Determination And Simulation Of Discrete Element Parameters For Concrete Failure Process

Concrete is a widely used engineering material,and concrete structures exist in large quantities in engineering projects.The complex process of damage to these structures affects the safety of the entire project,so it is of great significance to study their failure mechanism.Considering the limitations of experiments and theoretical research,the numerical method of using numerical methods to study the failure process of concrete and its influencing factors of mechanical properties from a detailed point of view has important theoretical significance and engineering application value.In this paper,a fine concrete model is established based on the discrete element method,the influence of aggregate shape and cement mortar strength on concrete failure is studied,and the concrete failure mechanism under impact load is analyzed.Firstly,through the Walraven formula,the aggregate content is converted from three-dimensional to two-dimensional equivalent,a fine modeling idea is proposed,and a fine model of concrete discrete elements is established.Secondly,the macro-fine influence analysis and calibration of discrete element mesoscopic parameters were carried out,the cracks and surface displacement of the concrete four-point bend test member were measured based on digital image correlation methods,and the test measurement and numerical simulation results were compared,which verified the rationality of model establishment and parameter determination.Then,the factors affecting the failure of concrete were studied,and the effects of aggregate shape change and cement mortar strength change on concrete mechanical properties were analyzed.Finally,the discrete element simulation analysis of concrete failure under impact load was carried out,the impact force application method was determined,and the failure mechanism and dynamic response of concrete beam under impact load were analyzed.The study concludes the following:1)Discrete element mesoscopic modulus E_C plays a decisive role in the macroelastic modulus of concrete,while the normal bond strength (?) regulates the peak strength.The simulation and destruction of the four-point bending component goes through three stages: microcrack,microcrack and macroscopic crack,and the failure mechanism,macroscopic crack morphology and component surface displacement are compared and verified in many aspects to confirm the correct validity of the established concrete discrete element refinement model and the calibration of the mesoscopic parameters.2)Stress concentration is an important factor affecting the bearing capacity of concrete,the smaller the sharp angle of aggregate,the lower the bearing capacity of concrete.The round reduces the bite between the mortar and aggregate,and the more rounded the aggregate,the lower the bearing capacity of the concrete.With the improvement of mortar strength,the peak stress level of concrete continues to increase,but when the mortar strength exceeds the corresponding aggregate,the concrete strength is mainly limited by the aggregate;with the improvement of mortar strength,the number and type of cracks are also changing,the cracks of the mortar and the bonding surface are reduced,and the aggregate destruction is more obvious;the integrity of the destruction form is maintained,there is no longer a local shedding phenomenon,and the damage changes from the local macroscopic crack to the overall fracture surface.3)The impact failure of the concrete beam is mainly the local failure area near the impact point,the crack penetration area of the impact stress wave propagation,and the stress wave reflection area at the bottom of the beam span.The crack generation of the local failure zone is mainly tensile and shear failure;the stress wave propagation area and the reflection area are mainly tensile failure;in general,the crack is generated on both sides along the direction of the impact velocity,and as the impact angle increases,the crack distribution on the left and right sides gradually tends to be symmetrical;the impact dynamic response shows a linear change trend at a lower impact speed,but with the increase of the impact speed,the change trend is fluctuating,and the stress and strain peaks of the bottom of the span are no longer increasing at the same time.