GATE Textile Engineering Textile Testing Syllabus

Textile Testing syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Textile Testing in GATE Textile Engineering, not a summary of it.

1. 1

   Sampling techniques for fibres, yarns and fabrics

   1 topic

   • Sample size and sampling errors
2. 2

   Moisture in textiles

   3 topics

   • Fibre length, fineness, crimp, maturity and trash content
   • Tensile testing of fibres
   • High volume fibre testing
3. 3

   Linear density of sliver, roving and yarn

   4 topics

   • Twist and hairiness of yarn
   • Tensile testing of yarns
   • Evenness testing
   • Fault measurement and analysis of yarns
4. 4

   Fabric properties and testing

   10 topics

   • Fabric thickness, compressibility, stiffness, shear, drape, crease recovery
   • Tear strength
   • Bursting strength
   • Pilling and abrasion resistance
   • Tensile testing of fabrics
   • Objective evaluation of low stress mechanical characteristics
   • Air permeability
   • Wetting and wicking
   • Water-vapour transmission through fabrics
   • Thermal resistance of fabrics

Textile Testing flashcards for GATE Textile Engineering

23 of 62 cards from the Textile Testing deck — real questions with worked answers.

1. In textile sampling, what is the difference between a 'sampling error' and a 'bias' (systematic error)?

   Sampling error is the random variation between a sample statistic and the true population value; it decreases as sample size increases and averages to zero over many samples. Bias is a systematic, directional error from a faulty sampling method that does not reduce with larger samples and must be eliminated by correcting the method.

2. How does the standard error of the mean depend on sample size $n$ and population standard deviation $\sigma$?

   $$SE = \frac{\sigma}{\sqrt{n}}$$ The standard error is inversely proportional to $\sqrt{n}$, so to halve the error the sample size must be quadrupled.

3. Define a 'numerical sample' versus a 'biased sample' in textile testing.

   A numerical (unbiased) sample is drawn so that every fibre/element has an equal chance of selection, giving correct proportions by number. A biased sample favours certain elements (e.g., longer fibres caught by a gripping method), distorting the result; length-biased samples must be corrected to numerical or weight-biased distributions.

4. What sample size $n$ is required to estimate a mean within a tolerance $E$ at confidence level $z$, given standard deviation $\sigma$?

   $$n = \left(\frac{z\,\sigma}{E}\right)^{2}$$ Equivalently, using coefficient of variation $CV$ and percentage error $P$: $n = \left(\dfrac{z\cdot CV}{P}\right)^{2}$.

5. What is the relationship between fibre fineness expressed in tex, denier and the metric count $N_m$?

   Tex is mass in grams per $1000\,\text{m}$; denier is mass in grams per $9000\,\text{m}$. Thus $\text{denier} = 9 \times \text{tex}$, and $\text{tex} = \dfrac{1000}{N_m}$ where $N_m$ is metres per gram.

6. Define fibre maturity for cotton and give the maturity ratio formula.

   Maturity is the degree of secondary cell-wall (cellulose) thickening relative to the fibre's potential. The maturity ratio is $$M = \frac{N - D}{0.7} + 0.7$$ where $N$ is the fraction of 'normal' fibres and $D$ the fraction of 'dead' fibres (sodium hydroxide swelling test).

7. What does the degree of thickening $\theta$ represent for a cotton fibre, in terms of wall area $A$ and perimeter $P$?

   $$\theta = \frac{A}{\dfrac{P^{2}}{4\pi}} = \frac{4\pi A}{P^{2}}$$ It is the ratio of the actual cross-sectional wall area to the area of a circle of the same perimeter; a fully solid circular fibre has $\theta = 1$.

8. What is fibre crimp and how is percentage crimp calculated?

   Crimp is the waviness of a fibre. Percentage crimp is $$C\% = \frac{L_e - L_c}{L_c}\times 100$$ where $L_e$ is the extended (straightened) length and $L_c$ the crimped (relaxed) length.

9. Name the principal instruments/methods for measuring cotton fibre length and what each reports.

   Comb sorter (Baer sorter) gives a staple/length distribution diagram; Fibrograph gives mean length, upper-half-mean length (UHML) and uniformity ratio; Almeter (electronic, from beard) gives length distribution by weight and number for combed slivers.

10. Define the uniformity ratio and uniformity index from Fibrograph length data.

    Uniformity ratio $= \dfrac{\text{Mean length}}{\text{Upper-half mean length}}\times 100$. Uniformity index $= \dfrac{\text{Mean length}}{\text{Upper-half mean length (UHML)}}\times 100$. Higher values indicate more uniform fibre length.

11. How is the Micronaire value of cotton related to fibre fineness and maturity?

    Micronaire is an airflow measurement of the specific surface area of a fixed mass of cotton. It reflects the combined effect of fineness and maturity: $\text{Micronaire} \propto$ (fineness $\times$ maturity). Two cottons can share a Micronaire value with different fineness/maturity combinations, so it is not a pure fineness measure.

12. State the airflow principle used to measure fibre fineness (e.g., in the Micronaire test).

    For a fixed mass of fibres compressed into a chamber of fixed volume, the airflow resistance depends on the total fibre surface area. Pressure drop $\Delta P$ and flow rate $Q$ relate via a Kozeny-Carman-type expression; finer fibres present more surface area and give lower flow (higher resistance) at constant pressure.

13. How is trash content of cotton typically measured and expressed?

    Trash (non-lint matter: leaf, bark, seed-coat fragments) is measured by the Shirley Analyser, which mechanically separates lint from trash, or optically by the HVI trash module. It is expressed as percentage trash by weight, or by trash count (number of particles) and area percentage covered.

14. Write the expression for tenacity of a fibre and state its common unit.

    $$\text{Tenacity} = \frac{\text{Breaking force}}{\text{Linear density}}$$ Common units are $\text{cN/tex}$ or $\text{gf/denier}$ (gpd). It is specific stress, normalising strength to fineness rather than cross-sectional area.

15. Distinguish the CRL, CRE and CRT principles of tensile testing machines.

    CRL (Constant Rate of Loading): load increases at a constant rate. CRE (Constant Rate of Extension): the jaw separates at a constant speed (most modern instruments, e.g., Instron, Tensojet). CRT (Constant Rate of Traverse): the pulling clamp moves at constant rate while load builds via a pendulum lever (e.g., classic pendulum testers).

16. Define work of rupture and how it is obtained from a load–elongation curve.

    Work of rupture is the energy needed to break a specimen, equal to the area under the load–elongation curve: $$W = \int_{0}^{e_b} F\,de$$ where $F$ is force and $e_b$ the elongation at break.

17. Define the 'work factor' of a fibre.

    Work factor is the ratio of the actual work of rupture to the work that would be done if the load–elongation curve were a straight line up to the breaking point: $$\text{Work factor} = \frac{\text{Work of rupture}}{F_b \times e_b}$$ For a linear (Hookean) material it equals $0.5$.

18. What is initial modulus of a fibre and how is it found?

    Initial (Young's) modulus is the slope of the initial straight-line portion of the stress–strain curve: $$E = \frac{\Delta(\text{stress})}{\Delta(\text{strain})}$$ expressed in $\text{cN/tex}$ or $\text{N/mm}^2$. It indicates fibre stiffness at small extensions.

19. State the principal measurements provided by a High Volume Instrument (HVI) for cotton.

    HVI measures: Micronaire (fineness/maturity), length (UHML) and length uniformity index, fibre strength (bundle tenacity) and elongation, colour (Rd brightness and +b yellowness), and trash (particle count and area). It does so rapidly for bale classing.

20. On what gauge length is HVI bundle strength measured, and why does gauge length matter?

    HVI measures bundle strength at a $\tfrac{1}{8}$ inch ($3.2\,\text{mm}$) gauge length. Gauge length matters because of the weak-link effect: longer gauge lengths include more weak places, giving lower measured strength; results must always quote the gauge length.

21. What is AFIS and how does it differ from HVI?

    AFIS (Advanced Fibre Information System) tests individual fibres after aeromechanical opening, giving distributions of length, fineness, maturity, neps and trash on a single-fibre basis. HVI tests fibres in bundles/beards and reports averaged classing values; AFIS gives more detailed distribution data but is slower.

22. Define twist of a yarn and the unit Twist Multiplier (TM) / Twist Factor.

    Twist is the number of turns per unit length (TPI = turns per inch, or TPM = turns per metre). Twist factor / multiplier relates twist to count: in the English system $$TM = \frac{TPI}{\sqrt{N_e}}$$ and in tex $$\alpha_{tex} = TPM \times \sqrt{\text{tex}}$$ giving twist hardness independent of count.

23. State the twist-contraction (retraction) relationship and define twist contraction.

    Twisting shortens a yarn because surface fibres follow a helical path. Twist contraction $$C = \frac{L_0 - L}{L_0}\times 100$$ where $L_0$ is untwisted length and $L$ the twisted length; the twisted helix angle increases with twist, increasing contraction.

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