Measurement of transient deformations by double‐pulsed holography

Holographic interferometry is used for the determination of surface deformation of items of equipment. The material failure which caused the surface deformation can then be identified. Because a double‐pulsed laser is used to plot the hologram, non‐vibration stabilized holographic equipment is necessary. Thus, non‐destructive testing of equipment components is also possible during plant operation. In this report, we present the experimental results of non‐destructive testing of composite materials. We examined centrifugally cast pipes and filament wound pipes, which were made from glass fibre reinforced plastic and carbon fibre reinforced graphite. As a rule, the severity of failure is characterized by the apparent perturbation of its holographically stored fringe pattern. In this report, we present the experimental results which yield the relationship between the perturbation of interference fringes and the extent of the specific types of failure. Measurement results were compared with displacements calculated by the finite element method. By using the interferogram, and with the knowledge of tension stress beneath the surface, the size of the crack can be estimated. The size of the smallest detectable flaw was clearly smaller than the critical flaw size. Thus, holographic interferometry is suitable for detecting damage to cylindrical containers.