L’objet de ce travail est l’évaluation du processus de vieillissement et de la durabilité des tissus techniques utilisés en ingénierie de construction. Deux types de tissu en polyester enduit de PVC ont été testés: VALMEX vieilli naturellement et AF9032 soumis au vieillissement accéléré. L'impact du processus de vieillissement a été observé en analysant les changements des valeurs des paramètres des modèles constitutifs: linéaire par morceaux, viscoélastique de Burgers et viscoplastique de Bodner-Partom. La comparaison de tissu VALMEX utilisé pendant 20 ans à l’Opéra de la Forêt à Sopot et du même tissu stocké à l’abri a montré que la matière, après 20 années de fonctionnement, a conservé ses propriétés mécaniques et pourrait être encore utilisée pendant plusieurs années. Le vieillissement dû aux conditions environnementales d’exploitation a provoqué une augmentation de la rigidité du revêtement (PVC), alors que la raideur des fibres en polyester est restée pratiquement inchangée. Le tissu AF9032 a été soumis au processus de vieillissement accéléré. Les échantillons de tissu ont été placés dans une chambre thermique à 80 et 90 °C durant 12 semaines. Les variations des paramètres des modèles constitutifs en fonction de temps de vieillissement ont pu être exprimées par des relations linéaires. Les résultats de vieillissement thermique accéléré ont été extrapolés d’après la méthode d’Arrhenius pour obtenir des valeurs correspondantes au vieillissement naturel. Pour les deux cas de vieillissement, les changements plus importants se sont produits dans la direction de la trame. Pour les fils de chaîne, les différences sont beaucoup plus petites et parfois négligeables. / This thesis describes the investigation on the durability of technical fabrics that are commonly used as the constructional-covering material for engineering structures. Two types of polyester reinforced PVC coated fabrics have been subjected to the exploitation ageing (VALMEX fabric) and the artificial, laboratory ageing (AF9032 fabric). The influence of the ageing process has been presented as the parameters evolution of the following constitutive formulations: the piecewise, the viscoelastic Burgers and the viscoplastic Bodner-Partom models. The comparative analysis between two types of the VALMEX fabric (the material used for 20 years on the structure of the Forest Opera roof and the not used one – kept as a spare material) have been conducted. The obtained results have shown the very good performance of the material used outdoor and indicated that it could still work satisfactorily for the next several years. The accelerated ageing of the AF9032 fabric has been performed at the elevated temperature of 80°C and 90°C in a thermal chamber for up to 12 weeks. The achieved parameters values versus ageing time have been approximated by linear functions. The results of the thermal ageing have been extrapolated using the Arrhenius methodology. The both types of ageing have significant influence on the mechanical properties of the tested fabrics for the fill direction while the warp direction is free of this effect. As a result of the performed identifications the parameters of three constitutive models have been obtained. They can be implemented for the numerical simulation of the polyester reinforced PVC coated fabrics performance and help to predict their life span under service conditions.

The structure and dynamics of the smectic-A liquid crystal 8CB (4 cyano-4 octylbiphenyl) when sheared and confined to mesoscale gaps (with crossed cylindrical geometry and mica confining surfaces) were studied using a Surface Forces Apparatus (SFA). Triangular shear patterns with frequencies of 0.01, 0.1, 1.0 and 10 Hz, and amplitudes of 62.5 nm, 625 nm and 6.25 m were applied to samples at gap sizes of 0.5 and 5.0 m. The study was performed at room temperature (20.5C) and at two higher temperatures (22C and 27C). In order to minimize the thermal fluctuations within the test chamber and hence to allow for the rapid re-initialization of test runs, the SFA was modified to allow for quick, precise and remote control of the confining surfaces. The procedure maximized the number of tests that could be undertaken with a single pair of surfaces so that a single gap geometry could be maintained for the duration of the test run. In order to run the SFA remotely, scripts written with a commercial software package, LabVIEW, were used to control of the SFA components, its FECO-monitoring camera and all its peripheral electronic equipment as well. Samples were agitated to disrupt any shear-induced liquid crystal domain alignment from previous testing following each shear test, and methodologies were developed to ascertain the extent of confinement quickly and remotely following agitation. Separate methods were developed for gap sizes at each extreme of the mesoscale regime, where the transition from bulklike structure and dynamics to nano-confinement occurs (between 1 and 10 microns for smectic-A 8CB). The results revealed that the greater amplitude-gap aspect ratio and surface-to-domain contact associated with smaller gaps facilitated reorientation of the domains in the shear direction. Evidence was also presented of domains at the higher end or outside of the mesoscale regime that, while straining and accreting, were unable to reorient and thereby led to an overall increase of viscoelastic response. The effective viscosity was found to obey a simple power law with respect to shear rate, , and the flow behaviour indices, n, slightly in excess of unity indicate shear thickening occurs with large enough shear amplitude, and that the viscosity reached a plateau near unity over shear rates of 0.005 to 500 s-1 within the mesoscale regime. Different K and n values were observed depending on the shear amplitude used. Unlike bulk smectic 8CB, whose domains do not align well in the shear direction with large shear-strain amplitude, at mesoscale levels of confinement large amplitude shearing (up to 12.5 shear strain amplitude) was found to be very effective at aligning domains. In general domain reorientation is found to be much more rapid within the mesoscale regime than has been reported in bulk. Aggressive shearing was found to result in a complete drop in viscoelastic response within seconds, while gentler shearing is found to produce a very gradual increase that persists for more than six hours, with individual shear periods exhibiting frequent and significant deviations from the expected smooth shear path that may be a product of discrete domain reorientations. From these findings, certain traits of the smectic 8CB domain structures under mesoscale confinement were deduced, including how they respond to shear depending on the level of confinement, and how their reorientation due to shear varies not only with shear rate but also independently with shear amplitude. An equation describing the viscosity change as a function of both shear rate and shear amplitude is proposed. The shear amplitude dependence introduces the notion of shearing beyond the proposed smectic 8CB “viscoelastic limit”, which was shown to exhibit behaviour in accordance with Large Amplitude Oscillatory Shear (LAOS) techniques developed for Fourier Transform rheology. The findings provided an understanding of the behavioural changes that occur as one reduces the level of confinement of smectic materials from bulk to nanoconfinement.

The structure and dynamics of the smectic-A liquid crystal 8CB (4 cyano-4 octylbiphenyl) when sheared and confined to mesoscale gaps (with crossed cylindrical geometry and mica confining surfaces) were studied using a Surface Forces Apparatus (SFA). Triangular shear patterns with frequencies of 0.01, 0.1, 1.0 and 10 Hz, and amplitudes of 62.5 nm, 625 nm and 6.25 m were applied to samples at gap sizes of 0.5 and 5.0 m. The study was performed at room temperature (20.5C) and at two higher temperatures (22C and 27C). In order to minimize the thermal fluctuations within the test chamber and hence to allow for the rapid re-initialization of test runs, the SFA was modified to allow for quick, precise and remote control of the confining surfaces. The procedure maximized the number of tests that could be undertaken with a single pair of surfaces so that a single gap geometry could be maintained for the duration of the test run. In order to run the SFA remotely, scripts written with a commercial software package, LabVIEW, were used to control of the SFA components, its FECO-monitoring camera and all its peripheral electronic equipment as well. Samples were agitated to disrupt any shear-induced liquid crystal domain alignment from previous testing following each shear test, and methodologies were developed to ascertain the extent of confinement quickly and remotely following agitation. Separate methods were developed for gap sizes at each extreme of the mesoscale regime, where the transition from bulklike structure and dynamics to nano-confinement occurs (between 1 and 10 microns for smectic-A 8CB). The results revealed that the greater amplitude-gap aspect ratio and surface-to-domain contact associated with smaller gaps facilitated reorientation of the domains in the shear direction. Evidence was also presented of domains at the higher end or outside of the mesoscale regime that, while straining and accreting, were unable to reorient and thereby led to an overall increase of viscoelastic response. The effective viscosity was found to obey a simple power law with respect to shear rate, , and the flow behaviour indices, n, slightly in excess of unity indicate shear thickening occurs with large enough shear amplitude, and that the viscosity reached a plateau near unity over shear rates of 0.005 to 500 s-1 within the mesoscale regime. Different K and n values were observed depending on the shear amplitude used. Unlike bulk smectic 8CB, whose domains do not align well in the shear direction with large shear-strain amplitude, at mesoscale levels of confinement large amplitude shearing (up to 12.5 shear strain amplitude) was found to be very effective at aligning domains. In general domain reorientation is found to be much more rapid within the mesoscale regime than has been reported in bulk. Aggressive shearing was found to result in a complete drop in viscoelastic response within seconds, while gentler shearing is found to produce a very gradual increase that persists for more than six hours, with individual shear periods exhibiting frequent and significant deviations from the expected smooth shear path that may be a product of discrete domain reorientations. From these findings, certain traits of the smectic 8CB domain structures under mesoscale confinement were deduced, including how they respond to shear depending on the level of confinement, and how their reorientation due to shear varies not only with shear rate but also independently with shear amplitude. An equation describing the viscosity change as a function of both shear rate and shear amplitude is proposed. The shear amplitude dependence introduces the notion of shearing beyond the proposed smectic 8CB “viscoelastic limit”, which was shown to exhibit behaviour in accordance with Large Amplitude Oscillatory Shear (LAOS) techniques developed for Fourier Transform rheology. The findings provided an understanding of the behavioural changes that occur as one reduces the level of confinement of smectic materials from bulk to nanoconfinement.