Papers by Keyword: Cyclic Stress Response

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Authors: Ying Lan, Li Jia Chen, Xin Che, Feng Li
Abstract: The low-cycle fatigue behaviors of as-extruded and T6 treated Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloys at room temperature have been investigated under those total-strain amplitudes ranged from 0.3% to 1.0%, and the influence of T6 treatment on the low-cycle fatigue properties of Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloy was clarified. The experimental results show that during fatigue deformation, the significant cyclic strain hardening and stable cyclic stress response can be noted for both as-extruded and T6 treated Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloys. The fatigue life of as-extruded Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloy at all strain amplitudes is longer than that of the alloy subjected to T6 aging treatment. The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior, and can be described by the Basquin and Coffin-Manson equations, respectively. The T6 treatment can significantly increase the cyclic strain hardening exponent and cyclic strength coefficient of extruded Al-6Zn-2.5Mg-2Cu-0.1Zr-0.1Sc alloy.
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Authors: Teng Yu, Lei Wang, Yong Qing Zhao, Yang Liu
Abstract: Effects of thermal exposure on low cycle fatigue behavior of Ti600 alloy were investigated by LSCM, SEM and TEM. The results demonstrated that both the NTE specimens and the TE specimens showed the cyclic softening, within a total strain amplitude range from ±0.45% to ±1.00%. Since the α2 phase precipitated in the αp phase during thermal exposure, the resistance of fatigue crack propagation of αp phase could be increased by the precipitation of α2 phase. Therefore, the low cycle fatigue (LCF) lives of Ti600 alloy after thermal exposure were longer than those without thermal exposure, at the same total strain amplitude.
611
Authors: Yuan Yuan Li, Feng Li, Xin Che, Li Jia Chen
Abstract: Abstract: The fatigue behavior of cast steel ZG20SiMn under strain control mode was investigated, and the influence of imposed total strain amplitude on the cyclic deformation and fracture behavior of the cast steel ZG20SiMn was determined. The experimental results reveal that during fatigue deformation, the cast steel ZG20SiMn may exhibit the cyclic strain hardening and stable cyclic stress response behavior, which mainly depends on the imposed total strain amplitude. The relationship between plastic and elastic strain amplitudes with reversals to failure shows a single linear behavior, and can be well described by the Coffin-Manson and Basquin equations, respectively. At different total strain amplitudes, the fatigue cracks initiate at the free surface of fatigue specimens and propagate for the cast steel ZG20SiMn.
2236
Authors: Du Yi Ye, Jin Yang Zheng
Abstract: The low-cycle fatigue (LCF) properties of a nickel-base precipitation-strengthened superalloy (GH4145/SQ), obtained at a temperature of 538 o C, were reported and discussed in this paper. The properties investigated include cyclic stress response, fatigue life, deformation microstructure and final fracture features as a function of applied strain amplitude. It was shown that the alloy exhibited a pronounced initial hardening followed by continuous softening to failure at high plastic strain amplitudes ( > 0.2% ap ε ), while at low plastic strain amplitudes ( < 0.2% ap ε ) the initial hardening was followed by a well-defined saturation stage. Bilinear behavior with a change of slope at a plastic strain amplitude of about 0.2% was observed in the cyclic stress-strain (CSS) and Coffin-Manson (C-M) plots. TEM observations revealed that slip band density increased with increasing total strain amplitude and precipitate degradation resulting from dislocation-precipitate interactions took place with continuous cyclic straining. The change in the microstructure during cycling is thus responsible for the fatigue hardening / softening behavior of the alloy. SEM examinations indicated that at low plastic strain amplitudes ( < 0.2% ap ε ) crack propagation was basically transgranular, while at high plastic strain amplitudes ( > 0.2% ap ε ) crack propagation exhibited intergranular features, as a whole. The variation in both the number of operating slip systems and the fracture modes with the strain amplitude employed was used to explain the observed two-stage LCF behavior of the present investigated superalloy.
249
Authors: Yuan Yuan Wang, Bao Sen Wang, Li Jia Chen
Abstract: High temperature low cycle fatigue properties and fracture behavior of Inconel 625 nickel-base superalloy welding joint at 760oC were investigated under fully reversed total strain-controlled mode. The fatigue life and cyclic stress-strain data were analyzed to determine the individual strain fatigue parameters. It is noted that the welding joint exhibits the cyclic strain hardening and stability. The fatigue cracks initiate predominantly on the free surface of fatigue specimens and propagate in an intergranular mode or a mixed transgranular and intergranular mode.
120
Authors: Shu Ying Yin, Li Jia Chen, Xin Wang
Abstract: In order to identify the influence of solid solution, aging and solid solution plus aging treatments on the low-cycle fatigue behavior of the extruded AZ61 magnesium alloy, the low-cycle fatigue tests were performed at room temperature for the extruded AZ61 magnesium alloy with different treating states. The results indicate that the cyclic stress response behavior of the extruded AZ61 magnesium alloy exhibits both cyclic strain hardening and stability. The solid solution, aging and solid solution plus aging treatments tend to decrease the cyclic deformation resistance of the extruded AZ61 alloy in most conditions. The solid solution treatment can enhance the fatigue lives of the extruded AZ61 alloy at medium total strain amplitudes. In addition, the aging treatment can prolong the low-cycle fatigue lives of the AZ61 alloy at most total strain amplitudes, while the case for the solid solution plus aging treatment is just contrary. For the extruded AZ61 alloy with different treating states, a linear relationship between cyclic stress amplitude and plastic strain amplitude is noted.
883
Authors: Xin Che, Feng Li, Li Jia Chen
Abstract: The low-cycle fatigue behaviors of permanent-mold cast and die-cast Al-Si-Cu-Mg-Sc alloys at room temperature were investigated. The results show that at the higher total strain amplitudes, both permanent-mould cast and die-cast Al-Si-Cu-Mg-Sc alloys exhibit the cyclic strain hardening. However, at the lowest total strain amplitude, the cyclic strain hardening occurs in the initial and middle stages of fatigue deformation and the stable cyclic stress response is noted in the later stage of fatigue deformation for the permanent-mould cast alloy, while the cyclic strain hardening phenomenon is observed during whole fatigue deformation for the die-cast alloy. At the same total strain amplitude, the die-cast alloy shows the higher cyclic deformation resistance than the permanent-mold cast alloy. Compared with the permanent-mold cast alloy, the die-cast alloy possesses the longer fatigue life at the lower total strain amplitudes. The relationship between both elastic and plastic strain amplitudes with reversals to failure shows a monotonic linear behavior for both permanent-mold cast and die-cast Al-Si-Cu-Mg-Sc alloys
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