Tensile and tear-type fracture toughness of gypsum material:Direct and indirect testing methods

In this context,four specimens,i.e.(i)circumferentially notched cylindrical torsion(CNCT),(ii)circum-ferentially notched cylindrical direct tension(CNCDT),(iii)edge notch disc bend(ENDB)and(iv)three-point bend beam(3PBB),were utilized to measure the modesⅠandⅢfracture toughness values of gypsum.While the CNCT specimen provides pure modeⅢloading in a direct manner,this pure mode condition is indirectly produced by the ENDB specimen.The ENDB specimen provided lower KⅢc and a non-coplanar(i.e.twisted)fracture surface compared with the CNCT specimen,which showed a planar modeⅢfracture surface.The ENDB specimen is also employed for conducting pure modeⅠ(with different crack depths)and mixed modeⅠ/Ⅲtests.KIc value was independent of the notch depth,and it was consistent with the RILEM and ASTM standard methods.But the modeⅢfracture results were highly sensitive to the notch depth.While the fracture resistance against modeⅢwas significantly lower than that of modeⅠ,the greater work of fracture under modeⅢwas noticeable.

Experimental and Numerical Assessment on Seismic Performance of Earth Adobe Walls

Earth buildings are common types of structures in most rural areas in all developing countries.Catastrophic failure and destruction of these structures under seismic loads always result in loss of human lives and economic losses.Wall is an important load-bearing component of raw soil buildings.In this paper,a novel approach is proposed to improve the strength and ductility of adobe walls.Three types of analyses,material properties,mechanical properties,and dynamic properties,are carried out for the seismic performance assessment of the adobe walls.These performed studies include that,material properties of the earth cylinder block,mechanical properties of adobe walls under quasi-static loads,and dynamic performance of adobe walls excited by seismic waves.On investigation of material properties,eighteen cylindrical specimens with a diameter of 100 mm and a height of 110 mm were divided into three groups for compressive,tensile,and split pull strength tests,respectively.The results of the three groups of tests showed that the yield strength ratios of compressive,tensile,and shear strength were about 1:0.3:0.2.In order to study the performance of structural components,three 1/3 scale model raw soil walls with a dimension of 1,200 mm in width,1,000 mm in height,and 310 mm in thickness were tested under cyclic loading.The average wall capacity of the wall obtained by the test was about 13.5 kN and the average displacement angle was about 1/135.The numerical simulation experiment is used to explore the mechanism of structural failure.A three-dimensional finite element model is established by choosing the material parameters based on the above test outcomes.The accuracy of the numerical simulation experiment is verified by simulation and comparison of the above quasi-static test results.Further,the collapse process of raw soil wall under a seismic wave is simulated for exploring the response and damage mechanism of structure.Based on those systematically analyzed,some useful suggested guidelines are provided for improving the seismic performance of raw soil buildings.

Experimental investigation on hard rock fragmentation of inserted tooth cutter using a newly designed indentation testing apparatus

This investigation aims to explore the effects of stress conditions and rock cutting rates on hard rock fragmentation through indentation tests on a newly designed triaxial testing apparatus.This apparatus was designed to realize a triaxial loading and indentation test of cylindrical specimens using inserted tooth cutter.The boreability and crushing efficiency of granite rock was investigated by analyzing the change rules of the thrusting force,penetration depth,characteristics of chippings and failure patterns.Several quantitative indexes were used to evaluate rock boreability in this investigation.The granite rock samples all had a chiselled pit and a crushed rock core.Under initial stress conditions,only flat-shape chippings were stripped from the rock surface when the thrusting force reached 20 kN.The rock cutting special energy had a close correlation with the initial stress conditions and inserted tooth shape.Moreover,a thrusting force prediction model was proposed in this paper.The contribution of this study is that for the first time the influence mechanism of the initial triaxial stress conditions on rock fragmentation is investigated using an inserted tooth and the newly designed testing apparatus.This study has a crucial importance for practical underground hard rock crushing in geoengineering.