Experimental investigation of defects influence on composites sandwich panels strength using digital image correlation and infrared thermography methods

The article is devoted to the experimental investigation of the defects influence on the residual strength of composites structure, as well as the possibility of using local repair operations. The objects of research are structurally similar elements of acoustical sandwich panels after a local repair of defects, such as through breakdown. The specimens were produced by serial technology from a fiberglass prepreg. Research was carried out using a universal electromechanical system Instron 5982 and servo-hydraulic system Instron 8801. For the analysis of the stress-strain state of the deformable elements the authors used the non-contact three-dimensional digital optical system Vic-3D, the mathematical apparatus which is based on the method of digital image correlation (DIC). To control the internal geometry of the specimen and assess the possible defect inspection infrared thermal imaging system FLIR SC7000 was used. The techniques of joint use of testing and measuring systems under static and cyclic tests were offered. For comparison, the repaired sandwich panel specimens were tested in tension and in tension under a preliminary cyclic loading with the registration of the deformation fields and thermal images. Their deformation and fracture mechanisms are analyzed, and their loading diagrams are obtained. The experimental data was obtained from the Vic3d system study of the evolution inhomogeneous fields of axial and transverse deformation on the surface of repaired sandwich panels under static loading and cyclic tests. By using infrared thermal imaging system internal structure, processes of the defects development and the temperature distribution on the surface of the test specimen were detected.