Abstract
Impulse hammer measurements on steel plates were carried out to clarify the potential of a new technique of thickness estimation using a hammering test during a hull inspection. Load signals of an impulse hammer with a impact speed control jig were recorded with a digital oscilloscope and a personal computer. We investigated relationships between characteristic values (impact, peak load, half value width, min-max ratio - the absolute ratio of minimum value to maximum value of differential load signal) of the load signals and thickness. We obtained 4th order polynomial expressions which transform characteristic values to thickness, and examined their effectiveness using 35 load signals picked up on 1m x 1m steel plates of different thickness. The thickness estimation with the impact value was proved to have the smallest estimation error among 4 characteristic values.
We also examined the effect of slit, fillet weld, impact speed, hammer weight, paint layer and surface roughness caused by corrosion to our thickness estimation technique and found the extent of the effective estimation.
