This paper describes the activities and test results of the Material Properties Council (MPC) working group on fracture toughness testing in the brittle-to-ductile transition region, a cooperative testing program. The MPC working group was organized in 1987 with the objective to study the problem of data scatter in the transition region and to develop the materials information needed to support the development of test procedures and testing philosophies or both. The MPC group was invited by the Japan Society for the Promotion of Science (JSPS) to coordinate a cooperative testing program in the United States and elsewhere.
A total of 18 laboratories participated in the test program with approximately 150 1T compact fracture toughness specimens being tested. The tests were conducted at three test temperatures in the ductile-to-brittle transition region. This paper presents an overview of the test program, details about the material, overall test matrix, test plan, and summary of the results.
The experiments were conducted between the temperature regions where the ASTM Test Methods for Plane-Strain Fracture Toughness of Metallic Materials and JIc Measure of Fracture Toughness (E 399 and E 813), respectively, are usually applied. The tests were conducted following the ASTM Test Method E 399 testing procedure except that the fracture toughness was determined using the equations in ASTM Test Method E 813 for the calculation of J at the point in the load displacement curve at which the specimen failed. The J values measured by using this procedure were converted to the units of K. Some of the laboratories used the unloading compliance procedure during the experiments to monitor the amount of crack extension prior to the cleavage failure.
A number of different procedures were used in the test program to estimate the lower bound fracture toughness values. The two and three parameter Weibull fits appear to be the best of the procedures used. The results from this cooperative test program should be of great value to researchers in this field as a data set useful for making decisive studies.