Composite Failure Detection in π-Joint Structure Using Fiber Bragg Grating Sensors

The use of composite structures in engineering applications has proliferated over the past few decades. This is mainly due to their distinct advantages of high structural performance, high corrosion resistance, high strength and weight ratio. They are however prone to fiber breakage, matrix cracking and delaminations which are often invisible. Although there are systems to detect such damage, the characterization of the damage is often much more difficult to achieve. A study is presented of the damage detection of a carbon fiber composite π-joint structure under bending loads using fiber Bragg grating sensor. Firstly, based on the general FEM software, the 3-D finite element model of composite π-joint is established, the failure process and every lamina failure load of composite π-joint were investigated by maximum stress criteria. Then, strain distributions belong the length of fiber Bragg grating were extracted, the reflection spectra of fiber Bragg grating have been calculated according to the strain distribution. Finally, to verify the numerical results, a test scheme was performed and the experimental spectra of fiber Bragg grating were recorded. The experimental results indicate that the failure sequence and the corresponding critical loads of failure were consistent with numerical predictions and the computational error of failure load is less 6.4%. Furthermore, it also verified the feasibility of the damage detection system.