Fracture behavior and damage evolution model of sandstone containing a single pre-existing flaw under discontinuous fatigue loading

Abstract

The process of disaster incubating in deep rock mass engineering is mainly related to the fracture behavior and damage mechanism of the rock mass. This paper proposes a new damage model based on Lemaitre's equivalent strain hypothesis with improved Harris distribution and laboratory discontinuous fatigue loading test (DFLT). Firstly, discontinuous fatigue loading tests were carried out on the jointed sandstone specimens and acoustic emission (AE) was used as a research tool. Based on the b-value and AF-RA theory, the failure mode of specimens was further explored in terms of the crack evolution process and crack classification. Meanwhile, digital image correlation (DIC) techniques were used to analyze the evolution of the deformation field on the surface of the specimen. Subsequently, the fracture morphological characteristics of the rock masses were analyzed from a microscopic perspective by scanning electron microscopy (SEM) techniques. The investigations found that in a short time, the low-level constant load will lead to the interlocking of particles inside the rock mass, reduced incremental coupled damage, and enhanced plasticity “with” reducing the coupled damage increment and enhancing the plasticity, thereby inhibiting the damage growth rate. In addition, as the stress level increases, the friction between the grains intensifies, the cuttings and roughness of the fracture surface increase, the fatigue softening effect is enhanced, and the specimen gradually transforms from brittle failure to ductile failure. At the same time, the proportion of stress-induced tensile cracks and shear cracks gradually increased, resulting in the specimen finally presenting tensile-shear composite failure.

Damage evolution analysis of concrete based on multi-feature acoustic emission and Gaussian mixture model clustering

“…The b -value originally derived from seismological applications in accordance with the Gutenberg-Richter law (GBR), serves as a quantitative tool for characterizing the relationship between the frequency of AE signals and their corresponding amplitude (Kurz et al., 2006). The b -value as a valuable indicator for assessing crack propagation, enabling it a measure of crack growth scale in the analysis of the crack evolution process (Shi et al., 2023). The classification of the evolution process of concrete becomes feasible by employing the qualitative measurement of crack scale through the b -value analysis.…”

Effect of strong dielectric substances on the damage characteristics of rocks exposed to microwave radiation: Insight from experiments and mechanisms

“…Considering the sandstone specimens treated by microwave-assisted reagent with the higher microwave power, the internal shear surface of the rock specimen will produce a different inclination, which leads to the shear damage. In the destruction process, the rock sample will be accompanied by some uneven surface fragmentation, part of the pulling crack, and showing shear damage along the weak surface (Shi et al., 2023). The characteristics of brittle damage were greatly diminished (Figure 8(b)).…”

Experimental Study on Energy Evolution and Acoustic Emission Characteristics of Fractured Sandstone under Cyclic Loading and Unloading

“…Therefore, this phenomenon can be used as a precursor to rock failure. cracks initiate multiple directional deformations at different locations and exhibit gradual spreading, branching, and deflection toward the ends [52].…”

“…Only two macroscopic microcracks develop, and there is also a trend for the lower tip of the pre-existing crack to extend downward. Macroscopic cracks initiate multiple directional deformations at different locations and exhibit gradual spreading, branching, and deflection toward the ends [52].…”