Continuous and discontinuous crack growth in brass embrittled by liquid gallium

The mechanics of liquid metal induced embrittlement (LMIE) are not well understood and this phenomenon is of a high degree of industrial importance. Discontinuous and continuous crack propagation in gallium-embrittled brass was studied using double cantilever beam specimens and crack propagation was found to be discontinuous when the imposed crack speed was less than 6mm/s and was more or less continuous if greater. The threshold K for cracking was found to be non-unique in this system and was weakly dependent on testing variables such as crosshead speed. The discontinuous crack propagation and dependence on crosshead speed were attributed to the tendency of the cracks to blunten by a process of dissolution at the crack tip. A comparison of the experimental results with existing theory suggests that crack growth may not be solely controlled by supply of embrittler to the crack tip.