13th International Conference on Fracture June 16–21, 2013, Beijing, China -10- y = -0.0008x + 0.4873 R2 = 0.9426 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0 100 200 300 400 500 600 700 Tm /ºC KI ini /MPa.m1/2 20℃ 65℃ 120℃ 200℃ 300℃ 350℃ 400℃ 450℃ 500℃ Mean value y = -0.0019x + 1.4115 R2 = 0.8674 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 0 100 200 300 400 500 600 700 Tm /ºC KI un/ MPa.m1/2 20℃ 65℃ 120℃ 200℃ 300℃ 350℃ 400℃ 450℃ 500℃ 600℃ Mean value (a) The tendency of KI ini with Tm (b) The tendency of KI un with Tm Fig.8. The tendency of residual fracture toughness with heating temperatures Tm Comparing the result shown in Table 2, it can be known that the value of KI un-A evaluated by formula (26) has a good coincidence to one calculated by inserting the values of Pmax and ac=D into the formula (24), i.e. the critical fracture toughness from analytical and experimental method. Fig.9 shows the relationship between the two parameters. The similar results could be concluded between the value of KI un-W from formula (26) and the experimental results from formula(24). 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.0 0.5 1.0 1.5 2.0 Experimental Value/MPa.m1/2 Analytical Value/MPa.m1/2 20ºC 65ºC 120ºC 200ºC 300ºC 350ºC 400ºC 450ºC 500ºC 600ºC 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Analytical Value/MPa.m1/2 Weight Function Value/MPa.m1/2 20ºC 65ºC 120ºC 200ºC 300ºC 350ºC 400ºC 450ºC 500ºC 600ºC Fig.9. Comparison between analytical and experimental Fig.10. Comparison between analytical and weight values of critical fracture toughness function values of critical fracture toughness In totally 45 effective specimens, the deviation between KI un-A and KI un-E of 22 specimens is below 5%, and of 40 specimens is below 15%, account for 89%of total specimens. Accordingly, the number of specimens corresponding to the same deviation between KI un-W and KI un-E is 20 and 42, respectively. Fig.10shows the weight function method agrees well with the analytical method, and the deviation below 5% accounts for 65% of total specimens. 7. Conclusion The determination of double-K fracture parameter using both analytical and weight function methods are carried out in present research. In calculating the cohesive fracture toughness, two conditions are divided at critical load: for specimens subjected to temperatures less than 120ºC, the critical CTODc is less than ws; whereas, for temperatures higher than 120ºC, the critical CTODc corresponding to maximum load Pu is wider than ws. This part of work would be a useful supplement to the existed analysis. Wedge-splitting tests with ten temperatures varying from 20ºC to 600ºC are implemented. The complete load-crack opening displacement curves are obtained and the initial and critical fracture toughness could be calculated experimentally.
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