Crack propagation from 3-D surface fractures in PMMA and marble specimens under uniaxial compression

This paper studies crack propagation emanating from pre-existing three-dimensional surface fracture (or flaw) in marble and PMMA of different flaw depths 'd' and flaw angles 'α'. From the experimental studies, the following conclusions were drawn: (1) Both tensile crack and petal crack may initiate form flaw tip in both PMMA and marble specimens; (2) Shell-like crack may initiate from the flaw tip of both PMMA and marble specimens at α=60°, (3) The length of crack propagation depends on the d/t (where t is the thickness of the specimen), a and the type of material used. Growth of wing crack is observed when d/t>0.1 in marble or d/t>0.3 in PMMA. When the specimen is relatively thin (i.e. d/t>0.3), wing crack propagates through the whole thickness for both PMMA and marble specimens. When α<45>, no wing crack initiation is observed in both PMMA and marble specimens; (4) The failure mechanism for PMMA specimens seems to closely resemble that for marble specimens.