Critical experiments, measurements, and analyses to establish a crack arrest methodology for nuclear pressure vessel steels. Fifth quarterly progress report, Task 62

A series of calculations are reported which explore the significance of a K/sub D/ that decreases with increasing crack velocity. The effect on K/sub a/, the crack propagation behavior, and the model instabilities which develop are described in detail. A series of experiments on contoured specimens are described and compared with MRL data. Several difficulties were encountered in these tests, among them being relatively short crack extensions to the first halt coupled with difficulties in making accurate crack velocity measurements near the onset of propagation. It is also found that the machine interaction may cause additional propagation. The model accurately describes the initial portion of the event but repropagations which occur due to energy input from the test machine are difficult to characterize. Additional K/sub D/ data for A533B have been collected and the complete set of data available to date is reported. At low temperature (NDT-66C) K/sub D/ is relatively independent of crack velocity with a possible increase starting at about 900 ms-1. At NDT K/sub D/ decreases modestly with increasing crack velocity. At a slightly higher temperature (NDT + 36C) K/sub D/ again appears to decrease with velocity. The relevance of K/sub D/ to K/sub d/, the dynamically-loaded, crack-initiation toughness, is discussed