Deformation characteristics of composite laminates—part I: speckle interferometry and embedded Bragg grating sensor measurements

An experimental method is presented to determine the mechanical behaviour of composite laminated plates subjected to bending. Cross-ply glass-polypropylene laminates are equipped with fibre-optic sensors situated centrally in the plates, at various locations through the thickness. Characterization tests are first carried out to verify specimen quality and ensure reproducibility in the global mechanical response. The influence of the embedded optical fibres upon specimen properties is also assessed. Electronic speckle-pattern interferometry and the embedded fibre optic sensors are then used in a combined manner to reach a full understanding of the specimen deformation behaviour in three-point bending tests. In- and out-of-plane speckle interferometry is employed to measure full-field displacements and strain on the surface of the plates, while the strain distribution through the thickness is derived using embedded fibre Bragg grating sensors. The distribution is found to be nonlinear for the greatest of the chosen plate thicknesses.