Single-fiber modulus

Asloun, El. M., Nardin, M. and Schultz, J. (1989). Stress transfer in single-fiber composites Effect of adhesion, elastic modulus of fiber and matrix and polymer chain mobility. J. Mater. Sei. 24, 1835-1844. 

Termonia, Y. (1993). Dependence of fiber critical length on modulus in single fiber composites. J. Mater. Sci. Lett. 12, 732-733. 

TMA measures the mechanical response of a polymer looking at (1) expansion properties including the coefficient of linear expansion, (2) tension properties such as measurement of shrinkage and expansion under tensile stress, i.e., elastic modulus, (3) volumetric expansion, i.e., specific volume, (4) single-fiber properties, and (5) compression properties such as measuring the softening or penetration under load. 

The highest modulus of a given substrate is obtained with a single crystal structure. Single crystal CVD-SiC whiskers (578 GPa) have a stiffen more highly ordered, structure than polycrystalline CVD-SiC fibers (190-400 GPa), and sapphire whiskers and fibers (415 GPa) are stiffer than slurry spun polycrystalline alumina fibers such as Fiber FP (380 GPa). Superimposed upon this relationship is a compositional factor. Fiber modulus and structural order generally also decrease with increasing compositional complexity, e.g., silicon carbide is intrinsically stiffer than silicon oxycarbide such as Nicalon, and slurry spun alumina fibers are stiffer than sol-gel or melt spun aluminate fibers. 

The tensile modulus of sisal fiber was 24 GPa. The tensile modulus of the sisal fiber made from the bundles of technical fibers was found to be lower than the real fiber (single fibril) since the individual fibrils are not loaded uniformly. The effective fiber modulus in the composite was 40 GPa. This point demonstrates a more favorable stress distribution in the sisal fibers in the composite material. 

All bast (stem) fibers (flax, kenaf, ramie, nettle, hemp, jute) as well as hard fibers (caroa, sisal) are suitable as for reinforcing fibers for natural fiber reinforced polymer composites, if they have a high tensile modulus and sufficient tensile strength. In addition to cultivation site, type and harvest, the properties of natural fibers depend significantly on the fiber extraction method. An extraction to technical fiber grades, i.e. production of bundles with different number of single fibers, is generally sufficient for use in plastics composites. The properties of such extracted fibers may be described as follows ... 

Zhou et al [163] also measured the tensile properties of carbonized PAN yarns. The 1000°C carbonized bundle had a tensile strength of 325 15 MPa and a modulus of 40 4 GPa. These values increased to 542 45 and 58 6 GPa, respectively, with the increase of the final graphitization temperature to 2200°C. The values are measured for the bundle which can differ from the properties of single fibers to a great extent. 

The stress-strain curve showed good linearity over a considerable strain, but did not show a typical yield point characteristic of polymer films and macrofibers. An elastic modulus of 45 MPa was determined for the PEO nanofibers (Tan et al. 2005a). A similar approach based on using AFM for assessing the single-fiber tensile properties of PAN was reported by Buer et al. (2001). 

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