Fibre Bragg grating smart bolt monitoring creep in bolted GRP composite

We have carried out a long-term test of the tension in bolted glass fibre reinforced composite plates that shows that significant tension is left in such joints after one year, and that re-tightening is an option. The tests have provided valuable information that would be very difficult to obtain with conventional techniques, and are a success despite practical difficulties: The data are strongly affected by the thermal expansion of the composite, and we see large contributions from the insufficient adherence of the acrylate coating to glass fibre. With minor redesign the principle should be applicable to field monitoring.