Monitoring of mining induced subsidence through measurement of ground strains with Fiber Bragg Grating sensors
In this paper the application of Fiber Bragg Grating based sensors for the monitoring of mining induced subsidence phenomena is illustrated. A high number of sensors were installed in the pavement of a major highway thanks to the use of Bragg Grating arrays encapsulated in composite rods. The sensors and the associated demodulation equipment provide continuous measurements and allow the immediate implementation of safety measures by the authorities responsible for the highway.
Pultrusion of smart FRP composites
A laboratory scale pultrusion process has been developed to fabricate smart fiber reinforced plastic (FRP) materials. Microstructural analyses of the smart pultruded FRP was carried out using both an optical microscope and a Scanning Electron Microscope. The tensile properties and shear strength, i.e. modulus and strength, of pultruded carbon/vinylester and glass/vinylester rods were determined through mechanical testing. Testing was carried out on baseline pultruded samples, as well as those containing one and two embedded optical fibers. The pultruded carbon reinforced rods with and without optical fiber showed higher shear and tensile strength, as well as greater tensile modulus than did the glass fiber analogue. An embedded optical fiber did not have a significant effect upon the tensile properties of either glass or carbon pultruded FRP rod, but it slightly affected the shear strength of the glass fiber rods. Increased numbers of embedded optical fibers in the FRP rods had a more pronounced influence upon the shear strength. The interfaces between the resin matrix and the buffer coating on the optical fibers were examined and interpreted in terms of the coating's ability to resist high temperatures and its compatibility with resin matrix. Polyimide buffers proved to be superior to acrylate buffers.
Development of a ground-based facility for simulating the omnidirectional near-earth electron environment
Abstract A method is detailed for simulating in the laboratory the omnidirectional near-earth electron environment. This technique can synthesize the directional and energy properties of an arbitrary omnidirectional electron flux by combining a sufficient number of weighted energy and direction increments. A large vacuum chamber has been built, capable of holding three-dimensional structures up to 30 cm in each dimension while maintaining pressures in the 10−6 mm Hg range. The support structure in the chamber rotates around two axes, thereby achieving all angular orientations necessary for the omnidirectional simulation. This chamber was coupled with a beam scanning system to a 4 MeV electron Van de Graaff accelerator which was tuned to provide specified fluences of electrons at the desired energies. The system was used to irradiate a series of hollow aluminum cubes having varying wall thicknesses. Using radiochromic film dosimeters, dose profiles were mapped in the interiors for both one-wall and six-wall exposures. Results of the dose mapping are presented for several monoenergetic cases as well as for the energy spectra from a 235U fission event. The one-wall exposures show dose variations within the interior by a factor of 3.2 ± 0.6 independent of energy or wall thickness. In the six-wall exposure, distributions varied only about 15%.