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.

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In Part I of this series of papers, structures and geometries of the four-step preforms were studied and analysed. In this part, an account is given of similar work conducted on the two-step preforms. Theoretical models for both regular and tubular two-step preforms are established with a few assumptions. Structu.ral geometries of the preforms are analysed aud discussed according to the theoretical models developed. Mathematical relations between the structural parameters, such as the fibre orientation, yam-volume ft-action, and prefoirm contour sizes, as well as their dependence on operating conditions, are derived. It is found that the preform structures are determined hy the constitucint yams, the braiding arrangements, and the process operating conditions. The extreme values ofthe parameters in the jamming conditions are also discussed. To verify the validity of the analytical models, experimental investigatic>ns were also carried out. The experimental results strongly support the theoretical predictions.

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.

An exploratory study of the fracture behavior and notch sensitivity of a 4-step, 3-D braid-reinforced graphite/epoxy composite has been made. Test methods based on the Mode I compact tension specimen were developed and lower bounds for the damage initiating force and the work of fracture were determined for certain notch-to-braid axis orientations. These values are higher than for laminate composites but showed severe anisotropy. Complementary in-situ and post-mortem optical and scanning electron microscopy were used to identify microstructural failure controlling features and to develop a volume-to-surface structural mapping strategy useful in accounting for some of the observed features of the failure process.

The first part of this series shows that empirical and theoretical relationships developed to relate cardability to fiber movement and distribution have no practical value without a technique to measure fiber loading on card elements. This paper closely examines and compares off-and on-line techniques and devices implemented by previous researchers to measure fiber loads on card elements. Additionally, this part presents research efforts to develop a new optimum device with flexible features to measure two-dimensional fiber loading on card elements.From the empirical and theoretical investigations reviewed in Part I [ 13 ] of this study on fiber movement and transfer, we realized immediately the need to measure fiber loading and the collecting power of carding elements to determine carding performance. Realizing the importance of fiber loading on the cards, Zeidman and Batra' proposed a general concept for assessing fiber loading on the cards. For a flat-top card, the feed stream or fiber loading on the doffer, the load on the flats, the fiber load on any one of the cylinder regions, and the waste ratios at different points must be known to determine the fiber density in all regions of the card; for a roller-top card, the feed stream or fiber loading on the doffer, the loads on all workers, the fiber load on one of the cylinder regions, and the waste ratios at different points must be known to determine fiber density in all regions of the card. Attempts to find an effective way to measure fiber loads on any carding elements go back to the early 1940s [ 1-5, '7-I 2, 14, 15].2 These attempts mainly depended on tedious offline manual measurement procedures [ 10, 12 J . It soon became apparent that stopping, collecting, and weighing to determine the fiber load was restricting research progress because of its slowness and discontinuity.During late 60s, light reflection methods simplified measurements on the cylinder and the doffer. Measurement Techniques OFF-LINE TECHNIQUESThe earliest attempt to measure fiber load on a roller-top card was made by Martindale [ 12 ] , who conducted an experiment to determine the collecting power of the workers. He assumed the amount of fibers on the cylinder was equal to the feed rate. He found the amount of fibers on the worker by stopping the card, removing the worker chain and stripper belt, turning the worker by hand, and stripping the fibers from it by an oscillating motion of the stripper. The criticism of this method was that the fiber on the worker was picked up while the machine was slowing down to a standstill, which did not represent actual working conditions. Martindale conducted further tests to support his argument. The machine was run at full speed as one of the workers was lifted clear off the cylinder and held until the machine stopped. The fiber on it was then removed for weighing. A comparison of the methods showed that they gave slightly different results, but the difference was not sufficient to invalidate the earlier experimental results. Abhiraman and George [I] ...

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

Extensive coverage of previous work in the area of developing a dimensionless number or index to express a woven fabric's 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 Ashenhurst's ends-plus-intersections theory and Love's racetrack geometry, is suggested. The advantages and limitation of the new tightness are discussed.