R.C. Dhingra

Measuring and Interpreting Low-Stress Fabric Mechanical and Surface Properties Part I: Precision of Measurement

The results of an extensive study are reported involving the variability of measuring low-stress fabric mechanical and surface properties for a range of 30 wool and wool blend suiting fabrics. Seven sets of KESF instruments were used for the interlaboratory tests in Australia, Japan, Germany, the United Kingdom, New Zealand, and the Peo ples Republic of China. Values are given for the repeatability and reproducibility of 37 parameters and ratios characterizing the elastic and inelastic components of fabric deformation in tension, shear, bending, and lateral compression, as well as fabric surface behavior, that is, surface topography and friction. Measurement precision is also specified in terms of the maximum error for these parameters. The variance of the measurements is quoted in terms of its within-laboratory, between-laboratory, and specimen-laboratory interaction components. Recommendations are made for both the in-house product and process development situations (within laboratory) and for specifications for commercial transactions (between laboratory) as to the number of tests that should be performed in order to achieve a given level of precision. Though varying numbers of tests are recommended for some parameters, a general rule of three tests per sample may be taken as a guide.

Measuring and Interpreting Low-Stress Fabric Mechanical and Surface Properties Part II: Application to Finishing, Drycleaning, and Photodegradation of Wool Fabrics

The concept of using engineering principles as an aid in designing textile fabrics with desirable aesthetic characteristics is further developed. Fundamental to this ap proach is the measurement of fabric mechanical and surface properties, e.g., fabric tensile, shear, bending, surface, and lateral compression properties. Examples are cited of the application of these measurements to fabric finishing, drycleaning, and steam pressing, and also to the study of photodegradation effects in wool fabrics. The study has quantified the effect of scouring (during finishing of wool fabrics) and heat setting/ scouring (during finishing of wool/polyester fabrics) in reducing the rigidities and hysteresis in fabric bending and shear deformations. A marked reduction after paper pressing in fabric compressibility, thickness, and surface roughness for both wool and wool/polyester fabrics is also evaluated quantitatively. The important influence of decatizing and chemical setting on the performance of pure wool fabrics during dry cleaning and steam pressing operations is evaluated and discussed. Wool photodeg radation results in a substantial fabric tensile strength loss, marked increase in the bending and shear hysteresis and rigidities, and also a decrease in the tensile and compressional resilience.

Measuring and Interpreting Fabric Low Stress Mechanical and Surface Properties Part V: Fabric Handle Attributes and Quality Descriptors

The concepts of overall handle discussed in Part IV of this series [21] for mens suiting fabrics are explained in this analysis using descriptors called handle attributes. Definitions and English word descriptors are provided for the Japanese primary hand expressions isolated by the Hand Evaluation and Standardisation Committee for these fabric types. Sleekness, fullness, firmness, and drape are isolated as the relatively in dependent descriptors of handle for winter fabrics. Similarly, firmness/hardness, crispness, and fullness also characterize mens suitings. From the results of two inter national studies of handle preferences, judges prefer a sleek, full handle with relatively little stiffness and good drape for winter fabrics. There are strong national preferences for the handle of summer fabrics: there is a common handle assessment for Australian, New Zealand, Indian, U.S., and Hong Kong/Taiwanese panels of judges. There are different, and in some sense opposite, handle preferences for the Japanese and P.R.C. (Chinese) panels, who are mutually consistent. These judges prefer a firm, crisp, hard handle for summer fabrics, while the remaining five national panels exhibit opposite preferences.

FABRIC MECHANICAL AND PHYSICAL PROPERTIES RELEVANT TO CLOTHING MANUFACTURE —: Part 1: Fabric Overfeed, Formability, Shear and Hygral Expansion during Tailoring

The mechanical properties of fabric longitudinal extension and compression, shear and bending have an important influence on the performance of fabrics during tailoring and also on the performance of garments during use. Fabrics are overfed or underfed in tailoring during the sewing operations in such a way that longitudinal compression and extension are allowed in the fabric plane in order to produce the three‐dimensional shape or fullness of the garment. Fabric buckling or puckering at the seams should not occur, or if it does, should be removed during subsequent steam pressing operations. An experiment is described to measure the maximum limit of overfeeding that is possible during seaming without the subsequent formation of seam puckers. The relationships are studied between the maximum degree of overfeed, the bias angle between the feed direction and the fabric warp or weft, fibre type and fabric mechanical properties, especially fabric formability defined as the product of fabric bending rigidity and fabric longitudinal compressibility. When fabrics are extended or compressed longitudinally at a bias angle to the warp or weft direction during seaming in order to produce garment fullness, the warp and weft threads are rotated relative to each other in such a way that a local shear deformation is applied to the fabric adjacent to the seam‐line. Measurements are reported of the variations in the local shear angle along the shoulder seam‐line of a mens jacket and the measured values are related to the high degree of overfeed required in the bias direction in this area of the garment. Finally, hygral expansion measurements for wool fabrics and yarns unravelled from the fabrics are measured and compared for six different wool fabrics.

Hygral Expansion of Woven Wool Fabrics

An experimental study is reported of the hygral expansion behavior of a wide range of laboratory produced and some commercially produced wool woven outerwear fabrics. A fabric hygral expansion apparatus simultaneously measures changes in fabric length and fabric moisture regain which occur when the relative humidity of the ambient environment is altered. Fabric and yam hygral expansion curves are analyzed and discussed in terms of the following parameters: hygral expansion coefficient (slope of the initial linear part of the hygral expansion versus moisture regain curve), hygral expansion at 25% regain, and hygral expansion at 30% moisture regain. F bric hygral expansion behavior depends largely on the magnitude of the weave crimp. The effect of weave construction on the fabric hygral expansion is very small at high moisture regains; at low regains, plain-weave fabrics tend to show slightly higher expansion than the corresponding twill structures of similar crimp magnitude. The effect of fiber properties on hygral expansion behavior has been examined for a series of wool plain-weave fabrics produced from yams of the same linear density.

The Low-Stress Mechanical Properties of Wool and Wool-Blend Woven Fabrics:

The uniaxial-tensile and bending properties have been examined for a series of wool and wool/polyester woven apparel outerwear fabrics. The fabrics tested include a wide range of laboratory-produced woven materials (varying systematically in weave structure and the ratio of the two yarn curvilinear lengths) and also a range of commercially-produced woven fabrics. The fabric load-extension curves and yarn- decrimping curves are analyzed and discussed in terms of the following dimensionless parameters: the normalized tension per thread (the applied tension divided by the yarn-bending rigidity and multiplied by the square of curvilinear length in the extended direction); the relative yarn or fabric extension (the yarn or fabric extension divided by the yarn crimp); the initial fabric tensile modulus (i.e., initial slope of the normalized tension vs. relative extension curves); the yarn-decrimping modulus; the relative energy of stretching (i.e., area under the normalized load-extension curve); and the energy loss due to hysteresis (i.e., area of the hysteresis loop of the normalized load-extension curve during tensile-recovery measurements). Inelastic and elastic parameters are described for the fabric-bending hysteresis curves. Fabric tensile and bending properties are shown to depend largely on the yarn linear density, the crimp value of yarns, under deformation, and the ratio of the two yarn curvilinear lengths in the structural repeat unit of the fabric. It is shown that there are considerable constraints imposed on the yarn curvature within the fabric, resulting in increased resistance to fabric stretching and bending compared to the results measured on yarns removed from the fabric. A study is made of the effect of yarn extensibility on the decrimping behavior of yarns unravelled from fabric. The effect of weave construction is prominent on the tensile behavior of fabric; its effect on the decrimping behavior of yarn and bending properties of fabrics is only marginal. The effect of blend composi tion on these mechanical properties has been examined for a series of wool/polyester woven fabrics produced from yarns of the same linear density and was found not to be significant.

Physical Ageing and Annealing in Fibers and Textile Materials Part II: Annealing Behavior of Textile Materials Produced from Wool and Manmade Fibers

The viscoelastic behavior of annealed fabric specimens produced from wool and manmade fibers has been assessed by measuring the fabric bending stress relaxation characteristics. The study reveals that the presence of water provides an effective me dium for de-ageing of fabrics produced from both wool and manmade fibers. Optimum annealing conditions occur when these fabrics are heated below the glass transition temperature of each fiber type at the equilibrium moisture regain corresponding to 20°C, 65% RH (the time taken depending on the annealing temperature). Under these conditions, the fabric bending stress relaxation rate is reduced to its minimum value, thus resulting in maximum fabric recovery from bending or wrinkling. The application of horizontal and vertical shift factors produces a master stress relaxation curve of aged and annealed fabric specimens produced from both wool and manmade fibers.

Air Permeability of Woven, Double-Knitted, and Warp-Knitted Outerwear Fabrics

The air permeability influences a number of important fabric properties, such as protection against wind in outerwear garments, efficiency of filtration in industrial cloths, performance of sail cloths and parachute fabrics, etc. It has been suggested by Olofsson [6] that there is a general interdependence between shear behavior (measured using the shear apparatus designed by Behre c21) and air permeability of woven worsted fabrics. The effect of two basic structural parameters for wool double-knitted fabrics-viz. the tightness factor and run-in-ratio-on air permeability has been studied by Postle and Suurmeyer [S]. Also, it has been shown by Knapton and Lo [4] that the air permeability of double-knitted fabrics is highly dependent upon fabric construction. In this letter, air permeability measurements are compared for a wide range of commercially produced woven, double-knitted, and warp-knitted outerwear fabrics. A total of 87 fabrics was tested, representing a number of different fabric manufacturers and finishers. Of the total, 37 fabrics were woven (all-wool or wool/ polyester blends), 4 plain-knits (3 wool and 1 polyester/ cotton blend), 17 wool double-knits, 13 textured polyester double-knits, and 16 synthetic warp-knits. A detailed description of the construction of these fabrics has been reported previously [3] together with a detailed analysis of their bending and shear behavior. The air permeability of a fabric, defined as the volume of air (measured in cubic centimeters) passing per second through 1 cm2 of the fabric a t a pressure difference of 1 crn head of water, was determined by employing a Cambridge air-flow apparatus. Owing to the openness of the knitted fabric structures, multiple layers were used, and the value of a u permeability for one layer of fabric was obtained from the product of air permeability of a composite of superimposed fabrics and the number of layers used in the composite [S, 71. For woven fabrics, no difficulty was encountered in testing single layers of the fabric. Measurements of fabric thickness were carried out under a pressure of 7 kPa c11. The air-flow results, for all types of fabrics investigated, are plotted against fabric thickness in (a) of Figure. 1 and against fabric weight per unit area in (b) of Figure 1. The similarity between both charts shown in Figure 1 is immediately evident, indicating (as ex-

Physical Ageing and Annealing in Fibers and Textile Materials Part III: Physical Ageing and Annealing in Blended Textile Assemblies

The theory of viscoelasticity in textile assemblies reported in Part I of this series of papers is extended to blended textile materials. The complex effects of ageing or an nealing or both of these on the stress relaxation processes in a blended textile material are separated into several regions according to the demarcation provided by the glass transition temperature of the constituent fibers in the blend. The influence of ageing or annealing processes on the mechanical properties contributed by constituent fibers in the blend can be represented by horizontally shifting the stress relaxation curves of the fibers in the logarithmic time scale. The time shift factors for each individual group of fibers in the blend take into account the changes in temperature and ageing or annealing history. The sufficient condition to obtain a single effective time shift factor for the blend is that all viscoelastic component fibers must have only one identical time shift factor with respect to the same reference state. The theory predicts that, in most real situations, there should be no single time shift factor obtainable for textile blends owing to the differences between the shift factor of the component fibers. The interaction between the fiber components in a blended fabric represents an important aspect of its viscoelastic behavior. An experimental study reveals that the interaction between fiber blend components in wool/polyester fabrics is influenced by the differ ences in the stress relaxation behavior of the blend constituents, blend composition, and fabric weave construction. The study also indicates that the annealing process improves the viscoelastic properties of wool/polyester blended fabrics. Optimum an nealing conditions occur when these fabrics are heated in the vicinity of the glass transition temperaure of wool fibers at the equilibrium moisture regain corresponding to 20°C and 65% RH.

Shear Properties of Warp-Knitted Outerwear Fabrics

In this paper an experimental study is reported of the low-stress deformations in shear for a wide range of warp-knitted fabrics, including commercially-finished synthetic apparel outerwear fabrics, laboratory-produced wool/polyester samples, and a series of laid-in warp-knitted constructions. Features of fabric shear deformation and recovery curves such as their shape, asymmetry, linearity, and degree of hysteresis are discussed by analyzing the results in terms of elastic and frictional resistance to shear deformation. The effect of tension on fabric shear parameters is investigated. The shear behavior of warp-knitted fabrics is compared with corresponding properties of woven and double-knitted fabrics; it is shown that the laid-in warp-knitted structures exhibit much lower values of frictional shear stress and in most cases lower values of shear rigidity than do the ordinary warp-knitted structures. The effect of warp-knit construction on fabric shear behavior is examined for a series of laboratory-produced fabrics, and the effects of fabric relaxation are studied. Fabric shear properties are shown to depend largely on the inherent nature of the warp-knit construction (viz. the combination of loop and underlap) and show very little systematic telationship with such structural variables as fahric thickness and weight per unit area of fabric. The effect of relaxation is found to be much less for shear deformation than the corresponding effect on bending behavior for warp-knitted fabrics.