Mechanical behavior and failure mechanisms of rock bolts subjected to static-dynamic loads

This study explores the effects of dynamic and static loading on rock bolt performance a key factor in maintaining the structural safety of coal mine roadways susceptible to coal bursts.Employing a housemade load frame to simulate various failure scenarios,pretension-impact-pull tests on rock bolts were conducted to scrutinize their dynamic responses under varied static load conditions and their failure traits under combined loads.The experimental results denote that with increased impact energy,maximum and average impact loads on rock bolts escalate significantly under pretension,initiating plastic deformation beyond a certain threshold.Despite minor reductions in the yield load due to impactinduced damage,pretension aids in constraining post-impact deformation rate and fluctuation degree of rock bolts.Moreover,impact-induced plastic deformation causes internal microstructure dislocation,fortifying the stiffness of the rock bolt support system.The magnitude of this fortification is directly related to the plastic deformation induced by the impact.These findings provide crucial guidance for designing rock bolt support in coal mine roadway excavation,emphasizing the necessity to consider both static and dynamic loads for improved safety and efficiency.

Characteristics of evolution of mining-induced stress field in the longwall panel:insights from physical modeling

The evolution of mining-induced stress field in longwall panel is closely related to the fracture field and the breaking characteristics of strata.Few laboratory experiments have been conducted to investigate the stress field.This study investigated its evolution by constructing a large-scale physical model according to the in situ conditions of the longwall panel.Theoretical analysis was used to reveal the mechanism of stress distribution in the overburden.The modelling results showed that:(1)The major principal stress field is arch-shaped,and the strata overlying both the solid zones and gob constitute a series of coordinated load-bearing structures.The stress increasing zone is like a macro stress arch.High stress is especially concentrated on both shoulders of the arch-shaped structure.The stress concentration of the solid zone in front of the gob is higher than the rear solid zone.(2)The characteristics of the vertical stress field in different regions are significantly different.Stress decreases in the zone above the gob and increases in solid zones on both sides of it.The mechanical analysis show that for a given stratum,the trajectories of principal stress are arch-shaped or inverselyarched,referred to as the‘‘principal stress arch’’,irrespective of its initial breaking or periodic breaking,and determines the fracture morphology.That is,the trajectories of tensile principal stress are inversely arched before the first breaking of the strata,and cause the breaking lines to resemble an inverted funnel.In case of periodic breaking,the breaking line forms an obtuse angle with the advancing direction of the panel.Good agreement was obtained between the results of physical modeling and the theoretical analysis.

Cobalt phthalocyanine-graphene complex for electro-catalytic oxidation of dopamine

Cobalt phthalocyanine-graphene （CoPc-Gr） complex are fabricated through 7r-Tr interaction of each components, with CoPc adsorbed/inserted on/in the graphene sheets. The obtained complex could be used in the electro-chemical detection of various medicines. CoPc-Gr modified glassy electrode shows excellent response to the electro-oxidation of dopamine （DA） and ascorbic acid （AA）, much better than those of CoPc, graphene oxide （GrO） or graphene （Gr） modified electrode. Significantly, the detection of dopamine is a diffusion-controlled process, highly selective, and has a low detection limit and broad linear range.

Graphene-supported nanoscale zero-valent iron:Removal of phosphorus from aqueous solution and mechanistic study

Excess phosphorus from non-point pollution sources is one of the key factors causing eutrophication in many lakes in China,so finding a cost-effective method to remove phosphorus from non-point pollution sources is very important for the health of the aqueous environment. Graphene was selected to support nanoscale zero-valent iron（nZVI）for phosphorus removal from synthetic rainwater runoff in this article. Compared with nZVI supported on other porous materials,graphene-supported nZVI（G-nZVI） could remove phosphorus more efficiently. The amount of nZVI in G-nZVI was an important factor in the removal of phosphorus by G-nZVI,and G-nZVI with 20 wt.% nZVI（20% G-nZVI）could remove phosphorus most efficiently. The nZVI was very stable and could disperse very well on graphene,as characterized by transmission electron microscopy（TEM） and scanning electron microscopy（SEM）. X-ray photoelectron spectroscopy（XPS）,Fourier Transform infrared spectroscopy（FT-IR） and Raman spectroscopy were used to elucidate the reaction process,and the results indicated that Fe-O-P was formed after phosphorus was adsorbed by G-nZVI. The results obtained from X-ray diffraction（XRD） indicated that the reaction product between nZVI supported on graphene and phosphorus was Fe3（PO4）2·8H2O（Vivianite）. It was confirmed that the specific reaction mechanism for the removal of phosphorus with nZVI or G-nZVI was mainly due to chemical reaction between nZVI and phosphorus.