Teruyuki Yokoi

Fiber Speed and Yarn Tension in Friction Spinning

To investigate fiber speed inside the transport channel, fiber flow and yarn tension are measured at the same time on a friction spinning machine. Fiber speed at the fiber flow detection point is calculated using the number of fibers in a cross section of the channel at the detection area, the number of fibers in the cross section of sliver, and the speed of sliver feeding. The cross correlation method is used to obtain the time lag between the variation of yarn tension and the number of fibers in the channel cross section. The mean fiber speed between the fiber flow detection point and the yarn-forming zone is calculated from the time lag. Fiber speed in both cases is calculated for various levels of suction air pressure. The results of this research show that fiber speed decreases from the beginning to the end of the transport channel, and increases with increasing suction air pressure in the yarn-forming zone. On the other hand, calculating the value of the correlation coefficient demonstrates that there is a high correlation between yarn tension variation in the yarn-forming zone and the number of fibers in the channel cross section.

FATIGUE BEHAVIOR OF ARAMID NONWOVEN FABRICS UNDER HOT-PRESS CONDITIONS. PART IV : EFFECT OF FIBER FINENESS ON MECHANICAL PROPERTIES

We set out to find the most suitable design for heat-resistant nonwoven fabrics to be used as components of laminated cushion materials. The changes in mechanical prop erties and durability of a nonwoven fabric subjected to repeated hot-press fatiguing treatments depend on the properties of the fiber material and the structure of the non woven. In this paper, we focus on fiber fineness, one of the material properties, and discuss its influence on the mechanical properties of nonwoven fabrics after hot-press fatiguing. We find that a nonwoven made of fine fibers has a higher tensile breaking strength and a higher tensile modulus than those made of larger diameter fibers. The nonwovens we prepared have the same fabric basis weight with different fiber diam eters. Accordingly, the finer fiber nonwoven has a larger number of component fibers than those of larger diameter fibers, and the degree of fiber entanglement in the finer fiber nonwoven is higher because the number of fibers caught by the needle is greater when the fibers are finer. Tensile breaking strength is proportional to the degree of fiber entanglement, so the finer fiber nonwoven has a higher tensile breaking strength. However, this strength decreases after too many fatiguing treatment cycles, probably due to the deterioration of the fiber material (Nomex). As regards compressive behav ior, the finer fiber nonwoven has a lower compressive strain and a higher modulus than those of the larger diameter fibers. These tensile and compressive properties are closely related to the nonwovens fiber packing factor.

Predicting the Penetrating Force and Number of Fibers Caught by a Needle Barb in Needle Punching

The mechanical properties of needle-punched nonwoven fabrics depend on the fiber entanglement effected by the needles. The needle barbs catch the fibers during punching and lead them into the thickness direction, creating fiber-to-fiber entanglement. In this research, we propose a method to estimate the number of fibers caught by a needle barb. We compare the results of our calculations with experimental data derived from micro scopic observations. Also, we consider the relationship between the number of caught fibers and the penetrating force of a needle barb, and we discuss the relationship between these factors and the tensile properties of the nonwoven fabric.

Fatigue Behavior of Aramid Nonwoven Fabrics Under Hot-Press Conditions: Part VI: Effect of Stable Base Fabrics on Mechanical Properties

The purpose of this investigation is to find the most suitable design for heat-resistant nonwoven fabrics to be used as a component of laminated materials. In the earlier parts of the series [1-5], we found that needle punched nonwoven fabrics have superior recovery from pressure compared to paper-like nonwoven and four-ply woven fabrics. The three-dimensional fiber arrangement made by the needle causes these fibers to behave like springs in the nonwoven. The degree of 3-D fiber arrangement depends on needle punching density, and is one of the most important factors that determine the mechanical properties of the nonwoven. But the 3-D fiber arrangement and its effec tiveness gradually diminish after repeated hot-press fatiguing treatments. In this new experiment, we create a needle punched nonwoven by inserting a few stable base fabrics between webs, so that the 3-D fiber arrangement is maintained as long as pos sible even after many hot-press fatiguing treatments. Generally, a stable base fabric is used for dimensional stability and deformation resistance of the nonwoven. We believe that a base fabric in a nonwoven will restric the movability of fibers, so the 3-D fiber arrangement can be maintained, and the recovery from pressure and durability against repeated hot-press fatiguing treatments may be further improved. The nonwovens are made from various base fabrics in different positions between the webs. We also study the effectiveness of the base fabrics on the mechanical properties of nonfatigued non wovens and the changes in their properties with fatiguing.

Fatigue Behavior of Aramid Nonwoven Fabrics Under Hot-Press Conditions Part V: Effect of Punching Density on Mechanical Properties

Changes in the mechanical properties and durability of a nonwoven fabric with repeated hot-press fatiguing treatment depend on the properties of the fiber material and the structure of the nonwoven. Following Part IV, which deals with fiber fineness, in this paper we focus on punching density, which greatly affects the nonwoven struc ture, and we discuss the influence of punching density on the mechanical properties of nonwoven fabrics after hot-press fatiguing cycles. We hypothesize that a nonwoven with greater punching density will have a larger number of fibers reaching perpendic ularly across its width. This will increase fiber entanglement because more fibers will be caught by the needle. In Part IV, we found that a nonwoven fabric with more entangled fibers has a higher tensile breaking strength, so it is natural to believe that a nonwoven with a higher punching density has a higher tensile strength than one with a low punching density. The experimental results show, however, that a nonwoven with too much punching density has a lower tensile strength due to fiber breakage by too much needle punching. Thus, there is an optimum punching density that gives the highest tensile strength. Regarding compressive behavior, a nonwoven fabric with higher punching density has a small compressive strain and high compressive modulus, meaning it is stiffer. We have found that changes in tensile and compressive behaviors with hot-press fatiguing closely relate to nonwoven fiber packing factors.

FATIGUE BEHAVIOR OF ARAMID NONWOVEN FABRICS UNDER HOT-PRESS CONDITIONS. PART I : MECHANICAL PROPERTIES

Tensile and compressive behaviors of aramid and polyamide nonwoven fabrics are studied under hot-press fatigue conditions. Tensile breaking strength and the maximum modulus of tensile strength-elongation curves for the polyamide nonwovens gradually decrease with increasing fatigue after around 15 cycles, while those of the aramid nonwovens substantially increase. Aramid nonwoven values are about three to five times those of the polyamide nonwovens. These fatigue behaviors result from the differences in heat resistance and mechanical properties of polyamide and aramid fibers, indicating that polyamide fibers greatly deteriorate with heat while aramid fibers deteriorate only a little. Although we have assumed that the aramid nonwoven fabrics compact their fiber assemblies under increasing cycles, there are no substantial dif ferences in the compressive behaviors of polyamide and aramid nonwovens.

Strain rate and temperature dependence of shear properties of epoxy resin with various molecular weight between cross-linkings

Epoxy resins with various molecular weights between cross-linkings were prepared. In order to examine the strain rate and temperature dependence of the shear yield strength and the shear strength, test specimens were subjected to shear deformation at various strain rates and temperatures. The shear yield strength and the shear strength increased almost linearly as the logarithm of the strain rate increased. The strain rate-temperature superposition held for these shear properties. In particular, an experimental equation of the strain rate-temperature superposition for the shear yield strength was found. The shift factor to obtain a master curve was given with the temperature dependence of an Arrhenius type. Furthermore, the strain rate-temperature-molecular weight between cross-linkings superposition held for the shear properties.

Fatigue Behavior of Aramid Nonwoven Fabrics Under Hot-Press Conditions Part VII: Effect of Needle Shape on Compressive Properties

Nonwovens used as components of laminated cushion materials for multi-daylight press molding are subjected to repeated hot-press fatiguing. Preferred heat-resistant nonwovens show little change in mechanical properties such as tensile and compression after repeated fatiguing. In Part III, needle-punched nonwovens had superior recovery from hot-press fatiguing compared with paper-like nonwovens and four-ply wovens, because the 3-D fiber arrangement (fibers arranged in the thickness direction) provided by the needle caused these fibers to behave like springs in the nonwovens. In Part VI, the 3-D fiber arrangement was maintained by the stable base fabrics after repeated fatiguing, and was one of the important factors determining the mechanical properties of these nonwovens. The 3-D fiber arrangement can be mainly constructed by the barb and throat of the needle. In this study, we discuss the influences of the barb and throat shapes on fiber arrangement and fiber-to-fiber entanglement. In particular, we discuss the relationship between the cross-sectional area of the throat and compression-recovery properties. Three kinds of nonwovens prepared with different needle types are subjected to repeated hot-press fatiguing treatments, and their compression-recovery behaviors are analyzed. The nonwoven made by the needle with the large cross-sectional throat area is thinner, very elastic, and provides good recovery from compression. This is because the fibers arranged in the thickness direction by the needles get more tightly entangled and may behave somewhat like springs during compression and recovery.

Effects of surface and sizing treatments on axial compressive strength of carbon fibres

Attempts have been made to estimate the fibre axial compressive strength of pitch-based graphitized fibres, and the effects of surface- and size-treatment on compressive strength was investigated. The estimated compressive strength of fibres decreases with increasing temperature. This decrease in compressive strength may be accounted for by a decrease in the radial compression force owing to a decrease in the residual thermal stress and a decrease in Youngs modulus of the resin matrix. There is a linear relationship between the estimated compressive strength and radial compression force in a temperature range from room temperature to 80 °C. The real compressive strength of the fibres, determined by extrapolating this straight line until the radial compression force is zero, increases with increasing shear yield strength at the fibre-matrix interphase. In order to obtain reinforcing fibres with a higher compressive strength, it will be necessary to surface- and size-treat the fibres.

Effects of Young's modulus of epoxy resin on axial compressive strength of carbon fibre

Using epoxy resins with various molecular weight between cross-linkings, attempts have been made to estimate the fibre axial compressive strength of pitch-based graphitized fibre, and the effect of Youngs modulus of epoxy resins on compressive strength was investigated. The estimated compressive strength of fibre decreases with increasing temperature. This decrease in compressive strength may be accounted for by a decrease in the radial compressing force due to a decrease in the residual thermal stress. There is a linear relationship between the estimated compressive strength and radial compressive force in a temperature range from room temperature to 80 °C. The estimated compressive strength of the fibre increases with increasing Youngs modulus of epoxy resins. In order to realize reinforcing fibres with a higher compressive strength, it will be necessary to use a resin matrix with a higher modulus.