Evaluation of Fracture Toughness Using SEVNB Method and IF Methodfor Zirconia (Y-TZP)

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  • Harada Kosuke
    Department of Crown and Bridge, School of Life Dentistry at Tokyo, The Nippon Dental University
  • Shinya Akiyoshi
    Department of Crown and Bridge, School of Life Dentistry at Tokyo, The Nippon Dental University

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  • SEVNB法とIF法によるジルコニア（Y-TZP）の破壊靭性評価

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Purpose: This study aimed to determine fracture toughness values of yttria-stabilized zirconia (Y-TZP), using the Single Edge V-notch Beam method (SEVNB) and the Indentation Fracture method (IF) to demonstrate a suitable measurement approach to fracture toughness values by examining measurement results.<br>Methods: Measurement with SEVNB was conducted using test specimens with the V-notch at two conditions of crosshead speed, 0.5, and 1.0 mm/min, according to International Organization for Standardization (ISO) 6872. A Vickers indenter was used for IF testing of specimens at 30 kgf of the load for 15 seconds, thus generating indentation and cracks to obtain measurements for calculating fracture toughness by use of a formula in Japanese Industrial Standards (JIS) R 1607. The multiple comparison was used to compare the fracture toughness values. The appearance of the fracture surface obtained in SEVNB and the indentation andcracks obtained in IF were observed using a Scanning Electron Microscope (SEM). X-ray Diffraction (XRD) was conducted for phase transformation of the fracture surface obtained inSEVNB.<br>Results: A significant difference was found in fracture toughness values between SEVNB and IF. SEVNB indicated higher fracture toughness values and a larger standard deviation than IF. In addition, SEVNB showed significantly higher fracture toughness values at 1.0 mm/min crosshead speed in comparison with 0.5 mm/min. SEM revealed that stable and unstable fractures were found in SEVNB, and indentation and cracks were clearly observed in IF. In the fracture surface obtained in SEVNB, a phase transformation resulting from bending stress was observed with XRD.<br>Conclusion: We suggest that IF is suitable for measurement of fracture toughness valuesof Y-TZP in comparison with SEVNB. Because the measurement approach of fracture toughness values of Y-TZP has a specific phase transformation feature, a development of new experimental conditions seems to be required for both SEVNB and IF.

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