correction of the local stress field has been improved by introducing a local stress concentration factor in a mean field theory model (Mori-Tanaka theory). In Part I, the microstructural analyses, mechanical behaviour and Damage Initiation mechanisms were presented. In Part III, the macroscopic behaviour of the tubing structure with and without Damage will be presented. The simulation results will be compared with experimental ones.
-
mechanical behaviour of 55 filament wound glass fibre epoxy resin tubes i microstructural analyses mechanical behaviour and Damage mechanisms of composite tubes under pure tensile loading pure internal pressure and combined loading
Composites Science and Technology, 1997Co-Authors: Jinbo Bai, Philippe Seeleuthner, Philippe BompardAbstract:Abstract This series of papers on ± 55 ° filament-wound glass-fibre/epoxy-resin tubes consists of three parts. In Part I, the microstructure of the composite tube was first investigated by image processing to qualify the microstructural defects produced during manufacturing. A series of mechanical tests was then carried out under various combinations of hoop and axial stresses to evaluate the tubes' mechanical behaviour under pure axial tensile load, pure internal pressure, and under combined loading. Observations on specimens loaded to 20–50% of the ultimate tensile strength showed that the main Damage Initiation mechanisms are microcracking (matrix and transverse cracks) and delamination. Depending on the loading conditions, one of the mechanisms dominates over the other. The effect of microstructural defects on the Damage Initiation was clearly demonstrated. In Part II, micromechanical modelling of the Damage Initiation will be conducted in order to determine (1) the mechanical conditions under which different microcracking mechanisms occur and (2) the critical σzzσ/θθ ratio which corresponds to the change from one mechanism to another. Emphasis is placed on assessing the influence of microstructural defects and the competition between the different mechanisms. In Part III, a macroscopical behaviour law for the tubing structure with and without Damage will be presented, and the simulation results will be compared with experimental ones.
