Question

Composite Structures Tutorial 7 (week 8) 7.1 Find the five strength parameters of a unidirectional glass/epoxy lamina with 40% fiber volume fraction. Use the properties of glass and epoxy from Table 3.1 and Table 3.2. Assume the fibers have circular cross-section and are in a square array packing. 1-52.0-$01674870 225 47 Find 208 Mechanics of Composite Materials, Second Edi Convert PO or Excel Orl Select PDF I TABLE 3.1 Typical Properties of Fibers (SI System of Units) Units Graphite Glass Aramid GPa GPa Property 2 Englrth (uS 85 85 124 Axial modulus Transverse modulus Axial Poisson's ratio Transverse Poisson's ratio Axial shear modulus 0.20 0.20 35.42 0.36 0.37 0.30 0.35 GPa μm/m/°C μ m/m/°C MPa MPa MPa MPa MPa xial coefficient of thermal expansion Transverse coefficient of thermal expansion Axial tensile strength Axial compressive strength Transverse tensile strength Transverse compressive strength Shear strength Specific gravity 4.1 1550 1550 1550 1550 2067 1999 1379 276 42 21 4 2.5 Windows uE TABLE 3.2

Answer 1

1. 1. Fiber properties Lili M.Sc (C.T.) 3rd sem.
2. 2. Definition-  Fiber properties are essential thing to know for various end uses and the products made from it qualify on the basis of certain parameters.  The various properties are-  High fiber length to width ratio.  Tenacity (adequate strength).  Flexibility or pliability.  Cohesiveness or spinning pliability  Uniformity.
3. 3.  Fiber morphology  Specific gravity  Elongation and elastic recovery  Resiliency  Moisture regain  Flammability and other thermal reactions  Electrical conductivity  Abrasion resistance  Chemical reactivity and resistance  Sensitivity to environmental conditions.
4. 4.  High length to width ratio-  A pre-requisite for processing of fibers into yarns and fabrics is that their lengths must be more than widths. The minimum length to breadth ratio is 100:1.  Length of fibers is also a basis for classifying them into two groups staple and filament. Staple fibers are of relatively short length fibers; and filament fibers are long length fibers.  The fineness of a natural fiber is a major factor in ascertaining quality and is measured in microns(1 microns= 1/1000millimeter). In general, finer fibers are softer, more pliable and have better drapability. They are, thus, considered superior and form better yarns and fabrics. Fineness of man-made
5. 5.  Tenacity-  the strength of textile fibers is referred to as their tenacity. It is determined by measuring the force required to rupture or break the fiber. Sufficient tenacity is required to withstand the mechanical and chemical processing as well as make textile products which are durable.  Tenacity is, directly related to the length of the polymers, degree of polymerization, strength in dry and wet conditions, and types of inter- polymer forces of attraction formed between the polymers.
6. 6.  Flexibility-  Fibers should be flexible or pliable in order to be made into yarns and thereafter into fabrics that permit freedom of movement. Certain end uses require greater flexibility, e.g., automobile seat belts.  Uniformity-  Uniformity of fibers towards its length, ensure production of even yarns which can then form fabrics of uniform appearance and consistent performance.
7. 7.  Cohesiveness or spinning quality-  It is the ability of the fiber to stick together properly during yarn manufacturing processes.  Natural fibers have inherent irregularities in their longitudinal or cross sections which permit them to adhere to each other during fiber arranging.  In case of synthetics, filament lengths aid in yarn formation. Texturing introduces coils, crimps, curls or loops in the structure of an otherwise smooth filament. It is used to impart
8. 8.  Morphology-  It is the study of physical shape and form of a fiber. It includes microscopic structure like longitudinal and cross sections. These also include fiber length, fineness, crimp, color and luster.  Physical shape-  shape of a fiber include, its longitudinal sections, cross section, surface contour, irregularities and average length.
9. 9.  Luster-  It refers to the sheen or gloss that a fiber possesses. It is directly proportional to the amount of light reflected by a fiber.  This in turn is affected by their cross section shape.  Among the natural fibers, silk or the queen of Cross sectional shape Degree of luster Round High Irregular Low Kidney shaped Low Oval High Trilobal High octagonal Low
10. 10.  Deluster-  A delusterant is a substance that is added to the dope before spinning of manufactured fibers.  Finally powdered metallic salts like titanium dioxide (TiO2) and geranium dioxide (GeO2) are used. These act as discontinuities in an otherwise regular, uniform reflection of light.  The amount of delusterant added could vary and thus result in semi-lustered or delustered fibers.
11. 11.  Specific gravity-  The specific gravity of a fiber is the density related to that of water(at 4°c).  The density of water at that temperature is 1. fiber density will affect their performance and laundering.  If the specific gravity of a fiber is less than 1, it will float in water, making its washing and dyeing very difficult. E.g. Olefins fiber.  A related property is density which is defined as the mass per unit volume and measured in
12. 12.  Elongation and elastic recovery-  The amount of extension or stretch that a fiber accepts is referred to as elongation. Elongation at break is the amount of stretch a fiber can take before it breaks.  Elastic recovery indicates the ability of fibers to return to their original length after being stretched. A fiber with 100% elastic recovery will come back to its original length after being stretched to a specific degree for specified period of time. After removing and re- measured.
13. 13.  Resiliency  Resiliency refers to the ability of a fiber to come back to its original position after being creased or folded. Resilient fibers recover quickly from wrinkling or creasing. Good elastic recovery usually indicates good resiliency. This property is described qualitatively and ranges from excellent to poor. Excellent resiliency is exhibited by polyester, wool and nylon fibers. Flax, rayon and cotton, on the other hand, have a low resiliency.
14. 14.  Moisture regain-  The ability of a bone dry fiber to absorb moisture is called moisture regain. Measurements are done under standard testing conditions (70°± 2F and 65% ±2% relative humidity). Saturation regain is the moisture regain of a material at 95-100% relative humidity. Both regain and content are expressed as a percentage.  Moisture regain= wt. of water in a material × 100 oven dry wt.  Moisture content= wt. of water in a material × 100 total wt.