ZUT-Testing: Dimensions of Fibres & Yarns 1 Dimensions of Fibres & Yarns Basic Concepts, Units &...

ZUT-Testing: Dimensions of Fibres & Yarns

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Dimensions of Fibres & YarnsDimensions of Fibres & Yarns Basic Concepts, Units & Unit SystemsBasic Concepts, Units & Unit Systems

Special QuantitiesSpecial Quantities

Measurement MethodsMeasurement Methods

Textile TestingTextile Testing

MA WildingMA Wilding


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Suggested Reading MaterialSuggested Reading Material

• JE BoothJE Booth "Principles of Textile Testing” (1983)"Principles of Textile Testing” (1983)Chapters 5 & 6Chapters 5 & 6

• BP SavilleBP Saville““Physical Testing of Textiles” (1999)Physical Testing of Textiles” (1999)Chapter 3Chapter 3


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Most Natural FibresMost Natural Fibres Length varies from about 1 Length varies from about 1 10 cm 10 cm

(“staple”)(“staple”)

Most Man-made/Synthetic FibresMost Man-made/Synthetic FibresCan be any length: 0 cm Can be any length: 0 cm “infinity” “infinity”

(“continuous filament”)(“continuous filament”)

Fibre DimensionsFibre Dimensions - Length- Length• Fibre length is an extremely important parameterFibre length is an extremely important parameter

• It has far-reaching influences on yarn & fabric It has far-reaching influences on yarn & fabric processing & product performanceprocessing & product performance

• Can divide fibres approximately into two groups: Can divide fibres approximately into two groups:


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Fibre LengthFibre Length - Measurement- Measurement

Continuous filamentContinuous filament• Length measurement not generally an issueLength measurement not generally an issue

Staple fibresStaple fibres• A given batch of raw fibre (eg cotton or wool) will A given batch of raw fibre (eg cotton or wool) will

contain many different fibre lengthscontain many different fibre lengths

• Most methods are therefore statistical in natureMost methods are therefore statistical in nature

• They are usually extremely difficult & time-They are usually extremely difficult & time-consuming to carry out; instruments include:consuming to carry out; instruments include:

Various “comb” sorters Various “comb” sorters (differ for cotton & wool)(differ for cotton & wool)

Various photoelectric sorters Various photoelectric sorters (“Shirley” & (“Shirley” & “Fibrograph”)“Fibrograph”)

““Sledge” sorterSledge” sorterSee, for example, Booth, Chapter 5See, for example, Booth, Chapter 5


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• Fibres typically ~ 20 microns (0.02mm) acrossFibres typically ~ 20 microns (0.02mm) across

• Cross-section very difficult to determineCross-section very difficult to determine

eg wooleg wool

Fibre DimensionsFibre Dimensions – “Thickness”– “Thickness”This is far from straightforward …This is far from straightforward …


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Yarns are often difficult, tooYarns are often difficult, too

Cross-section Cross-section ill-defined, possibly “hairy” ill-defined, possibly “hairy” etcetc

Fibre DimensionsFibre Dimensions – “Thickness”– “Thickness”


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There are two types of system …There are two types of system …

Usually specified in terms ofUsually specified in terms ofLinear Density (LD) or ‘fineness’Linear Density (LD) or ‘fineness’

• DirectDirecteg ‘tex’ systemeg ‘tex’ system

Value is Value is proportionalproportional to LD to LD increasesincreases with thicknesswith thickness

• IndirectIndirecteg Cotton Counteg Cotton Count

Value is Value is inversely proportionalinversely proportional to LD to LD decreasesdecreases with thicknesswith thickness

Fibre DimensionsFibre Dimensions – “Thickness”– “Thickness”


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Fineness as a Measure of Cross-SectionFineness as a Measure of Cross-Section

Mass = V x density (Mass = V x density () = ) = ALAL

Linear density = Mass/LengthLinear density = Mass/Length (eg in tex)(eg in tex)

= AL= AL/L = /L = AA

For a given bulk density (For a given bulk density (), linear density is ), linear density is proportional to proportional to fibrefibre cross-sectional area cross-sectional area


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Mass = V x density (Mass = V x density () = ) = ALAL

Linear density = Mass/LengthLinear density = Mass/Length (eg in tex)(eg in tex)

= AL= AL/L = /L = AA

It works for any regular shape – eg triangularIt works for any regular shape – eg triangular

Fineness as a Measure of Cross-SectionFineness as a Measure of Cross-SectionFor a given bulk density (For a given bulk density (), linear density is ), linear density is

proportional to proportional to fibrefibre cross-sectional area cross-sectional area


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1. Direct1. Direct tex =tex = weight (g) of 1km weight (g) of 1km decitex = decitex = weight (g) of 10 kmweight (g) of 10 km millitex =millitex = weight (g) of 1000 kmweight (g) of 1000 km kilotex =kilotex = weight (kg) of 1 kmweight (kg) of 1 km

Fineness UnitsFineness Units

Example:Example:

10 cm fibre weighing 0.02 mg10 cm fibre weighing 0.02 mg

= 0.00002/0.0001 g per km= 0.00002/0.0001 g per km

= = 0.2 tex0.2 tex = = 2 dtex2 dtex = = 200 mtex200 mtex


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2. Indirect2. Indirect

• Count Count

eg Cotton Counteg Cotton Count = No. of 840-yard "hanks" for 1 lb = No. of 840-yard "hanks" for 1 lb

weightweight

Fineness UnitsFineness Units

Example:Example:

Suppose a standard-length hank of yarn weighs 1/30 lb Suppose a standard-length hank of yarn weighs 1/30 lb

Therefore need 30 hanks for 1 lbTherefore need 30 hanks for 1 lb

Therefore yarn = 30's Cotton CountTherefore yarn = 30's Cotton Count


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Stiffness & handle Stiffness & handle (ie drape etc)(ie drape etc) Torsional rigidity (ie how hard to twist)Torsional rigidity (ie how hard to twist)

- square power dependence on fineness- square power dependence on fineness

Fineness Fineness - Technological importance- Technological importance

Light reflectionLight reflection- fine fibres soft sheen- fine fibres soft sheen- coarse fibres harsh glitter- coarse fibres harsh glitter

Absorption of liquids &Absorption of liquids & fibre cohesionfibre cohesion- related to surface area- related to surface area

Yarn uniformityYarn uniformity- finer fibres give more even yarn- finer fibres give more even yarn

Fibre fineness impacts on a wide range of other Fibre fineness impacts on a wide range of other properties - here areproperties - here are just some just some examples …examples …


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Knowledge of effective thickness is usually Knowledge of effective thickness is usually essential for results to be meaningfulessential for results to be meaningful

(particularly when comparing different fibre types)(particularly when comparing different fibre types)

Example:Example: Suppose a Suppose a given given cotton fibre can withstand a cotton fibre can withstand a

greater load (tension) than a greater load (tension) than a givengiven nylon fibre nylon fibre Is cotton inherently stronger than nylon Is cotton inherently stronger than nylon per seper se?? We can’t immediately tell, because We can’t immediately tell, because thickthick fibres fibres

are are strongerstronger than than thinthin fibres of the fibres of the same typesame type

Therefore, in most cases, results Therefore, in most cases, results must bemust be ‘normalised’‘normalised’

Fineness Fineness - Importance in testing- Importance in testing


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There is a wide range of methods availableThere is a wide range of methods available These include These include gravimetricgravimetric and and non-gravimetric non-gravimetric methodsmethods Some are direct; some are indirectSome are direct; some are indirect Some are extremely complicated & time-consumingSome are extremely complicated & time-consuming Some are straightforward and quickSome are straightforward and quick The most appropriate choice depends on many factorsThe most appropriate choice depends on many factors An important one: are we testing An important one: are we testing fibrefibre or or yarnyarn?? Several precautions may need to be takenSeveral precautions may need to be taken

– – such as preconditioning sample in the lab (discussed later)such as preconditioning sample in the lab (discussed later)

Fineness Fineness – Methods of determination– Methods of determination


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Typically, 100 metres (ie 0.1 km) of yarn is wound Typically, 100 metres (ie 0.1 km) of yarn is wound off using a “wrap wheel”off using a “wrap wheel”

- Usually motorised, has a diameter of 1 metre, and a - Usually motorised, has a diameter of 1 metre, and a revolution counter to make length determination easy revolution counter to make length determination easy and accurateand accurate

Suppose the piece of yarn weighs Suppose the piece of yarn weighs W gramsW grams Its linear density must therefore be Its linear density must therefore be W/0.1 tex W/0.1 tex

(=10W tex)(=10W tex) Shorter lengths (eg a few centimetres) may be Shorter lengths (eg a few centimetres) may be

measured using a metre rule and a sensitive measured using a metre rule and a sensitive electronic balanceelectronic balance

The count equivalent can be calculated using the The count equivalent can be calculated using the appropriate conversion formula; for example, for appropriate conversion formula; for example, for English Cotton Count (NEnglish Cotton Count (NEE):):

NNEE = 590.5/tex = 590.5/tex

Fineness Methods Fineness Methods - Yarns- Yarns

Simplest: weigh a known length on a balanceSimplest: weigh a known length on a balance


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Fineness Methods Fineness Methods - Fibres- Fibres

Range of methods availableRange of methods available Generally complicatedGenerally complicated Appropriate choice depends on factors Appropriate choice depends on factors

such as:such as:What physical form the fibre is inWhat physical form the fibre is in

- Bale? Sliver? Yarn? Fabric?- Bale? Sliver? Yarn? Fabric?

Is a single-fibre value required?Is a single-fibre value required?

Or some form of average for a bulk of fibres?Or some form of average for a bulk of fibres?


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• MayMay estimate fibre fineness from overall yarn tex estimate fibre fineness from overall yarn tex• Need the number of filaments in the cross-sectionNeed the number of filaments in the cross-section• May be provided by yarn-producerMay be provided by yarn-producer• If not, filaments need to be counted If not, filaments need to be counted

Microscope may be needed – tedious and slowMicroscope may be needed – tedious and slow

For uniform synthetic fibres in continuous-For uniform synthetic fibres in continuous-filament yarns …filament yarns …


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1. By microscopy1. By microscopy• Assumes fineness proportional to cross-sectional areaAssumes fineness proportional to cross-sectional area• Need to know the bulk densityNeed to know the bulk density may get approximate value from literature if know fibre typemay get approximate value from literature if know fibre type• Image of fibre cross-section projected & measuredImage of fibre cross-section projected & measured• Fibre area calculated from magnificationFibre area calculated from magnification• Fineness calculatedFineness calculated

For single fibresFor single fibresSingle fibres are usually too small to be weighed Single fibres are usually too small to be weighed reliably on a balance.reliably on a balance.

Two examples of alternative methods:Two examples of alternative methods:


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2. Using a “Vibrascope”2. Using a “Vibrascope”• Principle of a vibrating stretched stringPrinciple of a vibrating stretched string

- as in a musical instrument- as in a musical instrument• Frequency (“pitch”) depends on tension, length and Frequency (“pitch”) depends on tension, length and

linear densitylinear density• Fibre hung between knife-edgesFibre hung between knife-edges• Small known weight attached to lower endSmall known weight attached to lower end• Made to vibrate at fixed frequency using Made to vibrate at fixed frequency using

electrostatic plateselectrostatic plates• Length adjusted until get resonanceLength adjusted until get resonance• Fineness (usually in dtex) read off dialFineness (usually in dtex) read off dial• Relatively straightforward and moderately quickRelatively straightforward and moderately quick• May not be highly accurateMay not be highly accurate

For single fibresFor single fibres


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Illustration of the Vibrascope principleIllustration of the Vibrascope principle


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Air-flow methods usually bestAir-flow methods usually best• QuickQuick• Give an average valueGive an average value

For bulk fibres (eg cotton or wool staple)For bulk fibres (eg cotton or wool staple)

FromFrompressure meterpressure meter

Flow meter & suction Flow meter & suction pumppump

Chamber packed with wad of Chamber packed with wad of fibres of standard weightfibres of standard weight

AirAir Weighted insertWeighted insertwith perforated basewith perforated base

AirAir

Typical airflow systemTypical airflow system(schematic)(schematic)


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S is called the “specific surface” of the fibreS is called the “specific surface” of the fibre

Hence …Hence …

Fineness Methods Fineness Methods – Air-flow– Air-flow

Consider an idealised, cylindrical fibre …Consider an idealised, cylindrical fibre …

The finer the fibre the greater its specific surfaceThe finer the fibre the greater its specific surface

dddL

SVs

dLPL(s) area Surface

d(P) end ofPerimeter

d(V) Volume

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4

2

2

LL

ddPP


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2525 fibres of diameter fibres of diameter dd

55 fibres of diameter fibres of diameter 2d2d

Occupy the Occupy the same total volumesame total volume as as


Compare two equal-volume batches of fibres Compare two equal-volume batches of fibres with different diameters, and hence finenesswith different diameters, and hence fineness

… … but have but have twice thetwice the surface areasurface area

• Air-flow is restricted by drag over the fibre surfaceAir-flow is restricted by drag over the fibre surface• The finer fibres haveThe finer fibres have twice the resistance to airflow twice the resistance to airflow

LL

dd

LL

2d2d


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Resistance to airflow as a measure of finenessResistance to airflow as a measure of fineness

2d2d

Fine fibres high resistanceFine fibres high resistance

Coarse fibres lower resistanceCoarse fibres lower resistance


dd


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In practice may measure either the In practice may measure either the pressure for a given air-flowpressure for a given air-flow or the or the

air-flow for a given pressureair-flow for a given pressure

Fineness (in tex) is:Fineness (in tex) is:proportional to fibre cross-sectional areaproportional to fibre cross-sectional areaproportional to fibre diameter squaredproportional to fibre diameter squared

Specific surface is:Specific surface is:inversely proportional to diameterinversely proportional to diameterinversely proportional to square root of texinversely proportional to square root of tex

PressurePressure for given air-flow is:for given air-flow is:proportional to specific surfaceproportional to specific surface inversely proportional to square root of texinversely proportional to square root of tex

Ideally, for a mass of uniform cylindrical fibres …Ideally, for a mass of uniform cylindrical fibres …



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• Where the fibres are Where the fibres are not uniformnot uniform and/or and/or not not cylindricalcylindrical the results of air-flow measurements must the results of air-flow measurements must be treated with a degree of cautionbe treated with a degree of caution

• The overall result will be some form of The overall result will be some form of averageaverage for for the batchthe batch

• This This may notmay not be the simple arithmetic mean be the simple arithmetic mean


For further details and practical systems for For further details and practical systems for measuring fibre fineness see, for example, measuring fibre fineness see, for example,

Booth, Chapter 5Booth, Chapter 5


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Maturity (of Cotton Fibres)Maturity (of Cotton Fibres)

• ‘‘Maturity’Maturity’ is a dimensional characteristic is a dimensional characteristic of natural cellulose fibres – especially of natural cellulose fibres – especially cottoncotton

• It indicates It indicates how well-developedhow well-developed the fibres the fibres are at harvestare at harvest

• It is It is extremely importantextremely important in terms of in terms of down-stream down-stream processingprocessing and yarn/fabric and yarn/fabric qualityquality

• Maturity andMaturity and fineness fineness are interrelated, are interrelated, although not in a simple wayalthough not in a simple way


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Maturity (of Cotton Fibres)Maturity (of Cotton Fibres)Structure and growth of cotton fibres - in briefStructure and growth of cotton fibres - in brief

Longitudinal ViewLongitudinal View

Cross-sectional ViewCross-sectional View

““Convolution”Convolution”


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• Cotton fibres begin (after the flower dies) as Cotton fibres begin (after the flower dies) as thin-walled hollow cylindersthin-walled hollow cylinders

• They first They first lengthen without changing in lengthen without changing in diameterdiameter; takes around 20 days; takes around 20 days

• They then They then maturemature; takes about another 30 days; takes about another 30 days

• In maturation, cellulose is deposited on the In maturation, cellulose is deposited on the inside of the cylinder – the inside of the cylinder – the ‘‘secondary wallsecondary wall’’

• The hole down the centre (the The hole down the centre (the ‘‘lumenlumen’’) becomes ) becomes progressively smallerprogressively smaller

• The outer diameter of the fibre remains The outer diameter of the fibre remains virtually virtually unchangedunchanged


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A Cotton fibre grows first in length …A Cotton fibre grows first in length …

… … then in wall-thicknessthen in wall-thickness

lumenlumen

Maturity …Maturity …is related to the cell wall thickness in is related to the cell wall thickness in comparison to the lumen diametercomparison to the lumen diameter

Seed surfaceSeed surfaceEmerging fibreEmerging fibre


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Maturity (of Cotton Fibres)Maturity (of Cotton Fibres)Degree of thickening (Degree of thickening ())

AA

AAoo

= A/A= A/Aoo

LumenLumen

A = area occupied by celluloseA = area occupied by cellulose

CelluloseCellulose

Idealised cross-section of a cotton fibreIdealised cross-section of a cotton fibre

AAoo = total area (including lumen) = total area (including lumen)


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The fibres collapse The fibres collapse when they dry out on when they dry out on harvesting to give a “kidney-bean” shapeharvesting to give a “kidney-bean” shape


Cross-sectional area changes, but Cross-sectional area changes, but perimeterperimeter remains approximately constant remains approximately constant

On the plantOn the plant

PP PP

DryDry


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Technological importanceTechnological importanceMaturity largely determines whether a batch of Maturity largely determines whether a batch of cotton can be spun into a good yarn - or indeed cotton can be spun into a good yarn - or indeed intointo anyany yarnyarn

Mature/Over-matureMature/Over-mature

ImmatureImmature

“ “Dead”Dead”

Some maturity VariationsSome maturity Variations

Cause “neps” – clumps of Cause “neps” – clumps of matted fibresmatted fibres



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The fibre perimeter is related to The fibre perimeter is related to both fineness and both fineness and maturitymaturity, and is involved in , and is involved in airflowairflow methods for methods for measuring these properties – see Booth, Chapter 5measuring these properties – see Booth, Chapter 5


PP11

PP22>P>P11

Air flow restricted through fine fibres Air flow restricted through fine fibres because large specific surfacebecause large specific surface

Air flows more easily Air flows more easily through coarse fibres through coarse fibres because smaller specific because smaller specific surfacesurface


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Maturity (of Cotton Fibres)Maturity (of Cotton Fibres)Maturity Count and Maturity Maturity Count and Maturity RatioRatioSuppose a large sample of cotton fibres is Suppose a large sample of cotton fibres is

selected at random and treated with caustic selected at random and treated with caustic soda. The soda. The maturemature fibres will fibres will swellswell back to back to cylinders, and appear rod-like. The cylinders, and appear rod-like. The immatureimmature ones ones will not swell will not swell but will appear ribbon-likebut will appear ribbon-like

Now count under a microscope:Now count under a microscope:

• The total number of fibres (T) The total number of fibres (T) • The number of mature The number of mature (ie “normal”)(ie “normal”) fibres (n) fibres (n)• The number of “dead” fibres (d)The number of “dead” fibres (d)

- ie those with wall thickness less than 0.2 lumen- ie those with wall thickness less than 0.2 lumenThe number of immature (but not dead) fibres (m) The number of immature (but not dead) fibres (m) is then given by:is then given by:

m = T-n-dm = T-n-d


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Maturity (of Cotton Fibres)Maturity (of Cotton Fibres)Maturity Count and Maturity Maturity Count and Maturity RatioRatioTotal number of fibresTotal number of fibres = T = T Number of mature fibresNumber of mature fibres = n= nNumber of dead fibresNumber of dead fibres = d = d Number of immature fibresNumber of immature fibres = m = T-n-d= m = T-n-d

Two quantities defined:Two quantities defined:

Maturity Count = Maturity Count = 100 x m/T = % immature100 x m/T = % immature

Maturity Ratio (M) Maturity Ratio (M) = 0.7 + (N-D)/200= 0.7 + (N-D)/200

Now let Now let N = 100 x n/T = % “normal” fibresN = 100 x n/T = % “normal” fibres

andandD = 100 x d/T = % dead fibresD = 100 x d/T = % dead fibres


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Maturity (of Cotton Fibres)Maturity (of Cotton Fibres)Maturity Count and Maturity Maturity Count and Maturity RatioRatio

• M = 0.7 + (N-D)/200M = 0.7 + (N-D)/200

Gives M ~ 1 for a high-grade Egyptian cottonGives M ~ 1 for a high-grade Egyptian cotton

• M can be greater than 1M can be greater than 1

• M less than ~ 0.8 is not goodM less than ~ 0.8 is not good

• M less than 0.7 is very rareM less than 0.7 is very rare


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Maturity (of Cotton Fibres)Maturity (of Cotton Fibres)Summary of measurement methodsSummary of measurement methods

Direct Method (counting fibres)Direct Method (counting fibres)

- tediously slow!tediously slow!

Indirect MethodsIndirect Methods

- polarised light microscopy (?)polarised light microscopy (?)

- differential dyeing (slow)differential dyeing (slow)

- air-flow (best)air-flow (best)

ZUT-Testing: Dimensions of Fibres & Yarns 1 Dimensions of Fibres & Yarns Basic Concepts, Units &...

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Transcript of ZUT-Testing: Dimensions of Fibres & Yarns 1 Dimensions of Fibres & Yarns Basic Concepts, Units &...