Geometrical Modelling of Plain Weft Knitted Fabrics

In order to produce the fabric with maximum cover factor with the minimum weight, it’s only possible when GH is the distance between the loops in a horizontal direction and KJ is the correct length between the loops in a longitudinal direction. In this article knitting fair explains geometrical pattern of knitted fabrics.

The model of the relationship between the loop, the order of the loop length and the length of the loop in the loop was developed. The coordinate values of the points illustrated were calculated which define the central axis of yarn using the spline curves in Abaqus / CAE. Abaqus / CAE calculates the shape of the curve using a cubic spline fit between all points along the spline; In addition, the first and second derivatives of the spline are continuous. The 3D models of plain weft knit fabrics can be generated by sweeping the circular cross section of the yarn along the central axis of the yarn. Yarns were assumed to be incompressible in nature.

Knitted fabrics have a good stretch property that offers better conformability and avoids excessive pressure between the garment and body. Many researchers have analyzed the geometrical pattern of knitted fabrics. In 1926 Chamberlain presented a two-dimensional loop structure of the plain knitted fabric. He proposed that the theoretically correct fabric, in which GH represents the distance between the centres of two loops, GKH represent the equilateral triangle and KJ bisect the equilateral triangle.

In Chamberlain’s model, there is no consideration of loop in the third dimension in order to produce the fabric with a maximum cover factor, but it is only possible when GH is the distance between the loops in a horizontal direction and KJ is the correct length between the loops in the longitudinal direction. So the length of the loop cannot be predicted with high accuracy. In 1947 Peirce developed a geometric model of plain weft knit fabric on the assumption that the loop formed from the circular arc and straight line and the yarn central axis follows a path on the surface of cylinder following the direction of a course. In order to develop the relationship of stitch length in terms of yarn diameter, wales and course spacing.

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Knitted fabrics have a good stretch property which offers better conformability and avoids excessive pressure between the garment and body . Many researchers analysed the geometrical model of knitted fabrics. In 1926 Chamberlain presented a two-dimensional loop structure of the plain knitted fabric. He proposed that the theoretically correct fabric as shown in Equation-1, in which GH represents the distance between the centres of two loops, GKH represent the equilateral triangle and KJ bisect the equilateral triangle. In order to produce the fabric with maximum cover factor with the minimum weight, it’s only possible when GH is the distance between the loops in a horizontal direction and KJ is the correct length between the loops in a longitudinal direction.

In Chamberlain’s model, there was no consideration of a loop in the third dimension so the length of the loop cannot be predicted with high accuracy. In 1947 Peirce developed a geometrical model of plain weft knitted fabric on the assumption that the loop composed of a circular arc and straight line and the yarn central axis follows a path on the surface of cylinder following the direction of a course. In order to develop the relationship of stitch length in terms of yarn diameter, wales and course spacing he considered the flat structure of plain weft knitted fabric as shown in Figure 2. In his compact planned structure, the course ( p’ ) and wales ( w ) spacing can be calculated by Equation 8 & 9 respectively.

Leaf and Glaskin pointed out that the stable knitted fabric loop structure could not be produced by the model proposed by the Peirce. They showed that the Peirce considered the radius of curvature R = 4.172d for all types of the loop which gave the discontinuity in the torsion of yarn and eventually affected the shape of loops. They proposed a geometrical model of plain weft knitted fabric in which the central axis of yarn passes over a series of a circular cylinder and their model composed of circular arcs as shown in Figure 4.

Source: textiles school

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Although man-made fibers are becoming more and more technological, customers of the Knitting Fair said that some people only accept natural fibers.

Fibers obtained from nature are generally called natural fibers and the fabrics produced with such fibers are essentially natural fabrics. A large number of natural sources of cellulose content are tapped to produce textile products. Various fiber producing plants and animals are commercially grown in order to meet the growing requirements of textile products. Natural materials blended with regenerated polymers is a new trend in textile production due to the composite products’ specific characteristics, and easy availability of natural fibers.

Commercially available textile fabrics generated with natural fibers are classified below by the source of fibers.

1. Cotton Fabric

Cotton is a natural fiber that comes from the seedpod of the cotton plant and is used to make many fabric types.The fabric which is believed to be most soothing and safe is called as cotton fabric. Immense use of cotton fabric for infant’s dresses or beddings is a live testimony of its softness and skin-friendliness. Cotton fabric has a distinctive feature that it adjusts easily to climatic requirements that is why it is called all-season fabric. In summer season cotton fabric keeps the body cool and absorbs the sweat easily whereas they give a warm feel if worn in a winter season.A wide variety of fabrics such as Calico, Corduroy, Denim, Gingham, Drill, Terry Toweling, Chintz, Cambric, Lawn, Gabardine, Poplin, Velvet, etc. are produced with Cotton.

silk cocoonsSilk counts to the strongest natural fabric in the world. Known for its softness, luster, beauty and luxurious look, silk fabric is one of the higher grade fabric providing comfort to the wearer in all types of weather. Keeping the body cool in summer and warm in winter, silk was discovered during 2640 B.C. in China.Variety of silk fabrics such as Chiffon, Georgette, Damask, Taffeta, Organza, Crepe de Chine, Duponi, Noil, Pongee, Shantung, Tussar, Satin, Doupion, etc. are available in the market. Because of its sheer variety of designs, weaving, and quality, silk textile is popular worldwide.

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Silk fabric is mainly used for making luxurious and expensive dresses and home furnishings. Indian silk textile is popular worldwide whereas the USA is the worlds leading manufacturer of silk products in France and Italy are also involved in the same line producing high-value sophisticated silk fabrics in Europe.

2. Linen Fabric

flax plantsLinen is called as king of natural fabric. Linen is extensively used for apparel making and home furnishing as well. Linen, being a natural fiber is considered to be safe for all types of skin.

Linen fabric is also suggested for sensitive skin as its natural properties makes it resistant to allergies.

Linen fabric does not cause problems like irritation, allergic reaction etc. The natural fiber of linen makes it strong and durable. Linen is an easily maintainable fabric. No special treatments are required for linen; it can be simply cleaned by hands. Although linen is used for all kinds of clothing, yet mostly used for home furnishing items like a tablecloth, bedspreads, interlining, curtains etc.

3. Wool Fabric

Merino sheepSoft, strong and very durable wool fabric provide warmth and attractive appearance. It is the fabric which keeps the wearer dry while sweating and cool when it is hot. Wicking away perspiration from the body, the wool fabric does not wrinkle easily and is resistant to dirt wear and tear. It is also having the quality of not burning when put over the flame, it only smolders. Felt made of wool fabric is used as covers for piano hammers. It is also used in absorbing odors and noise in machinery and stereo speakers.Wool fabric is being used for clothing for over twelve thousand years does not only come from sheep only, whereas widely used Kashmiri sweaters are made from goats.

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Wool fabric is equipped with different characteristics like warm, resists to wrinkle, wear and tear, it is lightweight and durable which also absorbs moisture. Have been largely used in blankets and carpets, today almost every wardrobe contains garment made of woolen fabric.

Worsted, Shetland, Baize, Flannel, Jersey, Tweed, Serge, Fleece, Tartan are few generally used wool fabrics.

4. Cashmere/Kashmiri Fabric

cashmere-goatCashmere Fabrics are made from the hair fiber forming the downy undercoat of the Kashmir goat. The term Cashmere Fabric is often used for extremely soft wools as well. Cashmere wool obtained from goats is often treated as specialty or luxury fiber because of its high economic value, softness, luster, and scarcity.

5. Leather Fabric

Comfortable in both hot and cold condition, the leather fabric is not affected by surrounding temperature. Adding a classic luxury, pleasant to touch and comfortable, the leather fabric is soft, elastic and firm. Leather fabric is blessed with the quality of absorbing water vapor without losing dryness and retaining to the original shape when stretched.

6. Ramie Fabric

Ramie Fabrics are produced from Ramie plants, a plant with heart-shaped leaves having the white underside with dense hairs. Ramie is also called China Grass since it was grown in China as a fiber crop. Ramie is one of the strongest natural fibers. It exhibits even greater strength when wet. Ramie fiber is known especially for its ability to hold shape, reduce wrinkling, and introduce a silky luster to the fabric appearance. Ramie fabric having characteristics like moisture absorption, air permeability is valued as a summer fabric which is not harmed by mild acid and is resistant to alkali. Ramie was used to produce open weave fabrics called “Mechera”, suitable for warm climates.

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7. Hemp Fabric

Highly versatile hemp fabric is used in a countless number of products like shoes, furniture, apparel, accessories and home furnishing. Hemp fabric is a fabric which is commonly known for its warmth, softness, and durability.

Providing beautiful lusture, hemp fabric is best for making apparel which can withstand harsh conditions and last longer. UV protected apparel fabric have an insulative quality that allows clothing to be cool in summer.

Having characteristics like durability, absorption, insulation, apparel fabric withstands water better than any other textile product. It is obtained from the stem of the plant, the finest hemp fabric is produced in Italy. Acting as a great choice for comfortable work clothes, home decoration, hemp fabric is also used in the manufacturing of clothing, curtains, draperies, upholstery, bedspreads, table linens, sheets, dish towels, canvas, etc.

8. Jute Fabric

Being among the strong and durable fabric, jute fabric is ideally being used as bags or sacks for packing since ages. The jute fabric is a much-soughed item for fashionable clothes, home furnishing, and fashion accessories. Bangladesh counts to the largest cultivator of jute fabric with India as the second largest jute goods manufacturer.

The most important use of the jute fabric is in the manufacturing of carpets, linoleum, cordage, and twines. It is sometimes used as webbing to cover inner springs of the auto seats. Sometimes used as fashion accessory used for fashion garments, tapestries, soft luggage, etc.

Source: textiles school

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In the knitting exhibition, breathable fabrics have always been very popular, whether natural or chemical materials need to consider the issue of breathability.

The ease or otherwise of the passage of air is of importance for a number of fabrics end uses such as industrial filters, tents, sailcloth’s, parachutes, bulletproof, windproof, raincoat materials, shirting’s, down proof fabrics and airbags.

Fabric air permeability is a measure to what extent it gives air passing through the fabric. Air permeability, a given area in the vertical direction of the air flow rate, a given time period, as measured by the fabric test area inside the pressure difference of the fabric. Basically, it depends on weight, thickness and porosity of fabric. The porosity of fabric is the demonstration of the air gap as a percentage within the fabric. It has been important for especially the tent fabric and parachute.

The reciprocal of air permeability, air resistance, can be defined as the time in seconds for ImI of air to pass through 100s mm2 of fabric under a pressure head of 10mm of water. The advantage of using air resistance instead of air permeability to characterize a fabric is that in an assembly of a number of fabrics, the total air resistance is then the sum of the individual air resistance.

Fabrics, are porous materials which allow the transmission of energy and substances and are therefore interesting materials for different applications. In general, they are used for clothing, interior and wide range of technical applications

Garments must be characterized by good air circulation between the skin surface and the environment, good ventilation at skin level and the possibility of eliminating the excess humidity generated through perspiration.

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Air permeability Definition

The air permeability of woven fabrics is important because it influences the comfort properties of the final product – garments. The air permeability can be controlled during the design stage through: the characteristics of the raw material (the type of fibres and blend ratio), the geometric characteristics of the yarns used, the structural parameters of the woven fabrics, the technology used to produce the fabrics and the finishing process.

Air permeability, simply a physical ability of a fabric to let certain air flow through under differential pressure between either surface, refers to the speed at which water vapour molecules transmit into the top layer. Fabrics with different surface textures on either side can have a different air permeability depending upon the direction of air flow. Air permeability and fabric porous structure are correlated and indicate the breathability which makes great differences in the performance of materials. That is to say, air permeability and porous fabric structure affect how breathable a garment is; besides, air permeability can be measured, whereas breathability is more subjective.

In the British Standard test, the airflow through a given area of fabric is measured at a constant pressure drop across the fabric of 10mm head of water. The specimen is clamped over the air inlet of the apparatus with the use of rubber gaskets and the air is sucked through it by means of a pump as shown in Fig.A. The air valve is adjusted to give a pressure drop across the fabric of 10mm head of water and the air flow is then measured using a flow meter.

Five specimens are used each with a test area of 508mm2 (25.4mm diameter) and the mean air flow in ml per second is calculated from the five results. From this, the air permeability can be calculated in ml per 100mm2 per second.

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To obtain accurate results in the test, edge leakage around the specimen has to be prevented by using a guard ring or similar device (for example, efficient clamping). The pressure drop across the guard ring is measured by a separate pressure gauge. Air that is drawn through the guard ring does not pass through the flowmeter. The pressure drops across the guard ring and test area are equalized in order that no air can pass either way through the edge of the specimen. A guard ring of three times the size of the test area is considered sufficient.

Classification of fabrics: based on fabric type there are four types of fabrics

Woven fabric: this has been defined as the interlacing/ interlacement of warp and weft yarns where minimum two sets of yarns are needed and warp yarn stay in vertical and parallel to the selvedges.

Knitted fabrics: This has been defined as the interloping/interlocking/ intermeshing of warp yarn where minimum one set of yarn is needed.

Non-Woven fabrics: this has been defined as the mechanical/chemical/thermal bonding to make non-woven fabrics.

Braided fabrics: this is defined as the intertwining/diagonal/interlacement to make braided fabric where minimum three sets of yarns are needed

Factors that Affect Air Permeability/Fabric porous structure of textile fabrics

Correlation between porosity and air permeability of fabric is very complicated because changes of the textile structure (by the influence of the venting system), can be possibly classified as a horizontal increase in porosity. A correlation relationship has been elaborated between the percentage of open porosity for double layer fabrics and air permeability, considering the use of the different system of reed denting.

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Fabric porosity is an important parameter in the assessment of clothing comfort and physical properties of technical textiles and the porosity are defined by the ratio of free space to fibre in a given volume of fabric. The porous are by voids between weft and warp yarns in the fabrics. The air passes through the pores from the surface of the fabric. Tightness factor can be used for fabric air permeability forecasting. The high correlation between the permeability to air and the tightness factor confirms that. Porosity is affected by yarn number or yarn count number. … Increasing loop length, looser the structure and so the values of air permeability increases.

Source: textiles school

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