Off axis properties

Unlike short-fiber composites, modulus and strength in long-fiber composites are little affected by the interface. However, the interface does affect off-axis properties, such as compressive modulus, and the toughness and shear strength are affected. As shown in Eigure 5.107, a reduction in the interfacial strength, such as through the... 

With all the simplicity of the OA method it produces reasonable predictions for the fibre-dominated properties and low crimp, when deviations from the iso-strain assumption play a minor role. For off-axis properties, or for cases when transverse parts of the reinforcement (e.g. weft yams for warp-direction loading) play an important role, or in the presence of high-crimp yams (e.g. 3D reinforcements with significant fraction of binder), the iso-strain assumption is not valid any more, and quality of the OA predictions is decreased. There are approaches that combine iso-strain and iso-stress formulations [3], but these approaches leave open the choice of the combination mles open, which makes their predictive abilities limited. 

Considerable work has been performed to reduce the matrix porosity in order to enhance shear strength and off-axis properties, yet without the risk of material embrittlement. The matrix porosity can be adjusted by multiple infiltration of the as-sintered components e.g. with AICI3 solutions. Soaking the infiltrated specimens in ammonia induces the conversion to Al (0H)3 which transforms to alumina after calcination at nOO C. The re-infiltration... 

When considering off-axis properties, the fiber matrix adhesion has a greater effect on the transverse flexural strength than the transverse tensile strength. 

Properties of typical thermosetting and thermoplastic polymer matrices and single fibres are listed. The former have relevance to the upper working temperature and off-axis properties of the composite, while the latter can be used to estimate composite strength and stiffness parallel to the fibre direction. 

The advantages of fabrics are in the handling of the material when fabricating a composite so that fibre alignment is maintained and fibres are draped to follow the shape of a mould or tool, improved off-axis properties (essentially isotropic for a mat) and possibly better throughthickness properties. 

As the third major measurement to try to determine the remaining properties G 2 S, consider uniaxial tension loading at 45° to the 1-direction on a flat piece of iamina, i.e., a 45° off-axis test, as shown in Figure 2-26. By measurement of alone, obviously... 

Knowledge of the composition of samples in an off-axis deposited phase spread is important. Calibration runs were used to determine the thickness vs position for single components deposited in our system at a given power setting. The drop-off in thickness as a function of distance from the gun is approximately exponential and can be modeled accurately to about 5 at%. We find that the deposition rates are additive for the three guns. RBS measurements have been made on a number of samples to validate our assumptions. In addition, we routinely use RBS measurements as a double check on the specific compositions that we identify as having superior properties. 

Apart from the short beam shear test, which measures the interlaminar shear properties, many different specimen geometry and loading configurations are available in the literature for the translaminar or in-plane strength measurements. These include the losipescu shear test, the 45°]5 tensile test, the [10°] off-axis tensile test, the rail-shear tests, the cross-beam sandwich test and the thin-walled tube torsion test. Since the state of shear stress in the test areas of the specimens is seldom pure or uniform in most of these techniques, the results obtained are likely to be inconsistent. In addition to the above shear tests, the transverse tension test is another simple popular method to assess the bond quality of bulk composites. Some of these methods are more widely used than others due to their simplicity in specimen preparation and data reduction methodology. 

Chamis, C.C. and Sinclair, J.H. (1977). 10° off-axis test for shear properties in fiber composites. Exper. Mech. 17, 339-346,... 

A lot of research is being conducted on the seeded sublimation growth technique. The material properties are improving steadily and there should be no reason for worries. Yet, one worry is the need for off-axis substrates for high-quality epitaxial... 

Real situations demand more uniformity in composite properties than can be provided by unidirectional composites. Therefore lamina stacking sequences are made where the fiber orientation is altered to provide good properties in all directions. Lamina composed of fiber and matrix in which the fibers are all parallel to each other are stacked on top of each other with a systematic variation in fiber direction. These lamina are then bonded together and the resulting material has more uniformity in properties. Likewise in short fiber or discontinuous fiber composites fiber orientation is random. Therefore properties in directions other than parallel to the fiber (i.e. off-axis) are important70>. 

Figure 10.3 Definition of geometrical parameters for a CMA shown for the case of off-axis focusing of a point source (Q). Rt and Ra are the radii of the inner and outer field cylinders, respectively 4, is the radial image distance to the inner cylinder (in analogy, one can introduce a radial source distance ds, in the present case one has ds = R,) z is the total distance between source and image measured along the symmetry axis of the analyser zf is the corresponding distance for the field region is the entrance angle into the analyser (due to symmetry properties this is equal to the exit angle).

Figure 7. Strength properties of composites V5. water content. A. 10° off axis test, (X) resin I, (- -) resin II, B. cross-ply specimens of resin III, (X) 0/90/0 configuration, (+) 90/0/90 configuration.

Fig. 2. Point source images for Bragg-telescope as function of off-axis angle 5. Imaging Properties...

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