Interfacial sliding stress

Singh, D., Goretta, K.C., Richardson, J.W. Jr., and de Arellano-Lopez, A. (2002), Interfacial sliding stress in Si3N4/BN fibrous monoliths , Scripta Mater., 46, 747-751. 

Cho et al.52 developed an analytical model that relates the temperature rise during fatigue to the interfacial frictional sliding stress, as elaborated later. Holmes and Cho12 used the model to show that in SiCf/CAS-II, the interfacial shear stress, r, decreases from a value of around 15 MPa to 5 MPa within the first 25 000 fatigue cycles (Fig. 6.13). The approach used to determine r from temperature rise data is described in greater detail in the following section. 

In Eqn. (12), rd represents the dynamic interfacial shear stress, which may differ from that which would be measured from fiber push-out experiments, which are typically conducted at low sliding velocities. Equation (12) holds for partial sliding along the interface. When the minimum applied stress is equal to zero, the area of the hysteresis loop can also be calculated as the integral from zero to (Tmax of the difference between the strain paths for loading and unloading (Eqns. (3) and (4)) ... 

Increase in the area of hysteresis loops with the number of cycles leading to a decrease in ability to carry interfacial shear stress (t) resulting from a local sliding at the fiber/coat or coat/matrix interface. 

A full analysis of the relation between the shear stress at the top of a sliding bed and the shear layer parameters requires information about the distribution of local solids velocities below and within the shear layer. Since this was not available in our database, the force balance (verified above as being appropriate for en bloc sliding beds) and the measured flow parameters were used to estimate the position of the top of a sliding bed and the value of the interfacial shear stress Xb in flows exhibiting a shear layer (Tab. 2). Processed measurements confirmed a direct relationship between the thickness of a shear layer and the interfacial shear stress (Fig. 6). 

This phenomenon was attribnted to fibre breakage and void formation in the interior of the composite. Unlike in tungsten-wire-reinforced copper composites, in which interfacial sliding was suggested as the major deformation mechanism, in the copper/carbon composite void formation and growth were identified as the predominant mechanisms to relax the internal stress induced during thermal cycling. 

For example, consider the crack tip as it intersects a fiber (Fig. 16). The local stresses at the tip can cause fiber-matrix debonding. The crack tip continues to open causing the interfacial debonded region to extend. The fiber continues to interact with the matrix through a frictional sliding force even after the initial bond fails. The distance over which the force acts is the debonded length times the difference in strain between the fiber and the matrix. 

Here oy denotes the frictional shear stress occurring at the interface of area Aq. It is first assumed that during sliding, the whole rubber interfacial area moves... 

Wear is the process of physical loss of material. In sliding contacts this can arise from a number of processes in order of relative importance they are adhesion, abrasion, corrosion and contact fatigue. Wear occurs because of local mechanical failure of highly stressed interfacial zones and the mode of failure is influenced by environmental factors. 

An interesting question arises considering composites with multiwalled carbon nanotubes. In such materials there are two possible ways of stress relief upon mechanical strain On one hand, like in other fiber-reinforced composites, the interfacial interaction may be overcome by the mechanical forces so the polymer peels from the nanotubes. On the other hand, however, the individual walls of the MWNT may slide one inside another like a sword in a sheath (so-called interwaU sliding. Figure 3.85). Both effects may occur to varying extents depending on how strongly the multiwalled tubes are bound to the matrix. 

The shppage at the interface between a thin film of density Amf and the substrate is usually described in terms of an interfacial friction coefficient ( coefficient of shding friction ), x- This coefficient determines the stress acting between the film and the substrate, which move at different velocities. An infinite value of x implies that the non-sHp (sticking) boundary condition is applicable. When the interfacial friction coefficient equals zero, the film is free to slide with no energy dissipation. 

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