Study on Bending Damage Constitutive Model and Mechanical Properties of Limestone Based on Acoustic Emission

To reveal the mechanical characteristics and damage evolution mechanism of limestone in the bending process, the cumulative acoustic emission (AE) hits were used to define the damage variable, and the rock microbody hypothesis and the Weibull distribution function were applied to further improve the damage variable. Meanwhile, the bending damage constitutive model of limestone under three-point bending was developed based on the Lemaitre strain equivalence principle and the continuum damage theory. Then, the three-point bending test with acoustic emission monitoring was carried out to verify the rationality and validity of the model. Results showed that the modified damage variable D had an exponential distribution with the strain epsilon, and the damage was mainly concentrated in the macrocrack propagation stage. Moreover, the bending neutral layer moved towards the compressive zone in the bending damage process. The bending neutral layer, furthermore, moved slowly a small distance at the initial stage of bending fracture but moved fast a long distance at the end stage of bending fracture. In addition, the bending damage constitutive model could be quantitatively expressed by the cumulative AE hits Np, the stress sigma, the strain epsilon, and Young's modulus E. The theoretical stress-strain model curves agreed well with experimental results, which demonstrated that the proposed model could capture the damage evolution of limestone reasonably in the bending process.