Transition range drop tower J-R curve testing of A106 steel

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. This report describes a method being used to obtainJ _Ic, J-R curves, andJ 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 percent results in the drop tower 100 in./s (2.5 m/s) tests on this material in comparison with static tests when both tests are conducted on the ductile upper shelf. Nonetheless, for this materialJ _Ic andJ-R curves are not elevated by the loading rate. Looking at the elastic and plastic components ofJ one sees that theJ _EL increases with increased loading rate but also thatJ _PL decreases with loading rate. It is also demonstrated that for the high rate tests more crack extension is present at a given bend angle for the rapid tests than with the static tests. Paper was presented at the 1987 SEM Fall Conference on Experimental Mechanics held in Savannah, GA on October 25–28.