Minoru Miwa

Effects of fibre length on tensile strength of carbon/glass fibre hybrid composites

The tensile strength of epoxy resin reinforced with random-planar orientation of short carbon and glass fibres increased as the length of the reinforcing fibres increased, and the increase in tensile strength remained almost unchanged after the fibre length reached a certain level. The tensile strength of composites at any fibre length could be estimated by taking the strain rate and temperature dependence of both the yield shear strength at the fibre-matrix interphase and the mean critical fibre length into consideration. The tensile strength of the hybrid composite could be estimated by the additive rule of hybrid mixtures, using the tensile strength of both composites.

Volume fraction and temperature dependence of mechanical properties of silicone rubber particulate/epoxy blends

Abstract At all temperatures, both the Youngs modulus and tensile strength of silicone rubber particle/epoxy resin blends decreased as the volume fraction of the silicone rubber particles was increased, and this decrease became greater with falling temperature. A volume fraction-temperature superposition held for both the Youngs modulus and tensile strength of the blends. The shifted volume fraction of silicone rubber particles needed to obtain master curves increased with increasing temperature and the shift was almost the same for both properties. An optimum suitable volume fraction of rubber particles existed in terms of improving impact fracture energy. A volume fraction of silicone rubber particles of 5–10% appears to be the most suitable for obtaining a blend in which the decrease in Youngs modulus and the tensile strength is relatively low and the increase in impact fracture energy is relatively high.

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

Epoxy resins with various ratios from two kinds of curing agents, ethylenediamine (EDA) and N,N′-dimethylethylenediamine (MeEDA), 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 temperature. 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-mixing ratio of curing agent superposition held for the shear properties, and the shift factor for these superpositions increased with the increase in MeEDA.

Anisotropic transparency of polystyrene film with crazes

A crazing method was developed to create regular crazes in a polystyrene film. The crazes penetrated completely in the direction of film thickness. The tensile strength of the crazed films in both perpendicular and parallel directions to the processing direction was almost unchanged after the crazing-processing, regardless of crazing conditions. Youngs modulus in the parallel direction decreased with the film tension during the crazing-processing. If suitable crazing-processing was used, transmittance of incident light decreased between the incident angles of 0 to 20 deg, and increased above the angle of ca 20 deg with an increasing incident angle, which gives a W-shape to the light transmittance curve.

Critical fibre length and tensile strength for carbon fibre-epoxy composites

The tensile strength of epoxy resin reinforced with a random-planar orientation of short carbon fibres decreases with increasing temperature. This decrease may be estimated by the strain rate and temperature dependence of both the yield shear strength at the fibre-matrix interphase and the critical fibre length obtained by taking the distribution of fibre strength into consideration. The experimental value at room temperature is smaller than the calculated value. It is inferred that this result is attributed to the stress concentration caused by ineffective fibres produced during preparation which were shorter than the critical fibre length.