Effect of fiber reinforcement on the low velocity impact behaviour of woven fabric reinforced composites: integrated contribution of the thermographic, interferometric and speckle inspections

As it is the case for some parts or structures assembled from common isotropic engineering materials, fiber reinforced composites can be subjected to impact loading during their service life. Fiber composites have, nevertheless, a unique interaction with the externally applied load, since severe internal damages can be generated without any external indication. In fact, several damage mechanisms can be operating, viz. matrix cracking, fibre breakage, fibre pullout, fibre-matrix debonding and delamination. The challenge of non-destructive quality control is to establish safe boundaries for the use of a composite part or structure, which has been subjected to an impact event not causing non-repairable failure. The composite response to impact in a range of velocities is affected by a number of parameters. These include e.g., the mass and the geometry of the impactor, the laminate stacking sequence and the kind, architecture and volume of reinforcement fibres. In our work, we focused our attention on two woven fabric reinforced composites: one reinforced with E-glass fibres and the other with basalt ones, both subjected to low velocity impact at different energies. The damage generated has been evaluated non-destructively by means of three techniques, namely Square Pulse Thermography (SPT), Digital Speckle Photography (DSP) and Holographic Interferometry (HI) with the intention of providing supplementary and integrated results. An external source of energy (a lamp of 500 W in reflection mode) is used to produce a thermal contrast between the non-defective and the defective material to detect and quantify the degree of surface and subsurface damage. The experimental results obtained by the integrated application of these techniques demonstrate that is possible to detect delamination-type defects and to assess the impact severity on composite materials with glass and basalt fibres.