The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
John Montesano - One of the best experts on this subject based on the ideXlab platform.
-
Modelling the micro-damage Process Zone during cortical bone fracture
Engineering Fracture Mechanics, 2020Co-Authors: Daniel Dapaah, Raphael Badaoui, A. Bahmani, John Montesano, Thomas L. WillettAbstract:Abstract Cortical bone employs intrinsic toughening mechanisms to delay crack growth initiation and propagation hence increasing its fracture toughness. Computational models of the bone fracture Process though do not explicitly capture these intrinsic local toughening mechanisms. Such models could provide insights into possible sub-microscale mechanisms involved in the bone fracture Process. Therefore, in this study, the intrinsic toughening mechanism referred to as the micro-damage Process Zone (MDPZ) was modelled using a bi-linear continuum damage law. This model was then experimentally validated using single edge notch bending specimens and digital image correlation for strain field measurements. The size and shape of the micro-damage Process Zone as well as the load-deflection curves generated by the model reasonably replicated those measured experimentally. The results indicate that the continuum damage mechanics approach is a robust means of modelling the MDPZ at the continuum level and with further development of the model can provide a useful tool for studies of the fracture Process in cortical bone.
-
a continuum damage mechanics model of the microdamage Process Zone during cortical bone fracture
Materials Today: Proceedings, 2019Co-Authors: Daniel Dapaah, A. Bahmani, John Montesano, Thomas L. WillettAbstract:Abstract During fracture, cortical bone develops a large micro-damage Process Zone, which is thought to be vital to bone’s intrinsic fracture toughness. Willett et al. (2017) measured the micro-damage Process Zone using micro-computed tomography and barium sulphate staining after sub-critical loading of single edge notch (bending) (SEN(B)) specimens. Recently, we sought to provide a computational model of this important mechanism. A finite element (FE) model of a SEN(B) specimen was developed in ABAQUS using continuum damage mechanics (CDM) to simulate non-linear behavior due to micro-damage. Elastic behavior was modeled as linear, transversely isotropic. Micro-damage initiation was incorporated using the Hashin failure criterion. Failure behavior was modeled using a damage law based on fracture energies. CDM-FE can model the micro-damage Process Zone with good fidelity if relatively high viscous regularization settings are used. The Process Zone was found to mimic that measured experimentally. The load-deflection curve from the FE model was similar to experimental curves within
-
the micro damage Process Zone during transverse cortical bone fracture no ears at crack growth initiation
Journal of The Mechanical Behavior of Biomedical Materials, 2017Co-Authors: Thomas L. Willett, David S Josey, Gagan Minhas, John MontesanoAbstract:Abstract Objective Apply high-resolution benchtop micro-computed tomography (micro-CT) to gain greater understanding and knowledge of the formation of the micro-damage Process Zone formed during traverse fracture of cortical bone. Methods Bovine cortical bone was cut into single edge notch (bending) fracture testing specimens with the crack on the transverse plane and oriented to grow in the circumferential direction. We used a multi-specimen technique and deformed the specimens to various individual secant modulus loss levels (P-values) up to and including maximum load (Pmax). Next, the specimens were infiltrated with a BaSO 4 precipitation stain and scanned at 3.57-μm isotropic voxel size using a benchtop high resolution-micro-CT. Measurements of the micro-damage Process Zone volume, width and height were made. These were compared with the simple Irwin's Process Zone model and with finite element models. Electron and confocal microscopy confirmed the formation of BaSO 4 precipitate in micro-cracks and other porosity, and an interesting novel mechanism similar to tunneling. Results Measurable micro-damage was detected at low P values and the volume of the Process Zone increased according to a second order polynomial trend. Both width and height grew linearly up to Pmax, at which point the Process Zone cross-section (perpendicular to the plane of the crack) was almost circular on average with a radius of approximately 550 µm (approximately one quarter of the unbroken ligament thickness) and corresponding to the shape expected for a biological composite under plane stress conditions. Conclusion This study reports details of the micro-damage fracture Process Zone previously unreported for cortical bone. High-resolution micro-CT enables 3D visualization and measurement of the Process Zone and confirmation that the crack front edge and Process Zone are affected by microstructure. It is clear that the Process Zone for the specimens studied grows to be meaningfully large, confirming the need for the J-integral approach and it does not achieve steady state at Pmax in most specimens. With further development, this approach may become valuable towards better understanding the role of the Process Zone in cortical bone fracture and the effects of relevant modifications towards changes in fracture toughness in a cost effective way.
Thomas L. Willett - One of the best experts on this subject based on the ideXlab platform.
-
Modelling the micro-damage Process Zone during cortical bone fracture
Engineering Fracture Mechanics, 2020Co-Authors: Daniel Dapaah, Raphael Badaoui, A. Bahmani, John Montesano, Thomas L. WillettAbstract:Abstract Cortical bone employs intrinsic toughening mechanisms to delay crack growth initiation and propagation hence increasing its fracture toughness. Computational models of the bone fracture Process though do not explicitly capture these intrinsic local toughening mechanisms. Such models could provide insights into possible sub-microscale mechanisms involved in the bone fracture Process. Therefore, in this study, the intrinsic toughening mechanism referred to as the micro-damage Process Zone (MDPZ) was modelled using a bi-linear continuum damage law. This model was then experimentally validated using single edge notch bending specimens and digital image correlation for strain field measurements. The size and shape of the micro-damage Process Zone as well as the load-deflection curves generated by the model reasonably replicated those measured experimentally. The results indicate that the continuum damage mechanics approach is a robust means of modelling the MDPZ at the continuum level and with further development of the model can provide a useful tool for studies of the fracture Process in cortical bone.
-
a continuum damage mechanics model of the microdamage Process Zone during cortical bone fracture
Materials Today: Proceedings, 2019Co-Authors: Daniel Dapaah, A. Bahmani, John Montesano, Thomas L. WillettAbstract:Abstract During fracture, cortical bone develops a large micro-damage Process Zone, which is thought to be vital to bone’s intrinsic fracture toughness. Willett et al. (2017) measured the micro-damage Process Zone using micro-computed tomography and barium sulphate staining after sub-critical loading of single edge notch (bending) (SEN(B)) specimens. Recently, we sought to provide a computational model of this important mechanism. A finite element (FE) model of a SEN(B) specimen was developed in ABAQUS using continuum damage mechanics (CDM) to simulate non-linear behavior due to micro-damage. Elastic behavior was modeled as linear, transversely isotropic. Micro-damage initiation was incorporated using the Hashin failure criterion. Failure behavior was modeled using a damage law based on fracture energies. CDM-FE can model the micro-damage Process Zone with good fidelity if relatively high viscous regularization settings are used. The Process Zone was found to mimic that measured experimentally. The load-deflection curve from the FE model was similar to experimental curves within
-
the micro damage Process Zone during transverse cortical bone fracture no ears at crack growth initiation
Journal of The Mechanical Behavior of Biomedical Materials, 2017Co-Authors: Thomas L. Willett, David S Josey, Gagan Minhas, John MontesanoAbstract:Abstract Objective Apply high-resolution benchtop micro-computed tomography (micro-CT) to gain greater understanding and knowledge of the formation of the micro-damage Process Zone formed during traverse fracture of cortical bone. Methods Bovine cortical bone was cut into single edge notch (bending) fracture testing specimens with the crack on the transverse plane and oriented to grow in the circumferential direction. We used a multi-specimen technique and deformed the specimens to various individual secant modulus loss levels (P-values) up to and including maximum load (Pmax). Next, the specimens were infiltrated with a BaSO 4 precipitation stain and scanned at 3.57-μm isotropic voxel size using a benchtop high resolution-micro-CT. Measurements of the micro-damage Process Zone volume, width and height were made. These were compared with the simple Irwin's Process Zone model and with finite element models. Electron and confocal microscopy confirmed the formation of BaSO 4 precipitate in micro-cracks and other porosity, and an interesting novel mechanism similar to tunneling. Results Measurable micro-damage was detected at low P values and the volume of the Process Zone increased according to a second order polynomial trend. Both width and height grew linearly up to Pmax, at which point the Process Zone cross-section (perpendicular to the plane of the crack) was almost circular on average with a radius of approximately 550 µm (approximately one quarter of the unbroken ligament thickness) and corresponding to the shape expected for a biological composite under plane stress conditions. Conclusion This study reports details of the micro-damage fracture Process Zone previously unreported for cortical bone. High-resolution micro-CT enables 3D visualization and measurement of the Process Zone and confirmation that the crack front edge and Process Zone are affected by microstructure. It is clear that the Process Zone for the specimens studied grows to be meaningfully large, confirming the need for the J-integral approach and it does not achieve steady state at Pmax in most specimens. With further development, this approach may become valuable towards better understanding the role of the Process Zone in cortical bone fracture and the effects of relevant modifications towards changes in fracture toughness in a cost effective way.
M E R Shanahan - One of the best experts on this subject based on the ideXlab platform.
-
instrumented end notched flexure crack propagation and Process Zone monitoring part ii data reduction and experimental
International Journal of Solids and Structures, 2013Co-Authors: Michal K Budzik, Julien Jumel, Ben N Salem, M E R ShanahanAbstract:A mode II instrumented end notched flexure three point bending (ENF) adhesion test is described. The adhesive joint consists of two aluminium alloy (AW7075-T6) plates bonded with a structural epoxy adhesive (Hysol® EA 9395™). Strain gauges are attached to the outer surface (backface) of the substrates in the lengthwise direction to measure local surface strain during crack propagation. Simultaneously, load/displacement measurements are performed. Two cases were investigated. The first was static: the joint was loaded below the crack propagation threshold. In the second, applied load above the threshold led to crack propagation. The former test confirmed the predicted load transfer mechanism between bonded and unbonded parts of the joint. In the second case, the crack front Process Zone was revealed in situ in mode II, we believe for the first time. These new results permitted validation of simple or refined analytical/numerical models including those of the cohesive Zone. In addition, the backface strain gauge monitoring technique exhibited unexpected mode I contributions, quantitatively evaluated. Finally, R-curves are presented, as estimated with various standard models and compared with that postulated, where the Process Zone is accounted for.
A Chudnovsky - One of the best experts on this subject based on the ideXlab platform.
-
slow crack growth its modeling and crack layer approach a review
International Journal of Engineering Science, 2014Co-Authors: A ChudnovskyAbstract:Abstract A review of empirical equations for slow crack growth under fatigue and creep conditions is presented. The crack propagation rate is commonly expressed as a function of stress intensity factor or energy release rate. A concept of crack driving force and crack stability analysis is employed to predict crack behavior under different loading conditions; the concept of crack growth resistance, such as an effective surface energy, is used. It is shown that for a stable crack propagation (the energy release rate is a decreasing function of crack length) crack growth equation results from the crack equilibrium condition, if the crack resistance is assumed to be constant. Experimental studies demonstrate that crack growth resistance is not constant, but changes with crack propagation. Formation of the so-called Process Zone appears to be responsible for the changes. Process Zone (PZ) is a material reaction to stress concentration at crack tip and it is commonly observed under fatigue and creep conditions in most engineering materials. For an unstable crack growth (the energy release rate is an increasing function of crack length) the effect of PZ even more dramatic; for example, in a perfectly homogeneous elastic solid slow crack growth would be impossible without the stabilizing effect of PZ. A system of a crack and PZ is referred to as crack-layer (CL). CL driving forces that are thermodynamic forces associated with crack and PZ growth are introduced. CL growth equations are employed to explain the observed variations of crack growth resistance commonly known as R-curve behavior. The evolution of the Process Zone in a complex stress field is illustrated by an experiment demonstrating how Process Zone accelerates and decelerates crack growth. Modeling of the crack–Process Zone interaction is a challenging problem; recent advances in computational techniques make it solvable. The CL approach is illustrated on an example of engineering thermoplastics. Applications to lifetime prediction of structural components, as well as toughness and durability of materials are discussed.
-
application of the crack layer theory to modeling of slow crack growth in polyethylene
International Journal of Fracture, 1999Co-Authors: A Chudnovsky, Y ShulkinAbstract:A crack and a domain of highly fibrillated and stretched material ahead of the crack (Process Zone), commonly observed in polyethylene, are considered as a system called the crack layer. Slow crack layer growth is assumed to be a result of interactions between the crack, Process Zone and the rest of the body, as well as of degradation of the Process Zone material. The energy balance for Process Zone formation and crack layer advance is presented. The equations governing crack layer propagation are formulated and numerically solved. The proposed mechanism of fracture Process models the discontinuous crack growth often observed in polyethylene, and predicts the relationship between the crack growth rate and the stress intensity factor consistent with the experimental one. The dependence of the lifetime on load is discussed.
S Muralidhara - One of the best experts on this subject based on the ideXlab platform.
-
fracture Process Zone size and true fracture energy of concrete using acoustic emission
Construction and Building Materials, 2010Co-Authors: S Muralidhara, B Raghu K Prasad, Hamid Eskandari, Bhushan Lal KarihalooAbstract:Acoustic emission (AE) energy, instead of amplitude, associated with each of the event is used to estimate the fracture Process Zone (FPZ) size. A steep increase in the cumulative AE energy of the events with respect to time is correlated with the formation of FPZ. Based on the AE energy released during these events and the locations of the events, FPZ size is obtained. The size-independent fracture energy is computed using the expressions given in the boundary effect model by least squares method since over-determined system of equations are obtained when data from several specimens are used. Instead of least squares method a different method is suggested in which the transition ligament length, measured from the plot of histograms of AE events plotted over the un-cracked ligament, is used directly to obtain size-independent fracture energy. The fracture energy thus calculated seems to be size-independent.
