A simplified method for mapping samples with a fringes pattern in laser shearography

Abstract

Shearography is a non-invasive inspection technique that measures surface deformations by processing two replicate images obtained from an illuminated sample using coherent light beams. These beams are intentionally shifted relative to each other (shear) during the process. Shearography has a wide range of applications, from simple laboratory experiments to complex scenarios in the aerospace industry. In the field of composite materials, shearography serves as a valuable qualitative technique for detecting defects such as delaminations, cracks, and detachments. It offers the advantage of being immune to harsh environmental conditions, making it suitable for both laboratory and field measurements. However, commercially available shearography equipment often comes with a high price tag, making it unaffordable for many research laboratories and small businesses. As a result, there is a growing interest in developing cost-effective shearography setups using readily available optical components and integrated image acquisition systems. However, these setups require a deeper under standing of the technique and proper image processing techniques. In this study, we present a simple method for interpreting information obtained from basic shearography setups. Specifically, we address a common scenario where the distance of illumination and observation does not meet the requirement of being greater than the lateral shear separation. We describe a typical shearography setup applied to measure lateral deformations in epoxy resin samples and outline the straightforward steps for obtaining shear images or shearograms for subsequent analysis. The conclusions drawn from this work can be applied to a wide variety of materials and deformation strategies. The procedures presented here can be easily implemented to develop powerful and customizable shearography instruments for field applications, tailored to the specific requirements of users.