Study On Multi-scale Damage Mechanics Behavior Of Concrete Based On Mesoscopic Mechanics Method

Currently concrete structure is one of the engineering structures and it has been the most widely used structure in the world, in which the concrete is an important building material. Actually destruction of the concrete structure is the result of the accumulation of concrete material damage. Concrete is a kind of composite material consisting of water, cement, aggregate size, porosity and cracks. With the increases of external load or the changes of environmental temperature, a large number of micro-cracks and micro-holes inside the concrete extend and expand gradually until coalescence, making the concrete material damage accumulation, and carrying capacity reduced gradually until completely lost, and then loss bearing capacity of the structure of the boby, causing damage to the concrete structure, which is a serious threat to personal safety and property security.Based on the mechanical properties of concrete, this paper mainly studies the microscopic and macroscopic damage mechanical behavior of the concrete. At the mesoscopic level, concrete is a kind of three-phase inhomogeneous composite material consisting of coarse aggregate, mortar and interfacial transition zone (ITZ) that locates between coarse aggregate and cement mortar. First of all, to study the static mechanical properties of concrete, based on Mori-Tanaka method, the numerical relationship between the mechanical characteristics of the three phase medium and the equivalent elastic modulus of concrete is established, and the effects of mesoscopic influencing factors on the equivalent mechanical properties of concrete are analyzed. On condition of considering a large number of randomly distributed the initial voids located on the mortar and ITZ, the effects of micro defects on the equivalent elastic modulus of concrete is study. The initial damage of concrete is defined. Focusing on the damage evolution process of Mesoscopic micro cracks initiation,extension and coalescence, the numerical relationship between the porosity with the damage variable of concrete is established.Based on the study of the time-varying characteristics of equivalent elastic modulus of concrete, the establishment of equivalent damage model of three phase medium and concrete is further explored. The bearing capacity of concrete is not simply the sum of the bearing capacity of three phase medium. With the derivation of the Mori-Tanaka theory, the numerical relationship between the stress and strain fields of the three phase medium and the stress and strain field of concrete is established. The method proposed in this paper and Voigt series models are examples of comparative analysis. With the simple damage model of three phase medium, the complex damage constitutive model of concrete is established, and multi-scale damage mechanics behavior of concrete is studied.