Perfectly bonded interface

Apart from the elastic stress transfer at the perfectly bonded interface, another important phenomenon that must be taken into account is the stress transfer by friction, which is governed by the Coulomb friction law after the interface bond fails. Furthermore, matrix yielding often takes place at the interface region in preference to interfacial debonding if the matrix shear yield strength, Xm is significantly smaller than the apparent interface bond strength, tb. It follows thus... 

Micromechanical models such as Cox shear-lag and Halpin-Tsai are often used to predict the stiffness and strength of discontinuously short-fiber reinforced composites. Experimental results of tensile measurements are then compared or correlated with such theoretical models. The shear-lag analysis originally proposed by Cox considered a discontinuous fiber embedded in an elastic matrix with a perfectly bonded interface and loaded in tension along the fiber direction [25]. The analysis tabes into account the difference in strain displacements of the fiber and matrix along the interface. The stress transfer depends on the interfacial shear stress between the fiber and the matrix. The stress transfer from fiber ends is neglected in the analysis. The Cox model incorporates the aspect ratio (a = l/d where I is the fiber length and d the diameter) of the fiber into... 

At the interface, we do not know either or a 2 bnt it is reasonable to assume that they are equal. We already assumed that bonding across the interface was as strong and continuous as on either side, i.e., that the interface has no special weakness, and correspondingly we now assume that it is no kind of barrier either. If the interface were a barrier, then, for material to cross, one might ask about a stress difference or potential difference needed to drive diffusing material through the barrier, at the needed rate but if we assume a perfectly well-bonded interface, no stress difference or stress jump is needed and = [Pg.116]

Fig. 25.17 Calculated phase of the transmitted wave of fundamental frequency as a function of the ultrasonic transmission coefficient of the interface in the range from 0 (complete delamination) to 1 (perfect bond, i.e., complete transfer of ultrasound) ...

It is possible to measure the influence of the fibres on the di sion because, with a poor interfacial bond between the fibre and the resin, rapid transport will take place at the interface and can be differentiated from the resin-dominated diffusion at 90° to the fibres. If Dy is greater than Dx, then capillary diffusion at a poor interfacial bond must be occurring. For perfectly bonded fibres, Dx will be significantly larger than Dy because of the relatively higher surface area of resin in the 90° direction. Typical values of the diffusion constant are 10 mm /s for a resin and 10 mm /s for a composite. 

Perfect bonding between reinforcement and polymer interface and the ignorance of interfacial slip, reinforcement and pol5mier debonding or matrix cracking. 

P(5) The design of bonded Joints is based on the assumpdon of a perfect bond between the adhesive and adherends, i.e. cohesive faUure in the adhesive or adherend always occurs before adhesive faUuie at the interface. 

Fig. 9.4. Elastic deformation of the matrix near a fibre under tensile loads. Young s modulus of the fibre has been assumed to be 100 times larger than that of the matrix the fibre-matrix interface is perfectly bonded and cannot fail. Poisson s ratio of fibre and matrix has been assumed to be the same...

There are, in general, five assumptions underlying all the mechanistic interface theoretical studies, namely (1) elastic constituent material behavior, (2) zero thickness for the interface, (3) perfect bond, (4) identical constituent bulk and in situ properties, and (5) a regular or repeating array of fibers. It is known that actual composites violate most, if not all, of these assumptions. However, the theoretical predictions still are an invaluable tool in identifying important local geometry and material variables, and in obtaining quantitative estimates of the stress state at the interface. ... 

In this work, it is assumed that the platelets are perfectly bonded to the matrix material - a highly oversimplified view. In order to provide a more realistic description, atomistic modeling techniques (such as Monte Carlo or Molecular Dynamics, as discussed in [34]) can be used to provide important information regarding the polymer/platelet interface e.g., degree of adhesion, slip, etc.). 

J/m. The latter can be associated with the external interface between a tactoid and the matrix which, given the high value, is assumed to be perfectly bonded. Given the lack of information about strength and fracture energy in tension and shear, the same values are assumed for both modes of deformation. 

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