FRACTURE-TOUGHNESS OF PMMA AS MEASURED WITH INDENTATION CRACKS

Fracture toughness of polymethyl methacrylate (PMMA) was evaluated wit h indentation cracks. The cracks were developed by indenting in a liqu id acetone environment, as suggested by previous researchers. Due to t he inconsistency in crack configurations with varying indentation load s and to the negligible residual stress from indentation, the applicat ion of the indentation strength method was limited in evaluating fract ure toughness of PMMA. The semielliptical crack approximation, however , particularly at a low indentation load of 9.8 N, resulted in reasona ble agreement with the value determined by three conventional fracture toughness testings using the compact tension (CT), double cantilever beam (DCB), and single edge notched beam (SENB) specimens. Measurement s at other indentation load typically were in poor agreement with conv entional methods due to poorly developed crack configurations.