Noncontact Ultrasonic Measurement Technique for Surface Stress Distribution

Improved methods are required to measure surface stress in the structural design, evaluation, and monitoring of naval ship structures. The method should be capable of noncontact measuring of surface stresses, scanning and recording stress fields due to static and dynamic loads, and producing color stress plots which can be compared to finite element analysis. A portable PC-based ultrasonic C-scan instrument with air-coupled transducers is proposed to meet these specifications. Ultrasonics provides a direct relationship between the elastic properties of materials, which encompasses stress, and sound wave propagation. This relationship is readily modeled, predicted, and quantified using finite element analysis. Phase I will demonstrate feasibility of a noncontact ultrasonic method to measure surface stress distribution on naval structures. This will lead to the development, during Phase II, of a prototype instrument for use on naval structures in shipyard, shipboard, and laboratory environments.