Evaluation of dynamic fracture mechanics in the AISI 316 stainless steel using instrumented Charpy impact testing

The nuclear power plant's surveillance program is based in Charpy test. But, this test could be used to evaluate integrity's secondary circuit. The steel similar to AISI 316 stainless steel could be used in this circuit. Some secondary circuit's components could be failed in dynamic condition. The dynamic fracture mechanics behavior of the AISI 316 was studied by using instrumented Charpy impact testing. The dynamic fracture toughness (Jld) could be evaluated by four different methods: compliance changing rate, stretching zone, energy revised and maximum load energy. The tests were made in temperature -196 deg C, room and 200 deg C. At each temperature two specimens were tested. The impact energy was 300 J and the impact velocity was 5.12 m/s. The Charpy specimens 10 x 10 x 50 mm were pre-cracked until 5 mm according to ASTM E-23. Stretching zone size was measured and analyzed by observing the fracture surfaces that were obtained in a scanning electron microscope. The dynamic fracture toughness calculated among four different methods showed a large difference. All studied methods did not agree ASTM E1820 (2001) standard that indicated to plane strain did not occurred in the tip crack. (author)