Contact damage

Wang, X.T., Padture, N.P., Tanaka, H. et al., Contact-damage-resistant ceramic/ single-wall carbon nanotubes and ceramic/graphite composites, Nature Mater., 2004, 3(8) 539. 

Osterstock, F. (1993), Contact damage submitted to thermal shock a method to evaluate and simulate thermal shock resistance of brittle materials , Mater. Sci. Eng., A168, 41-44. 

Sulfuric acid — corrosive. If the battery case is broken acid leaks can damage skin and eyes on contact. Damage will also occur if in contact with materials and clothing. 

The introduction of surface compressive layers can strengthen ceramics and is a well-established technique for glasses (see Sec. 13.5 for more details). The underlying principle is to introduce a state of compressive surface residual stress, the presence of which would inhibit failure from surface flaws since these compressive stresses would have to be overcome before a surface crack could propagate. These compressive stresses have also been shown to enhance thermal shock resistance and contact damage resistance. 

Corrosive materials are those chemicals which, on contact, damage living tissue (skin, eyes, mucous membranes, plant life) and inorganic materials (metals, textiles, ceramics, glass, etc.). They include acids and bases. 

The quantity on the right-hand side of Eq. (11.25) is the square of the numerical aperture of the fibre. Uncoated fibres, surrounded by aiq would work well in the regions where the fibres do not touch, but light could pass between touching fibres, and the contact damage would cause losses. 

Ceramics are susceptible to contact damage and, thus, it is important to understand the stress fields that arise around contacts between two bodies. Consider the simple problem of a body being contacted by a linear force per unit thickness F, as illustrated in Fig. 4.22. The stress function for this problem can be expressed as x= CrOsinO, where C is a constant. From Eq. (4.27), the stress components are <7- =2Ccos 6/r, agg=a g=0. The constant C can be determined using statics for a force balance in the vertical direction, i.e.. 

Figure 8.42 Fracture surface of silicon nitride failure was initiated from a contact-damage surface crack.

Ceramics can often be damaged under low contact loads and, thus, it is important to understand these damage mechanisms. These processes not only give rise to strength degradation but are linked to wear and erosion. Indentation fracture mechanics has been found to be a very useful approach in understanding these contact-damage processes (see Section 8.8). 

F. Guiberteau, N. P. Padture and B. R. Lawn, Effect of grain size on Hertzian contact damage in alumina, J. Am. Ceram. Soc, 77(1994) 1825-31. 

S. K. Lee and B. R. Lawn, Role of Microstructure in Hertzian Contact Damage in Silicon Ntride II, Strength Degradation , Journal of the American Ceramic Society, 81, 1998, Nr. 4, 997-1003. 

Johansson, S. and Schweitz, J., 1988, Contact damage in single-crystalline silicon investigated by cross-sectional transmission electron microscopy, /. Am. Ceram. Soc., Vol. 71, pp. 617-623. 

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