The relative ratio of fatigue resistance to creep resistance of materials varies with test temper- ature.As the temperature decreases,the creep resistance,since it is a thermal activation pro- cess,becomes relatively ...The relative ratio of fatigue resistance to creep resistance of materials varies with test temper- ature.As the temperature decreases,the creep resistance,since it is a thermal activation pro- cess,becomes relatively larger than fatigue resistance.Therefore the fatigue damage becomes predominant,and results in expansion of fatigue fracture region(region F),and shrinkage even complete elimination of creep fracture region(region C).A materials parameter Ω can be defined to estimate the temperature at which the creep fracture region is completely de- pressed.This phenomenon could be understood on the basis of the integrated model of compet- itive and cumulative models of fatigue creep interaction.展开更多
Low-cycle fatigue experiments of tension-compression, torsion andtension-torsion with holding time were performed. The interaction law of creep and fatigue undermultiaxial stress at high temperature was investigated, ...Low-cycle fatigue experiments of tension-compression, torsion andtension-torsion with holding time were performed. The interaction law of creep and fatigue undermultiaxial stress at high temperature was investigated, and the micro-mechanism of equilibriumdiagrams was analyzed. A united equation of fatigue life under multiaxial stress was proposed.展开更多
The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for c...The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for cyclic load was of trapezoidal shape with a hold time of 10s at the upper stress level. The TEM was employed to examine the deformation process in strengthened γ' matrix in dependence of γ' precipitate morphology. The fracture lifetime and cycle number up to fracture were the criteria to evaluate the additional cyclic component efFect on the course of deformation展开更多
Itis understood that grain boundary cavitation is one of the detrimental processes for thedegradation of materials that reduces the creep fatigue life at high temperatures. Anewdamagefunction based on a modelforthecr...Itis understood that grain boundary cavitation is one of the detrimental processes for thedegradation of materials that reduces the creep fatigue life at high temperatures. Anewdamagefunction based on a modelforthecreep fatiguelife prediction in termsof nucleationand growth ofgrain boundarycavitiesisproposed. Thisdamagefunctionisacombination ofthetermsrelated to the cavitational damagein thelife prediction equation and is generallyapplicabletothe materialsin which failureis controlled by the grain boundary cavitationaldamage. Thecreep fatiguedatafrom thepresentandotherinvestigationsareusedtocheckthevalidityofthe proposed function, and itisshown thattheysatisfythereliability of damagefunction. Additionally, using this damage function, one may realize that allthe Coffin Manson plotsatthevariouslevelsoftensileholdtimeandtemperatureunderstrain controlled creep fatiguetestscan be normalizedto makethe mastercurve.展开更多
The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 1...The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 190 ℃） for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing（150-190 ℃）, the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 ℃,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.展开更多
In the creep fatigue crack growth of GH4169 alloy,oxidation is a prominent damage source,which is mainly manifested as the oxidation damage zone in front of crack tip.In order to investigate the property of the oxidat...In the creep fatigue crack growth of GH4169 alloy,oxidation is a prominent damage source,which is mainly manifested as the oxidation damage zone in front of crack tip.In order to investigate the property of the oxidation damage zone formed in the creep fatigue crack growth,crack growth tests of directly aged GH4169 alloy were conducted at 650℃ in air under various load conditions.Interrupted tests were performed to observe the damage characteristics at crack tip.Block tests were systematically executed to quantify the dependency of oxidation damage zone size on load and holding time.The crack propagation of the GH4169 alloy has a close relationship with grain boundary oxidation at 650℃.An oxidation damage zone in front of crack tip includes intergranular microcracks and oxidised but uncracked grain boundaries.Its size has been calculated from transient crack growth rate and described as a function of maximum stress intensity factor and holding time.Based on oxidation damage zone size,a novel model has been developed to predict the creep fatigue crack growth rate of the GH4169 alloy at 650℃.展开更多
The possibility of a life prediction model for nickel base single crystal blades has been studied. The fatigue creep (FC) and thermal fatigue creep(TMFC) as well as creep experiments have been carried out with differe...The possibility of a life prediction model for nickel base single crystal blades has been studied. The fatigue creep (FC) and thermal fatigue creep(TMFC) as well as creep experiments have been carried out with different hold time of DD3. The hold time and the frequency as well as the temperature range are the main factors influencing the life. An emphasis has been put on the micro mechanism of the rupture of creep, FC and TMFC. Two main factors are the voiding and degeneration of the material for the cre...展开更多
This paper introduces the key laboratory on bundle conductors for high voltage overhead lines built byElectric Power Construction Research Institute under the State Power Corporation of China. It consists of 4 sub-lab...This paper introduces the key laboratory on bundle conductors for high voltage overhead lines built byElectric Power Construction Research Institute under the State Power Corporation of China. It consists of 4 sub-laboratories, namely the Aeolian Vibration Lab, Spacer Vibration Lab, Conductor Fatigue Lab and Conductor CreepageLab. The paper introduces also laboratory’s facilities, functions and some experimental results.[展开更多
Micro-alloying of Mg,ranged from 30 to 70 ppm,may improve the high temperature ductility,stress rupture,especially,certain important mechanical properties,such as cyclic stress rupture,creep/fatigue interaction and cr...Micro-alloying of Mg,ranged from 30 to 70 ppm,may improve the high temperature ductility,stress rupture,especially,certain important mechanical properties,such as cyclic stress rupture,creep/fatigue interaction and crack propagation rate.The quantity, morphology and distribution of δ-phase may obviously influence the notched cyclic stress rup- ture life.The relevant microstructure shows that the Mg may also influence to certain extent on the feature of δ-phase.Thus,to keep the Mg and δ-phase under control may further im- prove the mechanical properties of alloy GH169.展开更多
Different components of deep-sea submersibles,such as the pressure hull,are usually subjected to intermittent loading,dwell loading,and unloading during service.Therefore,for the design and reliability assessment of s...Different components of deep-sea submersibles,such as the pressure hull,are usually subjected to intermittent loading,dwell loading,and unloading during service.Therefore,for the design and reliability assessment of structural parts under dwell fatigue loading,understanding the effects of intermittent loading time on dwell fatigue behavior of the alloys is essential.In this study,the effects of the intermittent loading time and stress ratio on dwell fatigue behavior of the titanium alloy Ti-6 Al-4 V ELI were investigated.Results suggest that the dwell fatigue failure modes of Ti-6 Al-4 V ELI can be classified into three types,i.e.,fatigue failure mode,ductile failure mode,and mixed failure mode.The intermittent loading time does not affect the dwell fatigue behavior,whereas the stress ratio significantly affects the dwell fatigue life and dwell fatigue mechanism.The dwell fatigue life increases with an increase in the stress ratio for the same maximum stress,and specimens with a negative stress ratio tend to undergo ductile failure.The mechanism of dwell fatigue of titanium alloys is attribute to an increase in the plastic strain caused by the part of the dwell loading,thereby resulting in an increase in the actual stress of the specimens during the subsequent loading cycles and aiding the growth of the formed crack or damage,along with the local plastic strain or damage induced by the part of the fatigue load promoting the cumulative plastic strain during the dwell fatigue process.The interaction between dwell loading and fatigue loading accelerates specimen failure,in contrast to the case for individual creep or fatigue loading alone.The dwell fatigue life and cumulative maximum strain during the first loading cycle could be correlated by a linear relationship on the log–log scale.This relationship can be used to evaluate the dwell fatigue life of Ti alloys with the maximum stress dwell.展开更多
China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium （Mg） and its alloys in the world from a solid base laid by its prominent metallurgist and m...China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium （Mg） and its alloys in the world from a solid base laid by its prominent metallurgist and materials scientists over the past decades. Nowadays, a large number of young-generation researchers have been inspired by their predecessors and become the key participants in the fields of Mg alloys, which consequently led to the establishment of China Youth Scholar Society for Magnesium Alloys Research in 2015. Since then, the first two China Youth Scholars Symposiums on Mg Alloys Research had been held at Harbin （2015） and Chongqing （2016） China, respectively. A number of crucial research inter- ests related to fundamental and applied Mg research were discussed at the conferences and summarized in this short perspective, aiming to boost far-reaching initiatives for development of new Mg-based materials to satisfy the requirements for a broad range of industrial employments. Herein, four main aspects are included as follows： i） Plastic deformation mechanism and strengthening strategy, ii） Design and development of new Mg-based materials, iii） Key service properties, and iv） New processing technologies.展开更多
文摘The relative ratio of fatigue resistance to creep resistance of materials varies with test temper- ature.As the temperature decreases,the creep resistance,since it is a thermal activation pro- cess,becomes relatively larger than fatigue resistance.Therefore the fatigue damage becomes predominant,and results in expansion of fatigue fracture region(region F),and shrinkage even complete elimination of creep fracture region(region C).A materials parameter Ω can be defined to estimate the temperature at which the creep fracture region is completely de- pressed.This phenomenon could be understood on the basis of the integrated model of compet- itive and cumulative models of fatigue creep interaction.
基金This work is supported by National Natural Science Foundation of China (No. 10172010)
文摘Low-cycle fatigue experiments of tension-compression, torsion andtension-torsion with holding time were performed. The interaction law of creep and fatigue undermultiaxial stress at high temperature was investigated, and the micro-mechanism of equilibriumdiagrams was analyzed. A united equation of fatigue life under multiaxial stress was proposed.
文摘The effect of different initial microstructures deftned by γ' precipitate morphology has been investigated at the creep/fatigue conditions of 900℃ and 500 MPa. The wave form of stress as a function of time for cyclic load was of trapezoidal shape with a hold time of 10s at the upper stress level. The TEM was employed to examine the deformation process in strengthened γ' matrix in dependence of γ' precipitate morphology. The fracture lifetime and cycle number up to fracture were the criteria to evaluate the additional cyclic component efFect on the course of deformation
文摘Itis understood that grain boundary cavitation is one of the detrimental processes for thedegradation of materials that reduces the creep fatigue life at high temperatures. Anewdamagefunction based on a modelforthecreep fatiguelife prediction in termsof nucleationand growth ofgrain boundarycavitiesisproposed. Thisdamagefunctionisacombination ofthetermsrelated to the cavitational damagein thelife prediction equation and is generallyapplicabletothe materialsin which failureis controlled by the grain boundary cavitationaldamage. Thecreep fatiguedatafrom thepresentandotherinvestigationsareusedtocheckthevalidityofthe proposed function, and itisshown thattheysatisfythereliability of damagefunction. Additionally, using this damage function, one may realize that allthe Coffin Manson plotsatthevariouslevelsoftensileholdtimeandtemperatureunderstrain controlled creep fatiguetestscan be normalizedto makethe mastercurve.
基金Funded by the National Natural Science Foundation of China(Nos.51375500,and 51375162)Scientific Research Project of Hunan Province Department of Education(No.17C0886)Open Funded Projects of Hunan Provincial Key Laboratory of Health Maintenance for Mechanical Equipment(No.201605)
文摘The hardness, the tensile and the high-cycle fatigue（HCF） performances of 7075 aluminum alloy were investigated under temper T651, solution treated at 380 ℃ for 0.5 h and aged at different temperatures（150, 170, 190 ℃） for 10 hours. The optimal microstructures and the fatigue fracture surfaces were observed. The results show that the hardness and the tensile performances are at their optimum at T651, but the fatigue life is the shortest. The hardness and the elongation are the lowest after solution treatment. With the aging temperature increasing（150-190 ℃）, the HCF is improved. The crack is initiated from the impurity particles on the subsurface. Treated at 170 ℃,the area of the quasi-cleavage plane and the width of parallel serrated sections of the crack propagation are the largest. With increasing aging temperature, the dimple size of finally fracture surfaces becomes larger and the depth deeper.
基金supported by the National Key R&D Program of China(No.2022YFF0609300)the National Major Science and Technology Projects of China(J2019-VI-0021-0137).
文摘In the creep fatigue crack growth of GH4169 alloy,oxidation is a prominent damage source,which is mainly manifested as the oxidation damage zone in front of crack tip.In order to investigate the property of the oxidation damage zone formed in the creep fatigue crack growth,crack growth tests of directly aged GH4169 alloy were conducted at 650℃ in air under various load conditions.Interrupted tests were performed to observe the damage characteristics at crack tip.Block tests were systematically executed to quantify the dependency of oxidation damage zone size on load and holding time.The crack propagation of the GH4169 alloy has a close relationship with grain boundary oxidation at 650℃.An oxidation damage zone in front of crack tip includes intergranular microcracks and oxidised but uncracked grain boundaries.Its size has been calculated from transient crack growth rate and described as a function of maximum stress intensity factor and holding time.Based on oxidation damage zone size,a novel model has been developed to predict the creep fatigue crack growth rate of the GH4169 alloy at 650℃.
基金National Natural Science F oundation of China (5 0 0 0 5 0 16) Aviation F oundation (0 0 B5 3 0 10 ) as well as theYangtze River Foundation
文摘The possibility of a life prediction model for nickel base single crystal blades has been studied. The fatigue creep (FC) and thermal fatigue creep(TMFC) as well as creep experiments have been carried out with different hold time of DD3. The hold time and the frequency as well as the temperature range are the main factors influencing the life. An emphasis has been put on the micro mechanism of the rupture of creep, FC and TMFC. Two main factors are the voiding and degeneration of the material for the cre...
文摘This paper introduces the key laboratory on bundle conductors for high voltage overhead lines built byElectric Power Construction Research Institute under the State Power Corporation of China. It consists of 4 sub-laboratories, namely the Aeolian Vibration Lab, Spacer Vibration Lab, Conductor Fatigue Lab and Conductor CreepageLab. The paper introduces also laboratory’s facilities, functions and some experimental results.[
文摘Micro-alloying of Mg,ranged from 30 to 70 ppm,may improve the high temperature ductility,stress rupture,especially,certain important mechanical properties,such as cyclic stress rupture,creep/fatigue interaction and crack propagation rate.The quantity, morphology and distribution of δ-phase may obviously influence the notched cyclic stress rup- ture life.The relevant microstructure shows that the Mg may also influence to certain extent on the feature of δ-phase.Thus,to keep the Mg and δ-phase under control may further im- prove the mechanical properties of alloy GH169.
基金the National Key Research and Development Program of China(No.2017YFC0305500)。
文摘Different components of deep-sea submersibles,such as the pressure hull,are usually subjected to intermittent loading,dwell loading,and unloading during service.Therefore,for the design and reliability assessment of structural parts under dwell fatigue loading,understanding the effects of intermittent loading time on dwell fatigue behavior of the alloys is essential.In this study,the effects of the intermittent loading time and stress ratio on dwell fatigue behavior of the titanium alloy Ti-6 Al-4 V ELI were investigated.Results suggest that the dwell fatigue failure modes of Ti-6 Al-4 V ELI can be classified into three types,i.e.,fatigue failure mode,ductile failure mode,and mixed failure mode.The intermittent loading time does not affect the dwell fatigue behavior,whereas the stress ratio significantly affects the dwell fatigue life and dwell fatigue mechanism.The dwell fatigue life increases with an increase in the stress ratio for the same maximum stress,and specimens with a negative stress ratio tend to undergo ductile failure.The mechanism of dwell fatigue of titanium alloys is attribute to an increase in the plastic strain caused by the part of the dwell loading,thereby resulting in an increase in the actual stress of the specimens during the subsequent loading cycles and aiding the growth of the formed crack or damage,along with the local plastic strain or damage induced by the part of the fatigue load promoting the cumulative plastic strain during the dwell fatigue process.The interaction between dwell loading and fatigue loading accelerates specimen failure,in contrast to the case for individual creep or fatigue loading alone.The dwell fatigue life and cumulative maximum strain during the first loading cycle could be correlated by a linear relationship on the log–log scale.This relationship can be used to evaluate the dwell fatigue life of Ti alloys with the maximum stress dwell.
基金support from Chinese Committee for Magnesium and its Application
文摘China has been developed into one of the most active regions in terms of both fundamental and applied research on magnesium （Mg） and its alloys in the world from a solid base laid by its prominent metallurgist and materials scientists over the past decades. Nowadays, a large number of young-generation researchers have been inspired by their predecessors and become the key participants in the fields of Mg alloys, which consequently led to the establishment of China Youth Scholar Society for Magnesium Alloys Research in 2015. Since then, the first two China Youth Scholars Symposiums on Mg Alloys Research had been held at Harbin （2015） and Chongqing （2016） China, respectively. A number of crucial research inter- ests related to fundamental and applied Mg research were discussed at the conferences and summarized in this short perspective, aiming to boost far-reaching initiatives for development of new Mg-based materials to satisfy the requirements for a broad range of industrial employments. Herein, four main aspects are included as follows： i） Plastic deformation mechanism and strengthening strategy, ii） Design and development of new Mg-based materials, iii） Key service properties, and iv） New processing technologies.
