Aly El-Shiekh

An Experimental Investigation of High Velocity Impact and Penetration Failure Modes in Textile Composites

The dynamic failure evolution of textile composites, which were subjected to impact velocities up to 1100 m/s, was investigated. Specialized machines were used to fabricate composites from combinations of Spectra®, Kevlara®, and Twaron® fibers and two- and three-dimensionally woven, braided, and needle-punched nonwoven fabrics. This control of fabrication and processing enabled us to characterize response as a function of areal density, fabric finish, and consolidation techniques. Failure was categorized in terms of material layers, debris mass, matrix cracking, fiber failure, and shear-plugging. Results indicate that shear-plugging occurs at velocities corresponding to decreases in debris mass.

Structural Analysis of 3-D Braided Preforms for Composites Part I: The Four-step Preforms

Three-dimensional (3-D) braiding technology using high-performance fibres for advanced composite structures is receiving great attention as a result of the outstanding mechanical and thermoelastic properties of the materials produced. There are now mainly two groups of 3-D braiding techniques, namely, the four-step and the two-step processes. The objective of the research reported in this paper was to study and analyse the preform structures. In this part, theoretical models for the four-step braided structures are established. Structural geometries of the preforms are analysed and discussed in accordance with these theoretical models. Mathematical relations among the structural parameters, such as the fibre orientation, yarn-volume fraction, and preform contour sizes, as well as their dependence on machine-operating conditions, are derived. The extreme values of the parameters due to geometric constraints under the jamming conditions are also analysed and determined. These extreme values dictate the limi...

Mechanics of Woven Fabrics Part IV: Critical Review of Fabric Degree of Tightness and Its Applications

Extensive coverage of previous work in the area of developing a dimensionless number or index to express a woven fabrics degree of tightness or firmness is critically reviewed. The review also includes applications of fabric tightness to designs of similar cloth, to weaving resistance, and to their relationships with fabric properties. A new tightness factor, based on a combination of Ashenhursts ends-plus-intersections theory and Loves racetrack geometry, is suggested. The advantages and limitation of the new tightness are discussed.

Mechanics of Woven Fabrics Part III: Critical Review of Weavability Limit Studies

Extensive coverage of previous work in the area of weavability limit theories, their experimental validation, and their practical importance is reviewed. The review also includes previous work on maximum construction relationships derived empirically, as well as a comparison of different theories and empirical studies.

The Mechanics of Bicomponent Fibers Part I : Theoretical Analysis

An analytical approach has been adopted to predict the amount of bulk that would develop in a hicomponent fiber having particular geometric distribution of the components of known physical properties. Theoretical expressions have been developed to predict the geometry and mechanical properties of bicomponent struc tures. In particular, an analytical relation has been developed for the radius of the loop of such a structure in terms of strains in the components and their physical dimensions and elastic moduli. The radius of the loop has been related to the bulk ratio. Expressions have also been derived to predict the load elongation relation for the coiled bicomponent structure

Mechanics of Woven Fabrics, Part I : Theoretical Investigation of Weavability Limit of Yarns with Thickness Variation

Theoretical maximum weavability relationships of fabrics woven from regular warp ends and variable thickness filling yarns are derived by developing a local geometry where the thick filling place is interlaced with warp ends and where warp yarn is interlaced with thick and thin filling yarns. Geometric relationships are derived from the local geometry, and hence a local weavability limit relationship is deduced. The average warp and filling spacings are calculated by developing an imaginary proba bilistic model of a time scale and relating the geometric parameters at different locations. The final expressions for the weavability limit, which represent the fabric sheet as a whole, relate the average maximum warp and filling cover factors to the ratio of average filling yarn to warp yarn diameters; the ratio of thick place of filling to warp yarn diameters; and the ratio of thick place length of filling to the wave length, warp and average filling densities, thick and thin places of filling yarn densities, number of filling yarns in the pattern repeat, and weave design.

Mechanics of Woven Fabrics Part II: Experimental Study of Weavability Limit of Yams with Thickness Variation

A wide range of tightly woven fabrics made from regular thickness warp ends and filling yams with pulse train irregularities was produced to test the validity of the theoretical weavability limit relationships developed in Part I of this study. The in vestigation includes periodic and random thickness variation filling yarns. The results show that the agreement between the theoretical and loom maximum fabric cover factors is fairly good up to eight-harness weaves.

Heat Transfer in False-Twist Texturing

A mathematical model for the heating of yarn in the false-twist texturizing process was formed, and an equation for the surface temperature of the yarn for contact-type heaters was derived. An expression for the temperature distribution in the cross section of the yarn in the heater zone was derived mathematically. The surface temperatures of nylon and polyester yarns of different deniers were measured and compared with predicted values. For measuring the surface temperature, a Fiber-temp® non-contact-type temperature measuring instrument was used. The yarns were heated using controlled short heaters 12 in. and 8 in. long. The temperature distribution in the cross section of the yarns was calculated from the equation for various yarn speeds and heater temperatures. The temperature difference between the surface and the center of the yarn was found to be small for the normal yarns used in texturizing, even at very high speeds. Polyester yarns were found to heat up faster than nylon yarns due to the lower heat capacity of polyester. The heavy denier yarns were heated more slowly than the lower denier yarns because of the lower A/M (surface area/mass) ratio of the high denier ones.

The Dynamic Modulus and Some Other Properties of Viscose-Polyester Blends

It is pointed out that little attention has I>een devoted to the mechanics of blended spun yarns. Most of the work done in this area is limited to strength and elongation, An experimental investigation of viscose/polyester blended yarns was undertaken. The eRect of twist and h)end levels on the initial modulus, dynamic modulus, tenacity, and elongation of these yarns is analyzed. It is shown that both the dynamic and initial moclulii of these yarns increases as polyester percentage increases and then decreases to reach its lowest level at 100% polyester. It is also shown that the dynamic modulus is appreciabty greater than the static modulus and that the former increases as the testing tension increases.

Tensile Behavior of Twisted Hybrid Fibrous Structures Part I : Theoretical Investigation

The energy method based on the first law of thermodynamics is employed to predict the whole range of stress-strain behavior of twisted hybrid fibrous structures. The model blend yams considered are sheath/core and mixed two-component yarns. Analytical expressions for the load-elongation response including failure are derived as functions of yam geometry and the mechanical properties of component fibers. The mathematical expressions are applicable to the hybrid yam structures made of nonlinear materials with any fractional combination of two components.