Fig 1.
Fibre bridging phenomenon during delamination in a glass fibre specimen.
Fig 2.
Finite element method simulation: stress σ22 distribution at the fracture process zone (FPZ) for Mode I fracture.
Fig 3.
Illustration of bridging zone stress distribution.
(a) Crack tip singular stress field and (b) schematic of a bridging law: relationship between the normal stress, σn, and separation, δn, across the FPZ.
Fig 4.
Fibre Bragg grating response in a free state.
Fig 5.
Embedded FBG response to a uniform variation of strain and/or temperature.
Fig 6.
FBG response under a transverse force: Birefringent effect.
Fig 7.
FBG response under a non-uniform strain.
Fig 8.
Different stages of the FBG response under a crack growth event.
Fig 9.
Constitutive behaviour of the cohesive element.
Fig 10.
Double cantilever beam geometry dimensions.
Table 1.
Double cantilever beam material properties.
Fig 11.
FEM simulation of different fracture modes in a DCB specimen.
Fig 12.
Mesh resolution study: cohesive zone and the stress/strain variation along the grating length.
Table 2.
Mesh resolution and result convergence study.
Fig 13.
Algorithm applied to the FEM model to obtain the FBG output prediction.
Fig 14.
FBG measurement point in the FEM model.
Table 3.
Fibre Bragg Grating Parameters.
Fig 15.
FBG sensor output simulation under crack growth: Mode I, II and mixed Mode fracture.
Fig 16.
FBG sensor position analysis scheme.
Fig 17.
a) Sensor output for Mode I fracture. b) Sensor output for Mode II fracture.
Fig 18.
Scheme of the three modes of loading that can be applied to a crack.
Fig 19.
Homogeneous mixed mode specimen scheme.
Fig 20.
Schematic illustration of the double cantilever beam test set-up.
Fig 21.
Sketch of the specimen geometry and FBG sensor position.
Fig 22.
DIC pattern painted on the side surface of the DCB specimen.
Fig 23.
Algorithm for calculating the wavelength shift Δλb and the width variation of the reflected peak ΔλWV from the reflected optical spectrum.
Fig 24.
Fracture modes addressed in the DCB testing.
Table 4.
Fracture Modes Tested.
Fig 25.
Crack face in the DCB specimen.
Fig 26.
FBG sensor output during crack growth in Mode II.
a) Before crack initiation; b) crack growth: compression field at grating position; c) crack growth: non-uniform strain at grating position; and d) crack growth and passing all grating length.
Fig 27.
Embedded FBG sensor output in a DCB specimen under Mode I fracture testing: numerical and experimental results.
Fig 28.
Embedded FBG sensor output in a DCB specimen under Mixed Mode fracture testing: numerical and experimental results.
Fig 29.
Embedded FBG sensor output in a DCB specimen under Mode II fracture testing: numerical and experimental results.