Reseach On Non-linear Fracture Of Concrete Based On Stochastic Damage And Cohesive Stress

The crack problem has always been concerned by civil engineering and water conservancy science and technology and engineering in concrete,while the notable features of concrete materials are nonlinear and stochastic.Thus it is of great significance for engineering and scientific research to study the non-linear fracture of concrete taking the stochastic damage mechanics into consideration.Combined with the national natural science foundation of China(51309073)“the coupling mechanism between nonlinear rupture and stochastic damage of concrete”,the following researches were carried out in this paper:1.Based on the energy consumption equivalence between stochastic damage and fracture,the cohesive laws of concrete were constructed using a series-parallel spring model and a series-parallel springs model which assume the micro-spring failure strain were a lognormal stochastic variable or a weibull stochastic variable.The dam concrete and wet screening concrete with the maximum aggregate diameter were 80 mm and 40 mm,respectively,were used to calculate the cohesive law.The obtained results by energy consumption equivalence method were compared with that obtained by the traditional displacement equivalence method.The influence of the layers of the spring bundles on the cohesive laws was also studied.The results showed that the layer sensitivity can be avoided using the equivalence principle method.2.Then the cohesive laws obtained were used to simulate the crack propagation processes of three-point bending notched beams.The applicability of the obtained cohesive law was verified by comparing the calculated P-CMOD curves with the existing experiment data.The variation range of the characteristic lengths of the dam-concrete and wet-screening concrete was also discussed,and it is suggested that the characteristic lengths should be taken as 4-6 times of the maximum aggregate size for the concrete based on lognormal distribution and 6-8 times of the maximum aggregate size for the concrete based on weibull distribution in this paper.3.The crack propagation of concrete was studied based on the nonlocal damage model.The nonlocal cohesive laws of concrete with its maximum aggregate diameter of 20 mm were obtained using the Mazars damage model.Then the obtained cohesive laws were used to calculate the P-CMOD.The results show that the cohesive laws were free from the size of specimen and that they were only affected by the characteristic lengths of the material.According to the P-CMOD curves,one can get that the calculation results and test results were closer when the characteristic lengths take 4 ~ 6 times the maximum aggregate diameter.4.Stochastic damage cohesive crack model which can be used to describe the whole destruction process of concrete was put forward based on stochastic damage mechanics and the cohesive stress of fracture.Then the method of the determination of the model parameters was provided.Using this model we described the four stages of destruction of the specimen and each of the stages was analyzed.