The Experts below are selected from a list of 3030 Experts worldwide ranked by ideXlab platform
R O Ritchie - One of the best experts on this subject based on the ideXlab platform.
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On the toughening of brittle materials by grain bridging: promoting intergranular Fracture through grain angle, strength, and toughness
2020Co-Authors: J W Foulk, G C Johnson, Patrick A Klein, R O RitchieAbstract:Abstract The structural reliability of many brittle materials such as structural ceramics relies on the occurrence of intergranular, as opposed to Transgranular, Fracture in order to induce toughening by grain bridging. For a constant grain boundary strength and grain boundary toughness, the current work examines the role of grain strength, grain toughness, and grain angle in promoting intergranular Fracture in order to maintain such toughening. Previous studies have illustrated that an intergranular path and the consequent grain bridging process can be partitioned into five distinct regimes, namely: propagate, kink, arrest, stall and bridge. To determine the validity of the assumed intergranular path, the classical penentration/deflection problem of a crack impinging on an interface is reexamined within a cohesive zone framework for intergranular and Transgranular Fracture. Results considering both modes of propagation, i.e., a Transgranular and intergranular path, reveal that crack-tip shielding is a natural outcome of the cohesive zone approach to Fracture. Cohesive zone growth in one mode shields the opposing mode from the stresses required for cohesive zone initiation. Although stable propagation occurs when the required driving force is equivalent to the toughness for either Transgranular or intergranular Fracture, the mode of propagation depends on the normalized grain strength, normalized grain toughness, and grain angle. For each grain angle, the intersection of single path and multiple path solutions demarcates "strong" grains that increase the macroscopic toughness and "weak" grains that decrease it. The unstable transition to intergranular Fracture reveals that an increasing grain toughness requires a growing region of the Transgranular cohesive zone be at and near the peak cohesive strength. The Preprint submitted to Journal of the Mechanics and Physics of Solids 30 November 2007 inability of the body to provide the requisite stress field yields an overdriven and unstable configuration. The current results provide restrictions for the achievement of substantial toughening through intergranular Fracture
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on the toughening of brittle materials by grain bridging promoting intergranular Fracture through grain angle strength and toughness
Lawrence Berkeley National Laboratory, 2008Co-Authors: J W Foulk, G C Johnson, Patrick A Klein, R O RitchieAbstract:The structural reliability of many brittle materials such as structural ceramics relies on the occurrence of intergranular, as opposed to Transgranular, Fracture in order to induce toughening by grain bridging. For a constant grain boundary strength and grain boundary toughness, the current work examines the role of grain strength, grain toughness, and grain angle in promoting intergranular Fracture in order to maintain such toughening. Previous studies have illustrated that an intergranular path and the consequent grain bridging process can be partitioned into five distinct regimes, namely: propagate, kink, arrest, stall and bridge. To determine the validity of the assumed intergranular path, the classical penentration/deflection problem of a crack impinging on an interface is reexamined within a cohesive zone framework for intergranular and Transgranular Fracture. Results considering both modes of propagation, i.e., a Transgranular and intergranular path, reveal that crack-tip shielding is a natural outcome of the cohesive zone approach to Fracture. Cohesive zone growth in one mode shields the opposing mode from the stresses required for cohesive zone initiation. Although stable propagation occurs when the required driving force is equivalent to the toughness for either Transgranular or intergranular Fracture, the mode of propagation depends on the normalized grain strength, normalized grain toughness, and grain angle. For each grain angle, the intersection of single path and multiple path solutions demarcates strong grains that increase the macroscopic toughness and weak grains that decrease it. The unstable transition to intergranular Fracture reveals that an increasing grain toughness requires a growing region of the Transgranular cohesive zone be at and near the peak cohesive strength. The inability of the body to provide the requisite stress field yields an overdriven and unstable configuration. The current results provide restrictions for the achievement of substantial toughening through intergranular Fracture.
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on the toughening of brittle materials by grain bridging promoting intergranular Fracture through grain angle strength and toughness
Journal of The Mechanics and Physics of Solids, 2008Co-Authors: J W Foulk, G C Johnson, Patrick A Klein, R O RitchieAbstract:Abstract The structural reliability of many brittle materials such as structural ceramics relies on the occurrence of intergranular, as opposed to Transgranular, Fracture in order to induce toughening by grain bridging. For a constant grain boundary strength and grain boundary toughness, the current work examines the role of grain strength, grain toughness, and grain angle in promoting intergranular Fracture in order to maintain such toughening. Previous studies have illustrated that an intergranular path and the consequent grain bridging process can be partitioned into five distinct regimes, namely: propagate, kink, arrest, stall, and bridge. To determine the validity of the assumed intergranular path, the classical penetration/deflection problem of a crack impinging on an interface is re-examined within a cohesive zone framework for intergranular and Transgranular Fracture. Results considering both modes of propagation, i.e., a Transgranular and intergranular path, reveal that crack-tip shielding is a natural outcome of the cohesive zone approach to Fracture. Cohesive zone growth in one mode shields the opposing mode from the stresses required for cohesive zone initiation. Although stable propagation occurs when the required driving force is equivalent to the toughness for either Transgranular or intergranular Fracture, the mode of propagation depends on the normalized grain strength, normalized grain toughness, and grain angle. For each grain angle, the intersection of single path and multiple path solutions demarcates “strong” grains that increase the macroscopic toughness and “weak” grains that decrease it. The unstable transition to intergranular Fracture reveals that an increasing grain toughness requires a growing region of the Transgranular cohesive zone be near the cohesive strength. The inability of the body to provide the requisite stress field yields an overdriven and unstable configuration. The current results provide restrictions for the achievement of substantial toughening through intergranular Fracture.
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on the effect of local grain boundary chemistry on the macroscopic mechanical properties of a high purity y 2 o 3 al 2 o 3 containing silicon nitride ceramic
MRS Proceedings, 2004Co-Authors: A Ziegler, J M Mcnaney, Michael J Hoffmann, R O RitchieAbstract:The effects of grain-boundary chemistry on the mechanical properties of a high-purity silicon nitride ceramics were investigated, with specific emphasis on the role of oxygen. Variations in the grain-boundary oxygen content, through control of oxidizing heat treatments and sintering additives, was found to result in a transition in Fracture mechanism from Transgranular to intergranular Fracture, with an associated increase in Fracture toughness. This phenomenon is correlated to an oxygen-induced change in grain-boundary chemistry that appears to affect Fracture by “weakening” the interface, facilitating debonding and crack advance along the boundaries, thereby enhancing the toughness by grain bridging. It is concluded that if the oxygen content in the thin grain-boundary films exceeds a lower limit, which is ~0.87 equiv% oxygen content, then the interfacial structure and bonding characteristics favor intergranular debonding during crack propagation; otherwise, Transgranular Fracture ensues, with consequent low toughness.
H K D H Bhadeshia - One of the best experts on this subject based on the ideXlab platform.
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effect of aluminium on hydrogen induced Fracture behaviour in austenitic fe mn c steel
Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2013Co-Authors: Joo Hyun Ryu, Sung Kyu Kim, Chong Soo Lee, Dongwoo Suh, H K D H BhadeshiaAbstract:It is known empirically that the addition of aluminium as a solute in high-Mn austenitic steels dramatically improves their resistance to hydrogen-induced embrittlement. A variety of experimental techniques, including the characterization of trapping sites and high-resolution observation of Fracture facets, have been used to reveal the mechanism by which aluminium induces this effect. It is found that Transgranular Fracture is promoted by the segregation of hydrogen to mechanical twin interfaces and to any ϵ-martensite that is induced during deformation. Because aluminium increases the stacking fault energy of austenite, the tendency for mechanical twinning is reduced, and the formation of deformation-induced martensite eliminated. These two effects contribute to the resistance of the aluminium-alloyed steel to hydrogen embrittlement.
Kaneaki Tsuzaki - One of the best experts on this subject based on the ideXlab platform.
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hydrogen induced cracking at grain and twin boundaries in an fe mn c austenitic steel
Scripta Materialia, 2012Co-Authors: Dierk Raabe, Motomichi Koyama, Kaneaki Tsuzaki, Eiji Akiyama, Takahiro SawaguchiAbstract:Hydrogen embrittlement was observed in an Fe–18Mn–1.2C (wt.%) steel. The tensile ductility was drastically reduced by hydrogen charging during tensile testing. The Fracture mode was mainly intergranular Fracture, though Transgranular Fracture was also partially observed. The Transgranular Fracture occurred parallel to the primary and secondary deformation twin boundaries, as confirmed by electron backscattering diffraction analysis and orientation-optimized electron channeling contrast imaging. The microstructural observations indicate that cracks are initiated at grain boundaries and twin boundaries.
Y Yan - One of the best experts on this subject based on the ideXlab platform.
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hydrogen induced cracking mechanism of precipitation strengthened austenitic stainless steel weldment
International Journal of Hydrogen Energy, 2015Co-Authors: Y Yan, Lijie QiaoAbstract:Abstract Precipitation strengthened austenitic stainless steels are widely used in hydrogen related applications. However, their applications may face hydrogen damage resulting in hydrogen-induced delayed failure. Results show that the weld is more sensitive to Fracture and hydrogen-induced failure than the matrix. High density curved dislocations, abundant of large size precipitates and considerable γ′ precipitates coarsening are found in the weld. Large size precipitates are found to be major hydrogen traps and preferential microcrack nucleation sites. The γ′ precipitates coarsening make the weld more ductile than the matrix. With the decrease of the applied stress, hydrogen-induced cracking mechanism in the weld changes from brittle Transgranular Fracture to brittle intergranular Fracture.
Motomichi Koyama - One of the best experts on this subject based on the ideXlab platform.
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hydrogen induced cracking at grain and twin boundaries in an fe mn c austenitic steel
Scripta Materialia, 2012Co-Authors: Dierk Raabe, Motomichi Koyama, Kaneaki Tsuzaki, Eiji Akiyama, Takahiro SawaguchiAbstract:Hydrogen embrittlement was observed in an Fe–18Mn–1.2C (wt.%) steel. The tensile ductility was drastically reduced by hydrogen charging during tensile testing. The Fracture mode was mainly intergranular Fracture, though Transgranular Fracture was also partially observed. The Transgranular Fracture occurred parallel to the primary and secondary deformation twin boundaries, as confirmed by electron backscattering diffraction analysis and orientation-optimized electron channeling contrast imaging. The microstructural observations indicate that cracks are initiated at grain boundaries and twin boundaries.
