Deformation Fields in Woven Composite Plates Under Impact

The deformation fields and kinematics of woven composite material systems due to impact loads are analyzed and characterized for various structural parameters. Target plates comprised of woven composites with 3D preforms are considered. The analysis examines fully consolidated as well as cellular systems and simulates actual experiments. Solution of the nonlinear dynamic/contact problem was obtained by a meso-mechanics based finite element model. The results quantify experimental observations, which reveal distinct behavior under impact among nonporous and porous systems. It was found that wave propagation effects at incident energies in the order of 500 J are significant and lead to penetration at the impact face. Localized shear damage in the 3D woven system precede penetration in both the nonporous and the porous systems. The porous system is capable of dissipating more energy prior to penetration due to containment of local damage, which emanates from the void boundaries, within subsurface locations.

Stress Analyses and Structural Modifications of Fabric Composite Seams

An adhesively bonded seam is a common method of joining coated fabrics in the manufacturing of inflatables. In this paper, Nylon and Polyester seams are studied both experimentally and numerically. In the numerical analyses, the seam components are described with layered models containing fabric composite layers. The in-plane and out-of-plane elastic constants of the fabric composite layers are derived using the crimp model and a stacked model respectively. An existing finite element code, ANSYS 5.7 is used to perform two-dimensional stress analyses of the seams under tension. In the analyses, a stress concentration factor is defined to evaluate the strength of the seams in comparison with their base fabric laminates. Numerical data show that Nylon seams are almost as strong as their base laminate but there is strength degradation in Polyester seams, which agrees well with test results. Finally, two structural modifications are proposed to improve the strength of the Polyester seams. The modifications are evaluated by both simulations and tests.

Effect of Curing Process on Intercalation and Exfoliation Behavior of Epoxy/Clay Nanocomposites

Effects of curing agents, curing conditions, and curing degree on intercalation and exfoliation behavior of epoxy/clay nanocomposites were investigated. Epoxy was cured with five curing agents, DETA, DDM, DMP-30 and two modified amines, with different curing speeds at various temperatures (from low to high). Curing degree and distance between layers of clay were measured by FTIR, XRD and TEM respectively. It was found that it was easy to intercalate clay in epoxy resin, while clay exfoliation in epoxy resin was dependent more on the curing conditions than on curing agents. Under certain curing conditions when curing speed of interlayer epoxy resin is faster than that of extralayer and fully reaches curing, exfoliation easily takes place with all these curing agents and epoxy/clay nanocomposites can be prepared. At the same time, the distance between clay layers increased from 17.5Å to about 100Å. When the curing temperature was too low, diffusion speed of the epoxy resin and the curing agents can influence the clay exfoliation. When the curing temperature was too high, epoxy was cured too rapidly, such that the high viscosity and the resultant mechanical forces will stop the exfoliation process. Only under properly temperatures when the curing speed of the interlayer epoxy is higher than that of the extralayer epoxy can exfoliation take place.

Diffusion and Performance of CAD/CAM in the U.S. Textile and Apparel Industry

This study examines the determinants of CAD/CAM adoption and diffusion in American textile and apparel industries. Innovation diffusion theory provided a conceptual framework and empirical base applicable to the study of technology adoption and implementation. A variety of sources were used to develop the survey which was mailed to a national random sample of 500 textile and apparel manufacturers. The responses of 103 manufacturers from 30 different states were analyzed. Factor analysis was used to identify the dimensions of reasons for CAD/CAM adoption. Hypotheses were tested with logistic regression analysis procedures. The diffusion of CAD/CAM practices was found to be driven primarily by the market and affected by the business-unit size. In addition, labor considerations affected recent CAD/CAM adoption.

Effect of Nesting of Fiber Bundles on Micro Fracture of Laminated Woven Fabric Composite

In laminated woven fabric composites, fiber bundles do not pack tightly because there are resin rich regions caused by crimp of fiber bundles. The fiber bundles in one layer are often fitted into the neighboring layer, which is called nesting. In this study, the effect of nesting by laminating on mechanical properties and micro fracture behavior of composites was investigated. Tensile testing of woven fabric composites with different number of layers and observation using optical microscopy were performed. With the increase of number of layers, nesting is more likely to occur, resulting in a decrease in thickness per layer increase in fiber volume fraction. This also lead to an increase in modulus and strength but a decrease in knee point stress. The locations at which cracks occurred were different in specimens with and without nesting.

Investigation of Yarn Twist Propagation in Rotor Spinning

This paper proposed an integrated mechanical approach for yarn dynamics in rotor spinning, especially the twist propagation in the yarn forming process from fibers collected in a rotor groove to the twisted yarn at the twist stopper. Equations of dynamic equilibrium in different yarn forming regions were established, and further, expressed in terms of dimensionless variables. Then the yarn tension and twist distribution, considering the dynamic coupling effects between different regions under the steady spinning conditions, were numerically simulated, in which influences of various dimensionless parameters of rotor spinning on the yarn tension and twist distributions were discussed in details.

Partially Miscible Hybrids Made From Chlorinated Polyethylene and 2,2′-Methylene-Bis-(4-Methyl-6-Tert-Butyl Phenol)

Damping behaviors and miscibility between a polar polymer (CPE) and an organic small molecule (AO-18) are mainly discussed in this paper. It is well-known that mixing two partly compatible polymers can produce a material with a wide range of the glass transition temperature (Tg) and thus good damping behavior. In this paper, since CPE and AO-18 are partially miscible, adding AO-18 to CPE causes Tg of the mixture shifts to higher temperature, and the relaxation of AO-18 appears when AO-18 content is high in CPE/AO-18 alloy, similar to two partly compatible polymers. The damping properties around CPE glass transition are greatly improved compared with pure CPE, which can be attributed to the hydrogen bonds between CPE and AO-18 in CPE/AO-18 hybrids.

Mechanical Properties of Square Braided Fabric

Cyclic compression test was performed on square braided fabric and the effects of the type of fiber bundle were examined for aramid and glass square braided fabrics. Moreover, the strength of the fiber bundles from the square braided fabric after cyclic compression loading was investigated with tensile testing of fiber bundles. It was found that the strength of the glass fiber bundle was decreased with the increase of compression cycle, whereas the strength of aramid fiber bundle was not decreased. The decrease in strength of glass fiber bundle caused an increase in cumulative deformation with compression cycle.

Nonlinear Deformation of Woven Fabrics

The large deformation of plain-weave fabrics consist of bundle yarns under biaxial loading is examined by a sinusoidal model. The nonlinear properties, flattening and transverse shear effects of the bundle yarn, as well as the yarn’s crimp interchanges are considered in this study. The constitutive equations are derived from the energy method. Comparison is made with the uniaxial experimental result, and the biaxial behaviors of the fabric are predicted and discussed.

A Novel 3-D Braiding Technology, Complex Shape Preforms and Composites

A brief overview of 3-D braiding technology and its two major branches, “row and column” and “rotary” braiding, opens the paper. An innovative 3-D braiding process that has been recently patented and implemented in a fully automated multi-modular industrial scale machine is introduced next. The machine enables producing complex, continuously variable shape preforms for composite structures. Each module of the machine incorporates some number of horngears with four yarn carriers placed on each of them. A novel gate switch mechanism, based on the gripping fork controlled rotation, provides smooth transfer of yarn carriers between adjacent horngears. Each gripping fork is controlled individually, thus allowing fabricating practically unlimited variety of complex cross section 3-D braided preforms. Examples of manufactured braided products include rectangular bars, T-, I- and J-stiffeners, box-beams, hollow tubes, etc. Results and discussion of mechanical characterization of 3-D braided carbon and E-glass composites conclude the paper.