Aspect ratio of fibres

Figure 9 Viscosity as a function of ase volume for various aspect ratio of fibres.

Figure 7.6 Workability versus fibre content for matrices with different maximum aggregate sizes [21]. Aspect ratio of fibres = 100.

If the matrix in 3.7 was reinforced with the same volume fraction of glass but in the form of randomly oriented glass fibres rather than continuous filaments, what would be the tensile strength of the composite. The fibres are 15 mm long, have an aspect ratio of 1000 and produce a reinforcement efficiency of 0.25. The fibre strength is 2 GN/m and the shear strength of the interface is 4 MN/m". 

The influence of aspect ratio of steel fibres on effective shielding may be illustrated... 

In the macrocomposite model it is assumed that the load transfer between the rod and the matrix is brought about by shear stresses in the matrix-fibre interface [35]. When the interfacial shear stress exceeds a critical value r0, the rod debonds from the matrix and the composite fails under tension. The important parameters in this model are the aspect ratio of the rod, the ratio between the shear modulus of the matrix and the tensile modulus of the rod, the volume fraction of rods, and the critical shear stress. As the chains are assumed to have an infinite tensile strength, the tensile fracture of the fibres is not caused by the breaking of the chains, but only by exceeding a critical shear stress. Furthermore, it should be realised that the theory is approximate, because the stress transfer across the chain ends and the stress concentrations are neglected. These effects will be unimportant for an aspect ratio of the rod Lld> 10 [35]. 

Before we discuss the relation between ultimate fibre strength and degree of polymerisation (zn or DP), we first show that this model in fact describes the relation between the composite strength and the aspect ratio of the rod. In the case of a monodisperse distribution, i.e. all rods or chains have the same diameter 2r and the same length a, the ultimate strength as a function of the aspect ratio fr= a(2r) 1 is given by... 

Fig. 41 Ultimate strength as a function of the aspect ratio of the building rod calculated for two values of p. The shear strength is 0.4 GPa and Vc=l. For PpPTA fibres ju 0.16,usingg=2 and ec=240 GPa...

Large aspect ratio Because the reinforcements are nanosized, the large aspect ratio (length/diameter) could make the composite behave like a continuous fibre composite. This scenario is unlikely as the aspect ratios of the NWs used are "- 100-200, which are lower than the value of "-T000 or so for a transition between short-fibre reinforced composite behaviour and the long-fibre reinforced one [18]. The specimen dimensions are also much larger than the NW dimensions. The anomalous increase from the relatively smaller sized specimens is ruled out. 

Finite element modelling of the effects of a 14% volume fraction of glass fibre with an aspect ratio of 30 (Fig. 4.29b), used fibre orientations that fitted a maximum entropy distribution. It predicted that the longitudinal Young s modulus increased non-linearly with cos B, and that constant strain conditions applied for averaging the properties of the unidirectional composite. 

Another factor that influences the value of pc is the aspect ratios of the metallic filler. Metal fibres, metal-plated glass fibers, and metal flakes can significantly lower the concentration required to achieve isotropic conduction as compared to spherical powders [3]. Values of pc as low as 1 vol % have been reported with stainless steel fibers having an aspect ratio of 750 [37]. 

The fibres usually have a log-normal distribution in length, with a mean value of the order of a few mm, depending on the type of pulp. The width of the fibres shows a normal distribution around a mean value of typically tens of microns. Apart from the dimensions of the fibres, the flexibility plays an important role in the formation characteristics. Increasing the wet fibre flexibility will affect both the fibre packing and bonding, and the more flexible the fibres are in a system, then the lower the tendency to flocculate. Despite the high aspect ratio of the fibres, typically 20-50, each fibre in the sheet only penetrates one or two fibre thicknesses and the structure of the paper sheet should therefore be characterized as layered rather than felted. 

Asbestos (anthophyllite, tremolite-actinolite, amosite, crocidolite, chrysotile), nonasbestos fibres Analytical electron microscopy of 50 lung tissue samples from Matsubase, where pleural plaques are endemic Number of asbestos bodies and fibres/ 5 g wet lung tissue frequency of pleural plaques size parameter of fibres Dy mineral type Anthophyllite (mean length 25.1 n, mean diameter 0.84 (un) might be responsible for the increased prevalence of pleural plaques in Matsubase. The aspect ratio of anthophyllite (mean = 38.7) was lower than that of amosite (mean = 81.8), which, as reported hy Murai and Kitagawa (1992), was found predominantly in cases of pleural mesothelioma. Murai et al. (1997) Differences in fibre size may be related to the strength of the carcinogenicity to the pleura. 

Historically, kenaf fibre was first used as cordage. Industry is now exploring the use of kenaf in papermaking and non-woven textiles. Like jute, most kenaf composite products exploit the long aspect ratio of kenaf fibres and fibre bundles. One way to do this is to form the kenaf into a non-woven textile mat that can be used for erosion control, seedling mulches or oil spill absorbents. After a resin is added to the kenaf mats, they can be pressed into flat panels or moulded into shapes. 

Impact strength and flexural modulus are the mechanical properties that can most be improved by careful selection of mineral flllers, and the shape of the particle is important. Fibre-like wollastonite particularly improves the flexural modulus while cube-shaped calcium carbonate can improve both impact strength and modulus. Talc offers many options because it is capable of many different modiflcations and surface treatments. The high aspect ratio of glass fibres means that they can provide the greatest improvement in mechanical properties. 

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