Fracture toughness of CaO-$ P_{2} %$ O_{5} $-$ B_{2} %$ O_{3} $ glasses and glass-ceramics determined by indentation

Abstract The fracture toughness, (KIC) of CaO-$ P_{2} %$ O_{5} $-$ B_{2} %$ O_{3} $ glasses and glass-ceramics was investigated using both Vickers indentation and the notched beam technique (NBT). Five representative equations were applied and it was found that for the variation of KIC with $ B_{2}...
Ausführliche Beschreibung

Abstract The fracture toughness, (KIC) of CaO-$ P_{2} %$ O_{5} $-$ B_{2} %$ O_{3} $ glasses and glass-ceramics was investigated using both Vickers indentation and the notched beam technique (NBT). Five representative equations were applied and it was found that for the variation of KIC with $ B_{2} %$ O_{3} $ content, the Lawn and Fuller equation showed the best correspondence with the NBT. The values of fracture toughness obtained from the Lawn and Fuller equation showed the same trend with $ B_{2} %$ O_{3} $ content as that determined by NBT, although the values from indentation were on average 33% lower. The determination of absolute fracture toughness by indentation requires a correction factor which can be obtained by calibration using NBT. A significant increase in KIC occurred after a 37CaO-$ 37P_{2} %$ O_{5} $-$ 20B_{2} %$ O_{3} $-$ 6Al_{2} %$ O_{3} $ (mol%) glass was converted to a glass-ceramic. The much higher KIC for the glass-ceramic measured by NBT (1.32 MN $ m^{−3/2} $) compared with that from indentation (0.89 MN $ m^{−3/2} $) is attributed to internal stresses due to thermal expansion differences between the crystalline and residual glass phases leading to additional microcrack toughening. Ausführliche Beschreibung