document: A bond failure is thought of as a micro-crack nucleation, specifically as a separation between the adjacent cells in the cellular structure along their common face. Initially, the micro-cracks may be dispersed in the model reflecting the random distribution of pore sizes and the low level of interaction due to force redistribution. Interaction and coalescence may follow as the population of micro-cracks increases. These situations are illustrated in Fig. 3. The structure of the failed surface can be represented with a mathematical graph, where graph nodes represent failed faces and graph edges exist between failed faces with common triple line in the cellular structure, i.e. where two micro-cracks formed a continuous larger crack. With reference to Fig. 3, each failed face is a graph node and each pair of neighbouring failed faces is a graph edge.
extractive_keyphrases: bond failure cellular structure crack failed face failed faces failed surface mathematical graph pore
abstractive_keyphrases: micro-crack nucleation micro-cracks separation between the adjacent cells in the cellular structure along their common face