Uniaxial experimental study of the deformation behavior and energy evolution of conjugate jointed rock based on AE and DIC methods

Conjugate joint is one of the most common joint forms in natural rock mass, which is produced by different tectonic movements. To better understand the preexisting flaws, it is necessary to investigate joint development and its effect on the deformation and strength of the rock. In this study, uniaxial compression tests of granite specimens with different conjugate joints distribution were performed using the GAW-2000 compression-testing machine system. The PCI-2 acoustic emission (AE) testing system was used to monitor the acoustic signal characteristics of the jointed specimens during the entire loading process. At the same time, a 3D digital image correlation (DIC) technique was used to study the evolution of stress field before the peak strength at different loading times. Based on the experimental results, the deformation and strength characteristics, AE parameters, damage evolution processes, and energy accumulation and dissipation properties of the conjugate jointed specimens were analyzed. It is considered that these changes were closely related to the angle between the primary and secondary joints. The results show that the AE counts can be used to characterize the damage and failure of the specimen during uniaxial compression. The local stress field evolution process obtained by the DIC can be used to analyze the crack initiation and propagation in the specimen. As the included angle increases from 0° to 90°, the elastic modulus first decreases and then increases, and the accumulative AE counts of the peak first increase and then decrease, while the peak strength does not change distinctly. The cumulative AE counts of the specimen with an included angle of 45° rise in a ladder-like manner, and the granite retains a certain degree of brittle failure characteristics under the axial loading. The total energy, elastic energy, and dissipation energy of the jointed specimens under uniaxial compression failure were significantly reduced. These findings can be regarded as a reference for future studies on the failure mechanism of granite with conjugate joints

Effect of Heterogeneity on the Failure of Rock with an Initial Crack under Uniaxial Compressions: A Numerical Study

AbstractFailure mechanisms of rock are intrinsically intertwined with heterogeneity and natural fracture. However, the effects of heterogeneity on the failure of rock with natural cracks are still far from clear. By simultaneously considering rock heterogeneity and natural fractures, this paper investigated the effects of heterogeneity on the failure of rock with a single initial crack under uniaxial compressions. The RFPA method with consideration of materials properties heterogeneity was employed, and numerical models with different crack angles were developed. The stress-strain curve, crack development, failure pattern, and AE characteristics were obtained. The numerical results were also compared with experimental results. Further, the effects of initial crack angle and heterogeneity on the strength, failure pattern, and acoustic emission (AE) characteristics were investigated by parametric studies. It has been found that, for a small homogeneity, rock failure is dominated by numerous microcracks within the crack bands that are smeared from the initial crack tips to the loading ends. Rock failure is dominated by macrocracks propagated from the initial crack tips to the loading ends for a large homogeneity. A logarithmic function is proposed to describe the relationship between the uniaxial compressive strength and the homogeneity. The AE characteristics and overall damage evolution are also significantly affected by the heterogeneity

MetaPortrait: Identity-Preserving Talking Head Generation with Fast Personalized Adaptation

In this work, we propose an ID-preserving talking head generation framework, which advances previous methods in two aspects. First, as opposed to interpolating from sparse flow, we claim that dense landmarks are crucial to achieving accurate geometry-aware flow fields. Second, inspired by face-swapping methods, we adaptively fuse the source identity during synthesis, so that the network better preserves the key characteristics of the image portrait. Although the proposed model surpasses prior generation fidelity on established benchmarks, to further make the talking head generation qualified for real usage, personalized fine-tuning is usually needed. However, this process is rather computationally demanding that is unaffordable to standard users. To solve this, we propose a fast adaptation model using a meta-learning approach. The learned model can be adapted to a high-quality personalized model as fast as 30 seconds. Last but not the least, a spatial-temporal enhancement module is proposed to improve the fine details while ensuring temporal coherency. Extensive experiments prove the significant superiority of our approach over the state of the arts in both one-shot and personalized settings.Comment: CVPR 2023, project page: https://meta-portrait.github.i

Sulfate diffusion in coal pillar : experimental data and prediction model

The stability of coal pillar dams is crucial for the long-term service of underground reservoirs storing water or heat. Chemical damage of coal dams induced by ions-attacking in coal is one of the main reasons for the premature failure of coal dams. However, the diffusion process of harmful ions in coal is far from clear, limiting the reliability and durability of coal dam designs. This paper investigates sulfate diffusion in coal pillar through experimental and analytical methods. Coal specimens are prepared and exposed to sulfate solutions with different concentrations. The sulfate concentrations at different locations and time are measured. Based on experimental data and Fick's law, the time-dependent surface concentration of sulfate and diffusion coefficient are determined and formulated. Further, an analytical model for predicting sulfate diffusion in coal pillar is developed by considering dual time-dependent characteristics and Laplace transformations. Through comparisons with experimental data, the accuracy of the analytical model for predicting sulfate diffusion is verified. Further, sulfate diffusions in coal dams for different concentrations of sulfate in mine water are investigated. It has been found that the sulfate concentration of exposure surface and diffusion coefficient in coal are both time-dependent and increase with time. Conventional Fick's law is not able to predict the sulfate diffusion in coal pillar due to the dual time-dependent characteristics. The sulfate attacking makes the coal dam a typical heterogeneous gradient structure. For sulfate concentrations 0.01–0.20 mol/L in mine water, it takes almost 1.5 and 4 years for sulfate ions to diffuse 9.46 and 18.92 m, respectively. The experimental data and developed model provide a practical method for predicting sulfate diffusion in coal pillar, which helps the service life design of coal dams

Abnormal Capacitance Increasing at Elevated Temperature in Tantalum Capacitors with PEDOT:PSS Electrodes

Due to the importance of capacitance temperature stability in precise analog circuit applications, capacitance instability at elevated temperature of 125°C was investigated in tantalum capacitors with PEDOT:PSS counter electrodes. Capacitance-voltage measurement supposed that residual ions in the PEDOT:PSS dispersion caused an accumulation of charges at the dielectric-cathode interface which contributed to an increase in the dielectric constant and resulted in the capacitance increasing at high temperature. Based on the hypothesis, water wash process was applied and capacitance dropped significantly at high temperature. This study shows that an additional water wash process is necessary to improve the capacitance temperature stability after each dispersion dip step

Analysis of Progressive Failure Mechanism of Rock Slope with Locked Section Based on Energy Theory

Progressive failure in rock bridges along pre-existing discontinuities is one of the predominant destruction modes of rock slopes. The monitoring and prediction of the impending progressive failure is of great significance to ensure the stability of the rock structures and the safety of the workers. The deformation and fracture of rocks are complex processes with energy evolution between rocks and the external environment. Regarding the whole slope as a system, an energy evolution equation of rock slope systems during progressive failure was established by an energy method of systemic stability. Then, considering the weakening effect of joints and the locking effect of rock bridges, a method for calculating the safety factor of rock slopes with a locked section was proposed. Finally, the energy evolution equation and the calculation method of safety factor are verified by a case study. The results show that when the energy dissipated in the progressive failure process of rock bridges is less than the energy accumulated by itself, the deformation energy stored in the slope system can make the locked section deform continuously until the damage occurs. The system energy equal to zero can be used as the critical criterion for the dynamic instability of the rock slope with locked section. The accumulated deformation energy in the slope system can promote the development of the cracks in the locked section, and the residual energy in the critical sliding state is finally released in the form of kinetic energy, which is the main reason for the progressive dynamic instability of rock slopes