13th International Conference on Fracture June 16–21, 2013, Beijing, China -9- double-K fracture parameters, i.e., KI ini and KI un-E and the residual fracture energy GF are summarized in Table 2. Here we only list part of the statistics. Table 2 The experimental results of fracture parameters speci men tempe rature Pini/ kN Pmax/ kN CMODc /mm CTODc /mm E GPa GF N/m KI ini MPa.m1/2 KI c-A MPa.m1/2 KI c-W MPa.m1/2 KI un-E MPa.m1/2 KI un-A MPa.m1/2 KI un-W MPa.m1/2 WS1 6.19 8.33 0.174 0.065 15.30 234.15 0.505 0.666 0.691 1.061 1.171 1.196 WS2 6.28 9.81 0.120 0.039 20.51 483.66 0.523 0.571 0.608 1.070 1.094 1.131 WS3 7.26 10.40 0.210 0.079 20.66 438.22 0.610 0.968 1.002 1.497 1.578 1.612 WS4 7.02 7.92 0.152 0.060 18.88 219.39 0.357 0.799 0.818 1.091 1.156 1.175 WS5 20ºC 5.65 9.39 0.237 0.096 15.45 321.05 0.503 0.715 0.742 1.213 1.218 1.245 Aver 6.55 9.17 0.178 0.068 18.16 339.30 0.498 0.744 0.772 1.186 1.243 1.271 WS11 5.03 8.37 0.191 0.056 10.65 396.52 0.518 0.45 0.489 0.900 0.968 1.007 WS13 4.69 8.25 0.224 0.084 11.87 517.82 0.417 0.745 0.754 1.058 1.162 1.171 WS12 4.71 7.53 0.357 0.152 9.48 654.73 0.419 1.016 1.070 1.202 1.435 1.489 WS14 2.79 7.53 0.198 0.083 15.42 345.46 0.249 0.858 0.951 1.107 1.107 1.200 WS15 120ºC —— —— —— —— —— —— —— —— —— —— —— —— Aver 4.31 7.92 0.243 0.094 9.48 478.63 0.401 0.767 0.816 1.067 1.168 1.217 WS21 1.89 3.40 0.653 0.283 2.45 437.92 0.168 0.45 0.478 0.556 0.618 0.646 WS22 3.48 5.53 0.667 0.280 3.49 611.47 0.309 0.553 0.597 0.841 0.862 0.906 WS23 1.82 3.38 0.672 0.271 1.91 341.77 0.162 0.374 0.386 0.480 0.536 0.548 WS24 2.61 4.97 0.577 0.262 1.99 564.12 0.232 0.359 0.381 0.589 0.591 0.613 WS25 300ºC 2.03 4.17 0.651 0.361 4.03 549.99 0.175 0.82 0.824 0.913 0.995 0.999 Aver 2.37 4.29 0.644 0.291 2.78 501.05 0.209 0.512 0.533 0.676 0.21 0.742 Aver 2.01 3.78 0.901 0.410 1.56 490.71 0.149 0.374 0.398 0.615 0.526 0.550 WS36 1.52 3.37 1.009 0.544 1.41 611.53 0.135 0.387 0.401 0.582 0.522 0.536 WS37 —— —— —— —— —— —— —— —— —— —— —— —— WS38 1.52 3.26 1.419 0.660 1.46 482.45 0.135 0.341 0.375 0.527 0.476 0.510 WS39 1.12 3.07 1.348 0.617 1.34 663.10 0.100 0.42 0.437 0.563 0.520 0.537 WS40 450ºC 0.99 2.94 1.394 0.666 1.58 678.79 0.088 0.513 0.508 0.659 0.601 0.596 Aver 1.29 3.16 1.293 0.622 1.16 608.97 0.115 0.415 0.430 0.583 0.530 0.545 WS46 0.76 1.13 1.482 0.684 0.47 228.23 0.067 0.174 0.188 0.221 0.231 0.245 WS47 0.53 1.48 2.082 0.684 0.48 395.06 0.063 0.209 0.216 0.277 0.284 0.291 WS48 0.81 1.65 1.908 0.813 1.14 539.22 0.072 0.478 0.512 0.550 0.550 0.584 WS49 0.58 1.14 1.687 0.973 0.38 331.99 0.052 0.188 0.198 0.225 0.225 0.235 WS50 600ºC 0.62 1.48 2.082 0.727 0.38 273.07 0.068 0.155 0.161 0.213 0.213 0.219 Aver 0.62 1.38 1.848 0.799 0.57 353.51 0.064 0.241 0.255 0.297 0.301 0.315 6.3. Discussion In order to express the influence on the residual fracture toughness in detail, Fig.8 plots the tendency of initial fracture toughness KI ini and the unstable fracture toughness KI un with heating temperatures Tm. It is concluded that the two fractures toughness decrease monotonously with Tm because of the thermal damage induced by the heating temperatures. The initial fracture toughness continuously decreases from 0.498 kN at room temperature to 0.269 kN at 200ºC, 0.115 kN at 450ºC, and finally 0.064kN at 600ºC, with a significant loss of 0.434 kN or 96%. The unstable fracture toughness decreases from 1.186 kN at room temperature to 0.297 at 600ºC, with a significant loss of 0.889 kN or 75%.
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