Contents of Assignment:
A. Why study textile physics?
B. Definition of:
1. 2. 3. 4. 5. 6. 7.
Stress Strain Flexural rigidity Tensile Strength Plasticity Elasticity Modulus of elasticity
Why study textile physics? Textile physics is very important subject for textile engineers or textile related students. Now I am going to discuss about bellow topics.
PHYSICS FOR TEXTILE FIBRE, YARN AND FABRIC Definition of yarn Factors affecting yarn strength Parameters affecting physical properties of yarn Classification of yarn Classification of yarn based on physical and performance characteristics Description of yarn Idealizes structural diagram of some yarns Continuous filament and staple yarn structure Fundamental structural features of yarn Yarn designation Relative consumption of yarn Sewing thread Thread sizes Thread selection Importance of twist Types and direction of twist Bedding or nesting Determination of twist Twist effects Angle of twist and twist factor Effects of twist on yarn strength, extensibility and luster Geometry of twisted yarn Idealized twisted yarn geometry Various comments on idealize yarn geometry Yarn size and twist multiplier Optimum twist factor Fiber packing in yarn Open packing of yarn Hexagonal close packing of yarn Real yarn packing Concentrating and disturbing factors Observed packing of fibers in real yarn Twist in relation to yarn bending Relation among twist angle, twist factor and yarn count Equation for yarn diameter Equation for specific volume of yarn
Show that d=4.44 x 10-6 Density Relation among twist, diameter and twist angle Estimation of Schwarz’s constant Yarn luster Twist contraction and twist retraction Limit of twist Contraction factor and retraction factor Derivation of expression for prediction of filament strain Limitations of Platt’s low strain equation
Geometry Cloth geometry Reasons for studying cloth geometry Weave and weave notation Crimp Warp crimp and weft crimp calculation Crimp percentage and take up percentage Distinction between crimp % (C) and take-up %(T) Relationship between crimp (%) and take-up (%) Pierce’s Flexible thread model Importance of crimp on fabric properties Fabric behavior during tensile testing Measurement of crimp Principles of edged crimped yarn Crimp measuring instrument Pierce’s model for plain weave Equation for pick spacing (P2) and end spacing (P1) Equation for maximum warp yarn displacement (h1) and weft yarn displacement (h2) Dependence of crimp percentage Crimp interchange Equation for crimp interchange Warp and weft yarn jamming Equation for warp and weft yarn jamming Biaxial, tri-axial and balanced structure Equation for rigid thread model Why rigid tread model was introduced Effect of yarn crimp on fabric properties Concept of similar cloth Cover factor Yarn and fabric strength relationship Handle, drape and shear Measurement of drape ability Some tensile properties of fabric Electrical properties of textiles
Dielectric properties of textiles Polarization and related effects Power factor and dissipation factor Measurement of dielectric properties Preparation of a test condenser Measurement of impedance by Scherring’s bridge and resonance method Factors influencing dielectric properties of textiles Electrical resistance of textiles Conductors, semiconductors and insulators Conduction of electricity in textiles Influence of dielectric constant on ions Normal, excited and ionized atom Electrical resistance of textiles Measurement of resistances of textiles Specimen preparation for measuring resistances of textiles Influence of various factors on resistance of textiles Static charge Explanation of static phenomenon Theories of static charge Measurement of charge in slivers by Faraday’s cylinder and Medley’s method Generation of static charge in polymers Amphoteric behavior of keratin Piezo and pyro electric charges Leakage of static charges in air Leakage of static charges in perfect insulators, moderate insulators, & conductors Problems of static charges in textile mills Minimization of static charges in textile mills The present view about static charges in textiles And many other textile field Textile Physics play an important role.
Stress: Stress is a quantity that characterizes the strength of the forces causing the deformation, on a “force per unit area” basis. Direct Stress or Normal Stress Stress normal to the plane is usually denoted "normal stress" and can be expressed as σ = Fn / A
(1)
Where, σ = normal stress ((Pa) N/m2, psi) Fn = normal component force (N, lbf (alt. kips)) A = area (m2, in2) Shear Stress Stress parallel to the plane is usually denoted "shear stress" and can be expressed as τ = Fp / A
(2)
Where, τ = shear stress ((Pa) N/m2, psi) Fp = parallel component force (N, lbf) A = area (m2, in2)
Strain: Deformation or change in shape of a material caused by an external loading. Strain is the ratio of the change in length (Δ l) per unit length (or original length (lo). Strain is defined as "deformation of a solid due to stress" and can be expressed as ε = dl / lo = σ / E Where,
dl = change of length (m, in) lo = initial length (m, in) ε = Strain
Stress-strain curve:
When fiber is deformed then the fiber follows the stress-strain curve. Here, A to B → linear region. This region follows Hook’s law (stress ∞ strain). So, fiber comes to its original position after removal of load. So, the region is called elastic region and the deformation is called elastic deformation. B to C → Plastic region. In this region chain breaks but fiber do not break. Here the deformation is known as plastic deformation. C → Breaking point. The fiber will be break at this point.
Flexural rigidity: Flexural rigidity is the stiffness of a textile fiber. It can be defined as the couple needed to bend a fiber.
Mathematically, Flexural rigidity = (1/4π) (ηET2/ρ) Where, η = shape factor, E = specific shear modulus, T =linear density (Tex), ρ = density (gm/cm3)
Tensile Strength: Tensile strength is the strength of a material under tension. Tensile strength is probably the next most important property of a composite after modulus of elasticity. Composites, particularly graphite, do not enter into an area of plasticity. If enough force is applied to push them beyond their tensile strength they break, often dramatically. For composites like graphite and fiberglass the tensile strength and elastic limit occur at about the same point on the curve. It is important to note that the tensile strength as shown on the modulus of elasticity curve is static tensile strength. The dynamic tensile strength for most materials, the tensile strength when force is being applied rapidly, for example when we are casting, is roughly one half of the static tensile strength. Actually, the faster we apply the force the lower the tensile strength will be but about one half is a reasonable number to use for composites. Most blank manufacturers do not publish static tensile strength numbers let alone numbers for dynamic tensile strength.
Plasticity: Plasticity is the reverse of elasticity; a plastic material will retain exactly the shape it assumes under load when the load is removed. Familiar examples are the stamping of images on coins and the multiplicity of domestic and ornamental objects produced by pressing synthetic resins and similar compounds in steam-heated dies. Plasticity is fairly similar to ductility.
Elasticity: All material bodies will deform. As the stress increased the deformation also increases and if the load on the material is removed at any stage up to the elastic limit it will return to its original shape and dimension (original length).
Conventionally tensile stresses are considered positive (+) and compressive stresses negative (-) Modulus of elasticity: In a tensile test a graph is produced of stress against strain as the load is gradually applied. The first portion of the graph will be a straight line as shown below.
The slope of this straight line is the constant of proportionality known as the MODULUS OF ELASTICITY
Where, F = applied axial force lo = original length A = area of cross-section Δ l = change in length E = modulus of elasticity
