A new method was proposed for the multiaxial creep-fatigue life evaluation under proportional loadings. Because this method was derived from the strain range partitioning method with a multiaxiality factor, it was pos...A new method was proposed for the multiaxial creep-fatigue life evaluation under proportional loadings. Because this method was derived from the strain range partitioning method with a multiaxiality factor, it was possible to consider the influence of both creep-fatigue interaction and multiaxial stress state on fatigue life. In order to predict the combined axial-torsional fatigue life the damage under combined loading was defined as linear summation of the damages under axial loading and torsional loading. Axial-torsional creep-fatigue tests were carried out using tubular specimens of 316LC austenitic stainless steel and the ferritic rotor steel. This rotor steel was developed for the permanent magnet type eddy current retarder in heavy trucks. Experimentally obtained lives of both steels were well corresponded with the lives predicted by the proposed method. It was found that the proposed method was effective in multiaxial fatigue life evaluation under proportional creep-fatigue loadings.展开更多
Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plasti...Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.展开更多
Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to...Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to a heavy structure. Because these methods are established on the basis that load cycles would only cause fatigue damage, ignore the strengthening effect of loads. Based on Palmgren-Miner Rule （PMR）, this paper introduces a new method for fatigue life prediction under service loadings by taking into account the strengthening effect of loads below the fatigue limit. In this method, the service loadings are classified into three categories： damaging load, strengthening load and none-effect load, and the process for fatigue life prediction is divided into two stages： stage I and stage II, according to the best strengthening number of cycles. During stage I, fatigue damage is calculated considering both the strengthening and damaging effect of load cycles. While during stage II, only the damaging effect is considered. To validate this method, fatigue lives of automobile half shaft and torsion beam rear axle are calculated based on the new method and traditional methods, such as PMR and Modified Miner Rule （MMR）, and fatigue tests of the two components are conducted under service loading histories. The tests results show that the percentage errors of the predicted life with the new method to mean life of tests for the two components are –3.78% and –1.76% separately, much lesser than that with PMR and MMR. By considering the strengthening effect of loads below the fatigue limit, the new method can significantly improve the accuracy for fatigue life prediction. Thus lightweight design can be fully realized in the design stage.展开更多
A large amount of cutting heat is produced during the heavy cutting process,and insert life is restricted by the effect of thermal load.The thermal load experiment of cemented carbide SCS,WF and YT15 is carried out,an...A large amount of cutting heat is produced during the heavy cutting process,and insert life is restricted by the effect of thermal load.The thermal load experiment of cemented carbide SCS,WF and YT15 is carried out,and the results show that the bending strength and fracture toughness of cemented carbide material decrease obviously under cyclic thermal load,while in the cooling process,the material mechanical property changes worse suddenly.The high-temperature mechanical property of SCS is the most stable,and that of YT15 is the worst.Further,a relation model among cutting temperature,cutting parameters and insert life is established.Finally,the measures to improve heavy cemented carbide inserts life are summarized from the aspects of cutting parameters selection,insert optimization design and TiCN,Al2O3,TiN complex insert coating.The research results are expected to provide support and reference for heavy cutting technology and insert technology.展开更多
Emily Dickenson’s poems have long enjoyed considerable acclaims from critics and common readers for her delicate and profound writing of life and death,love,nature,etc.Her short poem“My Life had stood—a Loaded Gun...Emily Dickenson’s poems have long enjoyed considerable acclaims from critics and common readers for her delicate and profound writing of life and death,love,nature,etc.Her short poem“My Life had stood—a Loaded Gun”is one receiving relatively few academic discussion.Among the rather few existent studies,many discuss Dickenson’s feminist ideas,religious bewilderment,literary creation views or even personal feeling in this poem.This article,instead,gives an interpretation of this poem from an ecocritical perspective.It points out that Emily Dickenson in this poem expresses her condemnation on human’s cruelty and indiffer?ence to nature.After a thorough interpretation of Dickenson’s reflection on human-nature relationship in this poem,the article fur?ther explores Dickenson’s attitudes toward nature through her personal writing background and clues in her other works to support this interpretation.展开更多
The ability of a pavement structure in carrying out its function reduces in line with the increase of traffic load, especially if there are overloaded heavy vehicle passing through the road. This study was done to kno...The ability of a pavement structure in carrying out its function reduces in line with the increase of traffic load, especially if there are overloaded heavy vehicle passing through the road. This study was done to know the effect of overloading vehicles on the road pavement and remaining service life of the pavement. In this study, the service life of pavement due to overloaded vehicles was analyzed using the AASHTO 1993. In Narayanghat-Mugling road the composition of traffic seems to be 83.76% heavy vehicles, 9.18% medium vehicle and 7.05% light vehicle. For the direction of Narayanghat-Mugling, the pavement service life might be reduced by 59.90% due to overloading condition, while for the opposite direction, the service life would not reduced caused by the same factor. The impact of overload conditions on the road pavement showed premature failure;that is, a condition which the damage reduced the life of roads before the design life of the road is reached. From the results, it can be concluded that overloaded vehicles on the road are very influential to the reduction in pavement service life. Therefore, it is expected that road users to comply with existing regulations in the conduct of transportation. As overloading is increasing, it has to be controlled by rules and regulations with penalty to control the overloading. So fines must be associated with intensified enforcement when considered in further strategy. Regular monitoring, inspection and enforcement are the effective ways to control overloading. Use of technology (Automatic overloading information system) may be the effective way to control the overloading.展开更多
A calculation method of fatigue life for slewing bearings under combined radial, axial and tilting moment loads was proposed. Single row four-point contact ball slewing bearing being used as a case, the statics model ...A calculation method of fatigue life for slewing bearings under combined radial, axial and tilting moment loads was proposed. Single row four-point contact ball slewing bearing being used as a case, the statics model of the slewing bearing was established and a set of equilibrium equations were obtained. By solving the equilibrium equatioas, the rolling element loads were obtained and the equivalent rolling element loads were calculated further. By using the geometrical parameters of the bearing, the rating rolling element loads were calculated, and the fa- tigue life of the bearing was calculated by using the rating rolling element loads and the equivalent rolling element loads. A calculation example shows the feasibility of the proposed method.展开更多
The application of prestressed carbon reinforced polymer （prestressed CFRP） in reinforced concrete （RC） members can improve the mechanical properties of strengthened structures and strengthening efficiency. This p...The application of prestressed carbon reinforced polymer （prestressed CFRP） in reinforced concrete （RC） members can improve the mechanical properties of strengthened structures and strengthening efficiency. This paper proposed a semi-empirical prediction fornmla of fatigue lives of the RC beams strengthened with prestressed CFRP under bending loads. The formula is established based on the fatigue life prediction method of RC beams and fatigue experimental data of non-prestressed CFRP reinforced beams done before. Fatigue effect coefficient of the formula was confirmed by the fatigue experiments of the RC beams strengthened with prestressed carbon fiber laminate （prestressed CFL） under cyclic bending loads. Fatigue lives of the strengthened beams predicted using the formula agreed well with the experimental data.展开更多
Suggests some calculating formulas and methods with respect to the damage evolvingrate da / dN|i and the fatigue life and in varied history from uncrack to microcrackinitiation until fracture for a crankshaft, which ...Suggests some calculating formulas and methods with respect to the damage evolvingrate da / dN|i and the fatigue life and in varied history from uncrack to microcrackinitiation until fracture for a crankshaft, which are suitable to stress concentration positionsabout its journal fillets and oil holes on a crankshaft, that it is undergone to bending, twistingand shearing loading and subjected to unsymmetric cyclic many-stage loading. Last the total lifein whole process is estimated by展开更多
Qingdao Jiaozhou Bay subsea tunnel is the second self-built tunnel in China with the designed service life over 100 years.The durability of lining concrete are one of an important factors to determinate the service li...Qingdao Jiaozhou Bay subsea tunnel is the second self-built tunnel in China with the designed service life over 100 years.The durability of lining concrete are one of an important factors to determinate the service life of tunnel.Considering the main environmental loads and mechanical loads of subsea tunnel,the durability properties of lining concrete under combined action of compressive load and carbonation has been studied through the critical compressive load test,accelerated carbonation test,natural carbonation test and capillary suction test.The tests results show that critical compressive load apparently accelerates the carbonation and deteriorates the anti-permeability of concrete.Under the combined action of critical compressive load and carbonation,the durability of lining concrete decreases.Based on the carbonization life criteria and research results,for the high-performance concrete with proposed mix ratio,the predicted service life of lining concrete for Jiaozhou bay subsea tunnel is about 80 years which fails to reach the required service life.It is necessary to adopt other measurements simultaneously to improve the durability of lining concrete.展开更多
文摘A new method was proposed for the multiaxial creep-fatigue life evaluation under proportional loadings. Because this method was derived from the strain range partitioning method with a multiaxiality factor, it was possible to consider the influence of both creep-fatigue interaction and multiaxial stress state on fatigue life. In order to predict the combined axial-torsional fatigue life the damage under combined loading was defined as linear summation of the damages under axial loading and torsional loading. Axial-torsional creep-fatigue tests were carried out using tubular specimens of 316LC austenitic stainless steel and the ferritic rotor steel. This rotor steel was developed for the permanent magnet type eddy current retarder in heavy trucks. Experimentally obtained lives of both steels were well corresponded with the lives predicted by the proposed method. It was found that the proposed method was effective in multiaxial fatigue life evaluation under proportional creep-fatigue loadings.
文摘Fatigue damage of materials includes static damage and cyclic damage.Static damage is a ratio of the plastic energy in first static loading to the statictoughness, while cyclic damage is the ratio of the cyclic plastic hysteresis energy to thefatigue toughness. In the calculation, cyclic hardening (or softening) of a material istaken into account, which results in the increase (or decrease) of the yield stress. Forsimplification, it is assumed that stress and strain in cyclic loading vary in accordancewith the hysteresis loop. Fatigue toughness of a material can be detennined bysymmetric cyclic stress controlled fatigue test. A method, rational and convenient forengineering, is proposed to estimate the fatigue life under random loading based onplastic hysteresis energy theorem. Preliminary verification by test is satisfactory.
基金Supported by National High Technology Research and Development Program of China (Grant No.2011AA11A265)National Natural Science Foundation of China (Grant Nos.50875173,51105241)Shanghai Municipal Natural Science Foundation of China (Grant No.11ZR1414700)
文摘Lightweight design requires an accurate life prediction for structures and components under service loading histories. However, predicted life with the existing methods seems too conservative in some cases, leading to a heavy structure. Because these methods are established on the basis that load cycles would only cause fatigue damage, ignore the strengthening effect of loads. Based on Palmgren-Miner Rule （PMR）, this paper introduces a new method for fatigue life prediction under service loadings by taking into account the strengthening effect of loads below the fatigue limit. In this method, the service loadings are classified into three categories： damaging load, strengthening load and none-effect load, and the process for fatigue life prediction is divided into two stages： stage I and stage II, according to the best strengthening number of cycles. During stage I, fatigue damage is calculated considering both the strengthening and damaging effect of load cycles. While during stage II, only the damaging effect is considered. To validate this method, fatigue lives of automobile half shaft and torsion beam rear axle are calculated based on the new method and traditional methods, such as PMR and Modified Miner Rule （MMR）, and fatigue tests of the two components are conducted under service loading histories. The tests results show that the percentage errors of the predicted life with the new method to mean life of tests for the two components are –3.78% and –1.76% separately, much lesser than that with PMR and MMR. By considering the strengthening effect of loads below the fatigue limit, the new method can significantly improve the accuracy for fatigue life prediction. Thus lightweight design can be fully realized in the design stage.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51205095)Support Program for Key Youth(Grant No.1154G39)
文摘A large amount of cutting heat is produced during the heavy cutting process,and insert life is restricted by the effect of thermal load.The thermal load experiment of cemented carbide SCS,WF and YT15 is carried out,and the results show that the bending strength and fracture toughness of cemented carbide material decrease obviously under cyclic thermal load,while in the cooling process,the material mechanical property changes worse suddenly.The high-temperature mechanical property of SCS is the most stable,and that of YT15 is the worst.Further,a relation model among cutting temperature,cutting parameters and insert life is established.Finally,the measures to improve heavy cemented carbide inserts life are summarized from the aspects of cutting parameters selection,insert optimization design and TiCN,Al2O3,TiN complex insert coating.The research results are expected to provide support and reference for heavy cutting technology and insert technology.
文摘Emily Dickenson’s poems have long enjoyed considerable acclaims from critics and common readers for her delicate and profound writing of life and death,love,nature,etc.Her short poem“My Life had stood—a Loaded Gun”is one receiving relatively few academic discussion.Among the rather few existent studies,many discuss Dickenson’s feminist ideas,religious bewilderment,literary creation views or even personal feeling in this poem.This article,instead,gives an interpretation of this poem from an ecocritical perspective.It points out that Emily Dickenson in this poem expresses her condemnation on human’s cruelty and indiffer?ence to nature.After a thorough interpretation of Dickenson’s reflection on human-nature relationship in this poem,the article fur?ther explores Dickenson’s attitudes toward nature through her personal writing background and clues in her other works to support this interpretation.
文摘The ability of a pavement structure in carrying out its function reduces in line with the increase of traffic load, especially if there are overloaded heavy vehicle passing through the road. This study was done to know the effect of overloading vehicles on the road pavement and remaining service life of the pavement. In this study, the service life of pavement due to overloaded vehicles was analyzed using the AASHTO 1993. In Narayanghat-Mugling road the composition of traffic seems to be 83.76% heavy vehicles, 9.18% medium vehicle and 7.05% light vehicle. For the direction of Narayanghat-Mugling, the pavement service life might be reduced by 59.90% due to overloading condition, while for the opposite direction, the service life would not reduced caused by the same factor. The impact of overload conditions on the road pavement showed premature failure;that is, a condition which the damage reduced the life of roads before the design life of the road is reached. From the results, it can be concluded that overloaded vehicles on the road are very influential to the reduction in pavement service life. Therefore, it is expected that road users to comply with existing regulations in the conduct of transportation. As overloading is increasing, it has to be controlled by rules and regulations with penalty to control the overloading. So fines must be associated with intensified enforcement when considered in further strategy. Regular monitoring, inspection and enforcement are the effective ways to control overloading. Use of technology (Automatic overloading information system) may be the effective way to control the overloading.
文摘A calculation method of fatigue life for slewing bearings under combined radial, axial and tilting moment loads was proposed. Single row four-point contact ball slewing bearing being used as a case, the statics model of the slewing bearing was established and a set of equilibrium equations were obtained. By solving the equilibrium equatioas, the rolling element loads were obtained and the equivalent rolling element loads were calculated further. By using the geometrical parameters of the bearing, the rating rolling element loads were calculated, and the fa- tigue life of the bearing was calculated by using the rating rolling element loads and the equivalent rolling element loads. A calculation example shows the feasibility of the proposed method.
基金Project supported by the National Natural Science Foundation of China (Nos. 11132004 and 51078145)the Guangdong Province Natural Science Foundation of China (No. 9251064101000016)
文摘The application of prestressed carbon reinforced polymer （prestressed CFRP） in reinforced concrete （RC） members can improve the mechanical properties of strengthened structures and strengthening efficiency. This paper proposed a semi-empirical prediction fornmla of fatigue lives of the RC beams strengthened with prestressed CFRP under bending loads. The formula is established based on the fatigue life prediction method of RC beams and fatigue experimental data of non-prestressed CFRP reinforced beams done before. Fatigue effect coefficient of the formula was confirmed by the fatigue experiments of the RC beams strengthened with prestressed carbon fiber laminate （prestressed CFL） under cyclic bending loads. Fatigue lives of the strengthened beams predicted using the formula agreed well with the experimental data.
文摘Suggests some calculating formulas and methods with respect to the damage evolvingrate da / dN|i and the fatigue life and in varied history from uncrack to microcrackinitiation until fracture for a crankshaft, which are suitable to stress concentration positionsabout its journal fillets and oil holes on a crankshaft, that it is undergone to bending, twistingand shearing loading and subjected to unsymmetric cyclic many-stage loading. Last the total lifein whole process is estimated by
基金Funded by the National Key Basic Research and Development Plans-973 Plans(2009CB623203)the Key Project of National Natural Science Foundation of China (50739001)+2 种基金the National Natural Science Foundation of China (50878109)the National Key Technology R & D Program (2007BAB27B03)the Education Ministry Doctor Foundation of China (20070429001)
文摘Qingdao Jiaozhou Bay subsea tunnel is the second self-built tunnel in China with the designed service life over 100 years.The durability of lining concrete are one of an important factors to determinate the service life of tunnel.Considering the main environmental loads and mechanical loads of subsea tunnel,the durability properties of lining concrete under combined action of compressive load and carbonation has been studied through the critical compressive load test,accelerated carbonation test,natural carbonation test and capillary suction test.The tests results show that critical compressive load apparently accelerates the carbonation and deteriorates the anti-permeability of concrete.Under the combined action of critical compressive load and carbonation,the durability of lining concrete decreases.Based on the carbonization life criteria and research results,for the high-performance concrete with proposed mix ratio,the predicted service life of lining concrete for Jiaozhou bay subsea tunnel is about 80 years which fails to reach the required service life.It is necessary to adopt other measurements simultaneously to improve the durability of lining concrete.
