Compressive strength, composite

If the interfacial shear strength is weak, this results in early failure of the composite. Conversely, if the treatment is too strong, then the composite becomes brittle. Increasing the fiber matrix adhesion does enhance the composite compressive strength. 

Figure 20.17 Compression strength of single carbon fibers Vs composite compression strength. Source Teprinted from Toray technical literature.

Figure 20.18 Anisotropy parameter l/fe composite compression strength. Source Reprinted from Toray technicai iiterature...

Polycrystalline-Alumina-Reinforced Aluminum Alloy Tensile Strength of Boron/Aluminum Composites Compressive Strength... 

Figure 1.6(b) The effect of fibre orientation on composite compressive strength. Measured for a 60 v/o, carbon fibre laminate. 

Density and polymer composition have a large effect on compressive strength and modulus (Fig. 3). The dependence of compressive properties on cell size has been discussed (22). The cell shape or geometry has also been shown important in determining the compressive properties (22,59,60,153,154). In fact, the foam cell stmcture is controlled in some cases to optimize certain physical properties of rigid cellular polymers. 

Fig. 5. The immediate effect of temperature on strength properties of clear wood, expressed as percentage of value at 20°C. Trends illustrated are composites from studies on three strength properties modulus of mpture in bending, tensile strength perpendicular to grain, and compressive strength parallel to grain. VariabiUty in reported results is illustrated by the width of the bands. MC = moisture content.

The hot mixes are designed by using a standard laboratory compaction procedure to develop a composition reflecting estabUshed criteria for volume percent air voids, total volume percent voids between aggregate particles, flow and stabdity, or compressive strength. Tests such as the Marshall, Unconfined Compression, Hubbard-Field, Triaxial Procedure, or the Hveem stabdometer method are used (109). 

Greater amounts of copper increase the proportion of needles or stars of Cu Sn in the microstmcture. Increase in antimony above 7.5% results in antimony—tin cubes. Hardness and tensile strength increase with copper and antimony content ductiUty decreases. Low percentages of antimony (3—7%) and copper (2—4%) provide maximum resistance to fatigue cracking in service. Since these low alloy compositions are relatively soft and weak, compromise between fatigue resistance and compressive strength is often necessary. 

Armor. Sihcon carbide is used as a candidate in composite armor protection systems. Its high hardness, compressive strength, and elastic modulus provide superior baUistic capabihty to defeat high velocity projectile threats. In addition, its low specific density makes it suitable for apphcations where weight requirements are critical (11). 

The compressive strength of composites is less than that in tension. Tills is because the fibres buckle or, more precisely, they kink - a sort of co-operative buckling, shown in Fig. 25.5. So wliile brittle ceramics are best in compression, composites are best in tension. 

Compression along the grain causes the kinking of cell walls, in much the same way that composites fail in compression (Chapter 25, Fig. 25.5). The kink usually initiates at points where the cells bend to make room for a ray, and the kink band forms at an angle of 45° to 60°. Because of this kinking, the compressive strength is less (by a factor of about 2 - see Table 26.1) than the tensile strength, a characteristic of composites. 

The mechanics of materials approach to the micromechanics of material stiffnesses is discussed in Section 3.2. There, simple approximations to the engineering constants E., E2, arid orthotropic material are introduced. In Section 3.3, the elasticity approach to the micromechanics of material stiffnesses is addressed. Bounding techniques, exact solutions, the concept of contiguity, and the Halpin-Tsai approximate equations are all examined. Next, the various approaches to prediction of stiffness are compared in Section 3.4 with experimental data for both particulate composite materials and fiber-reinforced composite materials. Parallel to the study of the micromechanics of material stiffnesses is the micromechanics of material strengths which is introduced in Section 3.5. There, mechanics of materials predictions of tensile and compressive strengths are described. 

Figure 3-60 Compressive Strength of Glass-Epoxy Composite Materials (After Dow and Rosen [3-28])...

Compressive Strength of Boron-Epoxy Composite Materials (After Lager and June [3-33])... 

H. Schuerch, Compressive Strength of Boron-Metal Composites, NASA CR-202, April 1965. 

John R. Lager and Reid R. June, Compressive Strength of Boron-Epoxy Composites, Journal of Composite Materials, January 1969, pp. 48-56. 

Figure 21 Compression strength as dependent on the content of GRP in jute fiber-reinforced hybrid-composites [67J.

In a further attempt to improve properties, Brauer, McLaughlin Huget (1968) examined the use of alumina as a reinforcing filler. Alumina is considerably more rigid than fused quartz. They achieved a considerable increase in strength. The preferred composition was the powder defined in Table 9.4, which had a compressive strength of 91 MPa. This zinc oxide based powder was the one most commonly used in subsequent studies by Brauer and coworkers. We shall refer to it as the EBA powder for it is the one used in commercial formulations and in a number of experimental studies. 

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