The Genesis of Echelon-Mode-Ⅰ Cracks in the Neighbourhood of a Mode-Ⅱ-Crack Tip under Uniaxial Compression

摘要

The mechanical background why the compressed brittle material fails in a shear mode is studied. Compression-induced shear fracture was experienced in a standard compression test of cylindrical mortar sample whereas a mode Ⅰ crack branching almost parallel to compression was dominant in a cracked specimen. In a uniaxial compression test of artificially-flawed PMMA plate, formation of a number of minute-surface cracks (en echelon cracks) as well as growth of wing cracks emanated from the artificial flaw tips were observed. The damage zone composed by en echelon-mode-Ⅰ cracks can be considered as a possible source of the macroscopic shear faulting. The relevance between the genesis of en echelon cracks and the compression-induced shear failure is discussed based on experimental observations and numerical analyses.