Microstructural material characterization of hypervelocity-impact-induced pitting damage

Nonlinear ultrasonic evaluation of disorderedly clustered pitting damage using an in situ sensor network

“…The intrinsic material nonlinearity refers to the intrinsic nonlinear elasticity of lattices, while the geometric nonlinearity is owing to the mathematic relation between the Eulerian coordinates and Lagrangian (material) coordinates. In the model, the nonlinearity is depicted using a three-dimensional (3-D) stress-strain relation with a second-order approximation 38 , as ( 1 2 ) Morphological analysis, conducted by the authors in their earlier study 6 , reveals that in a typical pitted region, on top of a large quantity of macro-scale craters and cracks, diverse microstructural changes, for instance micro-voids, micro-cracks, recrystallized fine grains and dislocations, co-exist, as observed in the example shown in Figure 2. These recrystallized fine grains, dislocation substructures and shock hardening jointly lead to an increase in material plasticity and hence intensification in material nonlinearity 35,36,42,43 .…”

“…Scanning electron microscope (SEM, JEOL JSM-6490) image of material microstructure underneath a pitted region produced by a hypervelocity debris cloud. 6 features time-dependent traits and initiate high-order harmonics. The in-plane displacement (U SÀ2f 0 n ) of CISS-induced n th -order symmetric modes at the double excitation frequency (2f 0 ) can be ascertained as 32,33…”

“…The in-plane displacements of both the 0°phase and 180°out-of-phase inverted GUWs are extracted at the measurement points and processed with an pulseinversion approach, with which the weak nonlinearity (i.e. U SÀ2f 0 n in equation (6)) stands out in the superimposed signals and in spectra (obtained via the shorttime Fourier transform (STFT)).…”

“…Pitting damage is a prevailing modality of material lesion in engineering assets. Amid numerous examples are pitting corrosion in maritime structures [1][2][3] , electrical pitting in bearings 4,5 , pitting craters in orbiting spacecraft induced by space junk or debris clouds [6][7][8] .…”

“…Amid numerous examples are pitting corrosion in maritime structures, [1][2][3] electrical pitting in bearings, 4,5 and pitting craters in orbiting spacecraft induced by space junk or debris clouds. [6][7][8] Material degradation and deterioration caused by pitting damage, usually initiated at an unperceivable scale but progressing at an alarming speed, can fairly compromise structural reliability, integrity, and performance and, without timely awareness, lead to fragmentation and even failure of the entire system. This has entailed early detection of pitting damage and accurate assessment of its severity, on which basis follow-up remedial measures can be implemented.…”