From NASA’s technical reports server on chevron-notched specimens

The chevron notched Chevron Notched Three-Point Bend Test Specimens by Bomasfour-point bend specimen provides a convenient method for measuring fracture resistance of very brittle materials which are difficult to precrack.

Read the full memorandum

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950005452.pdf