Depth of Cracking beneath Impact Craters: New Constraint for Impact Velocity

Both small-scale impact craters in the laboratory and less than 5 km in diameter bowl-shaped craters on the Earth are strength (of rock) controlled. In the strength regime, crater volumes are nearly proportional to impactor kinetic energy. The depth of the cracked rock zone beneath such craters depends on both impactor energy and velocity. Thus determination of the maximum zone of cracking constrains impact velocity. We show this dependency for small-scale laboratory craters where the cracked zone is delineated via ultrasonic methods. The 1 km-deep cracked zone beneath Meteor Crater is found to be consistent with the crater scaling of Schmidt (1) and previous shock attenuation calculations

Dynamic Testing System For Rocks Under In Situ Stresses

Rocks may be subjected to dynamic disturbances while under high in situ stresses. When disturbed by dynamic loads from blasting, seismicity or rockbursts, the underground structures would be vulnerable to failure. Depending on the distance from the underground opening, the in situ stress states change from hydrostatic in the far-field, to triaxial in the intermediate distance, and to the pre-tension nearby the opening. Thus, SHPB testing system is further adjusted with confining pressure system into dynamic testing system of rocks under different in situ states. In the experiment with this dynamic testing system, the Brazilian disc rock specimens are first subjected to pre-stresses simulating in-situ stresses underground (including pre-tension, hydrostatic confinement, and triaxial confinement) and then loaded dynamically using the modified SHPB system. The dependence of dynamic tensile strength of the rock material on the static pre-stress and loading rate is investigated. These experimental results will be of great importance in the design and safety of underground rock engineering projects

Experimental investigations of spontaneous bimaterial interfacial fractures

Following our innovative experimental spontaneous fracture models for frictional fractures (compression and shear) and mixed-mode fractures (tension and shear) in identical materials, we designed a laboratory model to investigate the effects of material contrast on mixed-mode spontaneous fracture along a bimaterial interface. A series of interesting phenomena are observed, including asymmetry of crack propagation, with different speeds and levels of fracture parameters. Crack tips fracture parameters are observed to depend on crack speeds, on far-field loading, and on far-field mode-mixity. A strong dependence is also identified between mode-mixity and crack length. Most importantly, the fracture parameters are found to exhibit a strong dependence upon crack length and only a weak dependence on crack speed as is commonly thought. These observations are discussed in details in relation to material contrast. It is expected that these observations will have a profound influence on engineering practice involving the application of materials and structures with bimaterial interface

Time-Resolved X-Ray Diffraction Investigation of Superheating-Melting of Crystals under Ultrafast Heating

The maximum superheating of a solid prior to melting depends on the effective dimensionless nucleation energy barrier, heterogeneities such as free surfaces and defects, and heating rates. Superheating is rarely achieved with conventional slow heating due to the dominant effect of heterogeneous nucleation. In present work, we investigate the superheating-melting behavior of crystals utilizing ultrafast heating techniques such as exploding wire and laser irradiation, and diagnostics such as time-resolved X-ray diffraction combined with simultaneous measurements on voltage and current (for exploding wire) and particle velocity (for laser irradiation). Experimental designs and preliminary results are presented

Intensity prediction model based on machine learning for regional earthquake early warning

Seismic intensity plays a crucial role in influencing the decision-making process of users utilizing earthquake early warning systems (EEWs) upon receiving warning information. Improving intensity warnings’ speed and accuracy is vital. We present a straightforward and dependable model for predicting intensity, which is based only on location and magnitude information. We use the catalog of intensity data from the Japan Meteorological Agency (JMA) released as a dataset, totaling 944,877 intensity instances. To address the issue of imbalanced dataset distribution, we employ the Synthetic Minority Over-Sampling Technique (SMOTE) as a means to improve this situation. Considering the distribution of high intensity data and the importance of features in the model, we construct and jointly apply intensity prediction models for magnitude below 5.7 and above 5.7, respectively. Further, we analyze the robustness of the model by adding random errors for magnitude and location information. We test the transfer capability of the proposed model with four earthquake events in China. Further, we use 466 seismic events (20,542 intensity instances) without published intensity data from the Kyoshin network (K-NET) as the application dataset. We simulate the phenomenon of underestimation of large earthquakes and overestimation of small earthquakes, which is used to analyze the possible application of the proposed model to EEWs. The findings indicate that the model achieves an accuracy of 97.77% when subjected to a magnitude error of 0.3 and a location error of 0.2°. Finally, we analyze the timeliness of the proposed model with a magnitude 7.4 event in 2022.The paper is supported by the National Natural Science Foundation of China 52278313, and Project to Attract Foreign Experts G2023133018L

Distinguishing Look-Alike Innocent and Vulnerable Code by Subtle Semantic Representation Learning and Explanation

Though many deep learning (DL)-based vulnerability detection approaches have been proposed and indeed achieved remarkable performance, they still have limitations in the generalization as well as the practical usage. More precisely, existing DL-based approaches (1) perform negatively on prediction tasks among functions that are lexically similar but have contrary semantics; (2) provide no intuitive developer-oriented explanations to the detected results. In this paper, we propose a novel approach named SVulD, a function-level Subtle semantic embedding for Vulnerability Detection along with intuitive explanations, to alleviate the above limitations. Specifically, SVulD firstly trains a model to learn distinguishing semantic representations of functions regardless of their lexical similarity. Then, for the detected vulnerable functions, SVulD provides natural language explanations (e.g., root cause) of results to help developers intuitively understand the vulnerabilities. To evaluate the effectiveness of SVulD, we conduct large-scale experiments on a widely used practical vulnerability dataset and compare it with four state-of-the-art (SOTA) approaches by considering five performance measures. The experimental results indicate that SVulD outperforms all SOTAs with a substantial improvement (i.e., 23.5%-68.0% in terms of F1-score, 15.9%-134.8% in terms of PR-AUC and 7.4%-64.4% in terms of Accuracy). Besides, we conduct a user-case study to evaluate the usefulness of SVulD for developers on understanding the vulnerable code and the participants' feedback demonstrates that SVulD is helpful for development practice.Comment: Accepted By FSE'2

Dynamic Mode Ⅱ fracture behavior of rocks under hydrostatic pressure using the short core in compression (SCC) method

The shear failure of rocks under both a static triaxial stress and a dynamic disturbance is common in deep underground engineering and it is therefore essential for the design of underground engineering to quantitively estimate the dynamic Mode Ⅱ fracture toughness KⅡC of rocks under a triaxial stress state. However, the method for determining the dynamic KⅡC of rocks under a triaxial stress has not been developed yet. With an optimal sample preparation, the short core in compression (SCC) method was designed and verified in this study to measure the dynamic KⅡC of Fangshan marble (FM) subjected to different hydrostatic pressures through a triaxial dynamic testing system. The formula for calculating the dynamic KⅡC of the rock SCC specimen under hydrostatic pressures was obtained by using the finite element method in combination with secondary cracks. The experimental results indicate that the failure mode of the rock SCC specimen under a hydrostatic pressure is the shear fracture and the KⅡC of FM increases as the loading rate. In addition, at a given loading rate the dynamic rock KⅡC is barely affected by hydrostatic pressures. Another important observation is that the dynamic fracture energy of FM enhances with loading rates and hydrostatic pressures.publishedVersionPeer reviewe

Research progress on dynamic response of deep rocks under coupled hydraulic-mechanical loading

Deep rock is under a complex geological environment with high geo-stress, high osmotic pressure, and strong dynamic disturbance, under the action of the three, the rock body is more prone to damage and rupture, inducing sudden water surges, seepage, blowouts and other engineering geologic hazards. Therefore, investigating the rock dynamics of the rock under hydraulic-mechanical coupling is one of the prerequisites for conducting rock engineering construction. In recent years, many scholars have obtained some fruitful research results in the study of rock dynamics properties under the consideration of water and different stress states. In order to provide more comprehensive guidance for engineering construction and facilitate the subsequent research, the above work is reviewed and summarized in terms of experimental setups, test results, and the mechanism of the confining pressure and water content. Firstly, the basic principle of the split Hopkinson pressure bar (SHPB) system and the device improvements used to simulate the deep rock storage environment are introduced, including the confine-ment-coupled SHPB system and pore-pressure (osmotic pressure)-coupled SHPB system. The advantages and shortcomings of each type of device in the study of rock dynamics under hydraulic-mechanical coupling are briefly analyzed. Secondly, the dynamic mechanical response characteristics of rocks hydraulic-mechanical coupling considering different stress states (uniaxial confining, triaxial confining) are summarized. The dynamic mechanical response of deep rocks under fixed preset pore pressure and osmotic pressure coupling and its law of variation with pore water pressure and osmotic pressure are described in detail. Subsequently, the mechanism of confining pressure on the dynamic properties of the rock is outlined, and the influence law under different stress states is analyzed. The strengthening and weakening microscopic mechanism and quantitative expression of the dynamic mechanical properties of the rock by water are recapped. Finally, the dynamic response of deep rocks under hydraulic-mechanical coupling is summed up, and the further experimental research work and the research direction of deep rock dynamics are proposed