Numerical Simulation Of Thermal Stress And Thermal Fatigue Behavior Of WC_P/steel Matrix Surface Composites

In recent years,scholars have conducted a number of studies on the thermal fatigue properties of ceramic particles reinforced metal-based surface composites,but due to differences in the thermophysical properties between the reinforcing particles and the substrate,composite layer and the substrate,they cause chilled heat.Thermal stress is generated during operation under the operating conditions,and the presence of thermal stress greatly affects the thermal shock performance.Therefore,in this thesis,WC_P/steel matrix surface composites with good interfacial bonding and compact structure were successfully prepared by high-energy ball milling and vacuum sintering.The cooling rate,particle shape,particle size and distribution were simulated using ANSYS finite element software.The influence of the stress-strain field;the influence of the above parameters on the thermal fatigue performance of the composite material was investigated through the thermal shock experiment,and the preliminary study on the initiation and propagation of the fatigue crack was conducted.The relationship between the fatigue stress and the fatigue properties of WC_P/steel matrix surface composites has been studied.The results of this correlation study will also provide sufficient theoretical basis for structural optimization of composite materials.The results of finite element analysis show that there are differences in thermal physical properties and mechanical properties between the steel matrix and the WC ceramic particles.During the cooling process,a large thermal stress field is formed in the composite material,and the particles are subjected to compressive stress and tensile stress exists in the matrix.The thermal stress of composite materials varies with time under different cooling rates.The faster the cooling rate,the more severe the thermal stress changes.The thermal stress will be retained instantaneously;the spherical WC particles have a uniform thermal stress at the interface,and the square particles are at the tip.The stress concentration is easy to form at the corners,and the thermal stress in the composites decreases with the increase of the angularity of the WC particles;the thermal stress gradually decreases with increasing the size and diameter of the WC particles,and the plastic strain and deformation zone in the matrix gradually increase;The different distribution of particles determines the distance between particles.When the particles are evenly distributed,the distance between the particles is large and the stress in the interference region can be neglected.When the particles are agglomerated and distributed,the particle spacing is small,and the stacking effect occurs in the stress-affected zone.The stress in the interference zone increases as the particle spacing decreases,and there is also a large stress field at the macroscopic interface.Thermal shock experimental results show that the number and speed of internal cracking of composites are different under different cooling rates.The faster the cooling rate is,the faster the cracks are generated and the highest in number.The cracks are not easily generated in spherical WC composites.Irregular WC particles are easily cracked at edges and corners,and the smaller the angular angle,the faster the speed of initiation and propagation of cracks.When the particles are agglomerated,they easily generate a large number of overlapping cracks between the particles;the cracks are easily initiated at the interface.In addition,when the interfacial bonding strength is high,a plurality of intertwined microcracks are initiated and propagated at the interface or within the particles,eventually resulting in comminuted shedding inside the particles.If a weak interface is generated,the cracks will follow the interface.Expansion eventually fell off as a whole.Therefore,in order to improve the thermal fatigue performance of WC_P/steel matrix surface composites,spherical or angular particles should be selected.A reasonable preparation process is used to evenly distribute the particles in the matrix.At the same time,avoid the greater temperature difference in the fatigue environment during the application of composite materials.