Discrete Element Simulation Of Isostatically Pressed Green ZrO₂ Ceramics Cracks In Machining Process

Ceramic materials have superior mechanical and chemical properties such as high strength,high hardness,high corrosion resistance,and high heat resistance.It has been widely used in modern industrial,aviation,medical and other fields.But it is difficult to process and cost in the processing due to these properties of ceramic materials.The green ceramic body is an unsintered ceramic green compact,which can be processed by a conventional processing method,and the workpiece after sintering can obtain a better surface quality.Based on the characteristics of green ceramic body,the processing of isostatically pressed green ZrO2 ceramic was simulated by discrete element method.The effects of different processing parameters on the surface quality after processing and the mechanism of chip formation were studied,and the results of the discrete element simulation were verified by the test results.The green ZrO2 ceramic was prepared by cold isostatic pressing technology,and the isostatically pressed green ZrO2 ceramic was subjected to uniaxial compression test and three-point bending test.The main mechanical properties of the material were measured.The modulus of elasticity is about 150 MPa,the flexural strength is about 8 MPa,and the compressive strength is about 2.5 MPa.The two-dimensional BPM(Bonded-Particle Model)model of green ZrO2 ceramic was established by PFC2D software,and the model was calibrated to obtain the discrete element model which matched the main mechanical properties of the actual material.Based on the established two-dimensional discrete element model,the machining process of isostatically pressed green ZrO2 ceramic was simulated.The effects of different processing parameters on surface cracks and cutting forces after machining were analyzed.According to the results of discrete element simulation,the cutting mechanism of isostatically pressed green ZrO2 ceramic was proposed.The turning test of the prepared isostatically pressed green ZrO2 ceramic material was carried out.The effects of different processing parameters on the surface roughness and tool wear after machining were analyzed.The 3D topography of the machined surface under different cutting conditions was discussed with the SEM topography of the tool wear area.The results show that the higher the cutting speed,the better the surface quality after processing;the greater the cutting depth,the worse the surface quality after processing.At high speed cutting,a smaller depth of cut can be used to reduce damage to the machined surface.The results of the actual test are consistent with the results of the simulation test.A three-dimensional discrete element model of isostatically pressed green ZrO2 ceramic was established and calibrated.The isostatically pressed green ZrO2 ceramic was smeared on the UMT-2 friction and wear tester.The influence of the loading force of the stylus and the sliding speed of the scriber on the surface quality of the scratch was analyzed.The results show that the crack density of the scratched surface increases with the increase of the scribing speed.But it increases with the increase of the indenter loading force firstly,and then decreases with the increase of the indenter loading force.This is in agreement with the results of the three-dimensional scribing discrete element simulation test.