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Erhard Krempl - One of the best experts on this subject based on the ideXlab platform.
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Viscoplasticity theory based on overStress: the modeling of ratchetting and cyclic hardening of AISI type 304 stainless steel
Nuclear Engineering and Design, 1992Co-Authors: Erhard Krempl, Sang H. ChoiAbstract:At room temperature, annealed AISI type 304 stainless steel exhibits Rate dependence that manifests itself in Rate sensitivity, creep and relaxation. It is also the driving force behind incremental elongation under zero-to-tension load-controlled loading, called ratchetting. It is shown to increase with decreasing Stress Rate and is independent of Stress Rate sequence. Accumulated ratchet strain has the same hardening effect as the strain in a monotonic test. For cyclic loading with load or strain reversal, significant cyclic hardening is observed. It is well known that this hardening depends on the path and seems to be most pronounced under 90° out-of-phase cycling. Other paths show various degrees of cyclic hardening. At the same effective strain range, the hardening under nonproportional loading is much more pronounced than under proportional loading. Experiments show that the Rate sensitivity is, as a first approximation, unchanged by the significant hardening, which is therefore Rate independent. The small-strain, isotropic viscoplasticity theory based on overStress (VBO) is used to model these phenomena. The theory is of the unified type and does not employ yield or loading/unloading criteria. The inelastic strain Rate is a function of the overStress, the difference between the Stress and the equilibrium Stress, which is a state variable of the theory. Its growth law is the repository for modeling nearly elastic regions and hysteresis. Under constant strain Rate loading, the theory admits asymptotic solutions, which show that the Stress is composed of viscous, Rate-independent (plastic) and kinematic contributions. For the modeling of cyclic hardening, a growth law for the Rate-independent contribution to the Stress is formulated. It models a different type of growth for proportional and nonproportional as well as cyclic and monotonic loadings. Numerical experiments for homogeneous states of Stress are performed by integrating the stiff, nonlinear ordinary differential equations using the IMSL routine DGEAR. They demonstRate the modeling capabilities for step-down and step-up two-amplitude loadings, for proportional and nonproportional cyclic loadings including elliptical and square paths as well as for ratchetting. © 1992.
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The interaction of cyclic hardening and ratchetting for AISI type 304 stainless steel at room temperature-I. Experiments
Journal of the Mechanics and Physics of Solids, 1990Co-Authors: M.b. Ruggles, Erhard KremplAbstract:Uniaxial zero-to-tension load controlled tests at Stress Rates differing by three orders of magnitude were performed on annealed AISI Type 304 stainless steel. The maximum Stress was determined either as the Stress reached in displacement control at one per cent strain (History I), or as the Stress reached after a 1050 s relaxation test at one per cent strain (History II). The tests of History III were identical to those of History I, except that the specimens were subjected to cyclic hardening prior to the start of the ratchetting test. The ratchet strain accumulations in Histories I and II are significant and depend on Stress Rate. A Stress Rate decrease increases the accumulated ratchet strain. The final ratchet strain accumulation is independent of Stress Rate sequence. In History II, no ratchet strain was found at any Stress Rate. If the steel had behaved in a Rate-independent fashion, no ratchet strain accumulation should have been found in any of the tests. They were performed with an MTS servohydraulic, computer controlled testing machine, a clip on-extensometer and digitized data acquisition. © 1990.
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The interaction of cyclic hardening and ratchetting for AISI type 304 stainless steel at room temperature-II. Modeling with the viscoplasticity theory based on overStress
Journal of the Mechanics and Physics of Solids, 1990Co-Authors: Erhard Krempl, M.b. RugglesAbstract:The viscoplasticity theory based on overStress (VBO) is used to predict ratchetting tests reported by Ruggles and Krempl in Part I (J. Mech. Phys. Solids 38, 575, 1990). The VBO predicts the influence of ratchetting Rate correctly. An increase in ratchet Stress Rate reduces the ratchet strain. Quantitative predictions are reasonable for tests with no prior cyclic hardening. For tests with prior hardening the theory predicts too large a ratchet strain. It is shown that this can be corrected by making the shape function dependent on history. Theory and experiment do not exhibit a Stress Rate history effect. © 1990.
M.b. Ruggles - One of the best experts on this subject based on the ideXlab platform.
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The interaction of cyclic hardening and ratchetting for AISI type 304 stainless steel at room temperature-I. Experiments
Journal of the Mechanics and Physics of Solids, 1990Co-Authors: M.b. Ruggles, Erhard KremplAbstract:Uniaxial zero-to-tension load controlled tests at Stress Rates differing by three orders of magnitude were performed on annealed AISI Type 304 stainless steel. The maximum Stress was determined either as the Stress reached in displacement control at one per cent strain (History I), or as the Stress reached after a 1050 s relaxation test at one per cent strain (History II). The tests of History III were identical to those of History I, except that the specimens were subjected to cyclic hardening prior to the start of the ratchetting test. The ratchet strain accumulations in Histories I and II are significant and depend on Stress Rate. A Stress Rate decrease increases the accumulated ratchet strain. The final ratchet strain accumulation is independent of Stress Rate sequence. In History II, no ratchet strain was found at any Stress Rate. If the steel had behaved in a Rate-independent fashion, no ratchet strain accumulation should have been found in any of the tests. They were performed with an MTS servohydraulic, computer controlled testing machine, a clip on-extensometer and digitized data acquisition. © 1990.
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The interaction of cyclic hardening and ratchetting for AISI type 304 stainless steel at room temperature-II. Modeling with the viscoplasticity theory based on overStress
Journal of the Mechanics and Physics of Solids, 1990Co-Authors: Erhard Krempl, M.b. RugglesAbstract:The viscoplasticity theory based on overStress (VBO) is used to predict ratchetting tests reported by Ruggles and Krempl in Part I (J. Mech. Phys. Solids 38, 575, 1990). The VBO predicts the influence of ratchetting Rate correctly. An increase in ratchet Stress Rate reduces the ratchet strain. Quantitative predictions are reasonable for tests with no prior cyclic hardening. For tests with prior hardening the theory predicts too large a ratchet strain. It is shown that this can be corrected by making the shape function dependent on history. Theory and experiment do not exhibit a Stress Rate history effect. © 1990.
S. Ramamurthy - One of the best experts on this subject based on the ideXlab platform.
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Influence of the applied Stress Rate on the Stress corrosion cracking of 4340 and 3.5NiCrMoV steels under conditions of cathodic hydrogen charging
Corrosion Science, 2011Co-Authors: S. Ramamurthy, Andrej AtrensAbstract:Abstract Stress corrosion cracking (SCC) of as-quenched 4340 and 3.5NiCrMoV steels was studied under hydrogen charging conditions, with a cathodic current applied to the gauge length of specimens subjected to Linearly Increasing Stress Test (LIST) in 0.5 M H 2 SO 4 solution containing 2 g/l arsenic trioxide (As 2 O 3 ) at 30 °C. Applied Stress Rates were varied from 20.8 to 6 × 10 −4 MPa s −1 . Both the fracture and threshold Stress decreased with decreasing applied Stress Rate and were substantially lower than corresponding values measured in distilled water at 30 °C at the open circuit potential. The threshold Stress values correspond to 0.03–0.08 σ y for 4340 and 0.03–0.2 σ y for the 3.5NiCrMoV steel. SCC velocities, at the same applied Stress Rate, were an order of magnitude greater than those in distilled water. However, the plots of the crack velocity versus applied Stress Rate had similar slopes, suggesting the same Rate-limiting step. The fracture surface morphology was mostly intergranular, with quasi-cleavage features.
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Influence of the Applied Stress Rate on the Stress Corrosion Cracking of 4340 and 3.5NiCrMoV Steels
2011Co-Authors: S. RamamurthyAbstract:Stress Corrosion Cracking (SCC) can occur in engineering structures where Stressed metallic parts are in contact with an aggressive environment, and can lead to catastrophic failures. High strength steels are particularly susceptible; increasing yield strength significantly decreases the threshold Stress intensity factor, KISCC. As a consequence, SCC of high strength steels has been widely studied and is an on-going effort. In this doctoral dissertation, an effort was made to understand the SCC behaviour of two high strength steels, namely 4340 and 3.5NiCrMoV steel under the following conditions: (1) SCC behaviour in aeRated 90 oC distilled water. (2) SCC behaviour in aeRated 30 oC distilled water. (3) SCC behaviour under hydrogen charging conditions. Stress corrosion cracking experiments were conducted using the Linearly Increasing Stress Test (LIST), which was developed as part of this dissertation. LIST is an improved form of the Constant Extension Rate Test (CERT) and was used to study both crack initiation and crack propagation under the above experimental conditions. In addition, a potential drop method was developed to determine the threshold Stress at which crack initiation occurred. The fracture surface morphologies were examined using scanning electron microscopy (SEM). Because the cracking is intergranular in the system of interest, localized electrochemical measurements were performed to determine the grain boundary electrochemical properties using micro-reference electrodes, and secondary ion mass spectrometry (SIMS) measurements were carried out to determine the grain boundary composition and the presence of grain boundary precipitates that could aid intergranular crack growth. LIST experiments conducted in 90 and 30 oC distilled water showed that SCC occurred at all the applied Stress Rates for 4340 steel, while for 3.5NiCrMoV steel SCC did not occur at applied Stress Rates greater than 0.034 MPa s-1 in 90 oC water and 0.002 MPa s-1 in 30 oC water. For the 4340 steel in 90 oC water, the threshold Stress at which cracks initiated was controlled by the development of corrosion pits at lower applied Stress Rates. At both temperatures, it was shown that the applied Stress Rate controlled the crack tip strain Rate. The crack velocity increased with the increase in the applied Stress Rate and the crack tip strain Rate; the maximum crack velocity at both temperatures corresponded to the plateau crack velocity, vII, determined from fracture mechanics tests at the same temperatures. Moreover, no effect of the steel composition on the crack velocity could be identified for the steels under investigation in the present work, indicating a similar Rate limiting step that was independent of steel composition for both steels. Finally the fracture surface morphology was mostly intergranular in both steels, and the applied Stress Rate did not influence the intergranular fracture surface morphology. Under hydrogen charging conditions, LISTs performed on as-quenched 4340 and 3.5NiCrMoV steels indicated that cracking occurred at all applied Stress Rates for both steels in contrast to the trends for experiments in 90 oC and 30 oC distilled water at open circuit potential where cracking did not occur at higher applied Stress Rates. The dynamic charging decreased the fracture Stress and the threshold Stress much more dramatically than that in the prior tests, however both Stresses were still dependent on the applied Stress Rate. The measured crack velocity increased with increasing applied Stress Rate and the crack tip strain Rate, and no effect of the steel composition on the crack velocity could be identified for the steels under investigation in the present work, indicating a similar Rate limiting step that was independent of steel composition for both steels. Moreover, the exponents of the least square fit data were similar to those from 90 oC and 30 oC distilled water experiments, indicating that the same Rate limiting step could be operating in all three sets of experiments. Finally, the fracture surface morphology was mostly intergranular fracture, with a significant amount of plasticity at higher applied Stress Rates. The results from the grain boundary potential measurements using Ag/AgCl micro-reference electrodes, on the as quenched 3.5NiCrMoV steel at room temperature indicated that some grain boundary potentials were more negative than their grain interiors, and the potential difference between the filmed and the film free surface was of the order of 1 V. These results suggest that, thermodynamically, the grain boundaries can dissolve preferentially and there was sufficient driving force for this dissolution, thus supporting the possibility of the anodic dissolution mechanism in this steel. SIMS imaging of as-quenched 4340 steel specimens before and after cathodic charging indicated the presence of carbides in the steel. Hydrogen appeared to be trapped at the carbide particles. Sulphides were present as discrete particles; however they did not appear to play a significant role in trapping hydrogen. The presence of carbides at the grain boundaries and the hydrogen trapped by the carbides could contribute to the anodic dissolution and hydrogen embrittlement mechanisms of Stress corrosion cracking. In summary the results presented in this dissertation indicate that the applied Stress Rate controlled the crack-tip strain Rate and that the crack velocity was dependent on both the crack tip strain Rate and the applied Stress Rate. The maximum crack velocities increased with the increase in the applied Stress Rates, to a maximum of vII measured with fracture mechanics tests. Because no effect of the steel composition on the crack velocity could be identified for the steels under investigation in the present work and was dependent only on the crack-tip strain Rate, the Rate-limiting step for the crack propagation was controlled by the crack-tip strain Rate. The grain boundary potential measurements and SIMS analysis of the grain boundaries indicate that the grain boundaries can thermodynamically provide favourable crack propagation path, thus explaining the intergranular nature of the cracking observed in this study.
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The influence of applied Stress Rate on the Stress corrosion cracking of 4340 and 3.5NiCrMoV steels in distilled water at 30 C
Corrosion Science, 2010Co-Authors: S. Ramamurthy, Andrej AtrensAbstract:Linearly Increasing Stress Tests conducted in 30 degrees C aeRated distilled water using as-quenched 4340 and 3.5NiCrMoV turbine rotor steels indicated that Stress corrosion cracking occurred at all applied Stress Rates for 4340 steel, whilst only at applied Stress Rates less than or equal to 0.002 MPa s(-1) for the turbine rotor steel. The crack velocity increased with increasing applied Stress Rate for both steels with the maximum crack velocity for 4340 steel corresponded to v(II) in fracture mechanics tests in room temperature water. The fracture surface morphology was mixed mode consisting of intergranular and transgranular fracture regions. (C) 2009 Elsevier Ltd. All rights reserved.
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The Stress corrosion cracking of as-quenched 4340 and 3.5NiCrMoV steels under Stress Rate control in distilled water at 90°C
Corrosion Science, 1993Co-Authors: S. Ramamurthy, Andrej AtrensAbstract:This paper presents experimental results from the Linearly Increasing Stress Test (LIST) applied to the Stress corrosion cracking (SCC) of as-quenched 4340 and 3.5NiCrMoV turbine rotor steel in aeRated distilled water at 90°C. Experiments were performed at applied Stress Rates ranging from 2.1 × 10−4 to 2.1 × 102 MPas−1. Parameters measured included the threshold Stress, the fracture Stress, the average crack velocity and the strain Rate at the threshold Stress. The crack tip strain Rates were evaluated using expressions derived from the literature. Stress corrosion was observed at all applied Stress Rates in 4340 steel but not at applied Stress Rates higher than 0.034 MPas−1 for the turbine rotor steel. In both steels, the crack velocity was strongly dependent on the applied Stress Rate. The fracture surface morphology was intergranular in all cases. Corrosion pits influenced Stress corrosion crack initiation.
Mark R. Cutkosky - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Tactile Sensing: Perception of Fine Surface Features with Stress Rate Sensing
IEEE Transactions on Robotics and Automation, 1993Co-Authors: Mark R. CutkoskyAbstract:Dynamic tactile sensing, which is defined as sensing during motion for perception of high spatial and temporal frequencies, is presented. Applications include sensing fine surface features and textures and monitoring contact conditions for dextrous manipulation. One type of dynamic tactile sensor, the Stress Rate sensor, is described in detail. It uses piezoelectric polymer transducers to measure the changes in Stress induced in the sensor's rubber skin as it traverses small surface features and textures. The signals are interpreted with the aid of a solid mechanics model of the contact interaction and a linear deconvolution filter. Experimental verification of the sensor's performance, including the detection of surface features only 6.5 μm high, are presented
Andrej Atrens - One of the best experts on this subject based on the ideXlab platform.
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Influence of the applied Stress Rate on the Stress corrosion cracking of 4340 and 3.5NiCrMoV steels under conditions of cathodic hydrogen charging
Corrosion Science, 2011Co-Authors: S. Ramamurthy, Andrej AtrensAbstract:Abstract Stress corrosion cracking (SCC) of as-quenched 4340 and 3.5NiCrMoV steels was studied under hydrogen charging conditions, with a cathodic current applied to the gauge length of specimens subjected to Linearly Increasing Stress Test (LIST) in 0.5 M H 2 SO 4 solution containing 2 g/l arsenic trioxide (As 2 O 3 ) at 30 °C. Applied Stress Rates were varied from 20.8 to 6 × 10 −4 MPa s −1 . Both the fracture and threshold Stress decreased with decreasing applied Stress Rate and were substantially lower than corresponding values measured in distilled water at 30 °C at the open circuit potential. The threshold Stress values correspond to 0.03–0.08 σ y for 4340 and 0.03–0.2 σ y for the 3.5NiCrMoV steel. SCC velocities, at the same applied Stress Rate, were an order of magnitude greater than those in distilled water. However, the plots of the crack velocity versus applied Stress Rate had similar slopes, suggesting the same Rate-limiting step. The fracture surface morphology was mostly intergranular, with quasi-cleavage features.
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The influence of applied Stress Rate on the Stress corrosion cracking of 4340 and 3.5NiCrMoV steels in distilled water at 30 C
Corrosion Science, 2010Co-Authors: S. Ramamurthy, Andrej AtrensAbstract:Linearly Increasing Stress Tests conducted in 30 degrees C aeRated distilled water using as-quenched 4340 and 3.5NiCrMoV turbine rotor steels indicated that Stress corrosion cracking occurred at all applied Stress Rates for 4340 steel, whilst only at applied Stress Rates less than or equal to 0.002 MPa s(-1) for the turbine rotor steel. The crack velocity increased with increasing applied Stress Rate for both steels with the maximum crack velocity for 4340 steel corresponded to v(II) in fracture mechanics tests in room temperature water. The fracture surface morphology was mixed mode consisting of intergranular and transgranular fracture regions. (C) 2009 Elsevier Ltd. All rights reserved.
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The Stress corrosion cracking of as-quenched 4340 and 3.5NiCrMoV steels under Stress Rate control in distilled water at 90°C
Corrosion Science, 1993Co-Authors: S. Ramamurthy, Andrej AtrensAbstract:This paper presents experimental results from the Linearly Increasing Stress Test (LIST) applied to the Stress corrosion cracking (SCC) of as-quenched 4340 and 3.5NiCrMoV turbine rotor steel in aeRated distilled water at 90°C. Experiments were performed at applied Stress Rates ranging from 2.1 × 10−4 to 2.1 × 102 MPas−1. Parameters measured included the threshold Stress, the fracture Stress, the average crack velocity and the strain Rate at the threshold Stress. The crack tip strain Rates were evaluated using expressions derived from the literature. Stress corrosion was observed at all applied Stress Rates in 4340 steel but not at applied Stress Rates higher than 0.034 MPas−1 for the turbine rotor steel. In both steels, the crack velocity was strongly dependent on the applied Stress Rate. The fracture surface morphology was intergranular in all cases. Corrosion pits influenced Stress corrosion crack initiation.
