Kara Peters

The goal of this project is to investigate three new approaches to maximize the energy converted from symmetric and antisymmetric Lamb waves into an optical fiber longitudinal mode for detection with an FBG sensor. In particular, the coupling physics of each approach will be probed numerically and experimentally. Many aspects of each of the individual approaches could be combined in an actual structural health monitoring system, therefore three approaches are not mutually exclusive.

The NSF IUCRC for Integration of Composites into Infrastructure (CICI) is specialized at innovating advanced fiber-reinforced polymer (FRP) composites and techniques for the rapid repair, strengthening or replacement of highway, railway, waterway, bridge, building, pipeline and other critical civil infrastructure. The Center consists of West Virginia University (WVU) as the lead institution in the current Phase II, with North Carolina State University (NCSU), the University of Miami (UM), and the University of Texas at Arlington (UTA) as partner university sites. The primary objective of the Center is to accelerate the adoption of polymer composites and innovative construction materials into infrastructure through joint research programs between the university sites in collaboration with the composites and construction industries. In Phase III, CICI aims to broaden its scope of research in composites to include: 1) nondestructive testing methods; 2) manufacturing techniques, such as 3D printing; 3) inspection techniques, such as the use of drones with high resolution cameras; 4) in-situ modifications of infrastructure systems, resulting in enhanced durability and thermo-mechanical properties; and 5) cost-effective recycling of high value composites.

Many of the fibers in production are naturally birefringent materials, which allows us to reveal the internal stresses, defects and non-uniformities that are developed in the fibers during production through optical polarization imaging. We will use a custom high-speed polarized imaging system to monitor the initiation and propagation of fiber defects during production. By varying the processing parameters, we can observe the evolution of the defects and non-uniformities and determine what parameters affect their development. The details of this research will provide understanding of the key limitations to speeding up production and in-situ feedback within fiber spinning equipment lines.

The goal of this NEUP infrastructure project is to acquire a state-of-the-art high resolution scanning acoustic microscopy system to enhance NCSU’s educational and research capabilities in high throughput characterization of nuclear fuels, nuclear sensor materials, cladding materials, reactor structural materials and 3D printed components.

This proposal addresses the high efficiency generation of acoustic modes in and low attenuation propagation through optical fibers. Applying the proposed sensor technology to structural health monitoring of large structures introduces the multiple challenges of adequately covering surface areas of complex structures, adapting to changes in the structure over the lifetime of the structure, and providing localized, high-resolution imaging of structural defects in regions not necessarily known a-priori.

The study of bi-material interfaces and interphase regions is important for many soft material applications. The performance of thin polymer films and multi-layer films depends highly on the gradient of material properties through the thickness of the film. These properties are altered relative to the bulk material due to chemical interactions with substrate or other material and geometric confinement. The proposed research will investigate an experimental technique, based on 3D micro-laser Doppler vibrometry, to measure both the material property gradients in the interphase region and the quality of adhesion at the interface.

In this proposal, we propose to investigate the direct collection of acoustic signals using the optical fiber simply as an acoustic waveguide and to couple the acoustic information to an already existing sensing optical fiber with FGBs through an acoustic coupler. The coupler does not require cleaving or splicing of the existing optical fiber in order to process the new acoustic information with the FBG sensors. We will design, model and experimentally demonstrate a 2 x 2 acoustic coupler where the amplitude of the two output channels can be independently designed.

The goal of this project is to investigate the unusual behaviors observed in Lamb wave to optical fiber guided mode coupling. First, these modes will be mapped out in the structure, in the transition zone and in the optical fiber using a 3D micro-scale laser Doppler vibrometer. In particular, the conditions that launch forward and backward longitudinal modes in the optical fiber will be studied, in order to better understand the conditions that create directional behaviors. Next, additional components will be added into the bond region, for example protective tubing to identify potential interactions between the different components. Finally, interactions between the forward and backward longitudinal modes propagating in a single optical fiber will be forced to create hardware level signal processing for structural health monitoring.

Quantifying the role of different bond parameters on the sensitivity of FBG sensors to surface ultrasonic and acoustic emission waves and optimizing their performance as sensors, requires an integrated experimental, characterization and computational effort. This research project will investigate the role of viscosity on the measured signal amplitude and distortion in a FBG coupled to a structure with a viscous agent. Further, the signal distortion as a function of frequency through an adhesive bond to FBG sensor and how this maps to signal distortion in narrow bandwidth (Lamb waves) and broad bandwidth excitations (acoustic emission) will be quantified. We will focus on FBG sensor measurement of two different excitation signals: Lamb waves due to a narrowband PZT actuator and acoustic emission signals. The primary difference between these two cases is the bandwidth of frequencies in the signals, changing the level of dispersion and therefore its relative influence on the output signal. Finally, the strength and fatigue life of high sensitivity fiber Bragg gratings from a novel fabrication process will be experimentally measured.

The proposed project has an information technology (IT) component that will be coordinated with CICI university partners (UM and NCSU). The following sections highlight the nature of the project’s data generation, storage, retention, and sharing components as per NCSU. Expected data This research is expected generate datasets similar to those produced by a typical materials/structures laboratory. The types of data include: 􀁸 Experimental measurements from voltage or current measurement devices. These measurements will be converted to useful units through calibration scales. Data will be collected by instruments and sensors such as: strain gauges, load cells, linear variable differential transformers (LVDTs), and displacement transducers. 􀁸 Quantitative information in the form of human or machine readouts from measurement devices such as rulers, meter tapes, volume measurement containers, scales, and environmental gauges. 􀁸 Qualitative information such as experimental behavior, test conditions, or other significant observations. 􀁸 Multimedia data such as photographs, videos, screen captures, audio/video logs captured by cameras, camcorders, or audio recorders, or other multimedia devices. 􀁸 Written documents such as progress logs, journal articles, periodic reports, presentations, or any other document detailing progress, results, or outcomes. Data will be collected for the entire duration of this project. In particular, data is expected to be collected during testing preparation, equipment calibration, testing, personnel training, and demonstrations. Data related to the dissemination of information such as written documents or multimedia data, as it relates to publication or sharing of results, creation of manuscripts for archival publication, presentations, and reports, is expected to be generated following significant milestones in the project, and can be expected on a monthly or longer frequency. The project will result in the creation of a software framework for data management, sharing, analysis, and visualization. The code will be managed by graduate students and will be supervised by the PI. The majority of the code will be uploaded to a code repository such as GITHUB, where the code will be made open source under a GNU license.