Fracture evolution process (initiation, propagation and coalescence) of cracked rock was observed and the force- displacement curves of cracked rock were measured under uniaxial cyclic loading. The tested specimens ma...Fracture evolution process (initiation, propagation and coalescence) of cracked rock was observed and the force- displacement curves of cracked rock were measured under uniaxial cyclic loading. The tested specimens made of sandstone-like modeling material contained three pre-existing intermittent cracks with different geometrical distributions. The experimental results indicate that the fatigue deformation limit corresponding to the maximal cyclic load is equal to that of post-peak locus of static complete force?displacement curve; the fatigue deformation process can be divided into three stages: initial deformation, constant deformation rate and accelerative deformation; the time of fracture initiation, propagation and coalescence corresponds to the change of irreversible deformation.展开更多
The fatigue properties of asphalts were investigated after various laboratory simulation ageing tests and outdoor natural exposure ultraviolet radiation ageing,by dynamic shear rheometer(DSR) time sweep fatigue test i...The fatigue properties of asphalts were investigated after various laboratory simulation ageing tests and outdoor natural exposure ultraviolet radiation ageing,by dynamic shear rheometer(DSR) time sweep fatigue test in constant strain model and a new type of specimen which was introduced to avoid the problem of adhesion failure between rotor and asphalt binder.The results show that outdoor natural exposure ageing(NEA) causes the decrease of retained fatigue life distinctly,and photodegradation caused by outdoor NEA of 1 250 μm thin films asphalt for three months,is found to be severer than pressure ageing vessel(PAV) with respects to retained fatigue life.The effect of photodegradation increases as the time of outdoor NEA increases.DSR time sweep fatigue test in constant strain indicates that the aged styrene-butadiene-styrene(SBS) modified asphalt still displays better fatigue properties than the corresponding base asphalt after ageing.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
To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treat...To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treatment (EBLPWHT) is a rather new heat treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in as-welded (AW) and EBLPWHT conditions have been investigated respectively. The results show that the microstructures of different zones of joints in as-welded condition are changed by EBLPWHT procedure, in which the welds from coarse needle martensite into lath-shaped martensite; the main structures of heat affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of welded joints can be improved by the EBLPWHT in some extent, especially the fracture toughness of the welds and the fatigue crack resistance of welded joints can be sufficiently improved. However, more appropriate heat treatment parameters of the EBLPWHT have to be studied in order to increase the mechanical properties of base metal near by the HAZ.展开更多
While various kinds of fibers are used to improve the hot mix asphalt(HMA) performance, a few works have been undertaken on the hybrid fiber-reinforced HMA. Therefore, the fatigue life of modified HMA samples using po...While various kinds of fibers are used to improve the hot mix asphalt(HMA) performance, a few works have been undertaken on the hybrid fiber-reinforced HMA. Therefore, the fatigue life of modified HMA samples using polypropylene and polyester fibers was evaluated and two models namely regression and artificial neural network(ANN) were used to predict the fatigue life based on the fibers parameters. As ANN contains many parameters such as the number of hidden layers which directly influence the prediction accuracy, genetic algorithm(GA) was used to solve optimization problem for ANN. Moreover, the trial and error method was used to optimize the GA parameters such as the population size. The comparison of the results obtained from regression and optimized ANN with GA shows that the two-hidden-layer ANN with two and five neurons in the first and second hidden layers, respectively, can predict the fatigue life of fiber-reinforced HMA with high accuracy(correlation coefficient of 0.96).展开更多
In this paper, 3 mm 6061 aluminum alloy sheets were welded by laser MIG hybrid welding. Based on the experiment, the best welding parameters were determined to ensure the penetration welding. The detailed microstructu...In this paper, 3 mm 6061 aluminum alloy sheets were welded by laser MIG hybrid welding. Based on the experiment, the best welding parameters were determined to ensure the penetration welding. The detailed microstructure,tensile and fatigue fracture morphology and surface fatigue damage of the welded joints were analyzed by optical microscope(OM), scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). The results show that there are two main kinds of precipitates, one is the long Si rich precipitates at the grain boundaries, the other is the intragranular Cu rich precipitates. The tensile test results show that the tensile strength of the joint is 224 MPa, which is only 70.2% of the base metal. Through the analysis of tensile fracture, there are great differences in the formation of tensile dimple. In the tensile-tensile fatigue test with a stress rate of 0.1, the conditional fatigue limits of base metal and welded joint are 101.9 MPa and 54.4 MPa, respectively. By comparing the fatigue fracture of the welded joints under different stress amplitudes, it was found that the main factor leading to the fracture of the joint is porosity. Through further analysis of the pore defects, it was found that there are transgranular and intergranular propagation ways of microcracks in the pores, and the mixed propagation way was also found.展开更多
Due to notable characteristics,sustainability concept and environmental issues,hybridisation natural with synthetic fibres to fabricate composites have been rapidly gaining market share in different applications(struc...Due to notable characteristics,sustainability concept and environmental issues,hybridisation natural with synthetic fibres to fabricate composites have been rapidly gaining market share in different applications(structural,military,aerospace and automotive vehicles).Compression,tension and fatigue tests of various stacking sequences of plain jute/carbon reinforced(PVB)polyvinyl butyral by hot hydraulic press technique were experimentally conducted.Six types of fabricated composites with various constituents(jute,carbon and their hybrids)were fabricated and tested.Notably,fatigue lifetime of hybrids increases with increasing the carbon content relative to the jute fibre content.On the other hand,Jute composites possess high strain compared to pure carbon composite,which gives an overall improvement in mechanical behaviours.Interestingly,H1 hybrid with Carbon/Jute/Carbon sequences offers similar fatigue stiffness behaviour of H3 hybrid with Carbon/Jute/Carbon/Jute sequences when subjected to cyclic loading.Carbon composite(C)exhibited the highest fatigue resistance,whiles jute composite(J)possessed the highest strain and semi brittle trends in both mechanical and fatigue performance.Results concluded that plain jute fibres could partially replace high-cost synthetic carbon fibres to produce more eco-friendly hybrids to be utilised in different composites industries.展开更多
基金Projects(50479023, 50708034) supported by the National Natural Science Foundation of ChinaProject(20070532069) supported by Specialized Research Fund for the Doctoral Program of Higher Education+1 种基金Project (20060400263) supported by China Postdoctoral Science FoundationProject(2007RS4031) supported by Provincial Science and Technology Plan of Hunan
文摘Fracture evolution process (initiation, propagation and coalescence) of cracked rock was observed and the force- displacement curves of cracked rock were measured under uniaxial cyclic loading. The tested specimens made of sandstone-like modeling material contained three pre-existing intermittent cracks with different geometrical distributions. The experimental results indicate that the fatigue deformation limit corresponding to the maximal cyclic load is equal to that of post-peak locus of static complete force?displacement curve; the fatigue deformation process can be divided into three stages: initial deformation, constant deformation rate and accelerative deformation; the time of fracture initiation, propagation and coalescence corresponds to the change of irreversible deformation.
基金Projects(2006BAB04A05) supported by the Eleventh Five-Year Plan of the National Key Technology Research and Development Program
文摘The fatigue properties of asphalts were investigated after various laboratory simulation ageing tests and outdoor natural exposure ultraviolet radiation ageing,by dynamic shear rheometer(DSR) time sweep fatigue test in constant strain model and a new type of specimen which was introduced to avoid the problem of adhesion failure between rotor and asphalt binder.The results show that outdoor natural exposure ageing(NEA) causes the decrease of retained fatigue life distinctly,and photodegradation caused by outdoor NEA of 1 250 μm thin films asphalt for three months,is found to be severer than pressure ageing vessel(PAV) with respects to retained fatigue life.The effect of photodegradation increases as the time of outdoor NEA increases.DSR time sweep fatigue test in constant strain indicates that the aged styrene-butadiene-styrene(SBS) modified asphalt still displays better fatigue properties than the corresponding base asphalt after ageing.
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To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treatment (EBLPWHT) is a rather new heat treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in as-welded (AW) and EBLPWHT conditions have been investigated respectively. The results show that the microstructures of different zones of joints in as-welded condition are changed by EBLPWHT procedure, in which the welds from coarse needle martensite into lath-shaped martensite; the main structures of heat affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of welded joints can be improved by the EBLPWHT in some extent, especially the fracture toughness of the welds and the fatigue crack resistance of welded joints can be sufficiently improved. However, more appropriate heat treatment parameters of the EBLPWHT have to be studied in order to increase the mechanical properties of base metal near by the HAZ.
文摘While various kinds of fibers are used to improve the hot mix asphalt(HMA) performance, a few works have been undertaken on the hybrid fiber-reinforced HMA. Therefore, the fatigue life of modified HMA samples using polypropylene and polyester fibers was evaluated and two models namely regression and artificial neural network(ANN) were used to predict the fatigue life based on the fibers parameters. As ANN contains many parameters such as the number of hidden layers which directly influence the prediction accuracy, genetic algorithm(GA) was used to solve optimization problem for ANN. Moreover, the trial and error method was used to optimize the GA parameters such as the population size. The comparison of the results obtained from regression and optimized ANN with GA shows that the two-hidden-layer ANN with two and five neurons in the first and second hidden layers, respectively, can predict the fatigue life of fiber-reinforced HMA with high accuracy(correlation coefficient of 0.96).
基金Project(51971129) supported by the National Natural Science Foundation of ChinaProject(19ZR1421200) supported by the Shanghai Natural Science Foundation,China。
文摘In this paper, 3 mm 6061 aluminum alloy sheets were welded by laser MIG hybrid welding. Based on the experiment, the best welding parameters were determined to ensure the penetration welding. The detailed microstructure,tensile and fatigue fracture morphology and surface fatigue damage of the welded joints were analyzed by optical microscope(OM), scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). The results show that there are two main kinds of precipitates, one is the long Si rich precipitates at the grain boundaries, the other is the intragranular Cu rich precipitates. The tensile test results show that the tensile strength of the joint is 224 MPa, which is only 70.2% of the base metal. Through the analysis of tensile fracture, there are great differences in the formation of tensile dimple. In the tensile-tensile fatigue test with a stress rate of 0.1, the conditional fatigue limits of base metal and welded joint are 101.9 MPa and 54.4 MPa, respectively. By comparing the fatigue fracture of the welded joints under different stress amplitudes, it was found that the main factor leading to the fracture of the joint is porosity. Through further analysis of the pore defects, it was found that there are transgranular and intergranular propagation ways of microcracks in the pores, and the mixed propagation way was also found.
基金I would like to thank the Ministry of Higher Education&Scientific Research of Iraq and to Mustansiriyah University,College of Engineering,Mechanical Engineering Department,for the support for the work contained in this study in Iraq.
文摘Due to notable characteristics,sustainability concept and environmental issues,hybridisation natural with synthetic fibres to fabricate composites have been rapidly gaining market share in different applications(structural,military,aerospace and automotive vehicles).Compression,tension and fatigue tests of various stacking sequences of plain jute/carbon reinforced(PVB)polyvinyl butyral by hot hydraulic press technique were experimentally conducted.Six types of fabricated composites with various constituents(jute,carbon and their hybrids)were fabricated and tested.Notably,fatigue lifetime of hybrids increases with increasing the carbon content relative to the jute fibre content.On the other hand,Jute composites possess high strain compared to pure carbon composite,which gives an overall improvement in mechanical behaviours.Interestingly,H1 hybrid with Carbon/Jute/Carbon sequences offers similar fatigue stiffness behaviour of H3 hybrid with Carbon/Jute/Carbon/Jute sequences when subjected to cyclic loading.Carbon composite(C)exhibited the highest fatigue resistance,whiles jute composite(J)possessed the highest strain and semi brittle trends in both mechanical and fatigue performance.Results concluded that plain jute fibres could partially replace high-cost synthetic carbon fibres to produce more eco-friendly hybrids to be utilised in different composites industries.
