Many experimental results have demonstrated the apparent discrepancy of a rock material between its flexural tensile strength measured using various bending methods and its tensile strength measured using direct tensi...Many experimental results have demonstrated the apparent discrepancy of a rock material between its flexural tensile strength measured using various bending methods and its tensile strength measured using direct tension method or Brazil disc(BD)method.To understand the physical mechanism for such discrepancy,numerical simulation using the realistic failure process analysis(RFPA)is carried out in this work to simulate the tensile failure of heterogeneous rocks.Direct tension and semi-circular bend(SCB)tests are simulated using RFPA for rock materials with different levels of inhomogeneity,which is characterized by the homogeneity index of the Weibull distribution used in RFPA.The numerical results show that the discrepancy in the tensile strength values is caused by the inhomogeneity of the rock material.Furthermore,non-local failure criterion is adopted to calculate the characteristic length of the rock materials used in the simulation.It is shown that below a certain value of the homogeneity index,both the characteristic length and discrepancy between two types of tensile strengths of rock decrease with increase of the homogeneity index up to a critical value,at which the discrepancy disappears and the rock material is essentially homogeneous.展开更多
Strain rate sensitivity index m is one of the vital mechanical parameters for deter- mining material superplasticity. In this paper, the existing formulae for measuring m value are reviewed, and it is found that the m...Strain rate sensitivity index m is one of the vital mechanical parameters for deter- mining material superplasticity. In this paper, the existing formulae for measuring m value are reviewed, and it is found that the m values can be classified into three classes: mi under constant length, mv under constant velocity, and mP under con- stant load. The constraint equation of the generalized m value is established ac- cording to the tensile constitutive equation and the basis theory for plastic me- chanics. Based on three typical deformation paths, the m value is redefined. Fur- thermore, from the formula of generalized m value, the formulae for measuring mi, mv and mP are theoretically deduced. The precise methods with numerical simula- tion are presented. The results prove that the m value is a non-constant and its dependence on ε changes with the deformation path. Under different deformation paths, the m values calculated from the same formula are different. Using different formulae, the m values under the same deformation path are also different. There- fore, deformation path and corresponding formula should be given during the measurement of the m value. Moreover, it is explained theoretically and experi- mentally that why the mv value under constant velocity is sometimes negative but the mP value under constant load is sometimes lager than 1. The aim of the analysis and measurement of the m value is to facilitate the study on the relationship be- tween macroscopical mechanical laws and microscopic physical mechanisms during superplastic deformation.展开更多
基金supported by the Natural Science Foundation of China(Grant Nos.51704211 and 11602165).
文摘Many experimental results have demonstrated the apparent discrepancy of a rock material between its flexural tensile strength measured using various bending methods and its tensile strength measured using direct tension method or Brazil disc(BD)method.To understand the physical mechanism for such discrepancy,numerical simulation using the realistic failure process analysis(RFPA)is carried out in this work to simulate the tensile failure of heterogeneous rocks.Direct tension and semi-circular bend(SCB)tests are simulated using RFPA for rock materials with different levels of inhomogeneity,which is characterized by the homogeneity index of the Weibull distribution used in RFPA.The numerical results show that the discrepancy in the tensile strength values is caused by the inhomogeneity of the rock material.Furthermore,non-local failure criterion is adopted to calculate the characteristic length of the rock materials used in the simulation.It is shown that below a certain value of the homogeneity index,both the characteristic length and discrepancy between two types of tensile strengths of rock decrease with increase of the homogeneity index up to a critical value,at which the discrepancy disappears and the rock material is essentially homogeneous.
基金Supported by the National Natural Science Foundation of China (Grant No. 50375064)"985 Project" of Jilin University of China
文摘Strain rate sensitivity index m is one of the vital mechanical parameters for deter- mining material superplasticity. In this paper, the existing formulae for measuring m value are reviewed, and it is found that the m values can be classified into three classes: mi under constant length, mv under constant velocity, and mP under con- stant load. The constraint equation of the generalized m value is established ac- cording to the tensile constitutive equation and the basis theory for plastic me- chanics. Based on three typical deformation paths, the m value is redefined. Fur- thermore, from the formula of generalized m value, the formulae for measuring mi, mv and mP are theoretically deduced. The precise methods with numerical simula- tion are presented. The results prove that the m value is a non-constant and its dependence on ε changes with the deformation path. Under different deformation paths, the m values calculated from the same formula are different. Using different formulae, the m values under the same deformation path are also different. There- fore, deformation path and corresponding formula should be given during the measurement of the m value. Moreover, it is explained theoretically and experi- mentally that why the mv value under constant velocity is sometimes negative but the mP value under constant load is sometimes lager than 1. The aim of the analysis and measurement of the m value is to facilitate the study on the relationship be- tween macroscopical mechanical laws and microscopic physical mechanisms during superplastic deformation.
