Nano-mechanics based crack growth characterization of concrete under fatigue loading

Abstract

Developments of scaling laws are crucially important for modeling an engineering phenomenon. Based on the type of physical problems scaling laws have been developed in conjunction with the concept of self-similarity. Scale effect should take into account when the size of an object reduces to extremely small-scale level. Therefore, scaling/power laws and similarity concepts have been considered to be important in nano mechanics in the recent times. In the case of quasi-brittle materials like concrete, crack growth phenomenon can considered as a multi-scale problem comprising of atomistic separation, nano scale level coalesce to form micro and subsequently, major crack. Therefore, it is necessary to have a clear understanding of cracking phenomenon in concrete at different length scales under the action of repetitive loading cycles.In this work, an attempt has been made out to understand the micro-fracture scale effect on the crack growth rate in concrete material under the action of fatigue loading. A theoretical model has been developed based on atomic fracture mechanics theory. Using the concept, the activation energy controls the random movement of the nano-crack front in the subcritical environment of micro-crack growth within the cyclic fracture process zone of quasi-brittle material. Kramer’s formula has been used for the prediction of net frequency of the forward crack front jumps by assuming, fatigue crack propagation rate is governed by thermally activated breakage of interatomic bonds. A multi-scale transition approach has been adopted from micro to the macro using scaling law considering energy dissipation in each cycle to grow a macro-crack is equal to the sum of the energy dissipations associated with the propagation of all the active micro-cracks inside the cyclic fracture process zone.