The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Lanhua Wei - One of the best experts on this subject based on the ideXlab platform.
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Thermal diffusivity maps: Case studies in ceramics
Journal of Materials Research, 1997Co-Authors: Lanhua Wei, Grady S. WhiteAbstract:A new methodology for mapping thermal diffusivity using a photothermal deflection method is introduced. Two case studies are made: fiber-reinforced composite structures and contact damage zones in alumina. In the former, characterization of thermal microstructural features is demonstrated; in the latter, Microcrack Density is quantified. Experimental data are analyzed and compared with literature results. Advantages and limitations of the technique are discussed.
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quantifying local Microcrack Density in ceramics a comparison of instrumented indentation and thermal wave techniques
Journal of the American Ceramic Society, 1995Co-Authors: Douglas T. Smith, Lanhua WeiAbstract:Instrumented indentation and thermal wave techniques are used as local, quantitative probes of Microcrack Density in a silicon nitride that has been subjected to severe Hertzian contact stress. The techniques act as local probes, sampling volumes of material <10{sup {minus}3} mm{sup 3}. Microcracked regions are created using a tungsten carbide spherical indenter, as a result of high shear stress in the compressive zone beneath the indenter. The Microcracked zones, studied in cross section using a ``bonded interface`` technique, increased both in size and in degree of damage with increasing Hertzian load. Within the zones, Young`s modulus is measured using instrumented indentation, and the thermal diffusivity using a thermal wave technique; both quantities are lower in the damaged regions than in the undamaged regions. The shifts in modulus and diffusivity are used independently to calculate Microcrack densities using related models of the effect of Microcracks on each property. The two techniques show the same functional relationship between Hertzian contact load and Microcrack Density, and yield densities that agree to within a factor of approximately 2.
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Quantifying Local Microcrack Density in Ceramics: A Comparison of Instrumented Indentation and Thermal Wave Techniques
Journal of the American Ceramic Society, 1995Co-Authors: Douglas T. Smith, Lanhua WeiAbstract:Instrumented indentation and thermal wave techniques are used as local, quantitative probes of Microcrack Density in a silicon nitride that has been subjected to severe Hertzian contact stress. The techniques act as local probes, sampling volumes of material
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Grinding force and Microcrack Density in abrasive machining of silicon nitride
Journal of Materials Research, 1995Co-Authors: Lanhua Wei, Said JahanmirAbstract:The relationship between grinding forces and the material`s resistance to microfracture is investigated in abrasive machining of silicon nitride ceramics. Surface grinding is performed on two forms of silicon nitride with different microstructures, and the grinding forces are measured. In addition, single-point scratching is performed on polished surfaces to amplify the damage associated with the action of an individual abrasive particle in grinding. A thermal wave measurement technique in then used on the cross sections to characterize the Density of subsurface Microcracks associated with scratching. Compared to a fine-grain silicon nitride, the Density of Microcracks in a coarse-grain silicon nitride is significantly larger, while the grinding force is smaller. The smaller grinding force for the coarse-grain silicon nitride is attributed to the ease of local intergranular microfracture and grain dislodgement during grinding. {copyright} {ital 1995} {ital Materials} {ital Research} {ital Society}.
Francoise Peyrin - One of the best experts on this subject based on the ideXlab platform.
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Synchrotron Radiation Micro-CT at the Micrometer Scale for the Analysis of the Three-Dimensional Morphology of Microcracks in Human Trabecular Bone
PLoS ONE, 2011Co-Authors: Aymeric Larrue, Aline Rattner, Zsolt-andrei Peter, Norbert Laroche, Cécile Olivier, Laurence Vico, Francoise PeyrinAbstract:Bone quality is an important concept to explain bone fragility in addition to bone mass. Among bone quality factors, microdamage which appears in daily life is thought to have a marked impact on bone strength and plays a major role in the repair process. The starting point for all studies designed to further our understanding of how bone microdamage initiate or dissipate energy, or to investigate the impact of age, gender or disease, remains reliable observation and measurement of microdamage. In this study, 3D Synchrotron Radiation (SR) micro-CT at the micrometric scale was coupled to image analysis for the three-dimensional characterization of bone microdamage in human trabecular bone specimens taken from femoral heads. Specimens were imaged by 3D SR micro-CT with a voxel size of 1.4 mm. A new tailored 3D image analysis technique was developed to segment and quantify Microcracks. Microcracks from human trabecular bone were observed in different tomographic sections as well as from 3D renderings. New 3D quantitative measurements on the Microcrack Density and morphology are reported on five specimens. The 3D Microcrack Density was found between 3.1 and 9.4/mm3 corresponding to a 2D Density between 0.55 and 0.76 /mm2. The Microcrack length and width measured in 3D on five selected Microcrack ranged respectively from 164 mm to 209 mm and 100 mm to 120 mm. This is the first time that various Microcracks in unloaded human trabecular bone-from the simplest linear crack to more complex cross-hatch cracks-have been examined and quantified by 3D imaging at this scale. The suspected complex morphology of Microcracks is here considerably more evident than in the 2D observations. In conclusion, this technique opens new perspective for the 3D investigation of Microcracks and the impact of age, disease or treatment.
David P. Fyhrie - One of the best experts on this subject based on the ideXlab platform.
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On sampling bones for Microcracks
Bone, 2007Co-Authors: R.b. Martin, Oscar C. Yeh, David P. FyhrieAbstract:Abstract This paper addresses the problem of designing experiments to measure Microcrack Density in cortical bone. Microcracks are relatively scarce in bone cross-sections, and their size requires microscope settings having small fields of view. Thus, substantial time is required to count cracks in each cross-section. Consequently, most studies evaluate a relatively small cross-sectional area from each specimen, the chance of finding a crack in any given field is small, and there is a significant chance of not finding even one crack in the specimens representing a particular subject. Therefore, a statistical model for Microcrack counting was created to develop guidelines for sampling bones for Microcracks. Three questions were addressed. 1) What are the relationships of sample size to variability in Microcrack Density results and the probability of crackless specimens? 2) How can sample size be chosen a priori so as to reduce the probability of crackless specimens and the associated variability in the data to an acceptable level? 3) What are the confidence intervals for the mean Density of Microcracks measured using microscopic counting? Using a Poisson model for the distribution of Microcracks within microscope fields the total area (mm 2 ) that should be examined for each specimen is given by A s = − ln( F ) / Cr.Dn, where Cr.Dn is the expected Microcrack Density for an individual sample and F is the desired probability (expressed as a fraction) that the individual sample will contain no Microcracks. This equation is validated against 8 results from three different experiments.
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Trabecular shear stresses predict in vivo linear Microcrack Density but not diffuse damage in human vertebral cancellous bone.
Annals of biomedical engineering, 2003Co-Authors: Yener N. Yeni, Fu J. Hou, Traci E. Ciarelli, Deepak Vashishth, David P. FyhrieAbstract:Linear Microcracks and diffuse damage (staining over a broad region) are two types of microscopic damage known to occur in vivo in human vertebral trabecular bone. These damage types might be associated with vertebral failure. Using microcomputed tomography and finite element analysis for specimens of cancellous bone, we estimated the stresses in the trabeculae of human vertebral tissue for inferosuperior loading. Microdamage was quantified histologically. The Density of in vivo linear Microcracks was, but the diffuse damage area was not, related to the estimates of von Mises stress distribution in the tissue. In vivo linear Microcrack Density increased with increasing coefficient of variation of the trabecular von Mises stress and with increasing average trabecular von Mises stress generated per superoinferior apparent axial stress. Nonlinear increase in linear crack Density, similar to the increase of the coefficient of variation of trabecular shear stresses, with decreasing bone stiffness and bone volume fraction suggests that damage may accumulate rather rapidly in diseases associated with low bone Density due to the dramatic increase of shear stresses in the tissue. © 2003 Biomedical Engineering Society.
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Decline in osteocyte lacunar Density in human cortical bone is associated with accumulation of Microcracks with age
Bone, 2000Co-Authors: Deepak Vashishth, Mitchell B. Schaffler, O. Verborgt, George Divine, David P. FyhrieAbstract:Abstract Despite osteocytes’ ideal position to sense the local environment and thereby influence bone remodeling, the function of osteocytes in bone remains controversial. In this study, histomorphometric examination of male and female femoral middiaphyseal cortical bone was conducted to determine if bone’s remodeling response, indicated by tissue porosity and accumulation of damage, is associated with osteocyte lacunar Density (number of osteocyte lacunae per bone area). The results support the sensory role of the osteocyte network as the decline in osteocyte lacunar Density in human cortical bone is associated with the accumulation of Microcracks and increase in porosity with age. Porosity and Microcrack Density increased exponentially with a decline in osteocyte lacunar Density indicating that a certain minimum number of osteocytes is essential for an “operational” network. No gender-related differences were found in the relationship of osteocyte lacunar Density to age, porosity, or Microcrack Density. The coefficient of variation of osteocyte lacunar Density increased linearly with age, indicating that aging bone tissue is characterized by increased heterogeneity in the spatial organization of osteocytes. Osteocyte lacunar Density, porosity, and Microcrack Density exhibited the same exponential probability Density distribution in the donor population, indicating their regulation by similar biological phenomena.
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In vivo trabecular Microcracks in human vertebral bone
Bone, 1996Co-Authors: T. E. Wenzel, Mitchell B. Schaffler, David P. FyhrieAbstract:Human vertebral cancellous bone from white males (N =19), black males (N = 16), white females (N = 12), and black females (N = 17) was examined histologically for the presence, numerical Density, and morphology of in vivo microscopic cracking (microdamage). Two patterns of Microcracks, linear and cross-hatched, were observed. Linear Microcracks were observed in both the central portion and near surfaces of trabeculae. Those inside trabeculae were usually single Microcracks approximately 50 pm in length and were found in both cement lines and in interstitial bone matrix. Linear Microcracks near the trabecular surface were usually multiple parallel cracks approximately 80 μm in length. Microcracks with a cross-hatched appearance were less prevalent. They were observed primarily in vertically oriented trabeculae and were often surrounded by an area of diffuse staining. Two-way ANOVA revealed no differences in Microcrack Density (Cr.Dn; #/mm2) between males and females [mean (SD) 5.13 (5.02) vs. 5.41 (6.26), respectively], but whites had significantly higher Microcrack Density than blacks [7.00 (5.71) vs. 3.63 (4.98), respectively, p < 0.05]. White males had a significantly higher Microcrack Density than black males [7.60 (5.56) vs. 2.21 (1.78), respectively, p < 0.05]. Although not statistically significant, white females also had higher Microcrack Density than black females. In contrast to what has been reported in the femur, regression analysis found no statistically significant relationship between Microcrack Density in the spine and age for any of the four race-gender groups. However, significant power relationships were found between Microcrack Density and bone area fraction for all groups except for black females. The difference between axial and appendicular bone remodeling rates, and their implications for microdamage accumulation, are discussed.
Amit Shyam - One of the best experts on this subject based on the ideXlab platform.
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Stress-induced Microcrack Density evolution in β-eucryptite ceramics: Experimental observations and possible route to strain hardening
Acta Materialia, 2018Co-Authors: Bernd R. Müller, Ryan Cooper, M.r. Wheeler, Amit Pandey, Amit Shyam, Axel Lange, Andreas Kupsch, Manfred P. Hentschel, A. Staude, Giovanni BrunoAbstract:Abstract In order to investigate their Microcracking behaviour, the microstructures of several β-eucryptite ceramics, obtained from glass precursor and cerammed to yield different grain sizes and Microcrack densities, were characterized by laboratory and synchrotron x-ray refraction and tomography. Results were compared with those obtained from scanning electron microscopy (SEM). In SEM images, the characterized materials appeared fully dense but computed tomography showed the presence of pore clusters. Uniaxial tensile testing was performed on specimens while strain maps were recorded and analyzed by Digital Image Correlation (DIC). X-ray refraction techniques were applied on specimens before and after tensile testing to measure the amount of the internal specific surface (i.e., area per unit volume). X-ray refraction revealed that (a) the small grain size (SGS) material contained a large specific surface, originating from the grain boundaries and the interfaces of TiO2 precipitates; (b) the medium (MGS) and large grain size (LGS) materials possessed higher amounts of specific surface compared to SGS material due to Microcracks, which decreased after tensile loading; (c) the precursor glass had negligible internal surface. The unexpected decrease in the internal surface of MGS and LGS after tensile testing is explained by the presence of compressive regions in the DIC strain maps and further by theoretical arguments. It is suggested that while some Microcracks merge via propagation, more close mechanically, thereby explaining the observed X-ray refraction results. The mechanisms proposed would allow the development of a strain hardening route in ceramics.
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Effect of Microcracking on the uniaxial tensile response of β-eucryptite ceramics: Experiments and constitutive model
Acta Materialia, 2017Co-Authors: Ryan Cooper, Giovanni Bruno, M.r. Wheeler, Amit Pandey, Thomas R. Watkins, Amit ShyamAbstract:A constitutive model for the nonlinear or “pseudoplastic” mechanical behavior in a linear-elastic solid with thermally induced Microcracks is developed and applied to experimental results. The model is termed strain dependent Microcrack Density approximation (SDMDA) and is an extension of the modified differential scheme that describes the slope of the stress-strain curves of Microcracked solids. SDMDA allows a continuous variation in the Microcrack Density with tensile loading. Experimental uniaxial tensile response of β-eucryptite glass and ceramics with controlled levels of Microcracking is reported. It is demonstrated that SDMDA can well describe the extent of non-linearity in the experimental uniaxial tensile response of β-eucryptite with varying levels of Microcracking. The advantages of the SDMDA are discussed in regard to tensile loading.
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Young’s modulus and Poisson’s ratio changes due to machining in porous Microcracked cordierite
Journal of Materials Science, 2016Co-Authors: Ryan Cooper, Giovanni Bruno, Thomas R. Watkins, Yener Onel, Axel Lange, Amit ShyamAbstract:Microstructural changes in porous cordierite caused by machining were characterized using microtensile testing, X-ray computed tomography, and scanning electron microscopy. Young’s moduli and Poisson’s ratios were determined on ~215- to 380-μm-thick machined samples by combining digital image correlation and microtensile loading. The results provide evidence for an increase in Microcrack Density and decrease of Young’s modulus due to machining of the thin samples extracted from diesel particulate filter honeycombs. This result is in contrast to the known effect of machining on the strength distribution of bulk, monolithic ceramics.
Aymeric Larrue - One of the best experts on this subject based on the ideXlab platform.
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Synchrotron Radiation Micro-CT at the Micrometer Scale for the Analysis of the Three-Dimensional Morphology of
2016Co-Authors: Microcracks Human, Trabecular Bone, Aymeric Larrue, Aline Rattner, Zsolt-andrei Peter, Norbert LarocheAbstract:Bone quality is an important concept to explain bone fragility in addition to bone mass. Among bone quality factors, microdamage which appears in daily life is thought to have a marked impact on bone strength and plays a major role in the repair process. The starting point for all studies designed to further our understanding of how bone microdamage initiate or dissipate energy, or to investigate the impact of age, gender or disease, remains reliable observation and measurement of microdamage. In this study, 3D Synchrotron Radiation (SR) micro-CT at the micrometric scale was coupled to image analysis for the three-dimensional characterization of bone microdamage in human trabecular bone specimens taken from femoral heads. Specimens were imaged by 3D SR micro-CT with a voxel size of 1.4 mm. A new tailored 3D image analysis technique was developed to segment and quantify Microcracks. Microcracks from human trabecular bone were observed in different tomographic sections as well as from 3D renderings. New 3D quantitative measurements on the Microcrack Density and morphology are reported on five specimens. The 3D Microcrack Density was found between 3.1 and 9.4/mm3 corresponding to a 2D Density between 0.55 and 0.76 /mm2. The Microcrack length and width measured in 3D on five selected Microcrack ranged respectively from 164 mm to 209 mm and 100 mm to 120 mm. This is the first time that various Microcracks in unloaded human trabecular bone- from the simplest linear crack to more complex cross-hatch cracks- have been examined and quantified by 3D imaging at this scale. The suspected complex morphology of Microcracks is her
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Synchrotron Radiation Micro-CT at the Micrometer Scale for the Analysis of the Three-Dimensional Morphology of Microcracks in Human Trabecular Bone
PLoS ONE, 2011Co-Authors: Aymeric Larrue, Aline Rattner, Zsolt-andrei Peter, Norbert Laroche, Cécile Olivier, Laurence Vico, Francoise PeyrinAbstract:Bone quality is an important concept to explain bone fragility in addition to bone mass. Among bone quality factors, microdamage which appears in daily life is thought to have a marked impact on bone strength and plays a major role in the repair process. The starting point for all studies designed to further our understanding of how bone microdamage initiate or dissipate energy, or to investigate the impact of age, gender or disease, remains reliable observation and measurement of microdamage. In this study, 3D Synchrotron Radiation (SR) micro-CT at the micrometric scale was coupled to image analysis for the three-dimensional characterization of bone microdamage in human trabecular bone specimens taken from femoral heads. Specimens were imaged by 3D SR micro-CT with a voxel size of 1.4 mm. A new tailored 3D image analysis technique was developed to segment and quantify Microcracks. Microcracks from human trabecular bone were observed in different tomographic sections as well as from 3D renderings. New 3D quantitative measurements on the Microcrack Density and morphology are reported on five specimens. The 3D Microcrack Density was found between 3.1 and 9.4/mm3 corresponding to a 2D Density between 0.55 and 0.76 /mm2. The Microcrack length and width measured in 3D on five selected Microcrack ranged respectively from 164 mm to 209 mm and 100 mm to 120 mm. This is the first time that various Microcracks in unloaded human trabecular bone-from the simplest linear crack to more complex cross-hatch cracks-have been examined and quantified by 3D imaging at this scale. The suspected complex morphology of Microcracks is here considerably more evident than in the 2D observations. In conclusion, this technique opens new perspective for the 3D investigation of Microcracks and the impact of age, disease or treatment.