Yarn modulus

In addition, the crimp ratio (i.e., the difference between the length of the yarn and the length of the fabric) can be determined for woven fabrics that feature yam undulations. The combination of the yam crimp ratio and the yarn modulus is needed to describe the tensile mechanical behavior of a composite fabric (Fig. 6.17). 

Determination of the fabric tensile behavior from the yarn modulus and the crimp ratio for a typical yarn. 

Standard Test Methods for Tire Yarns, Cords, and Woven Fabrics. ASTM standard D885M-94 includes test methods for characterizing tire cord twist, break strength, elongation at break, modulus, tenacity, work-to-break, toughness, stiffness, growth, and dip pickup for industrial filament yams made from organic base fibers, cords twisted from such yams, and fabrics woven from these cords that are produced specifically for use in the manufacture of pneumatic tires. These test methods apply to nylon, polyester, rayon, and aramid yams, tire cords, and woven fabrics. 

Fig. 2 Weibull plot of the filament strength for a test length of 10 cm of a PpPTA yarn yielding a Weibull modulus of 20.6. The average filament strength is 3.2 GPa... 

Weibull plots of various fibre properties, such as the filament count, modulus, elongation at break and the strength, can provide important information on the quality and performance of the manufacturing process. The results can be used to formulate a strategy for the improvement of the yarn properties. 

In cellulose II with a chain modulus of 88 GPa the likely shear planes are the 110 and 020 lattice planes, both with a spacing of dc=0.41 nm [26]. The periodic spacing of the force centres in the shear direction along the chain axis is the distance between the interchain hydrogen bonds p=c/2=0.51 nm (c chain axis). There are four monomers in the unit cell with a volume Vcen=68-10-30 m3. The activation energy for creep of rayon yarns has been determined by Halsey et al. [37]. They found at a relative humidity (RH) of 57% that Wa=86.6 kj mole-1, at an RH of 4% Wa =97.5 kj mole 1 and at an RH of <0.5% Wa= 102.5 kj mole-1. Extrapolation to an RH of 65% gives Wa=86 kj mole-1 (the molar volume of cellulose taken by Halsey in his model for creep is equal to the volume of the unit cell instead of one fourth thereof). 

Fig. 23 PpPTA yarn data showing the relation between strength and modulus together with the calculated curves... 

Figure 28 shows the observed relations between strength and modulus for polyetherketone or POK yarns. The experimental data have been obtained from... 

Fig. 29 The observed strength as a function of the initial modulus of filaments taken from a single yarn of cellulose II spun from a liquid crystalline solution compared with the calculated curves [26]...

Fig. 53 The sonic modulus as a function of the number-average molecular weight for a series of experimental PpPTA yarns with different molecular weights specified in Table 4...

Table 4 The molecular weight, sonic modulus and strength of experimental PpPTA yarns. The molecular weight of a single monomer is 238... 

Knowing the deleterious effects of ionising radiations on PTFE, much attention was paid on their effects on PVDF although the latter had been told to behave well under irradiation. As an example, PVDF multifilament yarns can be y irradiated up to the absorption of 80 kGy without any effect on their Young s modulus [38], However, the structure of the polymer was somewhat modified as its energy to break kept constant and even increased by about 50% while the adsorbed dose was less than 8 kGy but decreased for higher adsorbed doses, down to 1/3 of its maximum value (1/2 of its initial value) when the adsorbed dose reached 81 kGy. To avoid these bulky effects, the interest of... 

Produce High Modulus Graphite Yarn , AFML-TR-68-235, Contract F33615-67-C-1753, Hitco, Gordena (1968) 11) H.F. Mack, Ed, Ency-... 

The newest advances in C-C composite materials have resulted from fiber improvements, such as modulus increases of two to three times and diameter decreases of more than 50% in the last ten years. Weaving techniques have also been improved, so that increased fiber content and reproducible distribution of filaments and yarns (down to 0.75 mm center-to-center spacing between yarns in 3D composites) are possible. However, because the interrelationship of the filaments and yarns with the bonding matrix is not well understood, the improved fiber properties have not yet been fully translated into a corresponding magnitude of improvement in C-C composites. 

The mechanical response of composites, as shown in these exploratory studies, indicates dependence on the ease with which fracture can occur between fibers, yarns, and plies. Poorly crystallized matrices result in composites that are strong and stiff but with little yield so that failure occurs catastrophically. In contrast, more crystalline matrices seem to be not quite as strong and to have a lower effective modulus, but their increased strain capability ensures that failure is not catastrophic the composited strength decays gradually as further strain is applied. Thus, the energy required for total failure is increased, and the composite with more crystalline matrix is more tolerant of defects or stress risers. 

Since for the application of fibres in textile products (knitted and woven products, tire yam canvas, reinforcement of plastics) a high specific weight is a disadvantage, it is customary also to express modulus and strength in another way, viz. as specific quantities this is done by division of E and a by the density p.E/p and a/p have the dimension Nm/kg = J/kg. In order to relate these quantities to the yarn count number (expressed in Tex), the specific quantities are also expressed in N/tex. 

FIG. 13.87 Diagram of the specific tenacity (specific dynamic tensile modulus (Ea/p), for modern high-performance filaments. The diagonal lines have the indicated ratio, which is the theoretical elongation at break (fractional) high-performance yarns have refractory materials have values between 0.025 and 0.005. (ty = tire yarn). 

FIG. 13.88 Diagram of the specific tenacity (ffb/p) versus the initial specific modulus (Ea/p) for conventional man made fibres. 0 is the limiting tangential slope in the stress-strain diagram for strain tending to zero. The diagonal lines show the indicated ffbr/ 0-ratio this varies from = 1 for elastomeric filaments and 0.2 for tyre yarns (ty) to 0.03 for yarns such as polyacrylonitrile. 

FIG. 13.91 Influence of draw ratio on modulus of elasticity ( ) (three drawing series of polyester (PETP) yarns). 

Table 13.17 gives the values of some synthetic yams. The average value of the ratio EJCr is 7.5, where E0 is the initial modulus of the yam. For yarns with helical molecular chains (silk, hair, isot. polypropylene, etc.) the value of EJCy is lower (about 2). Native cellulose (cotton) is added to the series for comparison. After substitution of EJCZ = 7.5 and E = [Pg.485]

FIG. 13.102 PpPTA yarn data showing the relation between tensile strength and initial modulus together with the curves calculated with Eq. (13.171) for five different values of critical shear strain, P from left to right P = 0.12, 0.115, 0.11, 0.105 and 0.10 rad used values are gd = 1.8 GPa and ecu = 240 GPa (see Table 13.18). Constructed from Figs. 22 and 23 in Northolt et al. (2005). The points above ( ) and below (O) the line for P — 0.11 are from different sets of PpPTA fibres. 

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