The universal creep function derived from the kinetic equations is successful in relating the creep (ε) to the aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The rel...The universal creep function derived from the kinetic equations is successful in relating the creep (ε) to the aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental data for polystyrene (PS) specimens which were aged at a given temperature and different times (short term) and tested at a certain temperature and different stress levels. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master lines can be used to predict the long term creep behaviour and lifetime by extrapolating to a required ultimate strain. The verifications of results obtained with this method were shown as well.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 universal creep equation relates creep behavior (ε/ε 0) to aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental ...The universal creep equation relates creep behavior (ε/ε 0) to aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental data for pipe specimens of polypropylene block copolymer (PPC), which were aged for different days (short term) and tested under different stress levels at a certain temperature. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master straight lines can be used for extrapolation to predict the long term creep behavior and lifetime of the pipe materials of PPC in the same way as plate materials.展开更多
Creep tests under at a certain temperature and different stress levels were performed on two carbon constructional quality steels at a certain stress level and different temperatures,and their creep curves at high tem...Creep tests under at a certain temperature and different stress levels were performed on two carbon constructional quality steels at a certain stress level and different temperatures,and their creep curves at high temperature were obtained based on analyzing the testing data.Taking 45 steel at a certain temperature and stress as the example,the integral creep constitutive equation and the differential stress-strain constitutive relationship were established based on the relevant rheological model,and the integral core function was also obtained.Simultaneously,the viscous coefficients denoting the viscous behavior in visco-plastic constitutive equation were determined by taking use of the creep testing data.Then the viscous coefficients of three carbon steels(20 steel,35 steel and 45 steel) were compared and analyzed.The results show that the viscosity is different due to different materials at the same temperature and stress.展开更多
为建立准确、可行的混凝土徐变系数预测模型,基于FIB Model Code-2010模型、ACI 209R-92模型与徐变系数实测值偏差情况,以降低参数计算量和减小误差为原则分别提出了在上述两种模型基础上引入双曲幂函数和双曲线函数拟合回归对其修正的...为建立准确、可行的混凝土徐变系数预测模型,基于FIB Model Code-2010模型、ACI 209R-92模型与徐变系数实测值偏差情况,以降低参数计算量和减小误差为原则分别提出了在上述两种模型基础上引入双曲幂函数和双曲线函数拟合回归对其修正的方法,建立了徐变系数修正预测模型,并分析了修正后模型与实测关系曲线符合程度和偏差情况,最终评价了修正预测模型预测徐变系数的准确性。研究结果表明:加载早龄期的修正模型徐变系数预测值与实测值存在一定偏差,并随着混凝土强度等级提高,偏差情况愈加明显;但当持荷龄期逐渐增长后,修正模型徐变系数预测值与实测值符合程度较高,因此,采用修正后的徐变系数预测模型可较为精确的计算混凝土长期徐变系数,提高了原模型的计算准确度,具有一定的可操作性,可为混凝土结构设计和工程施工提供参考。展开更多
文摘The universal creep function derived from the kinetic equations is successful in relating the creep (ε) to the aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental data for polystyrene (PS) specimens which were aged at a given temperature and different times (short term) and tested at a certain temperature and different stress levels. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master lines can be used to predict the long term creep behaviour and lifetime by extrapolating to a required ultimate strain. The verifications of results obtained with this method were shown as well.
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.
文摘The universal creep equation relates creep behavior (ε/ε 0) to aging time (t a), coefficient of retardation time (β), and intrinsic time (t 0). The relation was used to treat the creep experimental data for pipe specimens of polypropylene block copolymer (PPC), which were aged for different days (short term) and tested under different stress levels at a certain temperature. Then unified master lines were constructed with the treated data and curves according to the universal equation. The master straight lines can be used for extrapolation to predict the long term creep behavior and lifetime of the pipe materials of PPC in the same way as plate materials.
基金Project(07031B) supported by the Scientific Research Fund of Central South University of Forestry and Technology
文摘Creep tests under at a certain temperature and different stress levels were performed on two carbon constructional quality steels at a certain stress level and different temperatures,and their creep curves at high temperature were obtained based on analyzing the testing data.Taking 45 steel at a certain temperature and stress as the example,the integral creep constitutive equation and the differential stress-strain constitutive relationship were established based on the relevant rheological model,and the integral core function was also obtained.Simultaneously,the viscous coefficients denoting the viscous behavior in visco-plastic constitutive equation were determined by taking use of the creep testing data.Then the viscous coefficients of three carbon steels(20 steel,35 steel and 45 steel) were compared and analyzed.The results show that the viscosity is different due to different materials at the same temperature and stress.
文摘为建立准确、可行的混凝土徐变系数预测模型,基于FIB Model Code-2010模型、ACI 209R-92模型与徐变系数实测值偏差情况,以降低参数计算量和减小误差为原则分别提出了在上述两种模型基础上引入双曲幂函数和双曲线函数拟合回归对其修正的方法,建立了徐变系数修正预测模型,并分析了修正后模型与实测关系曲线符合程度和偏差情况,最终评价了修正预测模型预测徐变系数的准确性。研究结果表明:加载早龄期的修正模型徐变系数预测值与实测值存在一定偏差,并随着混凝土强度等级提高,偏差情况愈加明显;但当持荷龄期逐渐增长后,修正模型徐变系数预测值与实测值符合程度较高,因此,采用修正后的徐变系数预测模型可较为精确的计算混凝土长期徐变系数,提高了原模型的计算准确度,具有一定的可操作性,可为混凝土结构设计和工程施工提供参考。
