Measurement of Potential Drop Distribution by Scanning the Closely Coupled Probes Sensor for Sensitive NDE of Shallow Surface Cracks

Highly sensitive nondestructive evaluation of shallow surface cracks is realized through the distributions of d-c potential drop obtained by scanning the closely coupled four-point-probes sensor around the crack. A methodology is developed for evaluating the depth and length of a three-dimensional surface crack from the potential drop profiles measured across and along the crack, where the experimental result is compared with the corresponding prediction of finite element analysis. The highly sensitive characteristic of the measured profiles is also extended to the potential drop imaging for identifying the location of cracks in a clear pictorial form. It is verified that the method is a powerful tool for characterizing very small fatigue cracks (sub-millimeter depth) on the surface of metallic structures

Relationship between the length of panel side and the deflection of sandwich panels with corrugated core

This paper reports the relationship between the length of panel side and the deflection of the sandwich panels with corrugated core. The deflections of the sandwich panels having the lengths of panel side from 100 to 1300 mm and the height of the panel of 13.6 mm were determined by finite element method, where the four sides of the panel were rigidly fixed and a uniformly distributed load was applied to the top surface of the panel. The maximum deflection at the center of the panel increases with increasing the length of panel side, confirming that a power law is established between the length of panel side and the deflection. The scaling exponent of the sandwich panel was about 3.3 and this value was smaller than that of the single plate, i.e., 4. The ratio of the weight of the sandwich panel to that of the single plate having the same length of the panel side and the different thickness, which becomes same deflection compared to the sandwich panel, was found to be smaller as the length of the panel side becomes longer. This effect of weight reduction was possible to be estimated analytically. Smaller value of scaling exponent of the sandwich panel compared to that of single plate was found be related with that the normal force applied to the panel was effectively converted to the shear force at the bonding interface between the core and the bottom plate