1. Fisher DM, Bubsey RT, Srawley JE (1966) Design and use of displacement gage for the crack extension measurements. NASA Technical Note D-3724. NASA Lewis Research Center, Cleveland
2. ASTM standard E399-09 (2009) Standard test method for linear-elastic plane-strain fracture toughness KIc of metallic materials. Annual book of ASTM standards, vol 03.01. American Society for Testing and Materials, West Conshohocken
3. ASTM standard E1820-17 (2017) Standard test method for linear-elastic plane-strain fracture toughness KIc of metallic materials. Annual book of ASTM standards, vol 03.01. American Society for Testing and Materials, West Conshohocken
4. Smith DJ, Gordon JR (1990) The linearity of clip gages used in fracture mechanics tests. J Test Eval 18(1):14–24
5. Tobler R, Shepic J (1985) Design and performance of a ring-shaped clip gage for fracture mechanics testing. J Test Eval 13(4):299–302