Eric Udd

Multidimensional strain field measurements using fiber optic grating sensors

Fiber optic grating sensors written into polarization preserving optical fiber may be used to monitor multidimensional strain fields in composite materials. This paper provides an overview of the characterization and test of multiaxis fiber grating sensors formed by writing 1300 and 1550 nm fiber gratings into polarization preserving optical fiber. A discussion of the usage of these multiaxis fiber grating sensors to measure two and three dimensional strain fields will be made. A brief review of practical applications of the technology to measure shear strain, transverse strain gradients as well as axial and traverse strain will be made with emphasis on aerospace and civil structure applications.

Health monitoring of an adhesive joint using a multiaxis fiber grating strain sensor system

The use of adhesive joints in aerospace structures is becoming increasingly important. From this, arises the problem of assessing joint integrity quickly, non- intrusively, accurately, and inexpensively. Current methods of assessing joint integrity, such as ultrasonics and x- rays, are time intensive and difficult to interpret. Blue Road Researchs solution to monitoring adhesive joint integrity quickly and accurately is to embed non-intrusive, multidimensional optical fiber grating strain sensors into or adjacent to the joints. Aluminum double lap adhesive joints were instrumented with the multi-axis grating strain sensors into or adjacent to the joints. Aluminum double lap adhesive joints were instrumented with the multi-axis senors and subjected to tension and fatigue test. Each specimen contained one sensor located either near the bond, embedded at the edge of the bond, or embedded towards the inner bond area. The joints with senors embedded into the adhesive showed minimal strength degradation. Basically, the multiaxis fiber grating strain sensors were found to provide information about transverse strain, axial strain, and transverse strain gradients that can provide important information throughout the adhesive joint. By changing the orientation of the sensor, shear strain and its effects can be clearly measured.

Fiber optic distributed sensing systems for harsh aerospace environments

Fiber optic sensors have the potential to be used in the very hostile environments necessary for advanced aerospace platforms. This paper reviews some of the key issues associated with the implementation of distributed fiber optic sensors in harsh environments and outlines baseline system designs.

Damage evaluation and analysis of composite pressure vessels using fiber Bragg gratings to determine structural health

With the augmented use of high performance composite materials in critical structures, it has become increasingly important for smart systems to monitor these materials and provide rapid evaluation. Using fiber Bragg gratings embedded into the weave structure of carbon fiber epoxy composites allow the capability to monitor these composites during manufacture, cure, general aging, and damage. Fiber optic sensors allow greater insight into damage progression and can be used to verify analytical models. This paper emphasizes the results of recent work in which multiple arrays of Bragg gratings were wound into composite vessels and monitored while the part was damaged. Based on the response of these sensors, algorithms were developed to identify the location of damage impacts. Results were verified against eddy current and ultrasonic NDE methods.

Progress on monitoring of adhesive joints using multiaxis fiber grating sensors

Previously, the results of embedding multi-axis fiber gratings into adhesively bonded joints were discussed. This paper presents more information on the testing of the adhesive joints and techniques employed to successfully embed a fiber grating sensor into such structures. These techniques include orienting the fiber, marking its orientation, and preparing it for embedment into the adhesive. Also discussed are strain relief methods for the egress of the fiber.

Traffic monitoring/control and road condition monitoring using fiber optic-based systems

There are several applications in the area of traffic monitoring and control as well as road condition monitoring where fiber optic based sensor systems are advantageous. This study focuses on the use of fiber optic sensors to monitor the strain state in structures. This monitoring accomplishes two main tasks: it assesses the health of the structure and provides useful data for traffic monitoring/control applications.

Higher-speed demodulation of fiber grating sensors

For very high-speed events, such as ballistics testing, strain measurement speed is not limited by the response of the fiber grating sensor, but rather the demodulation system used. This paper focuses on a current 10 kHz fiber grating demodulator used to support impact and ballistics testing of a composite panel. It also explores the next generation demodulator, pushing the emits of speed upwards of 3 Mhz.

Fiber optic smart bearing load structure

As proliferation of structures incorporating composite materials occurs, the benefits of in-situ monitoring of the building materials in order to increase reliability and improve maintainability of the overall structure are being recognized. For example, measurement of shear-strain and load within bridge bearings can be directly related to the health and longevity of the structure. In this paper, the embedding of single and multi-axis optical fiber strain sensors within liquid molded load cells for structures such as bridges is reported. Fabrication and testing processes are presented, as well as test results.

Fiber grating traffic monitoring systems

Previous studies have shown the capability of fiber Bragg gratings (FBGs) to monitor components of strain on bridges and structures. In past months, Blue Road Research and the Oregon Department of Transportation embedded long-gage FBG sensors into the Interstate 84 freeway east of Portland, Oregon to determine the feasibility of retro-install and for use of these sensors in monitoring freeway traffic speeds under conditions similar to loop inductors, piezo-ceramic weigh-in-motion (WIM) systems, and other vehicle monitoring devices. The objective of the study was to develop a working traffic sensor system with the potential to be more durable, reliable, informative, and cost-effective than currently available traffic sensors. A primary purpose of the freeway installation was to test the sensors for vehicle classifier and counter applications. In addition to discussion of the advantages of using FBGs for traffic classifiers and systems over conventional sensing methods, this paper overviews the installation and summarizes the use of FBG traffic sensors for vehicle counting and classification.

Fiber grating systems for traffic monitoring

Blue Road Research has designed, built, and installed fiber grating sensor systems onto bridges, and most recently into an asphalt and concrete highway test pad. The sensitivity levels of the fiber grating sensors are sufficiently high to enable detection of people standing on the bridge or highway. This paper briefly overviews the usage of these sensors for traffic monitoring.