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Ever since its publication, the Griffith theory is the most widely usedcriterion for estimating the ideal strength and fracture strength of materialsdepending on whether the materials contain cracks or not. A Griffith strengthlimit of ~E/9 is the upper bound for ideal strengths of materials. With theimproved quality of fabricated samples and the power of computational modeling,people have recently reported the possibility of exceeding the ideal strengthpredicted by the Griffith theory. In this study, a new strength criterion wasestablished based on the stable analysis of thermodynamical systems; thenfirst-principles density functional theory (DFT) is used to study the idealstrength of four materials (diamond, c-BN, Cu, and CeO2) under uniaxial tensileloading along the [100], [110], and [111] low-index crystallographicdirections. By comparing the ideal strengths between DFT results and theGriffith theory, it is found that the Griffith theory fails in all the fourmaterials. Further analysis of the fracture mechanism demonstrates that thefailure of the Griffith theory is because the ideal strength point does notcorrespond to creating of new surfaces, which is against the Griffithassumption that the crack intrinsically exists all the time; the failure pointcorresponds to the crack at the start of propagation.

Failure of Griffith Theory on Prediction of Theoretical Strength of Ideal Materials