Frictional stress

D. Kuhlmann-Wilsdorf, Frictional Stress Acting on a Moving Dislocation in an Otherwise Perfect Crystal. Phys. Rev., 120,773 (1960). 

Marshall, D.B. (1984). An indentation method for measuring matrix-fiber frictional stresses in ceramic composites. J. Am. Ceram. Soc. 67. C259-260. 

Based on the Coulomb friction law, which governs the frictional stress transfer in the debonded interface, and combining Eqs. (4.12) and (4.18) yield the MAS at the interface (r = a)... 

It follows that consists of two stress components a crack tip debond stress, at, and a friction stress component, at is not only a function of the interfacial fracture toughness, G c, but is also dependent on the debond length, t, relative to the total... 

In light of the foregoing discussion concerning the functional partitioning of the partial debond stress, the characteristic debond stresses can be evaluated. The initial debond stress, ao, is obtained for an infinitesimal debond length where the frictional stress component is zero, i.e.,... 

Jero, P.D., Keran, R.J. and Parthasarathy, T.A. (1991). Effect of interfacial roughness on the frictional stress measured using pushout tests. J. Am. Ceram. Soc. 74, 2793-2801. 

Karbhari, V.M. and Wilkins, D.J. (1990). A theoretical model for fiber debonding incorporating both interfacial shear and frictional stresses. Scripta Metall. Mater. 24, 1197-1202. 

The axial strength of the composite can be calculated by applying Eq. (5.107). In the most common case, the matrix is more ductile than the fibers, such that the matrix critical strain exceeds the fiber critical strain, > / 1 low volume fraction of fibers, the fibers located with their ends within a distance 5 of the failure plane do not fracture, but rather simply pull out of the matrix. This movement is resisted by the friction stress, r7. The proportion of fibers for which this occurs is IJl, and the mean stress resisting pull-ont is cryi. The fibers therefore contribute a mean stress of CT/ = el ll and from Eq. (5.107) the strength becomes... 

For dilute phase conveying numerical simulations with a commercial computational fluid dynamics code were carried out. The analysis of particle wall impact conditions in a pipe bend showed that they take place under low wall impact angles of 5-35° which results in low normal (5-25 m/s) and high tangential (33-44 m/s) impact velocity components. These findings lead to the conclusion that not only normal stresses caused by the impacts are important in dilute phase conveying but that sliding friction stresses play an important role as well. 

This was corroborated by experimental results obtained in single particle experiments carried out for polypropylenes. It was possible to show that the relative attrition behavior under pure sliding friction stresses was identical to that observed in a pipe bend whereas deviations to that under pure normal impact conditions were found. For polymethylmethacrylate and polystyrene on the other hand, the relative attrition behavior in the pipe bend corresponds to that of the normal impact experiments. 

A calculated radial compressive stress of 246 MPa on the fibre (corresponding to a frictional stress as large as 24.6 MPa) was obtained by Yu et al. (2002b), which was big enough to cause the SiC fibres to break when they were torn from the a-sialon matrix. 

Fig. 2.15 The interfacial frictional stress versus temperature for a Nicalon/SiC composite.75...

The existence of a static friction stress, corresponding in fact to the flow rate q on flow curves. Thus in the conditions used in this study, the polymer melts only slip above a critical stress threshold. They adhere when at rest. 

Figure 4a Friction curve of PDMS LG2. t is the static friction stress (Table 3).

---