Investigation of three different cooling treatments on dynamic mechanical properties and fragmentation characteristics of granite subjected to thermal cycling

Underground thermal engineering such as geothermal exploitation usually involves the response of impact loads due to the drilling operation and blasting load.This study investigated the dynamic mechanical properties and fragmentation characteristics of granite subjected to thermal cycling under natural cooling,water cooling,and liquid nitrogen cooling.Firstly,split Hopkinson pressure bar tests were performed on granite under three different cooling methods to study the dynamic mechanical parameters with thermal cycles.Subsequently,the damage factors were calculated to evaluate the damage on granite and the relationship between damage and stress.Finally,the granite fragments after impact were sieved,and the fractal dimension and average fragment size were introduced to analyze the fragmentation characteristics.The results demonstrate that the degradation of dynamic mechanical properties mainly occurs in the first four thermal cycles;with the increase of damage factor,the stress decreases linearly under the three cooling methods,and the damage caused by liquid nitrogen cooling to granite is the most significant,followed by water cooling.Fragments of granite change from axial splitting failure to a more complex composite failure mode.In addition,with the decrease of the average fragment size,the fractal dimension of the granite gradually increases,resulting in the higher fragmentation degree and the better uniformity of fragmentation.

Numerical investigation of rock dynamic fragmentation during rockslides using a coupled 3D FEM-DEM method

Rockslides are one of the most common geological hazards in mountainous areas and can pose significant threats to the safety of human lives and infrastructures. Studying the dynamic fragmentation process, and fragment characteristics of rock blocks during rockslides is of great significance. In this study,the influences of the slope angle on the dynamic fragmentation process, damage and energy evolution,and the fragments’ flying velocity and flying angle were systematically investigated using a coupled 3D FEM-DEM method. An improved fragment search algorithm was first proposed to more effectively extract the information of the fragments after impacting. The input parameters in the numerical modeling were carefully calibrated based on the quasi-static uniaxial compression tests and the rockimpact tests. The complex fragmentation process of rock block sliding along an inclined slope was simulated. The results indicate that the fragmentation intensity gradually increases with increasing the slope angle, and the fragmentation intensity of the front region of the rock block is always higher than that of the rear region. Additionally, the slope angle can significantly affect the damage ratio, energy dissipation, and the ratio of tensile crack to shear crack during the rockslides. The number of the fragments having higher flying velocities and larger flying angles increases with increasing the slope angle,which contributes to a larger spreading distance and a wider deposition area.

Micro-macro fracture mechanism of heterogeneous granite in percussive drilling

The conventional rotary rock breaking method faces a technical bottleneck in improving the rate of penetration(ROP)in deep hard formations.Percussive drilling is the most potential approach to increase rock-breaking efficiency and ROP.However,the rock-breaking mechanism of percussive drilling is still unclear enough,especially the micro-fracture mechanism of rock under confining pressure(under lateral pressure and hydraulic pressure).In this paper,the impact rock breaking experiments by four kinds of Polycrystalline Diamond Compact(PDC)cutters are carried out using a drop-weight impact testing machine and an acoustic emission(AE)recording system,the influence of parameters such as cutter shape,rake angle,and impact energy on rock-breaking are systematically analyzed.This study includes a numerical simulation to examine the process of crack initiation,propagation,and cuttings formation during the impact process with the consideration of confining pressure.The results show the conicalshaped cutter is the most aggressive with high breaking efficiency.The penetration depth of the cutter is mainly influenced by the impact energy and cutter shape than the rake angle of the cutter.There exists critical impact energy makes the rock breaking efficiency the highest.The critical impact energy is about 40 J when using the conical-shaped cutter with a rake angle of 15°.The rock mainly failed in tensile mode,and the inter-grain crack is the main crack.Hydraulic pressure can inhibit the formation of horizontal cracks,while lateral pressure can inhibit the formation of vertical cracks and reduce the proportion of tensile cracks.The research results can provide some reference and basis for improving the rock-breaking efficiency in deep hard formations.

Corydalis Rhizoma as a model for herb-derived trace metabolites exploration:A cross-mapping strategy involving multiple doses and samples

Deciphering the metabolites of multiple components in herbal medicine has far-reaching significance for revealing pharmacodynamic ingredients.However,most chemical components of herbal medicine are secondary metabolites with low content whose in vivo metabolites are close to trace amounts,making it difficult to achieve comprehensive detection and identification.In this paper,an efficient strategy was proposed:herb-derived metabolites were predicted according to the structural characteristics and metabolic reactions of chemical constituents in Corydalis Rhizoma and chemical structure screening tables for metabolites were conducted.The fragmentation patterns were summarized from representative standards combining with specific cleavage behaviors to deduce structures of metabolites.Ion abundance plays an important role in compound identification,and high ion abundance can improve identification accuracy.The types of metabolites in different biological samples were very similar,but their ion abundance might be different.Therefore,for trace metabolites in biological samples,we used the following two methods to process:metabolites of high dose herbal extract were analyzed to characterize those of clinical dose herbal extracts in the same biological samples;cross-mapping of different biological samples was applied to identify trace metabolites based on the fact that a metabolite has different ion abundance in different biological samples.Compared with not using this strategy,44 more metabolites of clinical dose herbal extract were detected.This study improved the depth,breadth,and accuracy of current methods for herb-derived metabolites characterization.

Multiple characteristic structure fragments scans coupled to high-resolution mass spectrometry strategy for discovering unknown structural analogs of mycotoxins in food

The cereals and their products,which have been easily infected by fungi and contaminated with mycotoxins,are serious threat to both human and animals alike.And yet,detection of these unknown fungal infection and mycotoxins contaminates remains a great challenge.In this work,a holistic approach based on multiple characteristic structure fragments scans and high-resolution mass spectrometry(HRMS)was proposed for discovering unknown structural analogues of mycotoxins.The structural similarity of the same class of compounds provides a direction for the discovery and identification of unknown structural analogues of mycotoxins.The following steps were carried out:the fragmentation pathways of four types of mycotoxins were elucidated through comprehensive fragment analysis.By the combination of fragmentation pathways,the multiple characteristic structure fragments were screened out,with the common fragments were obtained by Veen diagram.Finally multiple characteristic structure fragments scans were carried out to find the unknown structural analogues of mycotoxins.The approach,first proposed by us,was proved to be effective in discovering and identifying 5 structural analogues of mycotoxins in real samples.It was proved to be a simple,fast and accurate method for early detection of fungal infection and mycotoxin contaminants,even for trace amounts of chemicals in complex matrix,and is of great significance to prevent hazardous substances infection from the food supply chains worldwide.