Composite anisotropic properties

Whisker and Short Fiber Composites. Whiskers and short fibers tend to align during forming, lea ding to anisotropic properties and large... 

The Z-direction is perpendicular to the page. For simplicity the material is assumed to be isotropic, ie same properties in all directions. However, in some cases for plastics and almost always for fibre composites, the properties will be anisotropic. Thus E and v will have different values in the x, y and z direction. Also, it should also be remembered that only at short times can E and v be assumed to be constants. They will both change with time and so for long-term loading, appropriate values should be used. 

Like wood, wood-derived composites also have anisotropic properties. For instance, the bending strength of a certain SiC ceramic with a density of 2.5 g/cm3 varies from 2000 to 120 MPa, depending on the direction of the load in relation to the growth rings of the wood. 

Table 7.16 shows that for most cases the ratio between ultimate loads for center-point load and one-third point load is not exactly 1.5, as should follow from Eq. (7.20) and (7.26). It is around 1.50 only for square cross-sectional pickets. For all flat profiles (including an almosf oval-shaped handrail profile), fhe ratio is equal to 1.38 + 0.04 (an average for seven profiles). Apparenfly, this deviation from the theoretical figure of 1.5 is a reflection of anisotropic properties of the tested composite materials. 

The dental ceramics used in this study are described in Table I. Materials were selected in order to provide varied microstructures a) the glass-ceramic El is expected to have a homogeneous microstructure and isotropic properties b) the glass-ceramic E2 is expected to have anisotropic properties due to alignment of lithium disilicate fibers and c) the glass-infiltrated alumina composite IC, may have particle orientation, which could affect the mechanical properties. 

On the other hand, the environment of the surfactant-modified stationary phase is independent of micelle concentration in the mobile phase (for most surfactants and stationary phases), and similar to that of pure aqueous eluent systems. As a result, the alkyl-bonded stationary phase will have both invariable amphiphilic and anisotropic properties. In contrast, in aqueous-organic RPLC, the composition and structure of the alkyl-bonded phase change with the concentration of organic modifier in mobile phase. 

Mechanical properties of PMC are strongly influenced by the filler (by its size, type, concentration and dispersion) and by the properties of the matrix, as well as the extent of interfacial interactions and adhesion between them and their micro-structural configurations. The interrelation of these variables is rather complex. In FRC, the system is anisotropic where fibres are usually oriented uniaxially or randomly in a plane during the fabrication of the composite, and properties are dependent on the direction of measurement. Generally, the rule of mixture equations are used to predict the elastic modulus of a composite with uniaxially oriented (continuous) fibres under iso-strain conditions for the upper bound longitudinal modulus in the orientation direction (Equation 6.10). 

Anisotropic particles, such as patchy, multicompartment, and Janus particles, have attracted significant attention in recent years because of their novel morphologies and diverse potential applications. The noncentrosymmetric features of these particles make them a unique class of nano-or microcolloidal materials. Patchy particles usually have different compositional patches in the corona, whereas multicompartment particles have a multiphasic anisotropic architecture in the core domain. In contrast, Janus particles, named after the double-faced Roman god, have a strictly biphasic geometry of distinct compositions and properties in the core and/or corona. This property of Janus particles allows for distinct shape, composition, chemistry, polarity, functionality, electrical, and properties, making them suitable for applications in switchable display devices, interface... 

There are many parameters that can be adjusted to achieve desired features. A number of tuning/coupling effects can be achieved by the arrangement of the neutral axis, principal axes of inertia, or shear center relative to the position and direction of the loads. Moreover, the exploitation of the anisotropic properties of fibrous composites allows for additional tailorable couplings. Unlike the traditional rotor blade with almost constant structural properties over the blade length, future blades may be developed with the aid of advanced computational methods to evaluate arbitrary designs. 

Properties of fiber-reinforced composites with 40-65 wt % of fiber were influenced more by fiber used than by the matrix. In contrast to an E-glass composite, which is brittle, a basalt fiber composite exhibits properties near to carbon fiber composites, except for a lower elastic modulus. Material mechanical parameters independent of sample size were calculated from flexural tests with various span-to-sample height ratios. In contrast to composites reinforced with fiber rovings, composites reinforced with fabric fiber were more brittle and less anisotropic, which was reflected in material mechanical parameters. 

The model material used is a unidirectional carbon fiber-reinforced, thermoplastic polyether-etherketone (PEEK) composite with fiber diameter of = 8 fim. The fiber orientations studied are shown in Figure 1. The mechanical properties of this material are listed in Table 1. The first principal material direction, indicated by 1 in Table 1, is parallel to the fiber direction (Figure 1), the second and the third one are perpendicular to the fiber orientation. The anisotropic composite material properties were specified using the rule of mixture type equations. ... 

The engineering properties of the substrate materials may usually be found from handbooks of mechanical properties, although in the case of the fibre-composite materials, which possess of course anisotropic properties, some of the data may have to be determined by the adhesives technologist ... 

---