Browsing by Author "Yiping Qiu, Committee Member"

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Computer Modeling of Fiber Motion in High-Speed Airflow
(2003-07-16) Cai, Yiyun; George Hodge, Committee Member; Douglas Reeves, Committee Member; Yiping Qiu, Committee Member; William Oxenham, Committee Chair
High-speed airflow is widely used in many processes in today's textile industry. Even though the interactions between fibers and airflows have attracted many researchers' interest, there have been few published studies that focus on the computer modeling of fiber motion in airflow fields. The present research was aimed at developing a model that can effectively simulate the interactions between fibers and airflows, thus providing clearer understanding of the behavior of textile fibers in certain processing machines. A three-dimensional model of an aerodynamic component of a textile machine was developed. A commercial computation fluid dynamics (CFD) software package was used to compute the airflow field of this model and the results were analyzed to study the airflow field's characteristics. Resultant data were used as input for the fiber movement model by using a one-way coupling method. The mathematical model of fiber movement was constructed by integrating the governing equations with a model that describes the fiber configurations. A numerical method was developed to solve these equations and visualization programs were established to illustrate and animate the simulated fiber movements. The results obtained were studied and compared under different initial and boundary conditions. Fiber bending and twisting properties were integrated into the computer model. Their influences on the fiber movement were simulated and analyzed. The present research successfully demonstrates the effectiveness of computer modeling for studying the fiber motion in high-speed airflow. It can provide better understanding of fiber behavior in airflow fields and its potential and prospect in the research of textile processes, in which airflow plays an important role, are very promising.
Initiation and Evolution of Dynamic Failure Mechanisms in Woven Composite Systems
(2002-08-21) Baucom, Jared Newton; Mohammed Zikry, Committee Chair; Harvey Charlton, Committee Member; Eric Klang, Committee Member; John Bailey, Committee Member; Yiping Qiu, Committee Member
The unique reinforcement geometry of three-dimensional orthogonally woven fabric-reinforced composites offers the potential of improved penetration resistance, in comparison with other composite systems. However, there has been a lack of understanding of how dynamic energy dissipation and failure modes are affected by fiber orientation and distribution. The major objective of this investigation is to characterize damage progression in woven composites under transverse loading conditions at three distinct velocity regimes, ranging from 10 μm/s to 0.5 km/s. The investigated systems included two-dimensional plain woven laminates, three-dimensional orthogonally woven monoliths, and three-dimensional woven laminates. The three-dimensional structure has also been utilized with a matrix-cellularization technique to explore how porosity can be tailored for enhanced energy absorption. Quasi-static perforation experiments were conducted, where punch loads were recorded. Damage progression was monitored by backlit videography. The three-dimensional laminates required a higher punch force and absorbed more energy than the two-dimensional laminates and three-dimensional monoliths. Low-velocity impact damage progression was investigated with an instrumented drop-weight impactor. Measurements were obtained for impact force and energy dissipation for multiple strikes. The radial spread of damage was smallest for the two-dimensional laminates and largest for the three-dimensional woven composites, which also had the greatest resistance to penetration and dissipated the most total energy. High-velocity impact experiments were conducted to determine energy absorption and compare failure modes of two-dimensional and three-dimensional composite systems. Energy absorption was comparable for the various systems, but damage was more localized for the two-dimensional woven system. These results indicate that the three-dimensional laminates consistently had greater perforation resistance than the two-dimensional laminates and the three-dimensional monolithic composites. This is due to unique energy absorption mechanisms, which involve the crimped portion of z-tows in the three-dimensional composites. This implies that failure can be controlled by manipulation of the properties of the z-tows. Hence, three-dimensional architectures can provide both an inherent capability to dissipate energy over a large radial area and a greater perforation strength than comparable two-dimensional laminate and three-dimensional monolithic composites.
Relationship between the processing parameters and tensile properties of air textured Kevlar yarns
(2002-11-12) Renduchintala, Chaithanya; Yiping Qiu, Committee Member; Tushar Ghosh, Committee Member; Dr. William Oxenham, Committee Chair
Air texturing is an extremely versatile mechanical yarn bulking process that improves the handle and tactile properties of continuous multifilament yarns. Kevlar, poly(p-phenylene terephthalamide) , due to its excellent mechanical and thermal properties has found wide ranging applications in protective clothing, however the filament has poor tactile properties. Air texturing could thus be the process of choice for improving handle by imparting bulk to the multifilament yarn however improvement of the surface characteristics is at the expense of tensile strength of the yarn. The thesis reports an experimental study which was carried out to determine the influence of the key processing parameters on the resultant tensile strength, strain and moduli properties of the yarn. A further objective of the research work was to develop novel structures that will have good surface properties with minimal compromise in the axial strength. In order to accomplish this goal, a literature review along with preliminary trials was conducted to document the texturing process and to select the key process variables. Based on these findings a three factorial experiment was conducted to achieve the objectives. The results showed that processing conditions have an influence over the resultant tensile properties. The study also explores a novel yarn structure that has loops on the surface while the orientation of the core is retained.