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Fu-zhen Xuan - One of the best experts on this subject based on the ideXlab platform.
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Interaction of cyclic softening and stress relaxation of 9–12% Cr steel under strain-controlled fatigue-creep condition: Experimental and modeling
International Journal of Plasticity, 2017Co-Authors: Shang-lin Zhang, Fu-zhen XuanAbstract:Abstract Strain controlled fatigue of P92 steel with various strain hold Dwells introduced at the peak loading point were conducted at 625 °C. Two features which depend on the cycle and strain range level were observed under the fatigue-creep condition for the viscous and cyclic softening material. The first one is the accelerated cyclic softening response which is ascribed to the accumulated inelastic strain transformation from the creep mechanism during the strain Dwell period and becomes more significant with the decrease of strain ranges. The second one is the decelerated stress relaxation behavior which is caused by the reduced viscous stress related to the continuous cyclic softening and fades with the decrease of cyclic strain ranges. Accordingly, a new unified viscoplastic constitutive model within the framework of Chaboche model was developed by improving the nonlinear isotropic hardening rule and the kinematic hardening rule with a cyclic softening parameter. As a result, the accelerated cyclic softening and decelerated stress relaxation response of fatigue-creep interaction was finely reproduced by the proposed model.
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interaction of cyclic softening and stress relaxation of 9 12 cr steel under strain controlled fatigue creep condition experimental and modeling
International Journal of Plasticity, 2017Co-Authors: Shang-lin Zhang, Fu-zhen XuanAbstract:Abstract Strain controlled fatigue of P92 steel with various strain hold Dwells introduced at the peak loading point were conducted at 625 °C. Two features which depend on the cycle and strain range level were observed under the fatigue-creep condition for the viscous and cyclic softening material. The first one is the accelerated cyclic softening response which is ascribed to the accumulated inelastic strain transformation from the creep mechanism during the strain Dwell period and becomes more significant with the decrease of strain ranges. The second one is the decelerated stress relaxation behavior which is caused by the reduced viscous stress related to the continuous cyclic softening and fades with the decrease of cyclic strain ranges. Accordingly, a new unified viscoplastic constitutive model within the framework of Chaboche model was developed by improving the nonlinear isotropic hardening rule and the kinematic hardening rule with a cyclic softening parameter. As a result, the accelerated cyclic softening and decelerated stress relaxation response of fatigue-creep interaction was finely reproduced by the proposed model.
Weicheng Cui - One of the best experts on this subject based on the ideXlab platform.
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experimental investigation on Dwell fatigue property of ti 6al 4v eli used in deep sea manned cabin
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2015Co-Authors: Fang Wang, Weicheng CuiAbstract:Abstract The deep-sea manned cabin endures Dwell-fatigue loading process during service. The high strength titanium alloy Ti–6Al–4V ELI adopted for the manufacture manned cabin is of creep nature in the room temperature. So the Dwell-fatigue property of this material should be evaluated for service life estimation. This paper presents the experimental research results on Dwell-fatigue property of Ti–6Al–4V ELI. The strain accumulations under different loading conditions are reported. Results show that the strain accumulation behavior of the material under Dwell-fatigue loading conditions are very similar to that under the condition of normal creep with three stages; and the increase in total strain with respect to number of cycles was much more pronounced for specimen at higher stress level, while the Dwell time will affect strain accumulation when it is plotted versus cycles while strain accumulation tends to be similar in the abscissa of time for different Dwell time under test. Based on the results, a Dwell-fatigue life curve is derived based on the analysis, which can be applied in the material evaluation and service life estimation of the manned cabin.
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Prediction of Cold Dwell-Fatigue Crack Growth of Titanium Alloys
Acta Metallurgica Sinica (English Letters), 2015Co-Authors: Ke Wang, Fang Wang, Weicheng Cui, A.-li TianAbstract:The Dwell effect of the material can reduce the fatigue lives of titanium alloys at room temperature. A unified fatigue life prediction method developed by the authors’ group is modified in this paper to predict Dwell-fatigue crack growth taking into account the effects of Dwell time and maximum stress. The modified model can be successfully used to predict the crack growth rate and calculate the fatigue life of different titanium alloys under pure fatigue and Dwell-fatigue conditions. It is validated by comparing prediction results with the experimental data of several titanium alloys with different microstructures, Dwell time, hydrogen contents, stress ratios and stress levels .
Masood Dehghan - One of the best experts on this subject based on the ideXlab platform.
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Computations of mode-dependent Dwell times for discrete-time switching system
Automatica, 2013Co-Authors: Masood Dehghan, Chong Jin OngAbstract:Given a system that switches among N linear subsystems, this paper shows an approach that computes N Dwell times, one for each of the subsystems, such that the overall system is stable under switching signals that respect the Dwell times. The Dwell times are obtained progressively starting from the groups of all pairwise switching systems, and increasing the size of the group by one for each step. In each progressive step, a bisection search algorithm is used to obtain the mode-dependent Dwell times for that step. When the final step is reached, the N-mode Dwell times are obtained. These Dwell times are smaller, in terms of their sum, than an existing approach in recent literature for all the examples considered in this paper.
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brief paper discrete time switching linear system with constraints characterization and computation of invariant sets under Dwell time consideration
Automatica, 2012Co-Authors: Masood DehghanAbstract:This paper introduces the concepts of Dwell-Time invariant/contractive (DT-invariant/contractive) set, Constraint Admissible DT-invariant/contractive (CADT-invariant/contractive) set for a discrete-time switching system under Dwell-time switching. Main contributions of this paper include a characterization for a DT-contractive set, an algorithm for the computation of the maximal CADT-invariant set, a necessary and sufficient condition for asymptotic stability of the origin of switching systems under Dwell-time switching and computation of the minimal Dwell-time needed for asymptotic stability of the origin.
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discrete time switched linear system with constraints characterization and computation of invariant sets under Dwell time consideration
Conference on Decision and Control, 2011Co-Authors: Masood Dehghan, Chong Jin Ong, Peter C Y ChenAbstract:This paper introduces the concepts of Dwell-Time invariance (DT-invariance) and maximal constraint admissible DT-invariant set for discrete-time switching systems under Dwell-time switching. Main contributions of this paper include a characterization for DT-invariance; a numerical computation of the maximal CADT-invariant set; a necessary and sufficient condition for asymptotic stability of the origin of the switching systems under Dwell time switching and an algorithm for the computation of the minimal Dwell time needed for stability.
Shang-lin Zhang - One of the best experts on this subject based on the ideXlab platform.
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Interaction of cyclic softening and stress relaxation of 9–12% Cr steel under strain-controlled fatigue-creep condition: Experimental and modeling
International Journal of Plasticity, 2017Co-Authors: Shang-lin Zhang, Fu-zhen XuanAbstract:Abstract Strain controlled fatigue of P92 steel with various strain hold Dwells introduced at the peak loading point were conducted at 625 °C. Two features which depend on the cycle and strain range level were observed under the fatigue-creep condition for the viscous and cyclic softening material. The first one is the accelerated cyclic softening response which is ascribed to the accumulated inelastic strain transformation from the creep mechanism during the strain Dwell period and becomes more significant with the decrease of strain ranges. The second one is the decelerated stress relaxation behavior which is caused by the reduced viscous stress related to the continuous cyclic softening and fades with the decrease of cyclic strain ranges. Accordingly, a new unified viscoplastic constitutive model within the framework of Chaboche model was developed by improving the nonlinear isotropic hardening rule and the kinematic hardening rule with a cyclic softening parameter. As a result, the accelerated cyclic softening and decelerated stress relaxation response of fatigue-creep interaction was finely reproduced by the proposed model.
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interaction of cyclic softening and stress relaxation of 9 12 cr steel under strain controlled fatigue creep condition experimental and modeling
International Journal of Plasticity, 2017Co-Authors: Shang-lin Zhang, Fu-zhen XuanAbstract:Abstract Strain controlled fatigue of P92 steel with various strain hold Dwells introduced at the peak loading point were conducted at 625 °C. Two features which depend on the cycle and strain range level were observed under the fatigue-creep condition for the viscous and cyclic softening material. The first one is the accelerated cyclic softening response which is ascribed to the accumulated inelastic strain transformation from the creep mechanism during the strain Dwell period and becomes more significant with the decrease of strain ranges. The second one is the decelerated stress relaxation behavior which is caused by the reduced viscous stress related to the continuous cyclic softening and fades with the decrease of cyclic strain ranges. Accordingly, a new unified viscoplastic constitutive model within the framework of Chaboche model was developed by improving the nonlinear isotropic hardening rule and the kinematic hardening rule with a cyclic softening parameter. As a result, the accelerated cyclic softening and decelerated stress relaxation response of fatigue-creep interaction was finely reproduced by the proposed model.
Graham Currie - One of the best experts on this subject based on the ideXlab platform.
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Impact of Crowding on Streetcar Dwell Time
Transportation Research Record, 2013Co-Authors: Graham Currie, Alexa Delbosc, Samantha Harrison, Majid SarviAbstract:Streetcars are undergoing a renaissance, but developers need to plan for efficient Dwell times at stops to ensure good running time and reliability of performance. Research has established that tram stop configuration is a critical factor in streetcar Dwell times at platform stops that show good performance. However, research also shows that crowding can cause Dwell time problems. No known study to date has examined the impacts of crowding and tram stop design on Dwell times, a major gap in knowledge. This paper presents the first empirical study that explored those impacts. The comprehensive study covered Dwell time at busy stops to explore the influence of passenger volume, vehicle and stop crowding, tram entrance steps, and tram stop design on passenger flow times. Two multiple regressions measured the impact of these influences. Results demonstrated that crowding caused a significant deterioration in the Dwell time benefits that platform stops provided compared with curbside stops. A critical threshol...
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Modeling Dwell Time for Streetcars in Melbourne, Australia, and Toronto, Canada
Transportation Research Record: Journal of the Transportation Research Board, 2012Co-Authors: Graham Currie, Alexa Delbosc, James ReynoldsAbstract:Previous research indicates that Dwell time is a major factor influencing transit competitiveness. Streetcars have particularly uncompetitive running times, but no research has explored influences on streetcar Dwell time. There is also no analytical research on Dwell time effects of stop design despite anecdotal evidence showing that platform stops have reduced streetcar Dwell time. This paper presents an empirical study of factors affecting Dwell time on streetcars in Melbourne, Australia, and Toronto, Canada. It focuses on tram stop design. Results show that payment of fares to drivers on entry in Toronto increases Dwell time compared with onboard self-ticket validation in Melbourne (β = .26). For a typical case of 10 passengers boarding and five alighting, the Melbourne approach saves 9.4 s (48%) of Dwell time compared with Toronto. Tram stop design, notably platform stops, was the next most significant factor affecting streetcar Dwell time (β = -.18). For a typical case of 10 passengers boarding and five alighting, platform stops reduce Dwell time by 6.6 s or 25%. A positive link between the number of doors on trams and Dwell time was found; however, this is thought to result from insufficient examples of high boarding numbers on four-door trams. The results suggest that off-vehicle or postboarding ticket purchase and validation are significant strategies for reducing Dwell time. Providing platform stops is also a potential strategy for reducing Dwell time. Areas for future research are suggested.
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Modeling Dwell Time for Streetcars in Melbourne, Australia, and Toronto, Canada
Transportation Research Record, 2012Co-Authors: Graham Currie, Alexa Delbosc, James F. ReynoldsAbstract:Previous research indicates that Dwell time is a major factor influencing transit competitiveness. Streetcars have particularly uncompetitive running times, but no research has explored influences on streetcar Dwell time. There is also no analytical research on Dwell time effects of stop design despite anecdotal evidence showing that platform stops have reduced streetcar Dwell time. This paper presents an empirical study of factors affecting Dwell time on streetcars in Melbourne, Australia, and Toronto, Canada. It focuses on tram stop design. Results show that payment of fares to drivers on entry in Toronto increases Dwell time compared with onboard self-ticket validation in Melbourne (β = .26). For a typical case of 10 passengers boarding and five alighting, the Melbourne approach saves 9.4 s (48%) of Dwell time compared with Toronto. Tram stop design, notably platform stops, was the next most significant factor affecting streetcar Dwell time (β = -.18). For a typical case of 10 passengers boarding and f...
