Fast Full-field Strain Measurement System

ABSTRACT:To address the Air Force need for a noncontact full-field real-time strain measurement system, Physical Optics Corporation (POC) proposes to develop a new Fast Full-Field Strain Measurement (3F-SM) system. This proposed system is based on a shearography technique with an instant phase shifting procedure and exploits a tunable shear interferometer which matches system sensitivity to the expected strain range. Specifically, the innovation in system design will enable measurements of in- and out-of-plane strains and airflow wavefront associated with extreme thermal and acoustic loading conditions. The airflow wavefront data are used for correcting strain maps. Thus, the 3F-SM system offers noncontacting 3D full-field strain assessment on high-temperature metallic and nonmetallic aerospace structures, which directly addresses the Air Force critical need for verification and validation of computational methods and models used for structural analysis, design, and reliability assessment. In Phase I, POC will demonstrate the feasibility of a lab prototype by accurately full-field mapping strain distributions in thermal and mechanically loaded specimens. In Phase II, POC plans to develop, and deliver a fully operational standalone 3F-SM system, and work closely with the Air Force to demonstrate its performance on component-level tests at combined thermo-acoustic-mechanical loads, to reach technology readiness level (TRL)-6.BENEFIT:In addition to full-field strain measurements of aerospace structures for military hypersonic vehicles, the 3F-SM system can be used for inspection of composite materials and parts in land-based propulsion and power-generation systems, particularly in the automotive, boating, and wind energy industries to find disbonds, delaminations, and voids. Replacement of metal parts by composite structures in key military and civilian applications increases performance, reduces corrosion and cost, increases life, and saves fuel. The weakness of composite materials lies in their multilayer structure. Hidden defects can lead to total mechanical failure of the parts. Thus, 100% inspection of composite elements is required for crucial applications. The proposed 3F-SM technique applied to nondestructive evaluation of composite structures will, therefore, bring immediate benefits.