Issue 35

L. Chunjiang et alii, Frattura ed Integrità Strutturale, 35 (2016) 500-508; DOI: 10.3221/IGF-ESIS.35.56 506 Tab. 7 makes a list of unstable fracture toughness calculated by initial crack-depth ratio and maximum load P max , Serial number of specimen Valid crack growth quantity [cm] Unstable fracture toughness [MPa  m] Initial fracture toughness [MPa  m] RCC-1 8.1 0.944 0.415 RCC-2 8.6 1.039 0.316 RCC-3 8.3 1.016 0.420 RCC-4 7.8 0.968 0.351 RCC-5 8.7 0.957 0.344 RCC-6 7.8 0.996 0.486 RCC-7 9.9 0.775 0.385 RCC-8 9.4 0.784 0.360 RCC-9 9.6 0.811 0.407 RCC-10 9.5 0.797 0.359 RCC-11 11.6 0.815 0.361 RCC-12 11.4 0.900 0.307 RCC-13 10.9 0.852 0.305 RCC-14 11.6 0.948 0.269 C-1 8.3 1.01 0.481 C-2 7.7 1.06 0.582 C-3 6.8 1.09 0.555 C-4 8.0 1.05 0.648 C-5 7.9 1.11 0.621 C-6 7.8 1.19 0.648 C-7 8.7 1.18 0.517 C-8 7.6 1.15 0.529 C-9 8.0 1.23 0.514 C-10 9.6 1.21 0.518 C-11 8.6 1.20 0.543 Table 7 Unstable fracture toughness under different working conditions It can be seen from above table that S IC K value gets smaller as initial crack-depth ratio increases, so S IC K based on initial crack-depth ratio not only has size effect, but also changes with the changes of initial crack-depth ratio. That indicates that subcritical growth quantity of wedge splitting specimen changes with size, related to initial crack-depth ratio as well, which is different from three-point bending beam. Thus, it is obvious that small specimen has to take stable growth of crack into consideration. Flexibility coefficient applied in calculating valid subcritical crack growth length ( c a ) with double-K fracture criterion is diverse, thereby leading to different c a . After obtaining c a , fracture toughness S IC K and CMODc can be figured out, so valid subcritical crack growth length ( c a ) is believed to be an important parameter [12-13]. In two-parameter model,