Study of quasi-static crack growth in aluminum/alumina functionally graded material using crack gauge

Quasi static crack growth of Al/Al2O3 functionally graded materials prepared through powder metallurgy up to 30% weight fraction of Al2O3 is studied with crack on stiff (FGM I) and compliant (FGM II) sides using crack gauge in three point bend test. The variation of weight fraction of Al2O3 with distance from 100% aluminum face is measured through image analyzers to identify the composition corresponding to crack tip location. The measurement of crack tip location, load point displacement and load with time are carried out simultaneously. It is observed that crack grows stably when the crack traverses from stiff to compliant side and unstably from Compliant to stiff side. For stable quasi static crack growth (crack on stiff side), variation of the fracture toughness and crack tip opening displacement (CTOD) are evaluated and increase with distance from stiff side. Further, the fracture toughness is also evaluated using Raveendran's micromechanics prediction techniques and found that the experimental values are closer to Raveendran's lower bound for greater weight fraction of alumina and closer to Raveendran's upper bound for lower ceramic weight fraction. From fractography, mixed mode failure with greater deviation of crack path for FGM I is observed as compared to mode-I failure for FGM II.