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Crack Healing (crack + healing)
Selected AbstractsStrength recovery of machined Al2O3/SiC composite ceramics by crack healingFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 12 2007M. ONO ABSTRACT Alumina is used in various fields as a machine component. However, it has a low fracture toughness, which is a weakness. Thus, countless cracks may be initiated randomly by machining, and these cracks decrease the component's mechanical properties and reliability. To overcome this problem, a crack-healing ability could be a very useful technology. In this study, Al2O3/SiC composite was sintered. This alumina exhibits excellent crack-healing ability. Small specimens for a bending test were made from the Al2O3/SiC. A semicircular groove was machined using a diamond ball-drill. The machining reduced the local fracture stress from approximately 820,300 MPa. The machined specimens were crack-healed under various conditions. The fracture stress of these specimens after crack healing was evaluated systematically from room temperature (RT) to 1573 K. It was found that the local fracture stress of the machined specimen recovered almost completely after crack healing. Therefore, it was concluded that crack healing could be an effective method for improving the structural integrity of machined alumina and reducing machining costs. [source] A new methodology to guarantee the structural integrity of Al2O3/SiC composite using crack healing and a proof testFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2007M. ONO ABSTRACT Structural ceramics are brittle and sensitive to flaws. As a result, the structural integrity of a ceramic component may be seriously affected by inherent flaws. Self-crack-healing is an excellent answer to this problem. At the moment, however, there is no technique to heal embedded flaws. Therefore, a technique to guarantee the reliability of ceramic components is demanded, and thus a technique using crack healing followed by proof test was developed by K. Ando et al. to accomplish this. With this technique, testing the mechanical behaviour of the crack-healed zone is very important for ensuring the structural integrity of a ceramic component. In this study, first Al2O3/SiC composite with an excellent crack-healing ability was sintered. Second, a crack was introduced on the sample (3 mm × 4 mm × 36 mm), which reduced the bending strength by about 80%, and subsequently the crack was healed. Third, a proof test was carried out on the crack-healed sample. Last, using the crack-healed and proof-tested sample, a fracture test was carried out up to 1373 K. The measured minimum fracture stress (,Fmin) was compared with the theoretical minimum strength (,G) from room temperature (R.T.) to 1373 K. It was concluded that ,G showed good agreement with ,Fmin up to 1373 K and that the crack healing followed by proof test was an excellent technique to increase the survival probability by administering a proof test and to guarantee the reliability of Al2O3/SiC composite. [source] Preliminary study of the crack healing and strength recovery of Al2O3 -matrix compositesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2004L. JUN ABSTRACT This study focused on the crack-healing behaviour of three commercial Al2O3,ceramic-matrix composites: TiCP/Al2O3, ZrO2/Al2O3 and SiCW/Al2O3. Vickers indentation was used to introduce surface flaws with different loads of 49, 98 and 196 N. Then the cracked specimens were annealed in air for 1 h at 1000, 1200 and 1400 °C. The annealing treatment was also conducted at 1200 °C in vacuum for 1 h. Results showed that the annealing treatments increased the indentation strength, but the extent of the increase was different. When annealed in air, the main crack-healing mechanism of TiCP/Al2O3 and SiCW/Al2O3 composites was chemical reaction. When annealed in vacuum, stress relaxation caused much less strength recovery. The main crack-healing mechanism of ZrO2/Al2O3 was the existence of low melting eutectic and the rearrangement of grains caused by ZrO2(m), ZrO2(t) transformation in the crack-opening process zone. The effects of annealing temperature, atmosphere and indentation load on the degree of strength recovery were all related to the crack-healing mechanisms. [source] Crack-Healing Behavior of Liquid-Phase-Sintered Silicon Carbide CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2003Young-Wook Kim Crack-healing behavior of liquid-phase-sintered (LPS) SiC ceramics has been studied as functions of heat-treatment temperature and crack size. Results showed that heat treatment in air could significantly increase the indentation strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature depends on the softening temperature of an intergranular phase in each material. After heat treatment at the optimum temperature in air, the crack morphology almost entirely disappeared and the indentation strength recovered to the value of the smooth specimens at room temperature for the investigated crack sizes up to ,200 ,m. In addition, a simple heat treatment of SiC ceramics sintered with Al2O3,Y2O3,CaO at 1100°C for 1 h in air resulted in even further improvement of the strength, to a value of 1054 MPa (,150% of the value of the unindented strength). Crack closure and rebonding of the crack wake due to oxidation of cracked surfaces were suggested as a dominant healing mechanism operating in LPS-SiC ceramics. [source] | ||||||||||