Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lower than that of long cracks,and to decrease with the shortening of the crack length.The correla- tion among the threshold,crack...Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lower than that of long cracks,and to decrease with the shortening of the crack length.The correla- tion among the threshold,crack wake,and crack tip shielding of the short fatigue cracks was discussed.The super demarcation length and lowest theoretical threshold of short through fa- tigue cracks were presented.展开更多
While pre-deformation is often conducted before aging treatment to increase the strength and microhardness of 2195 Al-Li alloy, it often increases the fatigue crack growth(FCG) rate and thus reduces the fatigue life o...While pre-deformation is often conducted before aging treatment to increase the strength and microhardness of 2195 Al-Li alloy, it often increases the fatigue crack growth(FCG) rate and thus reduces the fatigue life of the alloy.To determine the effects and causes of pre-deformation and heat treatment on the mechanical properties and FCG rate of2195 Al-Li alloy, and to provide a suitable calculation model for the FCG rate under different pre-deformation conditions, 2195 Al-Li alloy specimens with different degrees of pre-rolling(0, 3%, 6%, and 9%) were investigated. The experimental results indicate that with the increase of pre-rolling, the density of the T1phase and the uniformity of the S′distribution and the microhardness, tensile strength, and yield strength of the alloy increase and at the same time the FCG rate increases, and thus the fatigue life is reduced. It was also found that the normalized stress intensity factor of elastic modulus(E) can be applied to correlate the FCG rate of pre-rolled 2195 Al-Li alloy with constant C and K parameters.展开更多
The fatigue crack initiation and early propagation behavior of 2A97 Al-Li alloy was studied. The smooth specimens were fatigued at room temperature under constant maximum stress control when stress ratio （R） is 0.1 ...The fatigue crack initiation and early propagation behavior of 2A97 Al-Li alloy was studied. The smooth specimens were fatigued at room temperature under constant maximum stress control when stress ratio （R） is 0.1 and frequency （f） is 40 Hz. Microstructure observations were examined by optical microscopy, transmission electron microscopy, scanning electron microscopy and electron back scattered diffusion, in order to investigate the relationship between microstructure and fatigue crack initiation and early propagation behavior of 2A97 alloy. The results show that the fatigue cracks are predominantly initiated at inclusions and coarsen secondary phases on the surface of 2A97 alloy. The fatigue crack early propagation behavior of 2A97 alloy is predominantly influenced by the interactions between grain structure and dislocations or persistent slip bands （PSBs）. When the misorientation of two neighbouring grains is close to the orientations of the favorable slip plane within these two grains, high-angle grain boundary severely hinders the PSBs passing through, and thus leads to crack bifurcation and deflection.展开更多
Fatigue crack growth rates of Al-Li alloy 8090 in air were found to be strongly dependent up- on the aging conditions.The naturally aged and underaged specimens showed the highest re- sistance to the fatigue crack pro...Fatigue crack growth rates of Al-Li alloy 8090 in air were found to be strongly dependent up- on the aging conditions.The naturally aged and underaged specimens showed the highest re- sistance to the fatigue crack propagation.The fatigue crack growth resistance of the overaged specimen is the lowest and that of the peakaged specimen in between.As compared to air, 3.5% NaCl solution does not change the effect of aging conditions on the fatigue crack growth,but causes a decrease of the resistance to the fatigue crack growth under the same ag- ing condition.Both short cracks from notch and physically short cracks showed much higher rates of fatigue crack propagation in comparison with long cracks under the same aging condi- tion and stress intensity level.The growth behavior of the short crack depends on its type.The growth rate of short crack from notch decreases first to a minimum and then increases with in- creasing △K.However,the physically short crack grows at a progressively increasing rate. The effects of aging conditions are explained in terms of the slip planarity of dislocations and the cyclic slip reversibility.The observed short crack behavior is considered to be dependent on the crack closure and the local plasticity near the crack tip.展开更多
文摘Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lower than that of long cracks,and to decrease with the shortening of the crack length.The correla- tion among the threshold,crack wake,and crack tip shielding of the short fatigue cracks was discussed.The super demarcation length and lowest theoretical threshold of short through fa- tigue cracks were presented.
基金Project(U21A20132) supported by the National Natural Science Foundation of ChinaProject(Gui Renzi2019(13))supported by the Guangxi Specially-invited Experts Foundation of Guangxi Zhuang Autonomous Region,China。
文摘While pre-deformation is often conducted before aging treatment to increase the strength and microhardness of 2195 Al-Li alloy, it often increases the fatigue crack growth(FCG) rate and thus reduces the fatigue life of the alloy.To determine the effects and causes of pre-deformation and heat treatment on the mechanical properties and FCG rate of2195 Al-Li alloy, and to provide a suitable calculation model for the FCG rate under different pre-deformation conditions, 2195 Al-Li alloy specimens with different degrees of pre-rolling(0, 3%, 6%, and 9%) were investigated. The experimental results indicate that with the increase of pre-rolling, the density of the T1phase and the uniformity of the S′distribution and the microhardness, tensile strength, and yield strength of the alloy increase and at the same time the FCG rate increases, and thus the fatigue life is reduced. It was also found that the normalized stress intensity factor of elastic modulus(E) can be applied to correlate the FCG rate of pre-rolled 2195 Al-Li alloy with constant C and K parameters.
文摘The fatigue crack initiation and early propagation behavior of 2A97 Al-Li alloy was studied. The smooth specimens were fatigued at room temperature under constant maximum stress control when stress ratio （R） is 0.1 and frequency （f） is 40 Hz. Microstructure observations were examined by optical microscopy, transmission electron microscopy, scanning electron microscopy and electron back scattered diffusion, in order to investigate the relationship between microstructure and fatigue crack initiation and early propagation behavior of 2A97 alloy. The results show that the fatigue cracks are predominantly initiated at inclusions and coarsen secondary phases on the surface of 2A97 alloy. The fatigue crack early propagation behavior of 2A97 alloy is predominantly influenced by the interactions between grain structure and dislocations or persistent slip bands （PSBs）. When the misorientation of two neighbouring grains is close to the orientations of the favorable slip plane within these two grains, high-angle grain boundary severely hinders the PSBs passing through, and thus leads to crack bifurcation and deflection.
文摘Fatigue crack growth rates of Al-Li alloy 8090 in air were found to be strongly dependent up- on the aging conditions.The naturally aged and underaged specimens showed the highest re- sistance to the fatigue crack propagation.The fatigue crack growth resistance of the overaged specimen is the lowest and that of the peakaged specimen in between.As compared to air, 3.5% NaCl solution does not change the effect of aging conditions on the fatigue crack growth,but causes a decrease of the resistance to the fatigue crack growth under the same ag- ing condition.Both short cracks from notch and physically short cracks showed much higher rates of fatigue crack propagation in comparison with long cracks under the same aging condi- tion and stress intensity level.The growth behavior of the short crack depends on its type.The growth rate of short crack from notch decreases first to a minimum and then increases with in- creasing △K.However,the physically short crack grows at a progressively increasing rate. The effects of aging conditions are explained in terms of the slip planarity of dislocations and the cyclic slip reversibility.The observed short crack behavior is considered to be dependent on the crack closure and the local plasticity near the crack tip.
