Study On The Effect Of Different Prefabricated Loading Angles On The Initiation Point Of Dynamic Brazilian Splitting And Its Failure Characteristics

Concrete is widely used in the process of coal mining.Temporary support or permanent support should be carried out after tunneling into and out of the space.As an important supporting material in mine construction projects,concrete is prone to compression,tensile and shear failure under the action of external loads.The failure mode at the time of failure is mainly manifested as tensile failure,so the accurate measurement of dynamic tensile strength of concrete material is very important for the safety of coal mine production and the safety design of mine support engineering structure.During the dynamic tensile strength test,the current mainstream experimental method is to use the platform Brazilian disc specimen with prefabricated loading Angle for splitting test.In the test,according to the tensile strength test criteria,only when the cracking position of the specimen is located in the central region of the disc and the crack growth direction is consistent with the loading direction,can the true dynamic tensile strength of the specimen material be accurately measured.In this paper,the comprehensive test system of "Hopkinson bar-digital image correlation method-strain gauge method" was used to conduct dynamic splitting test on the self-compacting concrete Brazilian disc specimen with high precision precast loading Angle.In order to obtain the high precision precast platform loading Angle,a mold model was independently designed by using Solid Works software.HP 3D printer to create the corresponding mold method.In the experiment,the basic mechanical properties of the experimental materials were obtained by static mechanical experiments,and the effects of the loading rate on the crack initiation point,crack growth characteristics,tensile strength and failure mode of the specimens with different prefabricated loading angles were studied by dynamic mechanical experiments.The numerical simulation of the complete Brazilian disc was carried out to verify the experimental results.The results show that the initiation point and propagation of the crack are closely related to the loading rate.With the increase of the loading rate,the initiation and propagation direction of the crack change symmetrically.The specimens with prefabricated loading Angle can better meet the central initiation conditions,and the reliability of the test results is higher.For the parameters of self-compacting concrete,it is recommended to set the prefabricated loading Angle to28°～30°,so that more accurate experimental data can be obtained.The dynamic tensile strength of self-compacting concrete has obvious linear correlation with the loading rate.In addition,the dynamic tensile strength of concrete with central cracking is higher than that of concrete with non-central cracking.Figure 51 Table 15 Reference 84...