Study On The Creep And Microscopic Mechanism Under Low Stress Repeated Impact Of Metallic Metal

Impact load refers to the high-speed load applied to the object. Because of the characteristics of impact load, the material will go cumulative macro-plastic deformation under even below 20%-50% of its yield point. As it deformation law is similar to the creep deformation, so this type of accumulated plastic deformation under the normal temperature and low stress repeated impact load is defined as"repeated impact creep". This paper studies the plastic deformation principle of 1Cr18Ni9Ti stainless steel under the low stress repeated impact load and discusses its microcosmic mechanism. Base on these researches, a mathematical model relevant to the plastic deformation is established.We firstly make experiments with 1Cr18Ni9Ti stainless steel which is always used in the fields of nuclear power station and chemical industry, under the following test condition of 4HZ repeated impact frequency and 100MPa repeated impact stress. According to the experimental data, we draw a curve related to average strain rate, accumulated strain, layer depth and impact times of the testing object. The data analysis shows that the plastic repeated impact accumulation only occurs at the section below the impact surface, and the deformation has the characters of skin effect, time nonlinearity and space nonlinearity, which explains that the testing object has the maximum strain rate on the surface and the value decreases until to zero with the impact times and layer depth increasing. It is also found that the growth rate of accumulated deformation reduces with the increase of impact times, and the accumulated deformation stops until the impact reaches a amount of times, keeping a stable state. Under some assumed conditions, a strain rate model of 1Cr18Ni9Ti stainless steel is established primarily by the duality return analysis.Based on the test data and the microstructure analysis of the testing object, this paper puts forward a dislocation slipping theory on the basis of dislocation vibration superposition principle, establishes a dislocation slipping micro model under repeated impact and analyzes it with test data. The Analysis result shows that the strain rate depends on the material properties, impact frequency, impact velocity and impact times.