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.