Spall smooth

Observations of smooth spalls in iron provided an early, dramatic demonstration of the importance of release wave behaviors. In 1956, Dally [61E01] reported the existence of remarkably smooth fracture surfaces in explosively compressed steel. The existence of these smooth spalls was a sensitive function of the sample thickness. Analysis and experiments by Erkman [61E01] confirmed that the smooth spalls were associated with interaction of release-wave shocks and shocks from reduction of pressure at free surfaces. These release shocks are a consequence of differences in compressibility at pressures just below and just above the 13 GPa transformation. 

The horizontal fiber structure is extruded in a ribbon 1%" x SVs" then wire cut to 8" lengths. The surface texture may be smooth. diamond pattern or have an emery grit surface. The horizontal fiber brick is more susceptible to spalling from excessive wheel load traffic and to thermal shock. Voids or blisters may form within the brick during the burning process. After a period of exposure, salts tend to filter into these voids and expand, resulting in spalling. While the exposed faces of this type of brick is more easily cleaned, the use of horizontal fiber brick is not often recommended. 

Fig. 2. Void and cavity formation beneath the A1203 scale on NiAl. a) SEM photo of the surface of Ni50Al50 after 40h oxidation at 1200°C, partly covered with oxide (lower part) and partly spalled area with smooth cavities and with ridges, which had been connected to the oxide b) schematics of the mechanism of void and cavity formation.

Fig. 5 Model for wet wear of SiC. a) first contact of asperities induces crack formation, microstructural grain diassemblage and spalling, b) water ingress in the wake of it, c) further collisions induce heat and hydrothermal oxidation followed by silica precipitation in cooling or depressurized regions, d) debris and precipitates fill up valleys between asperities, get compacted and form the smooth tribo-layer of the wear track...

Fouskitakis G, Fassois S (2002) Functional series TARMA modeling and simulation of earthquake ground motion. Earthq Eng Struct Dyn 31 399 20 Gersch W, Akaike H (1988) Smoothness priors in time series. In Spall J (ed) Bayesian analysis of time series and dynamic models. Marcel Dekker, New York, pp 431 76... 

For the smooth disk, it was quite difficult to situate the cross-sections in relation with the surface photographs due to the great amount of micro spalls. The micro cracks observed on the surface are less propagated. They induce micro spalling which not exceed 3 up to 4 pm (Figure 7-a.2, a.3 and a.4). As it was mentioned before, the load direction tends to close the cracks and stop the crack growth. 

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