Experimental Study On The Dynamic Mechanical Properties Of 3D Printed Rock Specimens

With the continuous development of underground engineering,the research on various physical and mechanical performance of rock mass structure has been difficult to evaluate with traditional experience,especially subjected to impact loads during excavation,resulting in deformation and energy dissipation.However,due to the heterogeneity of rock mass structure,there are great randomness and discreteness in the related experimental research,so it is difficult to accurately obtain the variation law of various physical and mechanical properties of rock mass under impact load,which proved to be a hinge problem in the field of rock engineering.Through the years,the swift and violent development of 3D printing technology can strictly prepare complex 3D objects with highly consistent internal structure,which can be applied to the field of rock engineering,and then select appropriate materials to simulate rock mass can effectively solve the above problems.Based on the previous research of the group,this paper continues to use GS19 sand and furan resin as the printing substrate to prepare 3D printed rock specimens for dynamic compression and tensile tests,and the dynamic mechanical tests under different impact pressures were carried out by SHPB test device.The effects of impact rate,inclination angle of prefabricated crack and specimen type on its strength,failure mechanism and energy dissipation characteristics are comprehensively analyzed.The main content and research results of this article are as follows:(1)The test principle of SHPB technology is introduced in detail,and the test device is improved according to the particularity of this kind of specimen.The shaping effect of copper sheet and rubber sheet is compared,and it is found that the rubber sheet as a wave shaper can effectively reduce the influence of dispersion phenomenon on the test results.In addition,compared with the ordinary resistance strain gauge,the accuracy of the test results is greatly improved by using the semiconductor strain gauge to measure the test data.(2)In the SHPB dynamic compression test,dynamic loads of different rates were applied to the 3D printed cylindrical specimens with different prefabricated crack inclination angles.The results indicated that the dynamic compressive strength of the specimens was much higher than the static compressive strength.With the increase of the prefabricated crack angle,the dynamic compressive strength of the 3D printed rock specimen firstly decreases and then increases at the same impact pressure,reaching the lowest strength at 30°.The incident energy and absorption energy of the 3DP specimen also show the same tendency as mentioned above,while the energy dissipation rate is on the contrary.The dynamic compressive strength of the same type of 3DP specimens increases with the increasing of atmospheric pressure,which has obvious strain rate correlation.However,the increase rate of specimens with distinct inclination angles of prefabricated cracks is different,and the increase rate of specimens with 30 ° is the slowest.The main cracks of the specimen include tension failure,tension-shear mixed failure and shear failure.When the impact velocity is small,the incident energy of the specimen is small,the fragmentation of the specimen is relatively complete,and the crack propagation path of the specimen can be basically seen after failure.With the increase of the impact velocity,the incident energy continues to increase,resulting in a gradual decrease in the fragmentation of the specimen and an increasing number of fragments.(3)In SHPB dynamic tensile test,the impact load of different rates was applied to 3D printed Brazilian disc specimen and platform Brazilian disk specimen respectively.It was found that the tensile strength of the specimens in dynamic tensile test are higher than that in static tensile test,showing a significant strain rate correlation.With the increase of strain rate,the dynamic elastic modulus and dynamic tensile sensitivity coefficient of 3DP specimen increase gradually,while the radial peak strain shows the opposite trend.After using the platform,the dynamic tensile strength of the specimen is somewhat increased.By analyzing the failure mechanism and energy dissipation characteristics,it is found that at a small impact rate,most of the 3D printed Brazilian disk specimens split into two halves along the direction of loading diameter,and some of the specimens fail into three halves,while the platform Brazilian disk specimens split along the direction perpendicular to the platform.Both ends in contact with the rod have a certain degree of triangular crushing area,and the crushing area of the specimen at the end contacting the incident rod is obviously larger than that of the contacting end of the transmission rod.There is a good linear correlation between the dissipated energy per unit volume and the strain rate.With the increase of the impact rate,the incident energy of the 3DP specimen has increased to a certain extent,resulting in a gradual increase of the crushing area,the decrease of the fragmentation and the increase of the number of comminuted specimens.In addition,the existence of the platform increases the contact area between the rod and the specimen,and effectively improves the stress concentration of the contact end face,so the failure form is better.