Determination of the load bearing capacity of pre-stressed expandable props for ground support in underground mines

This paper aims to determine the load bearing capacity of pre-stressed expandable props with different geometries and load eccentricities for flexible support in underground mining or excavation.It is deduced that the expandable device could have much higher strength(>89 MPa)by laboratory tests,and the load bearing capacity of the expandable prop may depend on the stability of the supporting steel pipe structure.A good agreement was found between the laboratory test and numerical results in terms of the load bearing capacity and the final macro-bending failure pattern for expandable props with heights of 1.5 and 2.7 m,and the theoretical calculation for the strength of traditional steel structures is not directly suitable for the expandable props.Moreover,additional numerical simulations were performed for the expandable props with different normalized slenderness ratiosλ_(n)and loading eccentric distances e.The variation of stability coefficient of the expandable prop is in line with the Perry-Robertson equation and its correlation coefficients are fitted as a of 0.979 and b of 0.314.For estimating the load bearing capacity of the expandable props,the strength equation for traditional steel structures is improved by introducing a bending magnification factor and by modifying the normalized slenderness ratio to a converted slenderness ratio.Based on the underground field monitoring for the strength of expandable props with different heights,the empirical eccentric distances were back calculated,and a safety factor is introduced to obtain the designed strength of the expandable prop.In addition,a four-step design procedure is proposed for the expandable prop.

高密度烧结金属齿轮的承载能力(英文)

This paper describes a study on the load bearing capacity of newly developed high density sintered metal gears with surface-densification. High density sintered metal gears were hobbed, and then surface-rolled. These gears were case-carburized after surface-rolling. The effect of surface-rolling on the surface property was examined by measuring porosity and hardness near surfaces of rolled gears. Running tests for these gears were performed. A failure mode and load bearing capacity of high density sintered metal gears and the effects of surface-rolling on the load bearing capacity of sintered metal gears were determined, and the results were compared with those of carburized wrought steel gears and conventional sintered metal gears. The experimental results show that the load bearing capacity of a newly developed high density sintered metal gear with surface-densification is higher than that of a carburized wrought steel gear.

Extremely low friction on gold surface with surfactant molecules induced by surface potential

An extremely low friction state was observed on the gold surface induced by applying a specific negative potential in cationic surfactant solution.The friction force showed a remarkable reduction from 8.3 to 3.5×10−2 nN(reduced by 99.6%)with increasing the period of negative applied potential,and the final friction coefficient could reduce down to 3×10−4.The extremely low friction state was robust,and it also exhibited an excellent load bearing capacity,which cannot be damaged by a high load.Moreover,the extremely low friction state achieved under negative applied potential could keep stable even after the removal of potential,but failed in a short time,once a specific positive potential was applied.It was demonstrated that there was a stable electro-adsorption of surfactant molecules on the gold surface induced by applying a negative potential,leading to the formation of a bilayer structure on the gold surface.The hydration layers of the bilayer on the gold surface and micelles on the silica probe provided a shear plane with an extremely low shear strength,leading to the extremely low friction state on the gold surface.This study provides a method to achieve extremely low friction state by applied potential.