Analysis Of Fracture Characteristics Of Gradient Material Under Mechanical Load And Thermal Load

As a kind of multiphase material,the functionally graded material has a continuous change in the space,with good heat and relaxation,corrosion resistance,high strength and good photoelectric effect,more and more attracts attention of the scholars.Because of its mechanical properties and composition of the continuity of change,different materials which are connected with the functional gradient of materials can reduce or even eliminate their physical properties and chemical properties of the mutation to reduce stress concentration,the good performance is what people are pursuing.the more and more applications to the aviation,space flight and other sophisticated areas.Due to the complexity of the environment,functional gradient material components of the service time and service quality is particularly important in the service period,during this period a variety of defects on the surface inevitably produceunder mechanical load and thermal load,the occurrence of cracks greatly reduce the service life of the material components.It is of practical significance to study the initiation and expansion of cracks to reduce the harm caused by the faults.In this thesis,the finite element model of the V-notch root crack of the functionally graded material is established under the mechanical load of the functional gradient plate.The stress of the crack tip of the crack in the middle is numerically analyzed.The relationship between the stress field and the angle α of the notch and the gradient parameter β is presented.Then,the propagation path of the G-shaped notch root crack is simulated in ABAQUS,and its relationship with the gradient parameters is discussed.Finally,the stress intensity factor K of the functionally graded material plate with elliptical crack under the thermal load is analyzed along the crack front.The research contents and achievements of this paper are as follows:(1)The equivalent stress,displacement and stress intensity factor of the crack tip in Surface crack front of the root crack under the mechanical load increase with the increase of the gradient parameter β,the stress intensity factor K decreases with the increase of the opening angle α range from 0° to 60° reduce slowly,and decreases range from 60° to 90° obviously,when the α is greater than 90°,stress intensity factor K decreases rapidly.Under the impact step load,the dynamic stress intensity factor issmaller as the gradient parameter β increases.(2)The deflection angle of the root crack decreases with the increase of the gradient parameter β under the mechanical load,that is,the slope of the extended path is getting lower and lower,and when the gap with two cracks,the cracks start to deflect toward the base side.To a certain extent,the cracks are attracted to each other more than the impact of material parameters and parallel to the close.(3)Under the action of thermal load,compressive stress is generated near the relatively high temperature region,and the tensile stress is generated from the high temperature region or near the low temperature region,which leads to the opening or closing of the crack surface.The larger the temperature gradient is the effect of opening or closing,the more obvious.Under the thermal load,the thermal stress intensity factor K decreases with the increase of Φ for any temperature gradient,that is,the stress intensity factor at the deepest point of the crack is the smallest.Under the thermal load,the thermal stress intensity factor K increases with Φ,that’s means that the stress intensity factor at the deepest point of the crack is the largest.