Flexural strength, composition dependence

Those stmctural variables most important to the tensile properties are polymer composition, density, and cell shape. Variation with use temperature has also been characterized (157). Flexural strength and modulus of rigid foams both increase with increasing density in the same manner as the compressive and tensile properties. More specific data on particular foams are available from manufacturers Hterature and in References 22,59,60,131 and 156. Shear strength and modulus of rigid foams depend on the polymer composition and state, density, and cell shape. The shear properties increase with increasing density and with decreasing temperature (157). 

Carbon-Fiber Composites. Cured laminates of phenoHc resins and carbon-fiber reinforcement provide superior flammabiHty resistance and thermal resistance compared to unsaturated polyester and epoxy. Table 15 shows the dependence of flexural strength and modulus on phenoHc—carbon-fiber composites at 30—40% phenoHc resin (91). These composites also exhibit long-term elevated temperature stabiHty up to 230°C. 

Figure 3. Composition dependence of the flexural and tensile strengths for the terpolymer/blends...

The composition dependence of the flexural strength of the aMS/AN-copolymer blend with polyarylether K appears in Figure 13. As the composition of the copolymer increases, the strength first increases, reaches a maximum, and then decreases. It actually exhibits a minimum at about 80% < MS/AN. This behavior can only substantiate earlier suggestions regarding the possible immiscibility of these systems. All of the other mechanical properties indicate that mixtures with polyarylether K may not be miscible but are mechanically compatible. Finally, it is interesting to note that at least one of the pendant chemical groups present on K exists on either of the a-methyl styrene interpolymers. It... 

Fig. 15. Microstructural dependence of flexural strength and fracture toughness of silicon nitride ceramics. The composition of these specimens was 90 wt % Si3N4-10 wt % Y3A15Op (27).

Fig. 22. Dependency of the relative changes in ILSS and flexural strength of the glass laminate composite of BACY/BMIP blend on composition of the matrix...

Non-irradiated blends of PMMA/SAN showed composition dependence of the flexural strength. It was found that adding as litfle as 20 wt% of SAN to PMMA reduced the degradation effect of irradiation by a factor of 4. Irradiated PMMA showed random chain scission without cross-linking — G(scission) in /unolT for PMMA decreases from 0.12 at 100% PMMA, to 0.24... 

The addition of styrene-acrylate causes a significant increase in the bending tensile strength (Fig.2). An increase from 7.4 MPa to 11.7 MPa at the age of 28 days can be observed. This value is reached with the 10% as well as the 20% dosage. Adding styrene-butadiene does not result in a considerable increase in the flexural strength, which is in compliance with the conclusion that not all of the polymer modifications bring about the desired properties. The required properties of the modified mortar are dependent up on the used dispersion and the composition. However, this can only be determined from experiments. 

Continuous carbon fiber reinforced SiC composites were prepared by Xu and Zhang [211] using CVI, in which the preforms were fabricated by the three dimensional braid method. For the composites with no interfadal layer, flexural strength and fracture toughness increased with the density of the composites and the maximum values were 520 MPa and 16.5 MPam , respectively. The fracture behavior was dependent on the interfacial bonding between fiber /matrix and fiber bundle/bundle, which was determined by the density of the composites. Heat treatment had a significant influence on the mechanical properties and fracture behavior. The composites with pyrolysis interfacial layers exhibited characteristic fracture and relatively low strength (300 MPa). 

Under three point bend loading of a composite (beam), cracks may be developed due to tensile stresses at the lower stratus of the specimen as well as compression stresses at the upper one, or due to interlaminar shear. The type of failure depends on the ratio of span to depth (L/D). Short beam specimens usually fail in shear and long ones by tensile or compression stresses. For interlaminar shear strength (ILSS) tests, a L/D = 5 was chosen (ASTM-D-2344-76). In case of flexural strength tests, this ratio was fixed to 40 (DIN 29971). 

Three-directional (3-D) orthogonal woven C/C composites, heat treated to 2200°C with a fibre volume fraction of 50 V/o in a fibre arrangement of 2, 2y, 3, have flexural strengths of 250 to 300 MN/m in the z direction.The strength is strongly dependent on the weave pattern and the fibre content in the x, y, and z directions and can be tailored from isotropic to anisotropic, according to special requirements, by means of the kind of weave pattern. 

Carbon fiber composite sand control depends on not only the cementation of resin, but also the increasing consolidation strength and flexural strength by adding special carbon fiber through surface treatment. 

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