Degree Of Fiber Alignment Research Articles

Mechanisms of fatigue in short glass fiber reinforced polyamide 6

AbstractAn adaptation to existing failure models for fatigue fracture of short fiber reinforced thermoplastics is presented, based on results using some new experimental methods. These results lead to the following conclusion: Cracks in polyamide remain bridged (by plastically drawn matrix material and/or fibers) until just before final fracture. Important is the conditioning of the polyamide: conditioned to equilibrium water content, this mechanism occurs, but not when it is dry as molded. Fatigue damage measurements were done on thin foils cut from the fatigued specimen. When tensile tested, these foils show a change in both strength and fracture strain after fatigue. Further observations during the experiments and SEM fractography strengthen the conviction that fatigue damage initiates and grows in the form of bridged cracks. A correlation between tensile strength and fatigue strength was found; the degree of fiber alignment has a similar effect on both tensile and fatigue properties.

Effects on Flexural Performance of Sawing Plain Concrete and of Sawing and Other Methods of Altering the Degree of Fiber Alignment in Fiber-Reinforced Concrete

Abstract The bulk of the paper deals with a comparison of the flexural performance of 102-mm (4-in.)-square standard molded specimens with corresponding specimens of the same size produced either by sawing the bottom (tension) surface of a 102 by 152-mm (4 by 6-in.) cross section or by sawing the bottom and sides of a 152 by 152 mm (6 by 6-in.) cross section. The performance of plain concrete is discussed in terms of its flexural strength under third-point loading [ASTM Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading) (C 78)]. The conclusion is that sawing need not adversely affect the measured strength when done carefully with proper equipment. The performance of fiber-reinforced concrete is discussed in terms of changes in first-crack strength and toughness parameters defined according to ASTM Test Method for Flexural Toughness and First-Crack Strength of Fiber-Reinforced Concrete (Using Beam with Third Point Loading) (C 1018). The majority of the results deal with changes in those parameters that are associated with differences in fiber alignment between the molded and sawed specimens. The results of two other small studies involving differences in fiber alignment are also included. In the first, alignment is varied by inserting steel plates in the freshly mixed concrete during consolidation, and in the second by using the same length of fiber in 102-mm (4-in.) and 152-mm (6-in.) cross sections. The conclusion is that preferential fiber alignment by the mold surfaces can increase first-crack strength and toughness indices. To avoid undue influence of fiber alignment in small specimens on flexural test data determined in accordance with Method C 1018, the ratio of minimum specimen cross section to fiber length should not be less than 3.0, except perhaps when strict compliance with this criterion means using specimens larger than 152 mm (6 in.) square.

Experimental characterization of the alignment of short fibers during flow

AbstractAn experimental approach has been made to investigate and characterize the alignment of short fibers contained in a suspension, during flow of the suspension through a convergent channel. Flow patterns have been obtained and analyzed for suspensions of various fiber concentrations. The influence of parameters such as fiber length, volume fraction and viscosity of the carrier medium on the degree of fiber alignment, has been examined. In order to minimize jamming, the viscosity of the carrier medium must be larger than a certain critical viscosity that is dependent on fiber length and volume fraction.

Short-Fiber-Reinforced Elastomer Composites

Abstract The reinforcement of elastomers with short fibers results in composites with a wide variety of properties. The performance and properties are a function of fiber type, fiber content, fiber aspect ratio, fiber orientation, fiber dispersion, fiber-matrix adhesion, processing methods, and properties of the elastomer matrix. A composite with almost any desired property can be obtained by manipulation of these parameters. Of the five fibers studied in this work, glass and carbon are the poorest for increasing mechanical properties. The cellulose, aramid, and nylon fibers all reinforce elastomers to give composites of approximately the same magnitude in properties. Alignment of reinforcing fibers by milling creates a significant anisotropy in the composite properties. The degree of fiber alignment is best for glass, carbon, and cellulose fibers. The uniformity of fiber dispersion is again best for glass, carbon, and cellulose fibers. Aramid and nylon fibers tend to clump together and do not disperse easily. Fiber-to-matrix adhesion is a problem. No evidence of consistently good fiber-matrix adhesion is observed except for the precoated cellulose fibers. The interaction between fiber and elastomer can only improve with a coating or sizing that is compatible with both the fiber and its matrix. Adhesion-promoting bonding agents also improve fiber-matrix adhesion. However, each fiber and/or elastomer may be influenced differently by a bonding agent. Adhesion promoters specific to the type of composite being prepared must be sought in order to obtain optimum properties.