Damage State Evaluation of X6CrNiNb18-10Alloys during Cyclic Deformation by Exploiting the Fractal Analysis of Ultrasonic Sampling Phased Array Backscatter Signals

In light of today’s problems concerning the life time of industrial components, scientists are searching for a commercially viable component control system to define the residual service. The understanding of the mechanisms leading to fracture is necessary to forecast the residual service time of metal constructions. A basic understanding of structural changes on different scaling levels is given by physical Mesomechanics. The plastic deformation and fracture of cyclically loaded materials is associated with the loss of stability, and is considered a relaxation process at different scales. The conventional approach of continuum mechanics describes this process on two levels, micro and macro. Mesomechanics fits between these two scales: the meso level. At this level and due to the high degree of freedom mainly in the near-surface areas, a new deformation structure, the so called mesostructure, develops. The hierarchical behavior of this structure leads to the hypothesis that the deformation structure is of fractal nature and the fractal dimension DF of the deformation structures should be a suitable parameter to characterize the material at different load phases. This approach offers a new concept for monitoring the material state by suitable nondestructive testing methods. The deformation structures of ferromagnetic steel were analyzed using surface topography and Barkhausen Noise signals [1]. In dependence of increasing loads, the derived parameter DF ensures a universal step-like behavior at three plateaus (levels). Thi