抄録
On the fracture surface of a KIc specimen, there exists a critical stretched zone between the fatigue pre-crack and overload fracture regions. This width, SZWc, has been correlated with the critical values of various fracture mechanics parameters. On the other hand, a sub-critical stretched zone appears as the loading progresses. In this paper, the data of sub-critical stretched zone width, SZW, obtained by many researchers were summarized and the relation between SZW, as a measure of crack tip plastic blunting, and the J-integral was investigated.
The followings are the summary of the results obtained.
(1) The relation between SZW and J/σflow showed an apparent dependence on flow stress, σflow: there was a tendency for SZW to become smaller for the same value of J/σflow as σflow became smaller. S0, the following equation did not stand,
SZW=C1J/σflow (C1: const.).
(2) The change of Young's modulus, E, had little influence on the relation between SZW and J/E, and no influence of test temperature was observed. SZW was given by the following expression,
SZW=89J/E
(3) The above mentioned relation between SZW and J was similar to the one between the striation spacing, S, and J. Under a small scale yielding condition, S was given by the following expression, in the case that the stress ratio is 0,
S=9.4J/E
That is to say, the width of the stretched zone as well as that of a striation formed by the same micromechanism of glide plane decohesion, was characterized by the very same fracture mechanics parameters.
(4) If the above-mentioned relation between SZW and J is established on other materials, there is a possibility of evaluating JIc simply by measuring SZWc with a single specimen by failured overload.
