Efficiency of stress transfer

The significance of Rosen s work lies in the attempt of quantifying the efficiency of stress transfer across the interface with respect to the fiber length, by introducing the concept of ineffective length . The ineffective fiber length, (2L), was defined by specifying some fraction, (f>, of the undisturbed stress value below which the fiber shall be considered ineffective. (2i) normalized with fiber diameter, 2a, is derived as... 

In the case of the y relaxation, it was concluded that there are two mechanisms for the change in modulus and hence for tan 5. The first is an increase in the efficiency of stress transfer (i.e. the shear lag factor) with falling temperature due to the quenching of molecular motions. These are predominantly if not entirely in the non-crystalline regions. Secondly, the quenching of these molecular motions also gives rise to an... 

The most commonly used theory used to model the stiffness of this type of composite was developed by Cox [1] and further improved by Krenchel [2, 3]. Cox s shear lag model was developed for aligned discontinuous elastic fibers in an elastic matrix. The applied load is transferred from the matrix to the fiber via interfacial shear stresses, with the maximum shear at the fiber ends decreasing to zero at the centre. Thus, the tensile stress in the fiber is zero at the ends and maximum in the middle. Thus, although the efficiency of stress transfer increases with fiber length, it can never reach 100%. In order to accommodate this dependence of reinforcement efficiency on fiber length, Cox introduced a fiber length efficiency factor -rij into the rule-of-mixtures equation for the composite modulus Eg. 

A discontinuous fiber composite is one that contains a relatively short length of fibers dispersed within the matrix. When an external load is applied to the composite, the fibers are loaded as a result of stress transfer from the matrix to the fiber across the fiber-matrix interface. The degree of reinforcement that may be attained is a function of fiber fraction (V/), the fiber orientation distribution, the fiber length distribution, and efficiency of... 

The high strength of polymer composites is dependent on a transfer of external stress from the resin matrix to the fiber or filler. The efficiency of this transfer is dependent on the strength of the interfacial bond between the... 

It should be stressed that the above-described approach is strictly valid at temperatures above 900°C, when the viscous flow represents the prevailing restraints to mass loss. This conclusion is reasonable, as the efficiency of heat transfer increases rapidly with an increasing temperature. 

For values of Ild less than l/d)c, the tensile stress in the fiber is always less than that in the matrix. The transfer of load from the matrix to the fiber is poor and the mechanical properties of the fiber are not fully utilized. If lid > l/d)c, the tensile stress at the interface remains at a maximum over a greater proportion of fiber length. Here, the transfer of stress from the matrix to the fiber is very efficient, but the average tensile stress in the fiber is always less than that in the matrix because of reduced tensile stress at the end of the fiber. 

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