Modelling of fibre Bragg grating sensor plates

In this paper is presented the design of a composite sensor plate, based on fibre Bragg grating (FBG) sensors, to be used as alternative to the conventional electric strain gages. The use of such composite sensor plate will permit to profit of FBG sensors advantages compared to conventional electrical strain gages increasing its safety considering that they are commonly simply surface mounted in structure using adhesives.

Here, contrarily to what is traditionally performed, FBG sensors are embedded in thin (0.4 mm of thickness) weaved carbon fibre reinforced composite plates. The FBG sensor is hence not oriented parallel to the surrounding reinforcement. Such configuration is known to induce changes on the reflected optical power spectrum of the FBG sensor resulting in an inaccurate answer. A methodology was then developed to guarantee that the resulting FBG sensor optical power spectrum didn’t exhibit any aspect change. The resulting composite sensor plate was mounted on the surface of a composite specimen which was submitted to tensile loading.

The axial strain answer of the composite plate sensor is compared to the answer of an electrical strain gage. A three dimensional finite element study is proposed to understand the relation between the strain measured by the FBG sensor and the strain imposed to the host plate and especially the consequence of using such composite sensor plate on the behaviour of tensile test specimen. The benefits and drawbacks of the use of composite sensor plate are then discussed in light of these results.