| In the field of geotechnical engineering,rock mass is often affected by cyclic load,which leads to the deterioration of its mechanical properties and poses a serious threat to engineering construction.Therefore,the study of the damage mechanical properties of rock mass under cyclic load has important engineering value.In this paper,the elastic modulus of sandstone under cyclic loading and unloading is divided into the elastic modulus under cyclic loading and unloading,which has the significance of studying the variation law of sandstone under cyclic loading and unloading.The main results are as follows:（1）According to the variation trend of residual plastic strain,the cyclic process can be divided into four stages:initial cyclic stage,stable development stage,accelerated deformation stage and failure stage;The hysteresis loop of cyclic stress-strain curve with equal load amplitude is characterized by"sparse"-"dense"-"sparse";Under cyclic loading,the elastic modulus of sandstone like increases first and then decreases with the increase of cyclic grade.（2）Under the action of graded cyclic load,the input energy density and elastic energy density increase with the increase of cyclic grade,the input energy density increases in a"concave"shape,the elastic energy density increases linearly,the energy consumption ratio first decreases and then increases slowly with the increase of cyclic grade,and suddenly increases near failure,showing the evolution characteristics of"spoon"shape;The energy density and energy dissipation ratio show three-stage evolution characteristics with the number of cycles under constant load amplitude cyclic load.（3）The growth process of damage variable calculated by plastic strain method can be divided into three stages:slow growth stage;Accelerated growth stage;Jump growth stage.The damage variable calculated by dissipative energy method increases exponentially with the increase of cyclic grade and linearly under cyclic load with equal load amplitude.（4）Based on the principle of strain equivalence,the damage constitutive model of graded cyclic loading and unloading sandstone is established.The parameter m is related to the concentration degree of micro element strength distribution.The greater the absolute value of m,the higher the concentration degree of sandstone like micro element strength distribution,the greater the material strength and the greater the brittleness;The parameter F0is related to the macro average strength of sandstone like.When m is less than 0,the larger F0,the lower the macro average strength of sandstone like;When m is greater than 0,the larger F0,the higher the macro average strength of sandstone like.Figure[46]Table[13]Reference[83]... |
