الفهرس 
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Abstract
In this thesis, the optical parameters to structural changes of polymeric fibres caused by stretching processes were correlated. This correlation can be achieved by finding the appropriate optical technique among three major techniques to characterize each deformation stage. The main techniques considered in this thesis are: two-beam interferometry, multiple-beam interferometry and digital holography. Also, we investigated the possibility of adapting these techniques to carry out online investigation. Drawing polymeric fibres results in different interesting phenomena, e.g. necking, crazing and thinning. Finding the optimum optical system for studying each stage of stretching is a challenging task. Chapter (2) introduces a comparative study of the three major optical techniques; by testing their applicability to characterize different deformation stages of fibres. In this chapter a set of recommendations and limitations were concluded to find the most effective technique at different stages of fibre deformations. The accuracy, reproducibility and limit of application of each system are reported. characterizing the viscoelastic response of polymeric fibres greatly influences the application of these fibres in industry. The relaxation behavior of these materials is a key issue to characterize their viscoelastic behavior. Chapter (3) reports the effect of relaxation recovery on polymeric fibres at different drawing stages including necking and craze propagation. Two- and multiple-beam interference techniques are utilized to study the relaxation effects on the fibres, in addition optical microscopy is used to quantitatively characterize crazes during the relaxation process. A supplementary diffraction technique is used to increase the accuracy of measuring the cross-section of the fibres during relaxation. The digital double-exposure holography technique provides visual and quantitative comparison of two different states of a fibre during stretching, e.g. deformed and undeformed states. Chapter (4) demonstrates the great potential of the digital double-exposure holography applied to polymeric fibres. In this chapter, a visual image of the two states of the fibres, i.e. before and after stretching, is introduced. In addition to this visual image, a quantitive study of the refractive index variation is carried out during stretching process. Although, this technique is a powerful comparative tool, it failed to characterize polymeric fibres during online studies. The failure of the digital double-exposure holography to carry out online investigations decreases the range of application to study polymeric fibres. This difficulty can be circumvented by modifying the design of the optical system. In chapter (5) a modified design of the Mech-Zehnder interferometer is introduced to carry out online investigation of polymeric fibres. The modified setup allowed us to capture parallel- and perpendicular-polarization holograms simultaneously during stretching process. This modification for the online double exposure technique is now possible, which is used to characterize the relative variation of optical parameters of polymeric fibres under dynamic processing. Also, the birefringence parameters of isotropic fibres can be accurately measured.