Stress Concentration Detection And Fatigue Damage Assessment Based On The Metal Magnetic Memory Technique

Metal magnetic memory testing technology is like pulse of traditional Chinesemedicine diagnosis patient, the detection process does not require additionalexcitation signal, through the probe receiving component itself out of the feedbacksignal (surface leakage magnetic field) of component to the stress distribution,internal damage evaluation, the signal can reflect the true effective internalcomponents to stress concentration of character of early damage.This paper, based on the electromagnetism and stress-magnetic conductance theory,ANSYS finite element software to20#steel stress-magnetic simulation. To differentspecimens, different load, the surface of the different paths leakage magnetic fielddata is analyzed, and the results show that: the magnetic memory signal distributionand stress distribution has good correspondence, along with the increase of stressconcentration degree, magnetic memory the more obvious signal, the greater the value.The20#steel tensile loading test, the results show that the stress concentration ofsurface defects high degree around magnetic memory signal apparently, and lowdegree of stress concentration of surface defects magnetic memory signal is notobvious or no magnetic memory characteristic signal, the simulation results and testthe same. Magnetic memory signals that can be used to characterize the stressconcentration degree of ferromagnetic materials, able to the harm of the defect levelsbetter evaluation.To45#steel center crack sample and40Cr three-point bend specimens in under theconditions of fatigue crack propagation under test. In the study, extraction cyclesdifferent under the surface crack tip leakage magnetic field distribution. Through thestatistical analysis and comparison, the extraction can reflect material fatigue damageof the magnetic memory characteristic parameters of the signal, the parameters in thewhole of crack propagation can be divided into three stages, including45#steelcenter crack tensile fatigue tests: the first stage (0-180000times) magnetic memorythe signal features faster speed increase; The second stage (18-1million times) stableslow increase; The third stage (100-1.092million times) dramatic increase. Throughthe analysis found that, magnetic memory signal characteristic parameters and brokenmechanical parameters of crack (crack growth rate, the stress intensity factor rangebetween good correlation, and make use of the relationship between the two Pairs ofthe parameters of the formula estimating value. Set up with magnetic memory signalsof fatigue damage parameter for evaluation model, when more than0.85degree, crackfast expand, this model can better response material fatigue damage. After the test, to40Cr three point bending fatigue specimen for the section of SEM electronmicroscope scanning, observe the fatigue fractures and microstructure characteristics,analyzes fatigue crack propagation and fracture mechanism. This paper for the metalmagnetic memory testing technology is used in the fatigue damage assessment and remaining life prediction providing basic research field.