Frictional sliding

In the second approach shown in Fig 3.12(b), a force is applied continuously using a Vickers microhardness indenter to compress the fiber into the specimen surface (Marshall, 1984). For ceramic matrix composites where the bonding at the interface is typically mechanical in nature, the interface shear stress, Tf, against the constant frictional sliding is calculated based on simple force balance (Marshall, 1984) ... 

However, some theoretical treatment considers only the special case of friction sliding of a single fiber along a mechanically bonded interface, particularly for some ceramic matrix composites, where the Coulomb friction law applies. See for example Zhou and Mai (1995) and Shetty (1988). Assuming a constant friction at the fiber-matrix interface and neglecting the Poisson effects, Shetty (1988) reported a simple force balance equation for the frictional shear strength, Tfr... 

Sigl, L.S. and Evans, A.G. (1989). Effects of residual stress and frictional sliding on cracking and pull-out in brittle matrix composites. Mech. Mater. 8, 1-12. 

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. 

A traction law crb(u) is now needed to predict rw. A law based on frictional sliding along debonded interfaces has been used most extensively and appears to provide a reasonable description of many of the observed mechanical responses (Eqn. 1). The traction law also includes effects of the interface debond energy, T,.1 For many CMCs, T, is small, as reflected in the magnitude of the debond stress, 2,-. 

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. 

Engelder, T. 1978. Aspects of asperity-surface interaction and surface damage of rocks during experimental frictional sliding. Pure Appl. Geophys., 116 705-716. 

Morrow, C.A.. Byerlee, J.D. (1989) Experimental studies of compaction and dilatancy during frictional sliding on faults containing gouge. J. Struct. Geol., 11, 815-825. 

INTERMITTENT MOTION IN FRICTIONAL SLIDING STICK-SLIP OSCILLATION... 

Heuberger M, Drummond C and Israelachvili J N 1998 Coupling of normal and transverse motions during frictional sliding J. Phys. Chem. B 102 5038-41... 

Surfaces in contact and moving parallel to each other exhibit phenomena that are encountered incessantly in our everyday life. These phenomena include friction, slide, wear, and lubrication (the process used to modify friction). We could not walk without controlled friction, nor could the internal combustion engine operate without the lubrication of its moving parts. The name tribology (from the Greek tribein—to rub) is given to phenomena that involve surfaces in relative motion. 

Friction, slide, and lubrication are the properties of surfaces in relative motion (tribological properties). 

The interface between fiber (or whisker) and matrix is the key to the overall mechanical properties of a composite. A weak interface allows a propagating crack to be deflected, which increases the toughness of the composite. A strong interface allows transfer of the load from the matrix to the fiber and produces an increase in modulus and stiffness of the composite. In CMCs we are usually more interested in producing a weak interface so that debonding occurs, which often leads to fiber pull-out by frictional sliding and substantial absorption of energy. 

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