Study On Mechanical Properties And Microstructure Of Sand 3D Printed Rock-like Samples Based On Different Post-processing Methods

As a rapid prototyping technology,3D printing has great application potential in the field of geotechnical engineering.The application of 3D printing technology to experimental research can effectively overcome the defects of uneven structure of traditional samples and large discreteness of experimental results.However,the poor similarity between 3D printed samples and natural rocks has always been one of the key problems to be solved.It is a common method in industrial production to achieve the expected goal of the final performance of 3D printing products through post-processing,and this method also brings new ideas to solve the above problems.In this paper,the applicability of 3D printing technology in rock laboratory test is studied.GS19 sand and furan resin are selected as raw materials.Sand 3D printing rock samples are prepared by establishing a digital three-dimensional model.The macro and micro level experimental study was carried out on the samples after different post-processing,and the changes of the samples in mechanical properties,microstructure and fractal characteristics were comprehensively analyzed.Finally,the mechanical properties and crack propagation characteristics of pre-cracked specimens with significantly improved strength and stiffness after post-processing under uniaxial compression are studied from the application point of view.The main work and conclusions of this paper are as follows :(1)The printing principle and sample preparation process of sand 3D printing technology were introduced.Combined with the process characteristics and material characteristics of sand3 D printing technology,in order to improve the strength and stiffness of the sample,the printed samples were subjected to post-processing including vacuum infiltration,low-temperature treatment,and combination of infiltration and low-temperature.(2)The mechanical properties of sand 3D printed samples with different post-processing and untreated control samples were tested.The experimental comparison shows that the uniaxial compressive strength of the samples after different post-processing is higher than that of the untreated samples.The method of infiltration combined with low temperature treatment can significantly improve the strength and stiffness of the untreated samples,while the tensile strength of the samples is mainly related to the internal cementing materials.The mechanical properties and failure modes of the samples were further compared with those of natural rocks.It was found that the low temperature treated samples and the low temperature combined treated samples had certain similarities with weakly cemented coarse-grained sandstone and granite,respectively.(3)The microstructure of sand 3D printing samples with different post-processing and untreated control samples was analyzed by mercury intrusion and scanning electron microscopy,and the fractal characteristics of the microstructure of the samples were studied by fractal theory.The study found that the internal pore structure of the sample without infiltration is single,and the fractal characteristics are not obvious,which is different from the natural rock.The fractal characteristics of the internal pores of the infiltrated sample are obvious and closer to the natural rock.The quantitative characterization of microscopic test results can be realized by using appropriate fractal dimension.The key to improve the strength and stiffness of the sample is to improve the internal compactness of the sample,improve the performance of the cementing material and strengthen the integrity between the particles and the cementing material.(4)The 3D printed rock mass samples with different dip angles of prefabricated single and double cracks were treated by combination of infiltration and low-temperature,and the uniaxial compression test was carried out to study the mechanical properties and crack propagation.The results show that the crack propagation form,strength variation law and failure characteristics of single fracture specimen under load are consistent with those of most brittle materials due to different crack inclination angles.However,due to the existence of horizontal prefabricated cracks,the double-crack specimens are mostly subjected to tensile failure,and the stress-strain curve appears to rise again in the post-peak stage.