| SiCp/Al composites made of aluminium alloy reinforced with silicon carbide particle offer greater specific strength and specific stiffness,lower thermal expansion coefficient,and wear resistance than continuous alloys.Therefore,SiCp/Al composites have the potential to replace those conventional alloys in various fields of application such as aerospace,electronic communication,automobile and other national defense and civil fields.However,one factor that prevents SiCp/Al composites from being widely used is their difficulty to be machined.The machining of SiCp/Al composites is a rather complex task owing to hard SiC particles embedded in the Al matrix,which results in rapid tool wear and a poor surface integrity.In the machining of SiCp/Al composites,SiC particles undergo two types of damage:particle fracture and interface debonding.It is precisely that the emergence of these two types of damage has brought huge challenges to the machining of SiCp/Al composite.Therefore,in this paper,the particle damage on the machining of SiCp/Al composite was studied.Through experimental observation and theoretical analysis,chip formation,dynamic compression deformation,cutting force and cutting temperature,which are closely related to the removal process of SiCp/Al composite,were investigated.(1)Research on particle damage and chip formation mechanism in SiCp/Al composite machining.The SiCp/Al composites with different particle content and particle size were machined orthogonally under different cutting conditions.And tool quick-stop experiment was carried out.The obtained chips,chip roots and chip cross-sections were observed microscopically,and the formation mechanisms of particle fracture and interface debonding were studied.Then,effect of particle damage on gross fracture was analyzed,and chip formation mechanism of SiCp/Al composites was revealed.The results showed that the particle-matrix decohesion was induced by the stress concentration due to the pile-up of dislocations in front of particles in machining of SiCp/Al composites.Four factors can induce the particle breakage in the chip formation,which included the stress concentration,the tool edge squeezing particle,the local extrusion of particles,and the formation of the rigid network of particles.The aggravation of particle damage,which facilitated the formation of visible gross fractures in the chips,enhanced the sawtooth of chips.During the machining of SiCp/Al composites,three modes of the shear zone deformation occur,namely plastic deformation,incomplete brittle fracture and complete brittle fracture.The mutual transformation of these three deformation modes leads to the evolution of chip morphology.Then,based on the three deformation modes of the shear zone in SiCp/Al composites machining,the physical models of chip formation in the plastic deformation state,the incomplete brittle fracture state and the complete brittle fracture state were established respectively.(2)Establishment of dynamic constitutive model of SiCp/Al composite considering particle damage effects.The dynamic compressive properties of SiCp/Al composites with various particle volume fractions and sizes were tested using the Split-Hopkinson pressure bar(SHPB)under different strain rates and temperatures,to study the effect of particle damage and thermal softening on the dynamic mechanical properties of SiCp/Al composite.Based on the Eshelby equivalent inclusion theory of metal matrix composites and the plastic dynamic constitutive relationship of the matrix material,a SiCp/Al dynamic constitutive model considering particle damage effects was established,and the dynamic mechanical properties of the SiCp/Al composite were predicted.The results indicated that the dynamic constitutive model of SiCp/Al composites considering the particle damage predicted the dynamic mechanical properties of SiCp/Al composites well at room temperature.However,the average error of the prediction results increased significantly with an increase in the temperature.To further increase the prediction accuracy at high temperature,the SiCp/Al dynamic constitutive model considering particle damage was improved,and the interaction between particle strengthening and thermal softening was analyzed.The dynamic constitutive model of SiCp/Al composite with particle-thermal coupling was established to achieve accurate prediction of dynamic mechanical properties of SiCp/Al composites at different temperatures.Finally,the effect of particle damage on the dynamic mechanical properties of SiCp/Al composites was studied.As the particle content and size increase,the probability of particle breakage and interface debonding increases.The enhancement of particle damage weakened the strengthening effect of the particles,resulting in the flow stress increasing first and then decreasing as the particle content increases,and decreasing as the particle size increases.(3)Modeling of cutting force and cutting temperature of SiCp/Al composite considering particles.By analyzing the chip formation of SiCp/Al composite and combing with the SiCp/Al composite particle-thermal coupling dynamic constitutive model,a cutting force model of SiCp/Al composite considering particles was established.Based on Shaw’s analytical model of cutting temperature,and considering the characteristics of heat generation in the shear zone of SiCp/Al composite,an analytical model of cutting temperature considering particle size was established.Then,combining the cutting force model and the cutting temperature model,a coupling prediction method of cutting force and cutting temperature of SiCp/Al composite material was proposed to predict the cutting force and temperature of SiCp/Al composite.Comparing the predicted results with the experimental results,it is found that the proposed model can more accurately predict the cutting force and temperature considering the influence of particles.Finally,the effect of particles on the cutting force and cutting temperature of SiCp/Al composites was studied,based on the cutting force model and the analytical model of cutting temperature.It was found that as the particle content increased,the cutting force increased first and then decreased,while the cutting temperature decreased.As the particle size increased,the cutting force and cutting temperature decreased.(4)Study on the particle damage degree in shear zone and its influence on cutting process of SiCp/Al composite.According to the Eshelby equivalent inclusion theory and Weibull statistical distribution,the particle damage probability in the shear zone was obtained.The particle damage probability in the cutting-edge area was obtained based on the tool-particle contact analysis,and cutting particle damage degree of SiCp/Al composite was obtained by adding the two particle damage probabilities.The particle damage status of chip root and chip cross-section was analyzed to verify the model effectiveness of the particle damage degree.Then,the effect of particle damage on cutting force,cutting temperature and surface quality was studied.It provided some guidance for the optimization of cutting parameters of SiCp/Al composites.When the particle content or size of SiCp/Al composite during cutting increased,the particle damage degree in the shear zone increased,which in turn caused the cutting force to rise first and then decrease as the particle content increased,and decrease as the particle size increased.An increase in the cutting speed can reduce the cutting force of SiCp/Al composite with low or medium particle content.By reducing the cutting speed,the particle damage in the shear zone was enhanced,and the cutting force of the 40vol.%SiC-30μm/Al composite could also be reduced.With an increase in particle size,cutting force decreased due to the particle damage,causing a decrease in cutting temperature of SiCp/Al composite.With an increase of particle damage in shear zone,the machined surface quality of SiCp/Al composites decreased.When SiCp/Al composites with higher particle content or coarser particles were machined,the particle damage degree in the shear zone maintained a large value,making the quality of the machined surface relatively poor.The increase of cutting speed and cutting thickness could reduce the particle damage degree in the shear zone and helped to improve the surface quality in SiCp/Al composite cutting. |
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