ESPI—a viable NDE tool for plant extension

Abstract

This paper reports on the ability of ESPI to detect in-plane displacements of a notched specimen, loaded in a 3-point bending method, particularly in the vicinity of the notch tip. Two different types of material were used for the specimens: perspex, a purely elastic material, and aluminium an elastic-plastic material. The results of the fringe pattern analyses were consistent with the expected behaviour of the material concerned from the start of the loading until failure. The events included necking, ductile tearing and permanent plastic deformation in the aluminium specimens, and brittle fracture in the perspex specimens. The paper also reports on the simulation of the ESPI method through the mechanics of a finite element analysis (FEA). The calculated fringe patterns can be helpful in the interpretation of the actual patterns obtained during an inspection and thus used to quantify the effects of the flaw. The example given here compares the patterns obtained from a pressure vessel model (cylinder) with axial and circumferential thumbnail cracks, to the patterns calculated using the finite element package ABAQUS.