Compressive strength of fibers

Deformation band studies of axially compressed PpPTA filaments revealed two distinct types of kink bands. In filaments that show tangential splitting, bands at an angle of about 55° are observed, whereas in radially split fibers the kink bands are oriented perpendicular to the fiber axis. Hydrogen-bonded planes acting as slip planes and intermicrofibril slip play an important role in the deformation process during axial compression.  

Tensile tests of axially compressed fibers revealed only a 10% loss in tensile strength, after application of as much as 3% compressive strain. 

In this study the regular spacing of the helical kink bands at 50° to 60° to the fiber axis was noticed. 

Compared with glass and carbon fibers the compressive strength of fibers made from lyotropic polymers is rather low. However, as shown by Van Dreumel, the negative effect of a low compressive strength on composite properties should not be overrated.  

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Obtaining the compressive strength of a slender fiber is even more difficult than measuring its tensile strength. An indirect technique has been devised to obtain compressive strength of fibers. It is well known that the recoil of a tensile stress wave generates a compressive wave. This principle is used in the recoil compression test, which allows one to estimate the compressive strength of fibers. 

Carbon fibers exhibit up to 50% lower compressive than tensile strengths. The compressive strength of fibers is calculated from compressive test data recorded from composite materials. A critical analysis of the compressive tests and compressive strength data for a variety of PAN based and mesopitch based carbon fibers can be found in reference [43]. 

In general, the compressive strength of a non-reinforced plastic or a mat-based RP laminate is usually greater than its tensile strength. The compressive strength of a unidirectional fiber-reinforced plastic is usually slightly lower than its tensile strength. Room-temperature compressive stress-strain data obtained per ASTM for several plastics are shown in Table 2-5. 

A totally unexpected observation was made when the compression strength of (0.1% by volume) fluorinated fiber concrete increased from about 31 MPa (unfilled) to about 38.6 MPa (filled with fluorinated fibrillated tape). This observation is in contrast to published results31 that PP fibers do not enhance compressive strength. 

The compressive strengths of the composites obtained increased and their temperature dependencies decreased with increasing fiber length, fiber-volume fraction, and density of the matrix foam. More specifically, the compressive strengtii of the composite was found to be proportional to that of the matrix and increased linearly with increased fiber-volume fraction in the experimental range employed (below 2% by volume). This result could be explained by Swift s sinusoidal model, assuming that the adhesion between fiber and matrix foam is perfect. 

Figure 8 exhibits the carbon fiber content vs. compressive strength of artificial woods. The compressive strength of the artificial woods decreases with increasing in the carbon fiber content, HPMC content and shirasu balloon content. Such compressive strength decrease may be explained by increases in both water-(cement+silica fume) ratio and voids in the artificial woods according to the water-cement ratio theory and voids theory, and is expressed by the following empirical equation ... 

Fig. 8 Carbon fiber content vs. compressive strength of artificial woods.

The flexural strength of artificial woods is greatly improved by the addidon of carbon fibers. The flexural deformation behavior of the artificial woods is markedly improved by using carbon fibers, HPMC and shirasu balloon. The bulk specific gravity, hardness and compressive strength of the artificial woods decrease with increasing carbon fiber content, HPMC content and shirasu balloon content. 

The mix proportions of artificial woods which can be nailed are recommended in 4. From an economical viewpoint, the carbon fiber content in the mix proportions can be reduced to 2 vol%. The optimum mix proportions with a carbon fiber content of 2 vol% is given in Table 7. The bulk specific gravity, flexural and compressive strengths of an artificial wood with the optimum mix proportions are 0.9, 12.0MPa and 19.0MPa respectively. The artificial wood also has good wood-processability like natural wood. 

One can see that epoxy polymer concrete exhibits higher compressive strength, with values ranging from 3.8-4.3 times higher than commercial concrete. Compressive strength of this PC shows an increase of 1.5 times when glass fibers are added to the epoxy resin matrix and 2.0 times with the use of carbon fibers [8],... 

We obtained the system of three equations with three unknowns, which can be solved for analytically, where N is the limiting compressive load b is the width of the cross-section of the sample Rk is the compressive strength of RubCon x is the distance from the most compressed fiber to the neutral axis of the cross-section eR is the deformation corresponding to maximal stress from the diagram o - e e is the deformation of extreme compressed fiber os is the tension stress As is the tension zone area of the cross section and h0 is the distance between centers of longitudinal reinforcements. 

FIGURE 2.36 Influence of reinforcement ratio p and aspect ratio L/d of the steel fibers on compression strength of fibrous RubCon. (Reprinted from Yu. Potapov, Yu. Borisov, D. Panfilov, O. Figovsky, and D. Beilin, Research of Polymer Concrete Based on Low Molecular Polybutadiene, Part VII Strength of Continuously Reinforced Polymer Concrete with Various Kinds of Fibers, J. Scientific Israel Technological Advantages 6, nos. 3-4 (2004) 71-74. With permission.)... 

Figure 4.23 Prediction of flexural and compressive strengths of steel fiber reinforced latex-modified mortars.

COMPRESSIVE STRENGTH OF GLASS-FIBER-REINFORCED COMPOSITES AT ROOM TEMPERATURE AND 77 K ... 

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