(1) Lack of physical models in quantifying the relations between the SMFL signal and plastic deformation. As mentioned above, the MMM technique is developed for inspecting the initial damage or plastic deformation induced by the local stress concentration. Naturally, traditional magneto-elastic models [19–21] cannot describe such phenomenon. Although the newly developed magneto-plastic model [29] differentiated the actions of the elastic and plastic deformation on the magnetization of ferromagnetic materials, no direct relation- ship between the plastic strain and SMFL signal has been presented.
(2) Lack of quantitative criteria in capturing the features of defects.
There are only two qualitative criteria for which the tangen-
tial component Hp(x) reaches the maximum value, and the
normal component H (y) changes positive–negative symbols p
and thus has a zero in the location of maximum stress. Due to the lack of quantitative defect criteria, the MMM technique can only be used as an assistant tool to diagnose the possible dangerous zone presently. More accurate results must be determined by other techniques. In fact, there must be some quantitative relations between SMFL signals and defect char- acters in MMM tests. In this aspect, systematic experiments and numerical simulations should be performed.
(1) Lack of physical models in quantifying the relations between the SMFL signal and plastic deformation. As mentioned above, the MMM technique is developed for inspecting the initial damage or plastic deformation induced by the local stress concentration. Naturally, traditional magneto-elastic models [19–21] cannot describe such phenomenon. Although the newly developed magneto-plastic model [29] differentiated the actions of the elastic and plastic deformation on the magnetization of ferromagnetic materials, no direct relation- ship between the plastic strain and SMFL signal has been presented.(2) Lack of quantitative criteria in capturing the features of defects.There are only two qualitative criteria for which the tangen-tial component Hp(x) reaches the maximum value, and thenormal component H (y) changes positive–negative symbols pand thus has a zero in the location of maximum stress. Due to the lack of quantitative defect criteria, the MMM technique can only be used as an assistant tool to diagnose the possible dangerous zone presently. More accurate results must be determined by other techniques. In fact, there must be some quantitative relations between SMFL signals and defect char- acters in MMM tests. In this aspect, systematic experiments and numerical simulations should be performed.
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