The tensile strength of yttria-stabilized tetragonal zirconia polycrystals (Y-TZPs) was measured and the fracture surfaces were analyzed by SEM-XMA. The fracture toughness,
KIC, SEPB, and the crack extension resistance curve (
R-curve) were evaluated by the single-edge-precracked-beam (SEPB) and the double cantilever beam (DCB) methods, respectively. The fracture toughness,
KIC, slopel, evaluated from the tensile strength and the fracture surface analysis shows 3.4 to 3.7 MPa√m, which is much smaller than
KIC, SEPB (5.0 to 5.2 MPa√m). The type of
R-curve is a rising one, and
KIC, slopel and
KIC, SEPB are close to the initial and the saturated values of the
R-curve, respectively. The fracture origins of the SEPB and the tensile test specimens are a relatively large precrack and a small natural flaw, respectivery. Therefore, the value of fracture toughness of the Y-TZPs with a rising
R-curve depends on the size of fracture origin.
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