Multi-axial strain transfer from laminated CFRP composites to embedded Bragg sensor: II. Experimental validation

Embedded optical fibre sensors are considered in numerous applications for structural health monitoring purposes. Since the optical fibre and the host material in which it is embedded have different material properties, the strain in both materials will not be equal when external load is applied. Therefore, the strain transfer from the host material to the embedded sensor (optical fibre) was studied in more detail in the first part of the paper. This second part presents an experimental evaluation of the response of uni-axial fibre Bragg grating sensors embedded in small cross-ply composite laminates subjected to out-of-plane transverse loading. This loading case induces high birefringence effects in the core of the optical fibre. Using the numerically determined strain transfer coefficients (Luyckx et al 2010 Smart. Mater. Struct. 19 105017) together with multi-axial strain formulations, the authors were able to measure with reasonable accuracy the total strain field inside a carbon fibre reinforced plastic specimen.