Issue 35

L. Chunjiang et alii, Frattura ed Integrità Strutturale, 35 (2016) 500-508; DOI: 10.3221/IGF-ESIS.35.56

Tab. 7 makes a list of unstable fracture toughness calculated by initial crack-depth ratio and maximum load P max ,

Unstable fracture toughness [MPa  m]

Initial fracture toughness [MPa  m]

Serial number of specimen

Valid crack growth quantity [cm]

RCC-1 RCC-2 RCC-3 RCC-4 RCC-5 RCC-6 RCC-7 RCC-8 RCC-9 RCC-10 RCC-11 RCC-12 RCC-13 RCC-14

8.1 8.6 8.3 7.8 8.7 7.8 9.9 9.4 9.6 9.5 8.3 7.7 6.8 8.0 7.9 7.8 8.7 7.6 8.0 9.6 8.6 11.6 11.4 10.9 11.6

0.944 1.039 1.016 0.968 0.957 0.996 0.775 0.784 0.811 0.797 0.815 0.900 0.852 0.948

0.415 0.316 0.420 0.351 0.344 0.486 0.385 0.360 0.407 0.359 0.361 0.307 0.305 0.269 0.481 0.582 0.555 0.648 0.621 0.648 0.517 0.529 0.514 0.518 0.543

C-1 C-2 C-3 C-4 C-5 C-6 C-7 C-8 C-9

1.01 1.06 1.09 1.05 1.11 1.19 1.18 1.15 1.23 1.21 1.20

C-10 C-11

Table 7 Unstable fracture toughness under different working conditions

It can be seen from above table that 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, S IC K value gets smaller as initial crack-depth ratio increases, so S IC

506