الفهرس 
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Abstract
Interferometric methods are powerful techniques of high accuracy capable of observing the in situ variations with time. Different structure deformations were observed during the elongation processes of polymeric fibres. Stretching and necking phenomenon observed during creep process was presented. Two-beam polarising light interference microscope designed by Pluta is used for in situ investigation of fracture mechanism of as-spun isotactic polypropylene (IPP) fibres by crazing during cold drawing process. In chapter 3 we presented a study of the opto-mechanical characterization of crazing phenomenon observed during the mechanical stretching of polypropylene fibres (involving craze initiation, craze propagation and craze breakdown) as a function of crazing strain, crazing temperature and stretching speed. The craze damage and the fracture of polymeric fibres was investigated as a function of the stretching speed. Moreover, the time to crazing, the time to failure and the areal craze density of IPP fibres during cold drawing process were estimated. Finally, observing the craze formation at different temperatures showed that there was a critical value of stretching temperature for the formation of crazes in IPP fibre. The obtained results are correlated to the corresponding variations in some optical and structural properties of IPP fibres due to stretching. Creep deformation under constant load leads to rupture when the polymer chains can no longer separate and accommodate the load. In chapter (4), the fracture phenomenon using multiple-beam interferometric technique was investigated. The creep behavior of as-spun isotactic Polypropylene (IPP) fibres was studied at different stresses, different initial lengths and different radii. The creep rate, which defines the velocity of the creep deformation and the dimensional stability of the material, was studied. The failure time and stress of IPP due to creep process was determined. The necking deformation was in situ detected during creep process. Double-arm multiple-beam Fizeau system in transmission enabled us to determine the mean refractive indices profiles of the same fibre of IPP fibres which were determined at different positions along the fibre axis before and after necking. Also the 3D – birefringence profiles of IPP fibres were determined at different stress values. The relation between the creep behaviour and different optical and structural parameters was investigated.