Composites random fiber

Studies were performed to demonstrate the effects of process variables such as light intensity, cure time, initiator concentration, and fiber loading on the evolution of the mechanical properties of the polymers and composites. Even with moderate incident light intensities (less than 500 mW/cm2) and high fiber loadings (60 wt.% random fibers) the photopolymerizations proceed to completion in minutes and exhibit mechanical properties equivalent to samples prepared by traditional... 

Short-fiber composites fabrication of, 26 766 Short fiber metal-matrix composites, casting process for, 76 168 Short fiber web layering systems, 77 504 Short oil alkyds, 2.T48 Short random fiber reinforcement,... 

Alexander, R.M., Schapery, R.A., Jerina, K.L. and Sander, B.A. (1982). Fracture Characterization of a random fiber composite material. In Short Fiber Reinforced Composite Materials. ASTM STP 722 (B.A. Sanders cd.), ASTM, Philadelphia, PA, pp. 208-224. 

Gaggar, S. and Broutman, L.J. (1975). Crack growth resistance of random fiber composites. J. Composite Mater. 9, 216-227. 

The effect of dispersoids on the mechanical properties of metals has already been described in Section 5.1.2.2. In effect, these materials are composites, since the dispersoids are a second phase relative to the primary, metallic matrix. There are, however, many other types of composite materials, as outlined in Section 1.4, including laminates, random-fiber composites, and oriented fiber composites. Since the chemical nature of the matrix and reinforcement phases, as well as the way in which the two are brought together (e.g., random versus oriented), vary tremendously, we shall deal with specific types of composites separately. We will not attempt to deal with all possible matrix-reinforcement combinations, but rather focus on the most common and industrially important composites from a mechanical design point of view. 

Crack Propagation Resistance of Random Fiber Composites... 

Linear elastic fracture mechanics (LEFM) approach can be used to characterize the fracture behavior of random fiber composites. The methods of LEFM should be used with utmost care for obtaining meaningful fracture parameters. The analysis of load displacement records as recommended in method ASTM E 399-71 may be subject to some errors caused by the massive debonding that occurs prior to catastrophic failure of these composites. By using the R-curve concept, the fracture behavior of these materials can be more accurately characterized. The K-equa-tions developed for isotropic materials can be used to calculate stress intensity factor for these materials. 

Inviscid melt spun calcium aluminate glass fibers have low strength (0.5-1.1 GPa) and moduli (46-58 GPa). Low strength and low stiffness can be attributed to the random structure frozen into the fibers during rapid solidification. As a result, they are not likely to become composite reinforcing fibers, despite their excellent alkali resistance which they share with quaternary calcium-aluminate fibers [9]. 

The properties of thermoplastic composites containing fibers as fillers are dependent on a number of parameters, which include the properties of the matrix material, the size and aspect ratio of the fibers, dispersion of the fibers and the interface. In development of these composites, two important issues need to be addressed, namely, the incompatibility between the natural fibers and polymer matrix, and the tendency of the fibers to form aggregates [67]. Additionally, the composites exhibit poor dimensional stability due to moisture absorption. The orientation of the fibers is also important. In short-fiber reinforced composites, the orientation of the fibers is usually random and therefore the properties of such composites are not as superior as those containing continuous fibers. Optimization of processing conditions and use of coupling agents/compatibilizers and treatment of fibers can enhance the properties of these composites. 

Courtney T H (1990) Mechanical Behavior of Materials, McGraw-HiU, Singapore, pp. 580-582. Atodaria D R, Putatunda S K and Mallick P K (1997) A fatigue crack growth model for random fiber composites, J Compos Moter 31 1838-1855. 

The case of fillers which adhere to the polymer matrix is important in most applications. This is general whether the adhesion is intrinsic to the materials or enhanced by surface treatment of the fillers or additives to the polymer. When the adhesion between the filler and the resin matrix is adequate, the resin and the filler coact under stress. From the standpoint of visualizing how these effects alter the performance of the composite to make the whole greater than the parts, we will examine the combination of a fibrous filled fiber glass and a suitable resin matrix such as an adhering polyester resin. The case of a simplified configuration of a bundle of parallel fibers before and after the addition of the resin matrix is illustrated. The analysis will be extended to random fiber orientation and then to other filler shapes. 

As stated earlier, most plant fibers are termed staple , i.e. short length fibers. Fibers derived from the stem of the plant, e.g. ramie and flax, and those derived from some plant leaves, e.g. sisal and henequen, could be longer than 1 meter. Although it is easier to fabricate random, short fiber composites, with some manipulation, unidirectional composites of small dimensions can also be made using these fibers. Lodha and Netravali [19] used chopped ramie fibers and SPI resin to make random fiber green composites. Nam and Netravali [23,90] fabricated unidirectional composites using SPC resin with ramie fibers. Flax yarn and fabric reinforced SPC and modified SPC resin composites have also been made and have shown to have excellent properties [20,22,32,105,106], Fabrication of these composites and their properties are briefly discussed in the next subsections. 

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