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R O Ritchie - One of the best experts on this subject based on the ideXlab platform.
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on the origin of the toughness of mineralized tissue microCracking or Crack Bridging
Bone, 2004Co-Authors: Ravi K Nalla, Jamie J Kruzic, R O RitchieAbstract:Abstract Two major mechanisms that could potentially be responsible for toughening in mineralized tissues, such as bone and dentin, have been identified—microCracking and Crack Bridging. While evidence has been reported for both mechanisms, there has been no consensus thus far on which mechanism plays the dominant role in toughening these materials. In the present study, we seek to present definitive experimental evidence supporting Crack Bridging, rather than microCracking, as the most significant mechanism of toughening in cortical bone and dentin. In vitro fracture toughness experiments were conducted to measure the variation of the fracture resistance with Crack extension [resistance–curve (R-curve) behavior] for both materials with special attention paid to changes in the sample compliance. Because these two toughening mechanisms induce opposite effects on the sample compliance, such experiments allow for the definitive determination of the dominant toughening mechanism, which in the present study was found to be Crack Bridging for microstructurally large Crack sizes. The results of this work are of relevance from the perspective of developing a micromechanistic framework for understanding fracture behavior of mineralized tissue and in predicting failure in vivo.
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fracture and fatigue resistance of mo si b alloys for ultrahigh temperature structural applications
Scripta Materialia, 2004Co-Authors: Jamie J Kruzic, R O Ritchie, J H SchneibelAbstract:Fracture and fatigue-Crack growth properties are examined for a series of Mo-Mo3Si-Mo5SiB2 containing alloys, which utilize a continuous a-Mo matrix to achieve unprecedented room-temperature fracture resistance (>20 MPaAm). Mechanistically, these properties are explained in terms of toughening by Crack trapping and Crack Bridging by the more ductile a-Mo phase.
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Crack blunting Crack Bridging and resistance curve fracture mechanics in dentin effect of hydration
Biomaterials, 2003Co-Authors: Jamie J Kruzic, Ravi K Nalla, J H Kinney, R O RitchieAbstract:Few studies have focused on a description of the fracture toughness properties of dentin in terms of resistance-curve (R-curve) behavior, i.e., fracture resistance increasing with Crack extension, particularly in light of the relevant toughening mechanisms involved. Accordingly, in the present study, fracture mechanics based experiments were conducted on elephant dentin in order to determine such R-curves, to identify the salient toughening mechanisms and to discern how hydration may affect their potency. Crack Bridging by unCracked ligaments, observed directly by microscopy and X-ray tomography, was identified as a major toughening mechanism, with further experimental evidence provided by compliance-based experiments. In addition, with hydration, dentin was observed to display significant Crack blunting leading to a higher overall fracture resistance than in the dehydrated material. The results of this work are deemed to be of importance from the perspective of modeling the fracture behavior of dentin and in predicting its failure in vivo.
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fracture and fatigue Crack growth behavior in ductile phase toughened molybdenum disilicide effects of niobium wire vs particulate reinforcements
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 1996Co-Authors: K Badrinarayanan, R O Ritchie, A L Mckelvey, K Venkateswara T RaoAbstract:A study has been made of the fracture toughness/resistance-curve (R-curve) and cyclic fatigue-Crack propagation behavior in a molybdenum disilicide composite, ductile-phase toughened with nominally 20 vol pct Nb-wire mesh reinforcements (Nb m /MoSi2); results are compared with monolithic MoSi2 and MoSi2 reinforced with 20 vol pct spherical Nb particles (Nb p /MoSi2). It is found that the high aspect ratio wire reinforcements induce significant toughening in MoSi2, both under monotonic and cyclic fatigue loading conditions. Specifically, the Nb m /MoSi2 composite exhibits R-curve behavior with a steady-state fracture toughness of ∼13 MPa $$\sqrt m $$ , compared to unstable fracture atK c values below 5 MPa $$\sqrt m $$ in unreinforced MoSi2 or Nb p /MoSi2. Such behavior is seen to be associated with extensive Crack deflection within the reaction layer between Nb and the matrix, which leads to Crack Bridging by the unbroken ductile phase. Similarly, resistance to fatigue-Crack growth is found to be far superior in the wire-reinforced composite over pure MoSi2 and Nb p /MoSi2. Although Crack paths are again characterized by extensive deflection along the Nb/matrix reaction layer, the role of Crack Bridging is diminished under cyclic loading due to fatigue failure of the Nb. Instead, the superior fatigue properties of the Nb m /MoSi2 composite are found to be associated with high levels of Crack closure that result from highly deflected Crack paths along the (Nb,Mo)5Si3 reaction layer interface.
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on the contrasting role of ductile phase reinforcements in the fracture toughness and fatigue Crack propagation behavior of tinb γ tial intermetallic matrix composites
Acta Metallurgica Et Materialia, 1992Co-Authors: K Venkateswara T Rao, G R Odette, R O RitchieAbstract:Abstract A comparative study has been made on the role of ductile-phase toughening under monotonic and cyclic loading at room temperature, specifically involving the fracture toughness and fatigue-Crack propagation behavior of a γ-TiAl intermetallic alloy reinforced with 10 vol.% of ∼ 50 μ -sized ductile TiNb particles. Under monotonic loading, substantial toughening is achieved in the composite primarily from Crack Bridging by unCracked TiNb particles in the wake of the Crack tip; additional contributions are provided by shielding from Crack-particle interactions. Compared to a K Ic value of ∼ 8 MPA√m for monolithic γ-TiAl, the composite shows significant resistance-curve behavior with a steady-state fracture toughness exceeding 25–30 MPa√m; in this regime, measured Bridging zones approach ∼ 4 mm in length. In contrast, under cyclic loading, such ductile-particle toughening is found to be far less effective, due to the susceptibility of the ductile metallic phase to fatigue failure. No evidence of Crack Bridging by TiNb particles is observed to within ∼ 150 μ m of the Crack tip, and fatigue-Crack propagation is observed at a stress intensity as low as 6 MPa√m, far below that required to initiate Cracking under monotonic loading.
Jamie J Kruzic - One of the best experts on this subject based on the ideXlab platform.
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on the origin of the toughness of mineralized tissue microCracking or Crack Bridging
Bone, 2004Co-Authors: Ravi K Nalla, Jamie J Kruzic, R O RitchieAbstract:Abstract Two major mechanisms that could potentially be responsible for toughening in mineralized tissues, such as bone and dentin, have been identified—microCracking and Crack Bridging. While evidence has been reported for both mechanisms, there has been no consensus thus far on which mechanism plays the dominant role in toughening these materials. In the present study, we seek to present definitive experimental evidence supporting Crack Bridging, rather than microCracking, as the most significant mechanism of toughening in cortical bone and dentin. In vitro fracture toughness experiments were conducted to measure the variation of the fracture resistance with Crack extension [resistance–curve (R-curve) behavior] for both materials with special attention paid to changes in the sample compliance. Because these two toughening mechanisms induce opposite effects on the sample compliance, such experiments allow for the definitive determination of the dominant toughening mechanism, which in the present study was found to be Crack Bridging for microstructurally large Crack sizes. The results of this work are of relevance from the perspective of developing a micromechanistic framework for understanding fracture behavior of mineralized tissue and in predicting failure in vivo.
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fracture and fatigue resistance of mo si b alloys for ultrahigh temperature structural applications
Scripta Materialia, 2004Co-Authors: Jamie J Kruzic, R O Ritchie, J H SchneibelAbstract:Fracture and fatigue-Crack growth properties are examined for a series of Mo-Mo3Si-Mo5SiB2 containing alloys, which utilize a continuous a-Mo matrix to achieve unprecedented room-temperature fracture resistance (>20 MPaAm). Mechanistically, these properties are explained in terms of toughening by Crack trapping and Crack Bridging by the more ductile a-Mo phase.
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Crack blunting Crack Bridging and resistance curve fracture mechanics in dentin effect of hydration
Biomaterials, 2003Co-Authors: Jamie J Kruzic, Ravi K Nalla, J H Kinney, R O RitchieAbstract:Few studies have focused on a description of the fracture toughness properties of dentin in terms of resistance-curve (R-curve) behavior, i.e., fracture resistance increasing with Crack extension, particularly in light of the relevant toughening mechanisms involved. Accordingly, in the present study, fracture mechanics based experiments were conducted on elephant dentin in order to determine such R-curves, to identify the salient toughening mechanisms and to discern how hydration may affect their potency. Crack Bridging by unCracked ligaments, observed directly by microscopy and X-ray tomography, was identified as a major toughening mechanism, with further experimental evidence provided by compliance-based experiments. In addition, with hydration, dentin was observed to display significant Crack blunting leading to a higher overall fracture resistance than in the dehydrated material. The results of this work are deemed to be of importance from the perspective of modeling the fracture behavior of dentin and in predicting its failure in vivo.
P J Withers - One of the best experts on this subject based on the ideXlab platform.
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effect of hydration and Crack orientation on Crack tip strain Crack opening displacement and Crack tip shielding in elephant dentin
Dental Materials, 2018Co-Authors: Shelley D Rawson, P J WithersAbstract:Abstract Objectives To quantify the extent of Crack-tip plasticity, Crack opening displacement (COD) and Crack Bridging for Crack growth perpendicular (HAH) and parallel (RAR) to the tubules in elephant dentin under both hydrated and dry conditions to better understand their influence on intrinsic and extrinsic toughening during Crack growth. Methods Compact tension test-pieces were prepared from a tusk of African elephant ivory. Crack-tip strain mapping and COD measurements by digital image correlation (DIC) technique were made under incremental loading and unloading of Cracks for hydrated and dry dentin of different orientations. Results For the RAR test-piece the plastic zones were significantly larger in the hydrated condition compared to when dry. By contrast, the plastic strains in the HAH test-piece were negligible in both wet and dry conditions. In the RAR condition the Crack front was broken up into overlapping longitudinal ‘fingers’ with Crack Bridging regions in between, the ligaments extending 400 μm behind the Crack front in the dry case. This could only be seen in 3D by X-ray CT. Extrinsic shielding reduces the Crack-tip stresses by 52% and 40% for hydrated and dry RAR test-pieces respectively. No significant Bridging was found in the HAH case. Significance For Crack growth parallel to the tubules, collagen plasticity determines the intrinsic toughening, whereas microCracking from the tubules governs extrinsic shielding via ligament Bridging, which is maintained further behind the Crack in the hydrated case. For Cracks grown perpendicular to the tubules, neither toughening mechanisms are significant.
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x ray microtomographic observation of intergranular stress corrosion Cracking in sensitised austenitic stainless steel
Materials Science and Technology, 2006Co-Authors: L Babout, Dirk Engelberg, T J Marrow, P J WithersAbstract:Intergranular stress corrosion Cracking in a sensitised type 302 stainless steel wire has been observed in situ using high resolution X-ray microtomography. Tomography enables the development and failure of Crack Bridging ligaments to be studied in detail in three dimensions. Direct comparison of these features has been made with scanning electron microscopy fractography. The Crack bridges failed in a ductile manner, with a morphology that is consistent with non-sensitised low energy grain boundaries.
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three dimensional observations and modelling of intergranular stress corrosion Cracking in austenitic stainless steel
Journal of Nuclear Materials, 2006Co-Authors: T J Marrow, Dirk Engelberg, P J Withers, L Babout, Andrey P Jivkov, Paul Wood, Nicholas Stevens, R C NewmanAbstract:Stress corrosion Cracking is a life-limiting factor in many components of nuclear power plant in which failure of structural components presents a substantial hazard to both safety and economic performance. Uncertainties in the kinetics of short Crack behaviour can have a strong influence on lifetime prediction, and arise due both to the complexity of the underlying mechanisms and to the difficulties of making experimental observations. This paper reports on an on-going research programme into the dynamics and morphology of intergranular stress corrosion Cracking in austenitic stainless steels in simulated light water environments, which makes use of recent advances in high resolution X-ray microtomography. In particular in situ, three dimensional X-ray tomographic images of intergranular stress corrosion Crack nucleation and growth in sensitised austenitic stainless steel provide evidence for the development of Crack Bridging ligaments, caused by the resistance of non-sensitised special grain boundaries. In parallel a simple grain Bridging model, introduced to quantify the effect of Crack Bridging on Crack development, has been assessed for thermo-mechanically processed microstructures via statically loaded room temperature simulant solution tests and as well as high temperature/pressure autoclave studies. Thermo-mechanical treatments have been used to modify the grain size, grain boundary character and triple junction distributions, with a consequent effect on Crack behaviour. Preliminary three-dimensional finite element models of intergranular Crack propagation have been developed, with the aim of investigating the development of Crack Bridging and its effects on Crack propagation and Crack coalescence.
Viktor Mechtcherine - One of the best experts on this subject based on the ideXlab platform.
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tailoring the Crack Bridging behavior of strain hardening cement based composites shcc by chemical surface modification of poly vinyl alcohol pva fibers
Cement & Concrete Composites, 2020Co-Authors: Iurie Curosu, Marco Liebscher, Ghaith Alsous, Erjon Muja, Astrid Drechsler, Ralf Frenzel, Alla Synytska, Viktor MechtcherineAbstract:Abstract With the aim of reducing the affinity of poly(vinyl alcohol) (PVA) fibers to cementitious matrices and allowing the tailoring of Crack-Bridging behavior in strain-hardening cement-based composites (SHCC), a study was conducted, in which PVA fibers typically used in SHCC were subjected to different types of chemical surface modification. Alkyl chains were covalently bonded to the fiber surfaces via an acid-catalyzed acetalization with butanal diluted in sulfuric acid (H2SO4) and hydrochloric acid (HCl), respectively. X-ray photoelectron spectroscopy and contact angle measurements documented the successful treatment and the hydrophobic character of the modified fiber surfaces when compared to the as-received oiled and non-oiled fibers. The single-fiber pullout experiments showed that the butanal modification performed in H2SO4 yielded a considerably more pronounced reduction in chemical adhesion in comparison to butanal-HCl. However, the butanal-H2SO4 modification yielded no significant improvement in composite ductility, which could be traced back to the relatively low abrasion resistance of the fibers and to the resulting surface damage amplified by the higher extent of slippage. Furthermore, the milder butanal-HCl modification yielded a balanced fiber-matrix adhesion, resulting in SHCC with distinctly superior tensile properties.
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Durability of strain-hardening cement-based composites (SHCC)
Materials and Structures, 2012Co-Authors: Gideon P. A. G. Van Zijl, Byung H. Oh, Eduardo M. R. Fairbairn, Atsuhisa Ogawa, Hideki Hoshiro, Folker H. Wittmann, Romildo Dias Toledo Filho, Petr Kabele, Volker Slowik, Viktor MechtcherineAbstract:Strain-hardening cement-based composites were named after their ability to resist increased tensile force after Crack formation, over a significant tensile deformation range. The increased resistance is achieved through effective Crack Bridging by fibres, across multiple Cracks of widths in the micro-range. Whether these small Crack widths are maintained under sustained, cyclic or other load paths, and whether the Crack width limitation translates into durability through retardation of moisture, gas and other deleterious matter ingress, are scrutinised in this paper by evaluation of test results from several laboratories internationally. This contribution is a short version of the State-of-the-Art report by RILEM TC 208-HFC, Subcommittee 2: Durability, developed during the committee life 2005–2009.
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Modelling of ageing effects on Crack-Bridging behaviour of AR-glass multifilament yarns embedded in cement-based matrix
Cement and Concrete Research, 2011Co-Authors: Marko Butler, Simone Hempel, Viktor MechtcherineAbstract:Abstract This article focus on modelling of ageing effects on Crack-Bridging behaviour of AR-glass multifilament yarns embedded in cement-based matrix. In the first step, age-dependent changes in the Crack-Bridging behaviour of AR-glass multifilament yarns were investigated at the meso and micro levels. Two cementitious matrices were considered where the binder contained Portland cement clinker and ground granulated blast furnace slag cement, respectively. Mechanical characteristics of the bond between matrix and multifilament yarns after accelerated ageing were measured by means of double-sided yarn pullout tests. In these tests the multifilament yarns bridged a single Crack in the matrix arising in a notched area of the specimen. Losses in performance with increasing age differed widely depending on matrix material composition. The essential cause of such losses was discovered to be the microscopic densification of the fibre-to-matrix interface. This led to increased bond intensity and restricted slip-ability of the filaments. Subsequently, these micro-structural phenomena were related to the mesoscopic material behaviour by means of a phenomenological bond model. This cross-linkage model describes the Crack-Bridging effect of the entire multifilament yarn at the single filament level. According to the model, each filament possesses a specific deformation length depending on its position in the cross-section of the yarn. This deformation length depends on bond characteristics between single filament and cementitious matrix, which vary with age. Characteristic values of the model were computed from load-Crack width curves obtained from the yarn pullout tests. The changes in the microstructure were represented by the characteristic values of the model.
W.o. Soboyejo - One of the best experts on this subject based on the ideXlab platform.
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mechanical properties of functionally graded hierarchical bamboo structures
Acta Biomaterialia, 2011Co-Authors: Ting Tan, Sayyed Mohsen Allameh, Nima Rahbar, Samuel Kwofie, D Dissmore, K Ghavami, W.o. SoboyejoAbstract:This paper presents the results of a series of multi-scale experiments and numerical models concerning the mechanical properties of moso culm functionally graded bamboo structures. On the nano- and microscales, nanoindentation techniques are used to study the local variations in the Young’s moduli of moso culm bamboo cross-sections. These are then incorporated into finite element models in which the actual variations in Young’s moduli are used to model the deformation and fracture of bamboo during fracture toughness experiments. Similarly, the measured gradations in moduli are incorporated into Crack Bridging models that predict the toughening observed during resistance curve tests. The implications of the results are discussed for the bio-inspired design of structures that mimic the layered, functionally graded structure of bamboo.
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Thermal Shock Resistance of a Kyanite-Based (Aluminosilicate) Ceramic
Experimental Mechanics, 2011Co-Authors: N. Rahbar, Josepha Zimba, B. O. Aduda, S. K. Obwoya, F. W. Nyongesa, I. Yakub, W.o. SoboyejoAbstract:This paper presents the results of a combined experimental and theoretical study of microstructure and thermal shock resistance of an aluminosilicate ceramic. Shock-induced Crack growth is studied in sintered structures produced from powders with different particle size ranges. The underlying Crack/microstructure interactions and toughening mechanisms are elucidated via scanning electron microscopy (SEM). The resulting Crack-tip shielding levels (due to viscoelastic Crack Bridging) are estimated using fracture mechanics concepts. The implications of the work are discussed for the design of high refractory ceramics against thermal shock.
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effects of na2o on the thermal shock resistance of aluminosilicate refractory ceramics
Materials and Manufacturing Processes, 2007Co-Authors: W.o. Soboyejo, Josepha Zimba, Edem T Akpa, Ishmael Ashi, N Hosannah, Sayyed Mohsen AllamehAbstract:This report presents the results of an experimental study of the effects of Na2O on the thermal shock resistance (number of cold shock cycles to failure) of aluminosilicate refractory ceramics. The addition of 4–6% mole is shown to improve the thermal shock resistance, which is characterized by the number of shock cycles to failure. The Na2O changes the viscosity-temperature characteristics, and the glass transition temperatures in ways that enhance the Crack-tip shielding due to viscoelastic/grain Bridging mechanisms. The improved thermal shock resistance is attributed to the shielding effects of viscoelastic Crack Bridging by glassy phases between mullite platelets
