Dynamic ESPI measurements for mechanical characterization of pipes

The use of electronic speckle pattern interferometry (ESPI) for non-destructive characterization of unplasticised Polyvinylchloride (uPVC) pipes is presented. When pipes are inflated slightly by internal pressurization ESPI may then be used to measure the resulting displacement over the area imaged by the video camera. The interferometric method used is non-contact and gives high-confidence results for strain and Young's modulus of thick PVC pipes. As a step towards using ESPI in dynamic rather than static applications, the ESPI data were recorded during the application of pressure increase. At the same time the change in pressure in the pipe was monitored using a pressure transducer and a specially written Labview Program so that the deformation caused could be modelled using Finite Element Analysis. A finite element model was developed for prediction of the mechanical behavior of the pipes undergoing transient pressure change. The model data have been used here for comparison with ESPI results for slow dynamic deformation of the pipe under test. Demonstration of the possibility of carrying out similar analyses in a dynamic system will greatly expand the applications for this technique.