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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
Chapter VIII Micro-hardness studies… Figures (8.11a -8.11c) are plots of variation of fracture toughness with applied load. From figures (8.11a -8.11c) one can observe that as the load increases from 0.5 to 0.8 N the fracture toughness of various crystalline samples decreases rapidly. The fracture toughness of various amino acids doped KDP crystals progressively decrease as the doping concentration increases. This indicates that the doping of amino acid into KDP reduces the fracture toughness of crystals. It is also observed that for higher concentration of amino acids the fracture toughness slightly increases on increasing load in the region of 0.3 to 0.5 N. Shaskol’skaya et al [109] and Guin et al [110] have analyzed the data by the Evans model with E = 38.7 GPa and the values of Kc was obtained as 0.24 ± 0.04 MPa.m 1/2 at 200 g load, whereas, the Anstis model gave the Kc as 0.17 ± 0.03 MPa.m 1/2 for the same load. However, Anstis model predictions are in agreement with reported values by Marion [111]. Comparing the models by Evans [115] and Anstis et al [116], both results were based on using young’s modulus E = 38.7 GPa. It was observed that the Evans model predicted fracture toughness that was a factor 1.2 to 1.45 times higher than the predictions of the Anstis model; however both models gave the same qualitative ranking of the data. In the present study the values of fracture toughness corresponds to the Evan’s Model/ Anstis Model for pure KDP crystals. The effect of amino acid doping in KDP decreases the fracture toughness values for particular load. 320
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Saurashtra University Re - Accredit
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Statements Under O. Ph.D.7 of Saura
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ACKNOWLEDGEMENT The author expresse
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in-law, Mother- in -law and all oth
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of NLO materials in rapidly develop
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doped samples in comparison to the
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micro-hardness decreases. Also, as
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Papers Published in National and In
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Seminar on Recent Advances in Conde
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Chapter I Brief Introduction... Cha
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Chapter II Solution Growth…. Tabl
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