Ron Postle

EXPERIMENTAL METHODS FOR MEASURING FABRIC MECHANICAL PROPERTIES: A REVIEW AND ANALYSIS

This is a review article of the various experimental approaches used for measuring fabric mechanical properties important in apparel handling, including the biaxial tension and in-plane shear parameters. First, the paper discusses the important issues encountered during such a fabric test. Then most existing biaxial tension and shear fabric testers are introduced and critically analyzed. Based on this information, a new tester concept is proposed in which tensile and shear forces can be applied simultaneously.

Mechanics of three-dimensional braided structures for composite materials – Part II: prediction of the elastic moduli

Abstract In the first part of this series of paper [Z.X. Zang, R. Postle, Mechanics of three-dimensional braided structures for composite materials – Part I: fabric structure and fibre volume fraction, Comp. Struct. 49 (2000) 451–459], it was demonstrated that the braiding angles and fibre volume fraction can be represented as functions of the normalized pitch length introduced as a key parameter of three-dimensional braided reinforced composite materials. In the present paper, the models for the prediction of the tensile and shear moduli of three-dimensional braided composites are established by numerical simulation and mathematical modelling. Three-dimensional braided preforms are produced from the material system comprising glass/polypropylene and their moduli are measured. The results predicted from the braided composite models are supported by the experimental data.

Mechanics of three-dimensional braided structures for composite materials - part I : fabric structure and fibre volume fraction

This paper is the first part of a series on the mechanics of three-dimensional braided structures for composite materials which include fabric structure and fibre volume fraction models, prediction of mechanical properties, finite element analysis and simulation of deformations. In the present paper, the normalized pitch length is introduced as a key parameter of three-dimensional braided structures. It is demonstrated that the braiding angles and fibre volume fractions can be represented as functions of this key parameter. The structures of three-dimensional braids were simulated and the braided fabrics and preforms were designed and produced. Fibre volume fraction models were established. The predictions from the fibre volume fraction models are supported by experimental results.

Mechanical properties of cashmere single jersey knitted fabrics blended with high and low crimp superfine merino wool

In this replicated experiment, we investigated the impact of cashmere in blends with superfine wools on the mechanical properties of single jersey knitted fabrics. We also investigated the relative performance of soft, low crimp/low fiber curvature superfine wool when compared with cashmere and also when compared with traditional high crimp/high fiber curvature superfine wool in pure and blended knitted fabrics. The results indicate both the cashmere blend ratio and fiber curvature/crimp of wool affected fabric properties. Pure cashmere fabrics were softer than pure wool fabrics. Adding cashmere to wool increased knitted fabric softness, smoothness, flexibility, and suppleness. The physical properties of pure low crimp wool fabrics were closer to the properties of pure cashmere fabrics than were knitted fabrics made from pure standard wool.

Design and construction of an atmospheric or environmental SEM—2

Abstract This paper is a continuation of a series of reports on the design and construction of an atmospheric or environmental SEM. The work described is an extended study of the gas jet developed above the pressure limiting aperture (Bell, 1974; Lacaze et al., 1977). Experiments specifically aimed to establish how the vacuum in the electron optics system was affected by the relative positioning of the objective and pressure limited aperture, as well as the pumping speeds employed, specimen chamber pressure, geometry and size of apertures, and by other means. Further, the nfluence of the jet deflectors, to control the effects of this jet on the microscope system were studied quantitatively using a specifically designed apparatus. In addition, the study of the pressure gradients below the pressure limiting aperture revealed that specimens can be placed as close as radius from the aperture and still experience an almost saturated vapour pressure environment. The results of the present study are currently being used in the design of an optimum detection configuration. A preliminary result has allowed the use of 140 μm pressure limiting aperture to observe specimens at atmospheric pressures as well as the use of low accelerating voltages (e.g. 7 kV) at TV scanning rates to record on video cassette dynamic phenomena, including wetting or recrystallizing salt solutions, etc.

Mechanics of three-dimensional braided structures for composite materials – part III: nonlinear finite element deformation analysis

Abstract In the previous two parts of this series of papers, the fabric structures of three-dimensional braided composites were simulated and the fibre volume fraction was derived [Z.X. Tang, R. Postle, Compos. Struct. 49 (2000) 451]. The models of tensile and shear moduli for three-dimensional braided composites were established by computer simulation and mathematical modelling. The results predicted from the modulus models were supported by the experimental data [Z.X. Tang, R. Postle, Compos. Struct. 51 (2001) 451]. In the present paper, a nonlinear finite element approach used for simulating and analysing the deformation of three-dimensional braided composites is derived. The corresponding computer codes are developed with 20-node hexahedral elements and 3×3×3 Gauss–Legendre quadrature. The tension and bending simulations are performed. The comparisons of the results obtained from simulation, experiment and prediction from the modulus models are reported. The results of simulation are supported by the experimental data and the values predicted by the previously published modulus models.

Determining the Cross-Sectional Packing Density of Rotor Spun Yarns

Packing density, the fiber distribution in a yarn cross section, can to a great extent influence the properties and quality of the yarn. Thus, the need for precise and concise information about packing density becomes a must for an in-depth understanding of yarn structure and hence yarn mechanics. This paper describes a detailed method for determining packing density. We begin by acquiring yarn cross-sectional images to provide input data for calculating yarn cross-sectional packing density. These data include the coordinates of each fiber center and fiber radius. A program whose general writing algorithm is also elaborated in detail is compiled to calculate the packing ratio zone by zone. With these discrete packing ratios, a curve-fitting technique yields a continuous packing density function. In addition, a study of the relationship between packing density and yarn parameters such as yarn count and twist factor is included.

Processing and quality of cashmere tops for ultrafine wool worsted blend fabrics

This study has focussed on three main areas. First, an evaluation of the physical attributes of cashmere tops available to commercial spinners; second, the influence of processing variables on the efficiency of producing cashmere tops from raw Australian cashmere; and third, the influence of design of cashmere ultrafine wool blends on the fibre curvature of tops. Testing the physical attributes of cashmere tops from traditional and new sources of supply, was followed by statistical analyses based on factors of origin, processor and other determinants. The analyses demonstrated important processor effects and also that cashmere from different origins shows commercially important variations in fibre attributes. It was possible to efficiently produce Australian cashmere tops with Hauteur, tenacity, extension, softness and residual guard hairs quality attributes equivalent to those observed in the best cashmere tops. The blending of cashmere with wool resulted in a reduction of the mean fibre curvature of the blend compared with the unblended wool. The present work demonstrated that the fibre curvature properties of blended low crimp ultrafine wool tops were closer to the properties of pure cashmere tops than were tops made from blended standard high crimp ultrafine wool. The attributes of textiles made from the relatively rare Australian low curvature cashmere could enhance the marketability of both Australian cashmere and low curvature wool.

An Analysis of Fabric Large Strain Shear Behavior Using Linear Viscoelasticity Theory

Linear viscoelastic theory is used to analyze fabric shear behavior under high shear strain conditions (up to maximum shear angles of 20°). A fabric trellis shear test method yields shear relaxation data as well as residual shear strain. Interfiber frictional stress in fabric shear under high shear strain conditions is evaluated.

Worsted Cashmere Top and Yarns Blended with Low or High Curvature Superfine Merino Wool

In this replicated experiment, we investigated the impact of cashmere on blends with superfine wools on the quality of tops, rovings, and worsted spun yarns. We also investigated the relative performance of soft, low crimp/low fiber curvature superfine wool when compared with cashmere and also when compared with traditional high crimp/high fiber curvature superfine wool in pure and blended yarns. The results indicate both the cashmere blend ratio and fiber curvature/crimp of wool affected processing requirements and the attributes of worsted pure and blended tops, rovings, and yarns. Adding wool to cashmere improved the processing of cashmere roving and reduced yarn faults. Mean fiber curvature was a good predictor of yarn hairiness and yarn tenacity.