Temperature-induced cracking during the construction of mass concrete is a significant concern.Numerical simulations of concrete temperature have primarily assumed that the concrete is placed in an open environment.Th...Temperature-induced cracking during the construction of mass concrete is a significant concern.Numerical simulations of concrete temperature have primarily assumed that the concrete is placed in an open environment.The problem of heat transfer between the air and concrete has been simplified to the concrete’s heat dissipation boundary.However,in the case of tubular concrete structures,where air inlet and outlet are relatively limited,the internal air temperature does not dissipate promptly to the external environment as it rises.To accurately simulate the temperature and creep stress in tubular concrete structures with enclosed air spaces during construction,we establish an air–concrete coupled heat transfer model according to the principles of conjugate heat transfer,and the accuracy of the model is verified through experiments.Furthermore,we conduct a case study to analyze the impact of airflow within the ship lock corridor on concrete temperature and creep stress.The results demonstrate that enhancing airflow within the corridor can significantly reduce the maximum concrete temperature.Compared with cases in which airflow within the corridor is neglected,the maximum concrete temperature and maximum tensile stress can be reduced by 12.5°C and 0.7 MPa,respectively,under a wind speed of 4 m/s.The results of the traditional calculation method are relatively close to those obtained at a wind speed of 1 m/s.However,the temperature reduction process in the traditional method is faster,and the method yields greater tensile stress values for the corridor location.展开更多
The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the ...The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.展开更多
Lap joints with a 1 mm^2 cross-sectional area were fabricated using Cu particle enhancemem 63Sn37Pb based composite solder and 63Sn37Pb eutectic solder to examine the influence of stress on the creep behavior of the s...Lap joints with a 1 mm^2 cross-sectional area were fabricated using Cu particle enhancemem 63Sn37Pb based composite solder and 63Sn37Pb eutectic solder to examine the influence of stress on the creep behavior of the solder joints. The results indicate that the creep resistance of the composite solder joints is generally superior to that of the conventional 63Sn37Pb solder joints. At the same time, the creep rupture life of the composite solder joints is declined with increasing stress and drops faster than that of the 63Sn37Pb eutectic solder joints.展开更多
This work focuses on the uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays under one-dimensional condition. An elasto-viscoplastic model is briefly introduced based on the rate-depend...This work focuses on the uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays under one-dimensional condition. An elasto-viscoplastic model is briefly introduced based on the rate-dependency of preconsolidation pressure. By comparing the rate-dependency formulation with the creep based formulation, the relationship between rate-dependency and creep behaviors is firstly described. The rate-dependency based formulation is then extended to derive an analytical solution for the stress relaxation behavior with defining a stress relaxation coefficient. Based on this, the relationship between the rate-dependency coefficient and the stress relaxation coefficient is derived. Therefore, the uniqueness between behaviors of rate-dependency, creep and stress relaxation with their key parameters is obtained. The uniqueness is finally validated by comparing the simulated rate-dependency of preconsolidation pressure, the estimated values of secondary compression coefficient and simulations of stress relaxation tests with test results on both reconstituted Illite and Berthierville clay.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 effects of stress,ageing time and ageing temperature on creep behavior of poly(methyl methacrylate) were studied.After annealing above its glass transition temperature for a period of time to eliminate the stress ...The effects of stress,ageing time and ageing temperature on creep behavior of poly(methyl methacrylate) were studied.After annealing above its glass transition temperature for a period of time to eliminate the stress and thermal history,the specimens were quenched and aged at various ageing temperatures for different ageing time,and then the short-term creep tests under different stress levels were carried out at room temperature.The creep strains were modeled by means of time-ageing time equivalence and time-stress equivalence,and the master creep curves were constructed via ageing time shift factors and stress shift factors.The results indicate that the creep rate increases with stress,while decreases with ageing time,and the ageing temperature history obviously affects the creep rate.For linear viscoelastic material,the ageing shift rate is independent on imposed stress,while for nonlinear viscoelastic material,the ageing shift rate decreases with increasing stress.The unified master creep curve up to 540 d at reference state was constructed by shifting the creep curves horizontally along the logarithmic time axis to overlap each other.It is demonstrated that the time-stress equivalence,united with the time-ageing time equivalence,provides an effective accelerated characterization technique in the laboratory to evaluate the long-term creep behavior of physical ageing polymers.展开更多
The effect of tensile stress and trace amounts of impurities on the creep activation energyof platinum was studied and the creep mechanism was disscussed.
Loading ability of straw bales was tested by using an Electronical Testing Machine. Linear regression models were proposed to describe the loading ability as a function of failure density and compressing energy. Based...Loading ability of straw bales was tested by using an Electronical Testing Machine. Linear regression models were proposed to describe the loading ability as a function of failure density and compressing energy. Based on an exponent model, the testing compression coefficients of straw bales were estimated by using the Levenberg-Marquardt Method. Results showed that the relation among failure density, loading ability and compressing energy was linear in the phase of high density, Loading ability of straw bales could meet the requirement for building bills .展开更多
This research is carried out on the basis of Constant Strain Rate (CSR) to measure creep internal stress. Measurements of creep internal stress are conducted on the material test machine by using the CSR method. A m...This research is carried out on the basis of Constant Strain Rate (CSR) to measure creep internal stress. Measurements of creep internal stress are conducted on the material test machine by using the CSR method. A mathematical model of creep internal stress is also proposed and its application is presented in this paper.展开更多
Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stres...Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stress and time,but also it has the corresponding relations to the triaxial stress-strain curves of rock.The deformation properties of soften-strain,harden-strain and ideal plasticity presented by conventional triaxial compressive test curves under the different stress states were utilized,and the creep characteristics,the creep starting stress and the different entire creep process curves of rock were studied systematically according to creep experiment results,and the relations of the triaxial stress-strain curves to the creeping starting stress,the terminating curve,the different creep processes,and the different creep fracture properties were established.The relations presented in this paper were verified partially by the creep experiment results of five types of rock.展开更多
Objective:Underwater shock can produce extremely high accelerations, resulting in severe human injuries on shipboard, and human thoraco lumbar spines are prone to suffer from injuries by ship shock motion. To observe ...Objective:Underwater shock can produce extremely high accelerations, resulting in severe human injuries on shipboard, and human thoraco lumbar spines are prone to suffer from injuries by ship shock motion. To observe the viscoelasticity of thoracolumbar of young fresh cadavers, and to provide biomechanical parameters for both research and clinical practice. Materials and Methods:5 fresh young male cadavers (aged 22 to 31 years) were provided, and 15 thoracolumbar spinal anatomies of 5 samples were harvested within 1 hour of death. WE-10A universal testing machine was used for creep and relaxation tests.Results:Stress relaxation and creep deformation equations are derived from the biomechanics model and the measured and simulated curves are compared. The creep in vertebral bodies and intervertebral discs exhibited significantly changes in the first 5 min and 10 min, respectively. The stress rapidly decreased in the first 2 min, and then gradually went balance during the relaxation process. Conclusion:The change in creep rate is significant at early stage,and gradually slows down.This indicates that the differences between internal pressure and local pressure are decreased until balance. The simulated curve derived from equation coincides with the experimental data to a large degree, which states that the equation is rational and reliable.展开更多
基金This work was supported by Construction Simulation and Support Optimization of Hydraulic Tunnel Based on Bonded Block-Synthetic Rock Mass Method and Hubei Province Postdoctoral Innovative Practice Position.
文摘Temperature-induced cracking during the construction of mass concrete is a significant concern.Numerical simulations of concrete temperature have primarily assumed that the concrete is placed in an open environment.The problem of heat transfer between the air and concrete has been simplified to the concrete’s heat dissipation boundary.However,in the case of tubular concrete structures,where air inlet and outlet are relatively limited,the internal air temperature does not dissipate promptly to the external environment as it rises.To accurately simulate the temperature and creep stress in tubular concrete structures with enclosed air spaces during construction,we establish an air–concrete coupled heat transfer model according to the principles of conjugate heat transfer,and the accuracy of the model is verified through experiments.Furthermore,we conduct a case study to analyze the impact of airflow within the ship lock corridor on concrete temperature and creep stress.The results demonstrate that enhancing airflow within the corridor can significantly reduce the maximum concrete temperature.Compared with cases in which airflow within the corridor is neglected,the maximum concrete temperature and maximum tensile stress can be reduced by 12.5°C and 0.7 MPa,respectively,under a wind speed of 4 m/s.The results of the traditional calculation method are relatively close to those obtained at a wind speed of 1 m/s.However,the temperature reduction process in the traditional method is faster,and the method yields greater tensile stress values for the corridor location.
基金Supported by the West Region Communication Construction Technology Project of the Ministry of Communications (2009318000001)the National Natural Science Foundation of China (50808187)
文摘The consideration of time dependence is essential for the study of deformation and fracturing processes of rock materials, especially for those subjected to strong compressive and tensile stresses. In this paper, the self-developed direct tension device and creep testing machine RLW-2000M are used to conduct the creep tests on red sandstone under uniaxial compressive and tensile stresses. The short-term and long-term creep behaviors of rocks under compressive and tensile stresses are investigated, as well as the long-term strength of rocks. It is shown that, under low-stress levels, the creep curve of sandstone consists of decay and steady creep stages; while under high-stress levels, it presents the accelerated creep stage and creep fracture presents characteristics of brittle materials. The relationship between tensile stress and time under uniaxial tension is also put forward. Finally, a nonlinear viscoelastoplastic creep model is used to describe the creep behaviors of rocks under uniaxial compressive and tensile stresses.
基金This study is financially supported by the Foundation of Henan University of Science & Technology(No.13420060) Luoyang Advanced Hydraulic Pressure Technology Ltd. ( 6142004).
文摘Lap joints with a 1 mm^2 cross-sectional area were fabricated using Cu particle enhancemem 63Sn37Pb based composite solder and 63Sn37Pb eutectic solder to examine the influence of stress on the creep behavior of the solder joints. The results indicate that the creep resistance of the composite solder joints is generally superior to that of the conventional 63Sn37Pb solder joints. At the same time, the creep rupture life of the composite solder joints is declined with increasing stress and drops faster than that of the 63Sn37Pb eutectic solder joints.
基金Projects(41372285,41272317,51278449,51238009)supported by the National Natural Science Foundation of ChinaProject(20110073120012)supported by Research Fund for the Doctoral Program of Higher Education of ChinaProject(PIAPP-GA2011-286397)supported by the European Program CREEP
文摘This work focuses on the uniqueness of rate-dependency, creep and stress relaxation behaviors for soft clays under one-dimensional condition. An elasto-viscoplastic model is briefly introduced based on the rate-dependency of preconsolidation pressure. By comparing the rate-dependency formulation with the creep based formulation, the relationship between rate-dependency and creep behaviors is firstly described. The rate-dependency based formulation is then extended to derive an analytical solution for the stress relaxation behavior with defining a stress relaxation coefficient. Based on this, the relationship between the rate-dependency coefficient and the stress relaxation coefficient is derived. Therefore, the uniqueness between behaviors of rate-dependency, creep and stress relaxation with their key parameters is obtained. The uniqueness is finally validated by comparing the simulated rate-dependency of preconsolidation pressure, the estimated values of secondary compression coefficient and simulations of stress relaxation tests with test results on both reconstituted Illite and Berthierville clay.
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.
基金Projects(10772156, 10672136) supported by the National Natural Science Foundation of ChinaProject(05C100) supported by the Scientific Research Fund of Education Department of Hunan Province,China
文摘The effects of stress,ageing time and ageing temperature on creep behavior of poly(methyl methacrylate) were studied.After annealing above its glass transition temperature for a period of time to eliminate the stress and thermal history,the specimens were quenched and aged at various ageing temperatures for different ageing time,and then the short-term creep tests under different stress levels were carried out at room temperature.The creep strains were modeled by means of time-ageing time equivalence and time-stress equivalence,and the master creep curves were constructed via ageing time shift factors and stress shift factors.The results indicate that the creep rate increases with stress,while decreases with ageing time,and the ageing temperature history obviously affects the creep rate.For linear viscoelastic material,the ageing shift rate is independent on imposed stress,while for nonlinear viscoelastic material,the ageing shift rate decreases with increasing stress.The unified master creep curve up to 540 d at reference state was constructed by shifting the creep curves horizontally along the logarithmic time axis to overlap each other.It is demonstrated that the time-stress equivalence,united with the time-ageing time equivalence,provides an effective accelerated characterization technique in the laboratory to evaluate the long-term creep behavior of physical ageing polymers.
基金Supported by the National Natural Science Foundation of China
文摘The effect of tensile stress and trace amounts of impurities on the creep activation energyof platinum was studied and the creep mechanism was disscussed.
基金Supported by National Natural Science Fund(50675071)Specialized Research Fund for Doctoral Program of Higher Education(20060564009)
文摘Loading ability of straw bales was tested by using an Electronical Testing Machine. Linear regression models were proposed to describe the loading ability as a function of failure density and compressing energy. Based on an exponent model, the testing compression coefficients of straw bales were estimated by using the Levenberg-Marquardt Method. Results showed that the relation among failure density, loading ability and compressing energy was linear in the phase of high density, Loading ability of straw bales could meet the requirement for building bills .
文摘This research is carried out on the basis of Constant Strain Rate (CSR) to measure creep internal stress. Measurements of creep internal stress are conducted on the material test machine by using the CSR method. A mathematical model of creep internal stress is also proposed and its application is presented in this paper.
基金Project(50774090) supported by the National Natural Science Foundation of China
文摘Based on the results of triaxial compressive creep tests for five kinds of rock under the different stress loading,unloading and cycle-loading-unloading conditions,the creep deformation is not only a function of stress and time,but also it has the corresponding relations to the triaxial stress-strain curves of rock.The deformation properties of soften-strain,harden-strain and ideal plasticity presented by conventional triaxial compressive test curves under the different stress states were utilized,and the creep characteristics,the creep starting stress and the different entire creep process curves of rock were studied systematically according to creep experiment results,and the relations of the triaxial stress-strain curves to the creeping starting stress,the terminating curve,the different creep processes,and the different creep fracture properties were established.The relations presented in this paper were verified partially by the creep experiment results of five types of rock.
文摘Objective:Underwater shock can produce extremely high accelerations, resulting in severe human injuries on shipboard, and human thoraco lumbar spines are prone to suffer from injuries by ship shock motion. To observe the viscoelasticity of thoracolumbar of young fresh cadavers, and to provide biomechanical parameters for both research and clinical practice. Materials and Methods:5 fresh young male cadavers (aged 22 to 31 years) were provided, and 15 thoracolumbar spinal anatomies of 5 samples were harvested within 1 hour of death. WE-10A universal testing machine was used for creep and relaxation tests.Results:Stress relaxation and creep deformation equations are derived from the biomechanics model and the measured and simulated curves are compared. The creep in vertebral bodies and intervertebral discs exhibited significantly changes in the first 5 min and 10 min, respectively. The stress rapidly decreased in the first 2 min, and then gradually went balance during the relaxation process. Conclusion:The change in creep rate is significant at early stage,and gradually slows down.This indicates that the differences between internal pressure and local pressure are decreased until balance. The simulated curve derived from equation coincides with the experimental data to a large degree, which states that the equation is rational and reliable.
基金the financial supports from the National Key Laboratory of Science and Technology for National Defence on High-Strength Lightweight Structural Materials of China(No.20190104)State Key Laboratory of High-Performance Complex Manufacturing of Central South University,China(No.ZZYJKT2020-03)the National Key Research and Development Program of China(No.2016YFB0300801)。