Transition Range Drop Tower J-R Curve Testing of A106 Steel.

摘要

Fracture toughness properties should be measured in the laboratory at loading rates and temperatures similar to those expected in the application of interest. This is not usually the case because of the experimental difficulties involved. The report describes a method being used to obtain J(Ic), J-R curves, and J at cleavage for three point bend tests conducted at drop tower rates through the ductile to brittle transition regime of the ferritic A106 steel being tested. The major conclusion is that these tests can now be accomplished, though a high degree of expertise and considerable practical experience is necessary to obtain good test results. The steel tested here is quite rate dependent as shown both by tensile tests and fracture toughness tests. A load elevation of 30 to 50% results in the drop tower 100 in/second tests on this material in comparison with static tests when both tests are conducted on the ductile upper shelf. Nonetheless, for this material JIc and J-R curves are not elevated by the loading rate and this rather surprising result corresponds to a tendency for crack initiation to occur at a smaller bend angle for the high rate tests than for the static tests and a correspondingly greater amount of crack extension in the rapid specimen at a given bend angle beyond crack initiation than is present in the static test.