Mustafa Reşit Usal

A comparison of compact-jet, compact, and conventional ring-spun yarns

This study compared the characteristic properties of the yarns produced on three different yarn spinning systems with the same material. These spinning systems are conventional ring, compact, and compact-jet. Compact-jet is a proper combination of compact and jetring-spinning systems and therefore it is less known. On the other hand, conventional ring and compact spinning systems are well known in the spinning field. When the compact-jet spinning system was designed, it was aimed to gather the advantages of the jetring and compact spinning systems. Therefore, an air nozzle was placed between the exit of the RoCoS compact unit and the yarn guide of the spinning system. At the end of the study, it was determined that the compact-jet yarn properties are different from that of the conventional ring and compact yarns. The compact-jet spinning system is mainly effective on yarn hairiness and compact-jet yarn is superior compared with other yarns.

Improvement in yarn hairiness by the siro-jet spinning method

Hairiness affects the post-spinning processes and fabric appearance. In order to reduce the yarn hairiness, the present work attempted to design and develop an air nozzle that can be easily attached on to the sirospun spinning system. The system, based on a nozzle attachment to the sirospun spinning system, is named the siro-jet. In our previous studies, the nozzle was used in ring and compact spinning processes and the changes in yarn properties were analyzed. In this study, various nozzles having different injector angles, main hole diameters, injector diameters, number of injectors, nozzle shapes and injector positions were used and siro-jet yarns were produced at different air pressure levels. At the end of the experiments, it was determined that there is an optimum value for each nozzle parameter, and that the number of injectors and injector position play the most important roles in reducing yarn hairiness, whereas nozzle shape shows the weakest effect. On the other hand, the findings showed that it is possible to get lower hairiness values by different modifications on the same nozzle design. Considering the hairiness results, a constant was defined indicating the relationship between nozzle structural parameters and hairiness of the yarns to ease the nozzle design efforts. Depending on nozzle type, the siro-jet spinning system truly improves the yarn hairiness by 40–75%. In the literature, many researchers used an air nozzle in the spinning and also the winding processes. However, the combination of the air nozzle and sirospun spinning system in this manner is still not a common application.

The Effects of Shear on the Deflection of Simply Supported Composite Beam Loaded Linearly

In this study two deflection functions due to both the flexure and the shear of an orthotropic simply supported beam loaded linearly are obtained by means of the anisotropic elasticity theory. In order to see the effect of shear, the deflections are calculated for different fiber directions. Two different composite materials are used during the deflection analysis. The error level and the shear deflection for the thermoplastic composite beam are the smallest for 45 orientation angle, and that for the polymer-matrix composite beam are the smallest for 90 orientation angle. When the cross-sectional height to the beam-length ratio increases, the shear effect also increases.

Static and Dynamic Analysis of Simply Supported Beams

In this study, two deflection functions due to flexure and shear have been obtained for the global form of composite materials. Two different composite materials are selected for comparison of these deflection functions. These composites are: polymer matrix composite simply supported beam, reinforced by unidirectional fibers; and thermoplastic simply supported beam, reinforced by woven Cr-Ni steel fibers. In accordance with these different material properties, analytical and numerical solutions have been carried out. For 0, 30, 45, 60, and 90 fiber orientation angles, static and dynamic behavior of the two different composite materials are examined. Numerical solutions are given as graphical forms. In addition to modal analysis, two different composite materials have been realized. Natural frequencies and vibration modes are given as graphical forms. ANSYS and MATLAB software are used for numerical analysis of the different composite materials.

A Mathematical Model for the Electrothermomechanical Behavior of Dielectric Viscoelastic Materials

This study examines the behavior of a material under electro-mechanical loads arising of the external medium in a viscoelastic and dielectric material, provided that isotropy constraint is imposed on the material. The reaction of the object to external loads is expressed in elastic stress, dissipative stress and electrical polarization. Based on constitutive axioms and concepts pertaining to the symmetry group of the material, constitutive functionals have been obtained. To materially determine arguments of these functionals, findings of the theory of invariants have been used as a routine method. As a result constitutive equations pertaining to elastic stress, polarization field and dissipative stress have been found in material and spatial coordinates whereas symmetric and asymmetric stresses have been found in terms of displacement gradient and its derivative by using the expressions of elastic stress, polarization field and dissipative stress.

A Mathematical Model for Thermomechanical Behavior of Arbitrary Fiber Reinforced Viscoelastic Composites - II

This study examines the behavior of a composite material under mechanical loads arising of the external medium in a viscoelastic medium reinforced by two arbitrary independent and inextensible fiber families, provided that isotropy constraint is imposed on the matrix material. Despite the fact that the matrix material is isotropic the model in consideration bears the characteristic of directed media included in the transverse isotropy symmetry group solely due to its fiber distribution. The reaction of the object to external loads is expressed in elastic stress and dissipative stress. Based on constitutive axioms and concepts pertaining to the symmetry group of the material, constitutive functionals have been obtained. To materially determine arguments of these functionals, findings of the theory of invariants have been used as a routine method. As a result constitutive equations pertaining to elastic stress and dissipative stress have been found in material and spatial coordinates whereas symmetric and asymmetric stresses have been found in terms of displacement gradient and its derivative by using the expressions of elastic stress and dissipative stress. K e y W o r d s : Viscoelasticity, balance equations, isotropy, balance equations, constitutive equations.

On Magneto-Viscoelastic Behavior of Fiber-Reinforced Composite Materials Part I: Anisotropie Matrix Material

In this work behavior of an arbitrarily fiber-reinforced viscoelastic and magneto-sensitive material is investigated systematically in the frame of modern continuum mechanics when they are subjected to external loadings. The matrix material is supposed to be made of viscoelastic material with magnetic sensitivity involving an artificial anisotropy due to fiber reinforcing by arbitrary distribution. Magneto-viscoelastic response of the material will show up as a stress consisting of a reversible and irreversible parts along with a magnetization field. Magnetic field and elastic stress field is derived from a thermodynamic potential, with the dissipative stress arising as a result of viscous properties of the material. Response functions in regard to objectivity axiom III depend in general to Green deformation and rate tensors, magnetic field, fiber distribution and temperature distribution. Constitutive equations for the stress and magnetization with the use of relevant balance equations yields field equations for the formulation and solution of boundary value problems for the bodies made of those materials under considerations.

A study on siro-jet spinning system

Nowadays, there is ever increasing interests regarding with the nozzle usage in spinning systems and also winding process. In this study, an air nozzle was attached on to the sirospun spinning system and the system was called as siro-jet. Sirospun is a spinning system combining spinning and doubling in one operation and a yarn like a two fold is produced. The principle of the siro-jet system is based on the placement of the nozzle at the exit of drafting unit on sirospun spinning system and pressurized air was fed into the nozzle by the compressor during the spinning. In literature, air nozzle application in this manner is not common and hence the system is very less known. For that reason, siro-jet and siropun yarns were produced with different fibre types, material qualities and yarn counts, and the properties of the yarns were compared. At the end of the study, it was determined that siro-jet spinning system truly improves the yarn hairiness in comparison to sirospun spinning system. Even, the siro-jet yarns are less hairy after winding process. Interestingly, hairiness results of siro-jet and sirospun yarns produced with short, non-uniform fibres showed that siro-jet spinning system allows working with low cost raw materials while maintaining yarn quality. Therefore, siro-jet can be considered as an innovative spinning system regarding with less hairy yarn production opportunity.

Determination of constitutive equations dependent on temperature changes for dielectric materials having micro-voids

Abstract A damage constitutive model based on continuum damage mechanics (CDM) is proposed to investigate the electro-thermomechanical behavior of a thermoelastic dielectric structure in the present paper. The solid medium is assumed to be dielectric, incompressible, homogeneous, dependent on temperature gradient, having micro-voids, and showing linear elastic behavior. The matrix material made of elastic material involving an artificial anisotropy due to the existence of micro-voids has been assumed as an isotropic medium. Damage is incorporated by two symmetric, second-rank, tensor-valued, internal state variables which represent the total areas of “active” and “passive” voids contained within a representative volume element. Using fundamental concepts of continuum electrodynamics, CDMs and irreversible thermodynamics, the constitutive functionals have been obtained. It has been detected as a result of the thermodynamic constraints that stress potential function depends on two symmetric tensors and a vector, whereas the heat flux vector function depends on two symmetric tensors and two vectors. Since the matrix material has been assumed as an isotropic medium, the constitutive equations based on the constitutive functionals, which are stress potential and heat flux vector, have been obtained using the theory of invariants. Finally, the constitutive equations belonging to symmetric stress, polarization field, asymmetric stress, heat flux vector, and strain energy density release rate have been written in terms of material coordinate description.

Flexure behavior of composite cantilevers subjected to different environmental conditions

Abstract This publication presents an experimental study which was conducted to examine the effects of various types of environments on the flexural stress and load-deflection relationships of the composite cantilever beams subjected to a single force at their free end for different exposure times. The study includes the testing of five different conditions which are cold, hot, humid, seawater environments and room temperature. Maximum flexure stresses and deflections of cantilever beam are presented analytically, numerically and experimentally. ANSYS FEA program is used for numerical analysis of composite materials. The test results carried out after generally one and two months of exposure to the different environmental conditions show that the flexure stress and deflection of the beams are affected at different levels. Moreover, it is shown that the analytical and numerical results are consistent with the experimental data.