Fractal characteristics of rocks and mesoscopic fractures at different loading rates

To investigate the rate dependence on the mechanical behaviours of rocks under intermediate strain rate, three types of rock were loaded by using a newly developed servo-controlled dynamic triaxial apparatus. In this study, the dynamic strength and crack damage thresholds of rocks under different confinements were investigated at the strain rate range of 10−3∼100s−1, which is of significance to understand the rock damage subjected to earthquakes or far-field blasts. The results indicate that the apparatus could ensure the rock samples being loaded under a stable strain rate without causing prominent disturbance on the confining stress. In addition, the strength and damage thresholds are dependent on the strain rate, i.e., the increasing strain rate would result in the increase of dynamic strength and crack damage thresholds. The increase of confinement leads to a higher failure strength, the crack initiation and damage stresses are also positively correlated to the confining pressure under dynamic loads. Based on the theory of fracture mechanics that considers the crack growth velocity, it is found that the dynamic stress intensity factor exhibits a negative correlation with both the strain rate and confining pressure, whilst the fracture toughness presents an inverse trend. Therefore, the larger axial stress is required to initiate the cracks, which might further induce the variation of crack initiation stress. 

Rate-dependent strength and crack damage thresholds of rocks at intermediate strain rate

In deep rock engineering, dynamic hazards such as blasting and earthquakes pose serious threats to the safety of underground rock structures, including mining and construction activities. To explore the dynamic mechanical properties and damage mechanisms of rocks under realistic ground stress conditions, this study utilized dynamic triaxial compression tests under hydrostatic pressure. These tests employed a modified split Hopkinson pressure bar (SHPB) technique at various strain rates. Wave velocities of the specimens were measured before and after the tests to calculate the damage factor based on the P-wave velocity. Additionally, dynamic uniaxial compression tests on the damaged sandstone specimens indicated a significant reduction in dynamic strength as the damage impact air pressure increased. There was also a notable correlation between the dissipated energy ratio and the level of rock damage, with more severe damage resulting in a smaller dissipated energy ratio. Macroscopic examination through sieve grain size results confirmed the formation of more cracks under high impact air pressure, while microscopic analysis using scanning electron microscopy (SEM) images uncovered the damage mechanisms within the rock post-impact. Ultimately, this study developed an improved ZWT model to effectively verify the dynamic response of the damaged sandstone. 

Dynamic response and constitutive model of damaged sandstone after triaxial impact

Multi-sensor data fusion method based on divergence measure and probability transformation belief factor

To realize aerial target recognition in a complex environment, we propose a multi-source Takagi–Sugeno (T-S) intuitionistic fuzzy rules method (MTS-IFRM). In the proposed method, to improve the robustness of the training process of the model, the features of the aerial targets are classified as the input results of the corresponding T-S target recognition model. The intuitionistic fuzzy approach and ridge regression method are used in the consequent identification, which constructs a regression model. To train the premise parameter and reduce the influence of data noise, novel intuitionistic fuzzy C-regression clustering based on dynamic optimization is proposed. Moreover, a modified adaptive weight algorithm is presented to obtain the final outputs, which improves the classification accuracy of the corresponding model. Finally, the experimental results show that the proposed method can effectively recognize the typical aerial targets in error-free and error-prone environments, and that its performance is better than other methods proposed for aerial target recognition.

Multi-Source T-S Target Recognition via an Intuitionistic Fuzzy Method

Experimental investigation on dynamic compressive mechanical properties of weathered granite and statistical damage constitutive model

Pre-existing joints within a rock mass has a significant effect on the hydro-mechanical properties of the rock mass. The study investigates the hydro-mechanical properties of rock-like materials wi...

Hydro-mechanical properties of rock-like specimens with pre-existing intermittent joints

In earthquake engineering, dynamic response of rock is a hot topic for investigating rock mechanism characteristics. In this article, limestone collected from the Hongshiyan landslide area induced by the 2014 “8.03” Ludian earthquake in southwest China is used to conduct multi-stage cyclic loading tests. The test results show that as confining pressure, loading frequency, and stress amplitude increase, the dynamic elastic modulus increases gradually. Damping parameters are dependent on confining pressure and can be divided into two evolution modes. Three stages can be obtained based on the residual strain curve, including stable, slow increase, and rapid increase, which correspond to the rock failure process. In addition, energy evolution characteristics are analyzed to express the influence of loading strategies. Dissipated energy gradually accumulates linearly, but stress amplitude and cyclic number promote it. 

Experimental Investigation and Energy Evolution of Brittle Limestone Subjected to Multistage Cyclic Loading

Experimental Investigation on the Effect of Strain Rate on Brittle Limestone in Post-earthquake Landslide Area

Field Investigations on Rock Fragmentation Under Deep Water Through Fractal Theory

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