G. Kister

Structural Integrity Monitoring of Concrete Structures via Optical Fiber Sensors: Sensor Protection Systems

This paper reports on the design requirements and a range of specific concepts for optical fiber-based sensor protection systems that can be used in concrete structures. The designs range from sensor protection systems that are manufactured involving stainless steel, fiber reinforced composites and concrete. The feasibility of manufacturing the sensor protection systems using these materials is also demonstrated. A detailed finite element analysis was carried out to optimise the stainless steel-based sensor protection system for concrete. Experimental results involving the sensor protection system will be presented in Part 2 of this series of papers.

Conventional E-glass fibre light guides: self-sensing composite based on sol–gel cladding

The aim of this study was to modify conventional reinforcing E-glass fibres to enable them to act as optical waveguides and subsequently as sensor devices. This required the glass fibres to be coated with a relatively homogeneous coating with a corresponding refractive index that was lower than the E-glass fibre (1.56). Although a range of coating materials are available, this study focused on using materials that are generally used as sizing agents for glass fibres to improve the adhesion to the matrix. Two different methods based on conventional sol–gel processing were used to obtain crack-free coatings. In the first method, tetraethoxysilane (TEOS) and polyvinyl alcohol were used as precursors. In the second method, acid-catalysed solutions of TEOS mixed with 3-glycidoxypropyltrimethoxysilane were used as precursors. UV–visible transmission results showed that the films had low absorption and high transparency in the visible range. The refractive indices of the films were found to be a function of the molar fractions of the major chemical components. A simple impregnation procedure was used to apply the coating to the E-glass fibre bundles. The light transmission characteristics of the coated fibres along with their mechanical properties were evaluated. The sol–gel coatings were shown to be effective in converting the conventional E-glass fibres into light guides.

Self-sensing E-glass fibres

Abstract The primary aims of this study were to demonstrate that conventional reinforcing E-glass fibres could be converted to act as waveguides. This was achieved by selecting and applying appropriate cladding material onto the glass fibre bundle. Three classes of cladding materials were evaluated: epoxy, polyurethane and sol–gel. The light transmission characteristics through the E-glass waveguides was evaluated and compared. The epoxy and polyurethane cladding were found to be superior compared to the sol–gel coated fibres in terms of the quality of the coating and the light transmission intensity over specified lengths. The effect of fibre-end preparation on the light transmission characteristic was also investigated. The feasibility of conducting in situ tensile tests where the light transmission intensity was passed through the E-glass fibres was demonstrated successfully. This in situ technique was capable of highlighting differences in the macroscopic tensile failure modes obtained using the various cladding materials.

Impact, penetration, and perforation of a bonded carbon-fibre-reinforced plastic composite panel by a high-velocity steel sphere: An experimental study:

In this work, the response of a bonded carbon-fibre-reinforced plastic composite panel, which had been manufactured by bonding two laminates together, to impact, penetration, and perforation by a high-velocity steel sphere has been studied. The response of a relatively thick (about 12 mm) laminate has been compared with similar data from previous work by Hazell et al. where relatively thin monolithic laminates were impacted by the same type of projectile. It was found that the ballistic performance of the system was increased over the impact energy range of interest when compared with these similar, relatively thin composite laminates. Furthermore, both the energy absorbed per unit thickness of laminate and the level of damage as measured by a C-Scan system when the panels were perforated at normal incidence and oblique incidence were similar. This raises the prospect of reducing experimental testing at oblique angles, if the behaviour at normal incidence is known.

An overview on the effect of manufacturing on the shock response of polymers

Scatter and non-linearity of the Hugoniot in the Us-up plane has been seen in a number of polymers including poly(methyl methacrylate) (PMMA), the polymer considered here. In this study the plate impact technique has been used to investigate the shock response of PMMA between particle velocities of 0.13 and 0.77 mm μs−1. From this data no scatter was seen between our data and the experimental data of Barker and Hollenbach, and Carter and Marsh. Also a linear Hugoniot in the Us-up plane was found, with the equation Us = 2.99 + 0.92up. The non-linearity observed by Barker and Hollenbach was not present in this data, probably due to the non-linearity occur at particle velocities of below 0.13 mm μs-1, within their experimental data. Gruneisen gamma has also been briefly considered using a shock reverberation experiment but more work is needed before a value can be ascertained.

Blind deconvolution of acoustic emission signals for damage identification of composites

The analysis of acoustic emission signals has been widely applied to damage detection and damage characterization in composites. Features of acoustic emission signals, such as amplitude, frequency, and counts, are usually utilized to identify the type of a damage. Recently, time-frequency distribution techniques, such as the wavelet transform and the Choi-Williams distribution, have also been applied to characterize damage. A common feature of these approaches is that the analysis is on the acoustic emission signal itself. Nevertheless, this signal is not the wave source signal as it has been modulated by the signal transfer path. Real information on damage is actually hidden behind the signal. To reveal direct information on damage, a blind deconvolution method has been developed. It is a quefrency domain method based on the cepstrum technique. With the method, acoustic emission signal is demodulated and information on the wave source can be revealed and thus damage can be identified. This paper presents preliminary test data to assess the validity of the proposed methodology as a means of identifying specific damage modes in fiber reinforced composites.