Structural health monitoring of composite materials with FBG sensors: damage detection and remaining useful life prediction

Advanced composites are widely employed in load bearing structures due to their high strength-to-weight ratios, stiffness, corrosion resistance and fatigue performance. Monitoring the manufacturing process and detecting the damage during service are rather troublesome. In this study, practicality and feasibility of fiber optic based sensors are evaluated for monitoring the state or the structural health of the composite materials from manufacturing phase to service phase continuously. 2D and 3D composite structures were designed and manufactured by resin transfer molding (RTM) method. A novel ingress/egress technique is utilized to embed the fiber optic sensors. The capabilities of fow and cure monitoring of fiber Bragg grating (FBG) sensors are presented. The strain and the temperature sensitivity of the embedded FBG sensors was calculated. Following the calculation of the sensitivities, a manufactured composite with embedded FBG sensor is subjected to cantilever beam experiments. To be able to show that the FBG sensor is capable of detecting damage formation in composites, the composite plate was drilled to create artificial defects of different size. The wavelength shift of the FBG was monitored as a function of the size of the hole and wavelength measurements are compared with those of sound structure to conclude on the health of the structure. Technique for prediction of remaining useful life (RUL) of composite materials with embedded FBG sensors is demonstrated and fatigue testing of composite materials are performed to verify this technique

Diesel engine NOx emission modeling with airpath input channels

Stringent international regulations in terms of emissions necessitate more efficient transient calibration procedures for diesel engines which in turn implies utilization of dynamic models of the combustion process. In this paper, a novel input design framework in terms of multi-sweep chirp signals is developed and airpath input channels are excited by designed chirp signals. Linear and nonlinear system identification methods are utilized to model NOx emissions with airpath input channels. Experimental results show that while linear identification techniques provide poor performance in terms of training and validation fits, nonlinear models achieve remarkable performance in training and validation fits

Prediction of fatigue response of composite structures by monitoring the strain energy release rate with embedded fiber Bragg gratings

Composite materials are becoming increasingly more valuable due to their high specific strength and stiffness. Currently, most components are operated for a number of service cycles and then replaced regardless of their actual condition. Embedded fiber Bragg gratings are under investigation for monitoring these components in real time and estimating their remaining life. This article presents research conducted on a novel technique for prediction of the remaining life of composites under fatigue loading using embedded fiber Bragg grating sensors. A prediction is made of the remaining life at every cycle based on data collected from the sensors and the previous loading history

Fiber Bragg grating and etched optic sensors for flow and cure monitoring of resin transfer molded composite structures

In this study, we present the research conducted on in situ process monitoring (cure and flow) of resin transfer molded glass fiber reinforced polymer composites using fiber Bragg grating (FBG), and etched bare fiber optic sensors. Both FBG and etched fiber sensors are embedded into glass fiber reinforced composites manufactured by the Resin Transfer Molding (RTM) method, and are used to monitor the flow front during the resin injection process and subsequently the cure cycle. The results of this study have shown that both the FBG and etched sensors can be used efficiently for flow and cure monitoring in the RTM process. The experimental results of etched sensors are in accordance with those of FBG sensors for cure monitoring

Fatigue monitoring of glass fiber reinforced composite using fiber Bragg grating

Glass fiber reinforced composite (GFRC) are widely used in all load bearing industrial applications. It is therefore critical to understand the fatigue characteristic of GFRC to improve the material characteristics of these composites and to prevent any untoward accidents. In this paper we describe the preliminary results of fatigue test on GFRC fabricated using an in-house laboratory scale resin transfer molding system. The fatigue tests are done for different load conditions – tension compression and reverse bending. Fiber Bragg grating (FBG) is embedded into the composite at the manufacturing step for monitoring the strain. The preliminary results of these experiments are presented