The use of shearography for nondestructive evaluation of damage in green composite laminates

Recently, increased awareness of the environmental disaster due to the inappropriate disposal of plastic items for private and industrial use, pushed both academic and industrial research towards the identification of new environmentally sustainable materials based on renewable resources. In this frame, promising results have been found looking at nature: biobased resins loaded with substances of natural origin such as vegetable fibers, lignocellulosic fillers and inert mineral particles (silica, talc, clays, and so on). Composites are characterized by several interacting failure modes such as matrix breakage, fiber failure and delamination and these new materials have a greater complexity, so it is important to have effective testing and control methods available. In this work, “green” composite materials based on flax, jute and basalt fibers and potentially usable for applications in the naval and automotive field, have been evaluated by means of shearography. Specimens of adequate size were subjected to different mechanical tests under dynamic conditions and non-destructive evaluation to investigate the damage response validating their use in specific applications. The shearography technique belongs to the interferometric optical methods and works through real-time surface illumination by visible laser (i.e. 660 nm). It records the surface field differential displacement, due to a thermal or mechanical perturbation and the range and the accuracy are related to the wavelength. This technique allows the non-contact and non-destructive detection of micro-deformations, micro-cracks, residual stress and delamination. Using a cmos sensor, the whole field deformation is recorded into an image to be processed thus obtaining a displacement map.