Method For Predicting Fracture And Determining True Material Parameters Of Rock

Accurate determination of the material's true parameters and reasonable assessment of the actual structure's true characteristics have been the scientific and engineering community's unflagging goal.For rock materials,fracture toughness and strength are important material parameters.At present,there are obvious size effects in small size specimens or structures,and large size specimens or structures are needed to obtain material parameters without size effect.In addition,the fracture toughness test of rock materials has strict limits on the testing type,the loading fixture,the loading mode and the test system,which makes the testing and testing of rock fracture toughness relatively complex,making it difficult to obtain material parameters(fracture toughness and strength),and the obtained material parameters can not be directly used to evaluate the actual properties of the material or structure.At present,the test method of fracture parameters of rock material is not uniform,and the test result has dimension effect.On the other hand,even if the material parameters are given,the corresponding fracture failure prediction curve of rock material has not yet been established.Based on the analysis of boundary effect theory,this paper studies the determination of the true material parameters(fracture toughness and strength)and the two key scientific problems which are not solved satisfactorily.Considering the important influence of rock particle size on fracture failure,the average particle size of rock is introduced into the modified boundary effect model,and the purpose of determining the parameters of rock non-size effect material is realized by the small size rock specimen under quasi-brittle fracture.A complete failure prediction curve of rock material with plastic-quasi-brittle-brittle properties is established based on the determined material parameters(fracture toughness and tensile strength).The theoretical minimum rock sample size under the condition of satisfying linear elastic fracture mechanics is determined.The experiments of geometric similarity,non-geometric similarity,geometric similarity and non-geometric similarity have proved that the theory and model are applicable to the real fracture parameters and fracture failure prediction analysis.