Structural health monitoring of Adhesive joints using Optical fibres

Due to an increase in the usage of composites in the world of engineering in the past few decades, a rise has been observed in research related to the joining processes, especially, between composite parts. This thesis is mainly focused on Structural Health Monitoring (SHM) in composite single-lap joints (SLJ). ADEKIT A236/H6236 has been used as the polyurethane adhesive manufactured by SIKA (CH) company and the adherends were made of carbon fibre/epoxy prepreg woven, named XPREG XC130. The backface strain on SLJ was measured employing two different methods at the same time: the optic fibres (LUNA ODISI-B) and Digital Image Correlation (DIC). Additionally, dimensional parameters of the joints (overlap length and adherend thickness) have been varied and consequently, the effect of these has been monitored in terms of loading conditions and strain magnitudes. Furthermore, the results obtained from both methodologies used to measure the backface strain showed that there is a point on the surface of SLJ that records a zero strain up to the point where the damage starts occurring in the joint. Afterwards, this zero-strain point starts obtaining strain up to the joint failure.