Anti-Parallel Fiber Orientation

Similar to the P-fiber orientation, it can be concluded in this case also that in a small region of the contact area, especially in the depth direction, plastic deformation appears in the matrix material. 

One can conclude that the shear and tension/compression type debonding is also one of the dominant failure mechanisms in the case of AP-fiber orientation. According to the results, the AP-fiber orientation produces lower fiber and matrix stresses than the P-fiber orientation. This would imply a lower probability for wear failure under AP- compared to P-fiber orientation. This is, however, opposite to the impression one has from the scratch experiments, and also in contrast to previous sliding wear studies on this material. Probably, in terms of the complete wear process and the complexity of wear mechanisms, the AP-fiber orientation is less advantageous, i.e., the wear debris as a third abrasive have a more dominant effect on the wear process than in the case of P-fiber orientation. 

Finite Eiement Simulation of the Fiber/Matrix Debonding 

Due to the complexity of the problem, the frictional contact problem is first solved on two levels (by using larger macro- and smaller micro-models), followed by a non-linear debonding analysis. 

The debonding models use a linear elastic-plastic material law for the matrix material that allows to study the plastic deformation in the matrix material. Due to this fact, the smaller diamond indentor (R = 100 jam) with a normal load Fn= 1N was used in the debonding simulation. The friction coefficient, obtained experimentally for N-fiber orientation, was = 0.1. The results presented here are only for N-fiber orientation, although additional investigations were carried out also for P- and AP-fiber orientation.  

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Figures 4, 6, and 7 reprinted from J. Compos. Mater., Vol. 38, 2004, Authors T. Goda, K. V radi, B. Wetzel, K. Fiedrich, Title Finite element simulation of the fiber-matrix debonding in polymer composites produced by a sliding indentor Part II - Parallel and anti-paraller fiber orientation, p. 1607, Copyright (2004), with permission from SAGE Publications. 

Fujiwara et al. [69] applied solid-state NMR to a structural study on oriented [l- C]Ala silk fibroin fiber from B. mori. They found that the Euler angles obtained from the simulated lineshapes of the Ala carbonyl group are slightly different from that of a typical anti parallel j8-sheet, [30] raising questions concerning the accuracy of the current models for silk II structure. However, our data are in agreement with the X-ray diffraction model within experimental error. 

Considering fiber orientation, the effect of sugarcane fiber has been studied on tribo-characteristics of polyester composites (El-Tayeb, 2008a). It has been found that fiber mats oriented parallel to the sliding direction showed lower wear performance than fibers oriented anti-parallel under the same test conditions. This was because in the parallel orientation, the path ahead of the wear debris is exposed, thus easing the... 

Figure 1. The studied fiber orientations with a hemispherical sliding asperity (a) normal (N), (b) parallel (P), and (c) anti-parallel (AP). ...

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