Elements of Fracture Mechanics

The characteristic of the materials known as the stress intensity factor comes from Griffith s theory of preexisting cracks in brittle solids, demonstrating a fully 

Practical considerations and experience tell us that in the metallurgy of Al, refractories are subjected to chemical wear, abrasion, and chemical attack, but they rarely go out of service because of cracking due to overloading. From a scientific point of view, the investigation of refractory brittleness is interesting [71], yet in industrial practice, people are usually satisfied with characteristics such as compression, flexural strength, elastic modulus, and abrasion resistance. The exception is carbon cathode blocks. 

The mechanical behavior of carbon cathode blocks is extremely critical for the service life of the reduction cell, especially in the begiiming of service. A single crack in a carbon cathode block leads to shutdown of the cell. The knowledge of mechanical characteristics such as compression, flexural strength, and elastic 

The difficulty with implementing fracture mechanics mechanisms to address the problems of crack openings in carbon cathode blocks arises because the mechanical behavior of carbon cathode blocks is not fully elastic. Even at room temperature, carbon cathode blocks demonstrate elastoplastic or pseudo-plastic behavior (Figs. 1.10, 1.12, and 1.13) [69]. 

It is well known that sometimes cathode heaving during heating and startup may exceed 100 mm in the center of the cell (Fig. 1.13) this deformation is sufficiently higher than the brittle material can withstand without cracking. The temperature of the preheating rarely exceeds 800 °C, which is not quite sufficient for the transformation from elastic to plastic behavior of a high-temperature material such as carbon. 

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