Research On The Bending And Impact Properties Of ZTA_p/Fe45 Composites And Their Numerical Simulation

As one of the main failure modes of mechanical components,wear and tear has resulted in huge economic losses.In many engineering applications,improving the wear resistance of mechanical components is considered a very important challenge.In many industries,such as mining machinery,metallurgy,building materials and environmental protection,many workpieces（such as the middle plate of the scraper conveyor,the driving teeth of the roadheader,the hammer head of the crusher,the lining plate of the ball mill,etc.）are subjected to work under extremely atrocious conditions,greatly shortening the service life.Researches on preparation of high strength,toughness and wear-resistant composites are of great practical significance for reducing production costs,improving production efficiency,promoting industrial upgrading,and promoting the development of high-end equipments for our country.In this thesis,zirconia toughened alumina ceramic particles reinforced Fe45 matrix composites（ZTA_p/Fe45）with different volume fractions（10%,20%,30%,40%）,particle sizes（1.0mm,2.0mm,2.5mm）,interfacial bonding states（unmodified,interfacial modification with Ti-Ni powders）were prepared by powder metallurgy sintering.The effects of particle volume fraction,particle size and interfacial bonding states on mechanical properties such as bending strength and impact toughness of composites and the damage and fracture mechanism of composites were studied by the mechanical experiments and finite element simulations.The main conclusions are as follows:（1）The research has determined the optimal process parameters for the preparation of ZTA_p/Fe45 composites:Fe45 is used as the matrix,millimeter-sized ZTA ceramic particles are used as the reinforced particles,and polyvinyl alcohol（PVA）with a mass fraction of 3%is used as the binder.The sintering temperature was 1215℃,and the holding time was 1h.The microstructure of the matrix is Fe-Cr-Ni solid solution and（Fe,Cr）₇C₃ and FeCrB precipitated at the grain boundary.There is no diffusion of elements at the interface of the composites,which leads to mechanical bonding.The surface of ZTA particles was coated with Ti-Ni powders by pre-sintering method,and then the interface-modified ZTA_p/Fe45 composites were prepared.The distribution of particles in the interface-modified composites is more uniform,the defects are reduced,and metallurgical bonding occurs at the interface.The hardness of Fe45 matrix in the modified composites is 28.52HRC,the interface hardness is 46.66HRC,and the hardness of ZTA particles is1737.06HV.The hardness of the interface is between the matrix and the particles,which can play a good role in transmitting loads.（2）A velocity-controlled rigid body dynamics method is proposed,and a parametric modeling program for particle reinforced composites is developed based on this method.Based on the general finite element software ABAQUS,and using Python language as a secondary development tool,the rapid construction of a macro-scale geometric model of high-volume fraction particle reinforced composites in three-dimensional space is realized.The method utilizes rigid particle motion,collision,and separation mechanisms to avoid particle overlap and is applicable to various particle shapes and high-volume fractions.A method of embedding multiple cohesive elements between high-order solid elements in a three-dimensional finite element model is proposed to simulate the interface of composites,and the improvement of the finite element-discrete element method（FEM-DEM）was realized and a numerical example was presented to demonstrate the efficiency of the approach.（3）Bending samples of ZTA_p/Fe45 composites with different volume fractions,particle sizes and interfacial bonding states were prepared by powder metallurgy sintering,and bending mechanics experiments were carried out.At the same time,the geometric models of composites with different particle volume fractions and particle sizes were established in three-dimensional space by using the velocity-controlled rigid body dynamics method,and the preparation such as meshing,adding loads and boundary conditions was completed.The effects of ZTA particle volume fraction,particle size and interfacial bonding states on the bending strength of ZTA_p/Fe45 composites were studied by three-point bending experiments and numerical simulations combined with the sample fracture surface analysis.The damage and failure mechanisms of ZTA_p/Fe45 composites were studied.（4）Impact samples of ZTA_p/Fe45 composites with different volume fractions,particle sizes and interfacial bonding states were prepared by powder metallurgy technology and grinding method,and the impact toughness of the composites was tested by Charpy impact tests.The geometric models of composites with different particle volume fractions and particle sizes were established by using the velocity-controlled rigid body dynamics method,and the preparation such as meshing,adding loads and boundary conditions was completed.Through Charpy impact tests and numerical simulations combined with the sample fracture surface analysis,the effects of ZTA particle volume fraction,particle size and interface bonding states in ZTA_p/Fe45 composites on the impact toughness of composites and the damage and failure mechanisms of composites under impact load were studied.The impact toughness of composites with a series of low volume fractions was predicted by numerical simulations.（5）Through experiments and numerical simulations,it is found that the most important factor affecting the bending strength and impact toughness of ZTA_p/Fe45 composites is the volume fraction of ZTA particles.With the increase of particle volume fraction,both the bending strength and impact toughness of composites showed a decreasing trend,and the decrease rate of bending strength did not change much;the impact toughness decreased the most when the volume fraction was small,and the decrease rate gradually decreased with the increase of particle volume fraction.The particle size has little effect on the strength and impact toughness of the composites.When the volume fraction is fixed,the bending strength and impact toughness of the composites under the conditions of three different particle sizes（1.0mm,2.0mm and 2.5mm）are relatively similar.The effect of interfacial modification on the mechanical properties of composites is also related to the particle volume fraction.At lower volume fractions,the interfacial modification has little effect on bending strength and impact toughness.When the volume fraction is higher than 20%,the bending strength and elastic modulus of the M-ZTA_p/Fe45 composites are significantly higher than those before modification.The impact absorption energy of the composites after interface modification decreased slightly,but the difference was not significant compared with that before modification.The fracture morphologies of Fe45 matrix and ZTA_p/Fe45 composites after fracture are cleavage brittle fracture.The failure modes of composites without interface modification are mainly the brittle fracture of the matrix and the debonding and pulling out of ZTA particles,accompanied by a small amount of particle fracture;after the interface modification,only the brittle fracture of the particles and the matrix occurs,and there is no debonding and pulling out of ZTA particles.