The Experts below are selected from a list of 216 Experts worldwide ranked by ideXlab platform
Jonathan A Salem - One of the best experts on this subject based on the ideXlab platform.
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ultra Fast Fracture strength of advanced ceramics at elevated temperatures
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: Sung R. Choi, Jonathan A SalemAbstract:An attempt was made to determine elevated-temperature, 'ultra'-Fast Fracture strengths of one alumina, two silicon nitrides and one silicon carbide by using constant stress-rate ('dynamic fatigue') testing with a series of 'ultra'-Fast test rates. Of the materials tested, the alumina exhibited a convergence of strength at stress rates below 3.3 x 10(exp 4) MPa/s. The strength approached approximately the room-temperature inert strength. By contrast, the silicon nitrides and silicon carbide did not reveal a strength approach, but exhibited elevated-temperature strengths 10 and 20% lower than their respective room-temperature strengths. Although the analytical results imply that the elevated-temperature 'inert' strength of a ceramic material can be obtained by using sufficiently high stress rates, the experimental testing rates were only sufficient to demonstrate convergence for the alumina.
Sung R. Choi - One of the best experts on this subject based on the ideXlab platform.
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ultra Fast Fracture strength of advanced structural ceramics at elevated temperatures an approach to high temperature inert strength
2002Co-Authors: Sung R. Choi, John P. GyekenyesiAbstract:The determination of “ultra”-Fast Fracture strengths of a total of 17 advanced ceramics at elevated temperatures has been made by using constant stress-rate testing in flexure with a series of “ultra”-Fast test rates. The test materials included two aluminas, eleven monolithic silicon nitrides, two SiC whisker-reinforced composite silicon nitrides, and two silicon carbides. Of the 17 ceramic materials tested, 15 advanced ceramics exhibited elevated-temperature strengths that approached (within 90%) their respective room-temperature strengths at an “ultra”-Fast test rate of 3.3 × 104 MPa/s. This indicates that slow crack growth responsible for elevated-temperature failure can be eliminated or minimized by using a sufficiently Fast test rate. These ongoing experimental results have shed light on laying a theoretical and practical foundation on the concept and definition of elevated-temperature “inert” strength behavior of advanced ceramics. The elevated-temperature, “inert” strength of a ceramic material could be determined by using test rates equal to or greater than the “ultra”-Fast test rate of 3.3 × 104 MPa/s
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Elevated-Temperature, ‘Ultra’-Fast Fracture Strength of Advanced Ceramics: An Approach to Elevated-Temperature “Inert” Strength
Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls Diagnostics and Instrumentation; Education, 1998Co-Authors: Sung R. Choi, John P. GyekenyesiAbstract:The determination of ‘ultra’-Fast Fracture strengths of five silicon nitride ceramics at elevated temperatures has been made by using constant stress-rate (“dynamic fatigue”) testing with a series of ‘ultra’-Fast test rates. The test materials included four monolithic and one SiC whisker-reinforced composite silicon nitrides. Of the five test materials, four silicon nitrides exhibited the elevated-temperature strengths that approached their respective room-temperature strengths at an ‘ultra’-Fast test rate of 33 × 104 MPa/s. This implies that slow crack growth responsible for elevated-temperature failure can be eliminated or minimized by using the ‘ultra’-Fast test rate. These ongoing experimental results have shed light on laying a theoretical and practical foundation on the concept and definition of elevated-temperature “inert” strength behavior of advanced ceramics.Copyright © 1998 by ASME
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ultra Fast Fracture strength of advanced ceramics at elevated temperatures
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: Sung R. Choi, Jonathan A SalemAbstract:An attempt was made to determine elevated-temperature, 'ultra'-Fast Fracture strengths of one alumina, two silicon nitrides and one silicon carbide by using constant stress-rate ('dynamic fatigue') testing with a series of 'ultra'-Fast test rates. Of the materials tested, the alumina exhibited a convergence of strength at stress rates below 3.3 x 10(exp 4) MPa/s. The strength approached approximately the room-temperature inert strength. By contrast, the silicon nitrides and silicon carbide did not reveal a strength approach, but exhibited elevated-temperature strengths 10 and 20% lower than their respective room-temperature strengths. Although the analytical results imply that the elevated-temperature 'inert' strength of a ceramic material can be obtained by using sufficiently high stress rates, the experimental testing rates were only sufficient to demonstrate convergence for the alumina.
Fei Zhang - One of the best experts on this subject based on the ideXlab platform.
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slow crack growth resistance of electrically conductive zirconia based composites with non oxide reinforcements
Journal of The European Ceramic Society, 2019Co-Authors: Jerome Chevalier, C Olagnon, Fei Zhang, Shuigen Huang, Wout Veulemans, Kim Vanmeensel, Jef VleugelsAbstract:Abstract Slow crack growth (SCG) behavior of four zirconia-based composites reinforced with 40 vol% WC, TiC, NbC or TiCN were studied by means of double-torsion testing. Compared to monolithic zirconia, the composites had a higher resistance to Fast Fracture, i.e., higher Fracture toughness. The extent of toughening depended on the reinforcement type, shifting the V-KI (crack velocity versus stress intensity factor) curve parallel to higher KI values. More importantly, these composites were less sensitive to SCG. Identical V-KI/KIC curves with steeper slopes compared to monolithic zirconia were observed for the investigated composites, independent on the reinforcement type. No rising R-curve was measured, at least in the crack-size domain investigated by SCG. Therefore, the higher SCG resistance of the composites was due to the intrinsic stress-assisted corrosion resistance of the covalent non-oxide secondary phase.
Yiu-wing Mai - One of the best experts on this subject based on the ideXlab platform.
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on Fast Fracture in an elastic plastic viscoplastic solid part ii the motion of crack
International Journal of Fracture, 2004Co-Authors: Yiu-wing MaiAbstract:The motion of a crack in an elastic-(plastic )-viscoplastic medium is studied in terms of an energetic analysis. Combined with the stress and velocity fields obtained in Part 1, Kishimoto's energy integral, Ĵ, is used as a crack driving force to determine its motion. The major results obtained are: (1) dependence of crack speed on a modified near-field parameter, KI tip, (or equivalently, a modified dynamic energy release, GI tip), which is different from the usual stress intensity factor KI of an elastic crack-tip field but is related to it; (2) influence of inelastic effect, such as the viscoplastic exponent n, on the motion of the crack; and (3) stability condition of crack motion. In particular, for the last point, it has been found that, for a given loading and material coefficients, there exist two possible motions of the crack: one is stable crack growth and the other is unstable Fracture. The lower and upper bounds of crack motion are also discussed. It is finally shown that the maximum crack velocity is lower than the Rayleigh wave speed, and is dependent on the viscoplastic exponent of the material.
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Crack-tip field for Fast Fracture of an elastic-plastic-viscoplastic material incorporated with quasi-brittle damage. Part 1. Large damage regime
International Journal of Solids and Structures, 2001Co-Authors: Yiu-wing MaiAbstract:Abstract An asymptotic analysis of the near-tip field is presented in terms of the coordinate perturbation technique for Fast crack propagation in an elastic–plastic–viscoplastic material with damage. A damage variable is incorporated in the constitutive relation based upon the strain-equivalence principle of damage mechanics. The damage evolution law used is a quasi-brittle type, in which both equivalent and hydrostatic stresses are involved. A non-singular stress field is obtained, as the damage has such a substantial influence on the material behaviour that the high stresses are relaxed at the crack tip. An analytical expression is obtained which explicitly shows the variation of stresses approaching the crack tip, and numerical computations of the angular distributions of stresses and strains are also presented.
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on Fast Fracture in an elastic plastic viscoplastic solid 1 stress and velocity fields with loading and unloading processes
International Journal of Fracture, 2001Co-Authors: Yiu-wing MaiAbstract:An asymptotic analysis of the near-tip field is given for Fast crack propagation in an elastic-plastic-viscoplastic solid. The plasticity of the material is characterised by power law hardening, and the visco-plasticity covers primary, secondary and tertiary creep depending on a parameter q being smaller, equal to and larger than zero, respectively. The yield condition used is Von Mises criterion. Explicit results are given for the order of the crack-tip singularity, the angular position at which unloading occurs, and the angular variations of stresses and velocities in the near crack-tip fields. In particular, it is shown that the eigenvalue, which determines the order of stress singularity, relates only to the viscoplastic parameters but is independent of the crack-tip speed, boundary and loading conditions. Also, it is found that the plasticity effect cannot explicitly enter the asymptotic stress field. Otherwise, additional assumptions would be required.
Andrej Atrens - One of the best experts on this subject based on the ideXlab platform.
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hydrogen induced Fast Fracture in notched 1500 and 1700 mpa class automotive martensitic advanced high strength steel
Corrosion Science, 2021Co-Authors: Jeffrey Venezuela, Timothy A Hill, Qingjun Zhou, Zhiming Shi, Futao Dong, Ruth Knibbe, Mingxing Zhang, Matthew S Dargusch, Andrej AtrensAbstract:Abstract Hydrogen embrittlement of notched martensitic advanced high-strength steels was studied. Notched specimens had (i) higher tensile strength and lower ductility, and (ii) increased hydrogen sensitivity, manifested by reductions in ductility and strength. Hydrogen-induced Fast Fractures (HIFF) initiated when the load-controlled specimen became mechanically unstable. The HIFF velocity (61−130 m/s) was greater than the velocity of ductile Fracture (46 m/s). HIFF susceptibility increased with increasing steel strength, increasing hydrogen fugacity, and decreasing stress rate. HIFF exhibited brittle features (quasi-cleavage, transgranular and intergranular Fracture) in the initiation zone, suggesting hydrogen-enhanced plasticity-mediated decohesion (HEPD). These features increased in area with increasing hydrogen embrittlement.
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comparison of the linearly increasing stress test and the constant extension rate test in the evaluation of transgranular stress corrosion cracking of magnesium
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2008Co-Authors: N Winzer, Andrej Atrens, W Dietzel, Guangling Song, Karl Ulrich KainerAbstract:Abstract Transgranular stress corrosion cracking (TGSCC) of the Mg alloy AZ91 in distilled water and 5 g/L NaCl solution has been evaluated using the linearly increasing stress test (LIST) and the constant extension rate test (CERT). The differences between these techniques, with respect to fractography and the measurement of SCC parameters, are discussed. The LIST and CERT techniques are both useful in identifying the occurrence of SCC and, when coupled with a technique for characterizing crack extension, measuring the threshold stress and crack velocity. During a LIST Fast Fracture ensues a relatively short time after the threshold stress is attained, whereas during CERT crack growth over a much longer time period is facilitated by a reduction in stress. Consequently, the LIST is typically 30–50% shorter in duration, whereas the CERT produces a larger SCC Fracture surface.