A STUDY ON FATIGUE PROPERTIES OF COMPACTS OBTAINED FROM READY-MADE AND POLYMER GRAFTED ALUMINA

Riyadh Mohammad, Hadi Al-Lami, Muhammed
2016 unpublished
This study was devoted to outlining the fatigue behaviour of alumina as a widely used ceramic material and to predict their life under cyclic loads. Two types of α-alumina have been studied to predict their fatigue behaviour and the effects of physical properties, particularly, and porosity and their pore size; and mechanical properties such as fracture strength, modulus of elasticity, and toughness of materials; in addition to pressing loads. The first type was alumina made especially for
more » ... ing. The second type of alumina was commercial high purity grafted with random copolymer (n-butyl metacrylate-methacrylic acid) as a lubricant. Dry pressing forming technique with different loads has been used to form different alumina compacts. They were fired in two stages, 1200°C and 1600°C. It was found that porosity affects fatigue behaviour in a complicated manner. Firstly, it weakens the ceramic material. Secondly, pore sizes, particularly surface pores, have a great harmful influence on fatigue life. Therefore, reduction in porosity and good surface finishing can elongate the fatigue life. Furthermore, it was predicted that specimens of alumina made especially for pressing, which was pressed under relatively low loads (0.5, 1, 2 kN) were relatively better than those pressed under higher loads. That is due to the initiation of fractures in the specimens, pressed under higher loads with worst case for specimens, pressed under 9kN, on the contrary of their static mechanical behaviour. Gradual enhancement of fatigue properties for specimens, pressed under higher loads (11-16 kN) because of toughening mechanisms, which emerges due to the more closeness, higher internalfriction, and meandrous paths of cracks. Whereas grafted alumina is better in static mechanical properties, and their fatigue properties are close to, or even better than their predecessors. Design and applications of ceramics should be based upon K TH .
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