On radial, circumferential, and spiral cracks in fractured glass plates

Abstract This is a fractographic case study of a mechanically loaded glass plate that formed a remarkable spiral crack when the plate fractured. Common radial and circumferential cracking in disks and plates in general are first reviewed. The exceptional spiral crack is then analyzed. The origin of failure was an unusual flaw on the nominal compression side of the plate. The complex spiral fracture pattern has been observed in other large plate glass fractures that break under blunt impact conditions. Spiral cracks can form and propagate from flaws on the front side of a flexed plate that is rigidly supported at its rim or, alternatively, is supported from underneath and has a large overhang.