Characterization of the dynamic stretching stages of polymeric fibers using dispersion measurements.

In this paper, we characterize the dynamics of the molecular chains at different stages of stretching polymeric monofilament fibers. The main stages characterized in this work are shear-bands, necking, crazes, cracks, and fracture regions. Digital photoelasticity and white-light two-beam interferometry are utilized to study each phenomenon by finding the dispersion curves and the 3D birefringence profiles using a single-shot pattern, which is performed for the first time, to our best knowledge. We also suggest an equation to find the full-field distribution of the oscillation energy. This study presents a clear vision on the behavior of the polymeric fibers at a molecular level during dynamic stretching until reaching its fracture point. Patterns of these deformation stages are given for illustration.

Interferometric investigation of the opto-mechanical and structural properties of iPP/TiO2 nanocomposite fibers.

Fibers that missing specific features and functionalities could be innovated and functionalised via nano additives, in particular metal oxides. Titanium oxide (TiO2 ) nanoparticles have been added to isotactic polypropylene (iPP) to form iPP/TiO2 nanocomposite fibers. Three samples of iPP/TiO2 fibers were extruded at three extrusion speeds 25, 50, and 78 m/min were considered in this study. Mach-Zehnder interferometer was used to assess the changes in the opto-mechanical and geometrical parameters of iPP/TiO2 nanocomposite fibers along the fiber axis. The mechanical drawing device along with Mach-Zehnder interferometer was utilized to stretch the filaments to different draw ratios. The effect of mechanical cold drawing and extrusion speed on the optical and physical characteristics of iPP/TiO2 nanocomposite fibers were determined along the fiber axis. The optical and physical variation along the nanocomposite samples were characterized by measuring their refractive indices, birefringence, refractive index profile along the fiber axis. The diffraction of He-Ne laser beam was used to define the variation of the fiber diameter along the fiber axis through their cross-sectional area and shape. A sample of uniform diameter from neat iPP fibers was used as reference material for studying the variation of the iPP/TiO2 fiber diameter along the fiber axis. As result, the iPP/TiO2 nanocomposite fibers exhibited nonuniform diameters. The dispersion of TiO2 particles in nanocomposite fibers influences the properties' consistency along and across the fiber.

A novel dynamic opto-thermo-mechanical stress testing device 2: In situ stretching process of polymeric fibers.

In this article, we used the opto-mechanical stress testing-device to stretch a monofilament of isotactic Polypropylene, iPP, fibers. This device was used to obtain the mechanical behavior of these fibers by measuring the complete stress-strain curves at different stretching conditions. Using this device, the different regions of iPP fiber where the mechanical deformation takes place was characterized, including the necking region and fracture initiation process. The obtained mechanical behavior of iPP fibers was correlated to the variations of different optical parameters by attaching the device with the Pluta polarizing interference microscope. This microscope and the stress device allowed us to simultaneously measure the optical parameters and stress-strain data during stretching process at different stretching speeds. These data provide us with comprehensive information on the opto-mechanical behavior of polymeric fibers. Interferograms are included for illustration. The opto-mechanical stress testing-device was used to stretch a monofilament of, iPP, fibers. The mechanical deformation takes place was characterized, including the necking region and fracture initiation process at different stretching speeds.

A novel dynamic opto-thermo-mechanical stress testing device 1: Design of the device.

This article presents a dynamic opto-thermo-mechanical stress testing device to characterize fiber properties. The device has multi-modes and consists of many functions. These modes include stretching, bending, rotating, twisting, and heating processes. Every process can be controlled by micro-controller unit via software programs specially designed for this purpose. The micro-controller unit can execute two different processes at the same time. Such as, dynamic stretching process under the effect of thermal treatment, dynamic stretching process and relaxation, bending process under the effect of thermal treatment, and so forth. Software programs with their flow charts are designed for the application of these processes. The advantage of this device is that it can be done statically and dynamically to characterize all types of fibers (polymer and optical). The device is designed to be attached with two-beam polarizing interference microscope to investigate the dynamic opto-thermo-mechanical properties of the tested fiber under the effect of different applied stresses. Isotactic polypropylene, iPP, fiber is used for some applications of this device, as examples, in stretching, rotation, and twisting modes. Interferograms and graphs are given for illustration.

Experimental investigation of craze morphology of isotactic polypropylene using computed tomography.

In this paper we investigated the morphology of crazes formed during the fracture process of polymeric fibres. Computed tomography technique was applied to reconstruct the image of fibrils-voids structure of crazes. This allowed us to investigate the initial stages of crazes formation during the fracture process of mechanically stretched isotactic polypropylene fibres. The density and morphology of crazes were studied at different regions inside the stretched sample. Accordingly, we are able to visualize the internal structure of the stretched fibres in three dimensions. This revealed in-depth information on the fracture process of polymeric fibres.

A novel method for identifying the order of interference using phase-shifting digital holography.

In this paper, we introduced a mathematical method for measuring the optical path length differences (OPDs), which is suitable for large OPD values where the fringes connections are difficult to detect. The proposed method is based on varying the width of the fringes, without changing the wavelength of the used coherent source. Also, in this work, we discussed the need for such method in off-axis phase-shifting digital holography. Low-resolution off-axis holograms failed to detect the correct interference order. In general, off-axis phase-shifting digital holography is limited by the resolution of the captured holograms. The results obtained using our proposed technique were compared to the results obtained using off-axis phase-shifting digital holograms and conventional two-beam interferometry. Holograms were given for illustration.

A proposed method to reconstruct the three-dimensional dispersion profile of polymeric fibres based on variable wavelength interferometry.

In this paper, we suggest a modification to the conventional variable wavelength interferometry. This modification allowed us to calculate the dispersion curve of each point inside polymeric fibres instead of calculating the mean dispersion of these fibres. This modified mathematical treatment was used to calculate the three-dimensional dispersion profile of isotactic polypropylene fibres suffering from necking deformation. The different steps of calculating the three-dimensional dispersion profile of the fibre were demonstrated. The application of this modified method revealed the variation of the fibre material dispersion before, inside and after the necking region. In addition, the birefringence profile of the necked isotactic polypropylene was determined using the proposed mathematical treatment. This allowed us to diagnose the interaction of the incident waves with necked polypropylene fibres, which gives extensive information on the orientation of the molecular chains during the formation of the necking phenomenon.

Nonray-tracing determination of the 3D refractive index profile of polymeric fibres using single-frame computed tomography and digital holographic interferometric technique.

In this paper, we present a nonray-tracing technique for evaluating the three dimensional distribution of the refractive index values inside polymeric fibres. This technique, named 'single-frame computed-tomography (SFCT)', is applied to digital holography. A comparative study between the calculated optical phase values using ordinary tomography and SFCT is carried out, and a negligible deviation is detected. The proposed technique is used to determine the three-dimensional refractive index profile of isotactic Polypropylene fibres, IPP. The variation of the optical properties is measured before, during and after the formation of the necking phenomenon. In addition, SFCT technique is applied to the online determination of the change of the optical properties of IPP fibres. Holograms are given for illustration.

A novel double-image Fizeau system for accurate investigation of anisotropic polymer fibres.

This paper introduces a double-image multiple-beam Fizeau fringes system. The introduced system can dynamically determine the variations of the refractive indices for both parallel and perpendicular polarization simultaneously. This is achieved by the simultaneous capturing of two multiple-beam interference patterns during the mechanical processing of isotactic polypropylene fibre. This parallel determination of the refractive indices of both polarization directions allowed us to determine the full-field distribution of the stress vector, S. To accomplish this, a mathematical model was deduced to calculate the components of the stress vector, S, i.e. parallel stress component, S1, and perpendicular stress component, S2. Double-image Fizeau fringes system and the deduced mathematical model were used to investigate the variation of the refractive index and stress components of the fibre during the stretching process and propagation of necked regions.

A novel simultaneous photoelastic and two-beam interferometric system: I. Dynamic full-field evaluation of the elasticity modulus profile of polymeric fibres.

A novel optical setup for simultaneous capturing of photoelastic and two-beam interference patterns was designed. The designed optical setup was used to simultaneously record two types of patterns. The first pattern is two-beam interference pattern, and the second one is photoelastic interference pattern produced by objects under stress. This simultaneous capturing of the two patterns allowed us to calculate the full-field distribution of the elasticity modulus profile of fibres. A mathematical expression of the profile of the elasticity modulus was derived. This was applied to evaluate the elasticity modulus of anisotropic isotactic polypropylene fibres during stretching processes. The profile of the elasticity modulus was determined for both static and dynamic in situ cases where the propagation of different structural deformations was observed and studied using the designed optical setup. Patterns were given for illustration.