This paper presents a general overview of a number of optical fibre sensor systems which have been developed and used in advanced fibre-reinforced composites for in-situ process and condition monitoring. The in-situ process monitoring techniques were optical-fibre-based evanescent wave spectroscopy, transmission near-infrared spectroscopy and refractive index monitoring. The optical fibre sensors were successful in tracking the cure reaction. The condition monitoring of advanced fibre-reinforced composites was carried out using two intensity-based optical fibre sensor systems: an extrinsic multi-mode Fabry-P érot sensor and Bragg gratings. In addition to this, the feasibility of using the reinforcing fibre as a light guide was demonstrated. These sensor systems were evaluated under quasi-static, impact and fatigue loading. The test specimens consisted of prepreg-based carbon-fibre-reinforced epoxy and glass-fibre-reinforced epoxy filament-wound tubes. Excellent correlation was obtained between surface-mounted strain gauges and the embedded optical fibre sensors. The feasibility of using these sensor systems for the detection of impact damage and stiffness reduction in the composite due to fatigue damage was successfully demonstrated.

This paper describes a comparative study of in situ cure monitoring by three methods: (i) evanescent wave spectroscopy; (ii) refractive index change; and (iii) near-infrared spectroscopy.The cure characteristics of an epoxy/amine reaction were followed in real-time during the crosslinking reaction via the above-mentioned techniques. The evanescent wave spectroscopy technique was based on monitoring the characteristic infrared absorption bands of the resin system to compute the concentration of the amine hardener as a function of cure time. Good correlation was obtained between the evanescent wave spectroscopy data and a conventional method of studying cure reactions, i.e. infrared spectroscopy.During the cure reaction, the refractive index of the resin system increases as a function of the crosslink density. This increase in the refractive index was monitored using two optical fibre techniques. In the first case, a declad region of the optical fibre was immersed in the resin system and in the second method an optical fibre reflectometer was used to track the changes in the refractive index. Once again, good correlation was obtained between the optical fibre techniques and infrared spectroscopy cure data. The results obtained from the optical fibre sensor experiments were used to model the cure kinetics of the resin system. The cure kinetic models were found to predict the cure reaction up to approximately 60% of the reaction.

Resting buds from five locations on long shoots in each of six crown positions were compared for 30 Larix laricina (Du Roi) K. Koch saplings. At each locus, bud sizes, numbers of bud scales and preformed leaf primordia (basal and axial for long-shoot buds), and apical widths were positively related to parent-shoot length. Along individual shoots, (i) terminal and lateral long-shoot buds contained fewer basal-leaf primordia than the more proximal short-shoot buds; (ii) terminal buds contained the most bud scales and axial-leaf primordia; and (iii) numbers of bud scales increased, while numbers of axial-leaf primordia generally decreased, basipetally among lateral buds. Comparison of bud leaf content with leaves on elongated shoots by regression showed that numbers of preformed and neoformed leaves increased with shoot length, but numbers of neoformed leaves did so to a greater degree. Internode lengths, numbers of leaves per lateral bud produced, and leaf lengths were greater on neoformed than on preformed shoot segments. Because of their capacity for neoformed growth following preformed growth and because of increases in internode lengths among all axial leaves, shoots from subjacent lateral buds replaced experimentally decapitated tree leaders (terminal buds) in one season, with little or no loss of height growth.

Production of seed cones from 1978 to 1987 and of pollen cones from 1980 to 1982 by young black spruce (Piceamariana (Mill.) B.S.P.) trees was recorded in five plantations aged 8, 10, 12, 14, and 16 years in 1980. Variations in cone production and percentages of trees bearing cones were assessed in relation to changing tree age and cone numbers per tree. The first seed cones and pollen cones were noted on 7- and 10-year-old trees, respectively. After ages 10–12 for seed cones and 12–14 for pollen cones there were substantial yearly fluctuations of average numbers of cones per tree. Similarly, the percentages of trees bearing cones fluctuated among years, but differences between poorer and better years decreased as the proportion of bearing trees gradually increased. Up to age 14, the number of seed cones borne per tree was generally higher than the number of pollen cones. Thereafter, pollen-cone production was always higher than seed-cone production and reached 6.6 pollen cones per seed cone by age 18. Pollen cone bearing trees were good indicators of seed cone bearing trees at all ages. Most 12-year-old and older seed cone bearing trees were good indicators of pollen cone bearing trees. Annual production of seed cones was correlated with warm weather in early May and early July, and with relatively low rainfall in early June of the previous year.