Smart Textiles: Evaluation of Fiber Optic Sensors Embedded in 3 D Orthogonal Woven Composites and their Impact on the Host Structure Integrity

3D woven preforms are known for their advantages over the nonwoven and 2D woven preforms in that they provide higher resistance to crack propagation, eliminate delamination, faster in resin transfer, and higher fiber volume fraction. These types of structures are being implemented in different field and have the potential in numerous applications such as aerospace, civil engineering, transportation, and wind mills. With the increase in the awareness of safety, the need of Structure Health Monitoring system that can detect the damage and monitor structure behavior to predict the potential damage is increased. Due to the straight path of the constituents of the 3D orthogonal woven structures, they are excellent host for optic fiber sensors.;The main goal of this research is to evaluate different types of optic fibers and identify their potential use as sensors for predicting composite structure failure. This research is focused on relatively newly developed graded index, perfluorinated POF (GI-PF-POF) as potential embedded sensors. End to end loss and backscattering techniques using Optical Time Domain Reflectometer (OTDR) were used to investigate and characterize sensing properties of embedded optical sensors. In this dissertation, literatures are reviewed in chapter 2 research objectives are presented in Chapter 3.;Chapter 4 reports a study structured to evaluate the effect of the macrobending optical fibers on signal power integrity to identify its capability as integrated sensors into fiber reinforced composites. Newly developed Graded Index Perfluorinated POF (GI-PF-POF) and two types of SOFs were evaluated in 3-point macrobending test bed using laser light source. The relationships between the optic fibers signal loss and bending radius, bending deflection and wrap angle around the middle rod were established. The results showed that POF provides higher sensitivity and range of bending deflection compared to SOF. The work also unveiled the bending radius of optical fibers at which minimum or no signal loss occurred.;In Chapter 5, the effect of Vinylester and Epoxy resin systems on the signal loss of embedded perfluorinated, graded index POFs were measured. OTDR was used to monitor the signal attenuation and backscattering level of the POFs throughout the resin curing cycle. FTIR and optical analyses were also conducted to assess the results. Results showed that vinylester resin caused a significant increase in the backscattering level of POF sensors and therefore induced high fiber signal losses. On the other hand, the POF treated with Epoxy showed no change in backscattering level indicating no chemical or physical change had occurred to POF.;Chapter 6 presents systemic investigation to find out whether incorporating POF into 3D orthogonal woven composites affects their structure integrity and performance characteristics. Range of 3D orthogonal woven composites with different number of layers and different weft densities was fabricated with and without POF. Results revealed that the tensile and bending properties of 3D orthogonal woven composites were not affected by the presence of POF.;Chapters 7 report study designed to evaluate POF as an embedded sensors in 3D orthogonal woven composite structures. The evaluation included the sensor response during manufacturing process and under bending and repeated impact tests using OTDR. Results indicate minor effect of weave structures on POF signal loss and increase in signal loss as curing time increases. Under bending loads, signal loss increase as load increase until structure fails. POF recovered and loss decreased after unloading. Impact results indicate that different configuration of 3D orthogonal woven composite structure has different response on POF signal loss. Deformation of composite under impact tests transferred throughout the structures to POF. As signal loss at failure location increase as the distance that can be monitored decreases. While each of Chapters 4-7 includes a conclusion specific to the study covered in each chapter, Chapter 8 covers the overall conclusion based on the entire findings of the research. Abbreviation, Definition related to optic fiber, and OTDR specifications are included in appendix C, D, and F respectively.