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Chapter VIII Micro-hardness studies…
Kc = ( 0.016 ± 0.002) (E/H) 1/2 P/c 3/2 (8.21)
The model proposed by Anstis et al [116] is based on the assumption
that the observed surface cracks are surface traces of sufficiently large radial
cracks, on the other hand, the Evans model [115] is applicable for both shorter
near surface cracks, where c P, as well as for deeper radial cracks.
The cracks observed on the (100) surface of the pure and amino acid
doped KDP crystals are shown in figures (8.4a -8.4d). The cracks for different
loads were measured and the fracture toughness (Kc) of pure and amino acids
doped KDP crystals were calculated with the help of equation (8.21). Figure
(8.10a -8.10c) show plots of fracture toughness Vs load for pure and amino
acids doped KDP crystals, which show that as the load increases obviously the
crack length increases. The values of fracture toughness Kc for pure and doped
KDP crystals are listed in table (8.4) for various loads.
Load
(N)
Table: 8.4 Values of Fracture toughness Kc at different loads for pure and
amino acid doped KDP crystals.
Pure
KDP
KDP + L- histidine
In MPa
KDP + L-threonine
In MPa
319
KDP +DL-mehtionine
In MPa
0.3 % 0.4 % 0.5 % 0.3 % 0.4 % 0.5 % 0.3 % 0.4 % 0.5 %
0.294 0.257 0.223 0.184 0.173 0.222 0.198 0.185 0.240 0.210 0.183
0.491 0.256 0.232 0.211 0.202 0.222 0.208 0.185 0.243 0.221 0.202
0.588 0.230 0.203 0.196 0.189 0.209 0.195 0.179 0.211 0.196 0.182
0.686 0.190 0.182 0.166 0.162 0.178 0.175 0.160 0.171 0.161 0.149
0.784 0.156 0.144 0.131 0.126 0.145 0.137 0.132 0.160 0.141 0.131
0.981 0.167 0.154 0.143 0.135 0.157 0.151 0.147 0.167 0.164 0.154