PROCEDURES FOR DETERMINING K SUB IC FOR 180/210 KSI YIELD-STRENGTH STEELS,
Abstract:
The linear-elastic-fracture mechanics approach is widely used to determine the resistance to fracture of steels and weldments having yield strengths equal to or greater than 200 ksi. However, for steels having yield strengths less than 200 ksi, reliable test procedures for measuring K sub IC have not been established. Therefore, so that evaluations based on K sub IC values could be included in the program to determine the feasibility of developing an HY-180210 steel weldment, a study was initiated to develop procedures for obtaining valid K sub IC measurements for steels at this strength level. Preliminary studies indicated that a slow-bend test specimen was best suited for K sub IC measurements on steels having yield strengths lower than 200 ksi because the large specimens required for planestrain fracture can be tested at much lower loads than those required for axial tests. Therefore the slow-bend test was selected for further study. Evaluation of the slow-bend test indicated that pop-in could be simply and sensitively measured by means of a strain gage located at the tip of the fracture-initiating fatigue crack. In selecting the best geometry for the slow-bend test, the depth of the specimen was observed to be much more important than the width as long as the width is above a minimum value or the length of specimen.