Shearography is an optical interferometric technique derived from the technique of Holography. Shearography detects both surface- and hidden-defects by sensing abnormal strains induced by areas of weakness in the structure.
During testing, a shearogram (or the image of the laser illuminated surface of the object) is first recorded. After an incremental load is applied on the object, causing a small deformation of the illuminated surface, a second shearogram is recorded. Subsequent subtraction of the two images yields visible interference fringes that are related to surface strains.
Load can be applied by vacuum, heat or ultrasound.
Composite & Sandwich structures
Cracks, delaminations & disbonds to
hull, decks & superstructures. Panels, critical joints with stiffeners and other internal reinforcements.
Assessment of bond-lines between skin and core material.
Carbon fibre Mast & Spars
Cracks, delaminations, disbond within the main structure and at critical reinforcements.
Wood Composites
Delaminations between layers of cold-moulded constructions.
A limitation of shearography is the need to apply suitable stress-increments to the test object during inspection. Thick monolithic or extremely stiff structures might not permit this process.
