Study On Rock-like Material Simulation Method Based On EFF 3D Printing Technology

3D printing technology is an advanced rock physics simulation technology that can be applied to the field of geotechnical engineering,but it is faced with the problem of poor similarity between printed materials and natural rocks.Free Extrusion(EFF)is a 3D printing technology which takes clay material as the printing raw material,extrudes and accumulates layers to print,and then sinteres at high temperature.In this paper,a systematic molding quality test and a physical and mechanical property test were carried out on the EFF 3D printing samples.The shrinkage rate,homogeneity,density,hydrologic properties,uniaxial compressive strength,elastic modulus,tensile strength and other parameters of the 3D printing samples were determined.The similarity between the EFF 3D printing samples and natural rocks was analyzed.The influence law of forming parameters on physical and mechanical parameters of samples is studied,and a rock-like material simulation method based on EFF 3D printing technology is proposed.The main conclusions are as follows:(1)Under the firing temperature of 800?1200?,the size shrinkage rate of the sample printed by EFF 3D varies from 6?21%,and the shrinkage rate increases significantly with the increase of the firing temperature.The Shapiro-Wilk normality test and T test show that the size and quality of the samples conform to the normal distribution and there is no significant difference.At the same time,the ultrasonic acoustic information also shows that the internal filling effect of the samples is good and there is no defect,and the external and internal samples meet the requirements of homogeneity,which can be used for repeated physical and mechanical test research.Under the conditions of different forming parameters,the physical and mechanical parameters of the samples can vary widely,such as density 1.61?2.63 g/cm3,saturated water absorption0.09%?22.82%,softening coefficient 0.55?0.93,uniaxial compressive strength16.46?50.49 MPa and tensile strength 0.82?17.18 MPa.(2)SiO₂ and Al₂O₃ are the main chemical components of the EFF 3D printed materials,which have a high similarity with sedimentary rocks in the mineral composition and content proportion of the constituent materials;The 3D printed samples have obvious bedding structure and are formed by high temperature dehydration,which is similar to the forming process of sedimentary rock.Taking brittleness index?_c?_t/2,deformation index E/?_c,strength index?_c/?,?_t/?,strength softening index?₁/w_s,?₂/w_s as the evaluation basis,the similarity relationship between the EFF 3D printed sample and natural rock in stress-strain characteristics,failure mode,strength,deformation and brittleness is analyzed.It is verified that the EFF 3D printed samples have a high similarity with natural rocks,especially for sandstone and mudstone with a more comprehensive simulation effect.(3)Three molding parameters,nozzle diameter,printing layer thickness and firing temperature,were used as control variables to analyze the influence of EFF 3D printing molding parameters on physical and mechanical parameters of the sample.The firing temperature is the most important factor affecting the physical and mechanical properties of the sample.The higher the firing temperature,the higher the density,the lower the water absorption and the higher the strength of the molded sample.Reducing the thickness of the printing layer and increasing the diameter of the nozzle can increase the density,water absorption and strength of the sample to a certain extent.(4)By carrying out multiple linear regression on the physical and mechanical test results of samples with different forming parameters,the quantitative empirical equation between forming parameters and physical and mechanical parameters is obtained,the range of rock physical and mechanical parameters that can be simulated by EFF 3D printing samples is calculated,and a rock-like simulation method based on EFF 3D printing technology is proposed:1)According to the physical and mechanical parameters table of the EFF 3D printed samples proposed in this paper,the firing temperature required by the 3D printed samples was determined by interpolation method according to the range of physical and mechanical parameters of the rock to be simulated;2)Adjust the diameter of nozzle and the thickness of printing layer according to the empirical formula of multiple linear regression,and try to calculate the density,hydrologic parameters and strength parameters of 3D printing sample;3)The physical and mechanical parameters of target rock were simulated by 3D printing of the forming parameters that could meet the similar requirements.