Evaluation of the K_ISCC Testing Procedure by Round Robin Tests on Steels

Round robin test programs of the tentative test procedure for the determination of the threshold stress-intensity factor K_ISCC were conducted under the auspices of the 129th Committee, Japan Society for the Promotion of Science. The test programs used JIS SNCM 439 (AISI 4340) steels. Thirty-one laboratories participated in these programs. Tests were carried out with both 25.4-mm (1-in.)-thick bolt loaded wedge-opening-loading (WOL) specimens and 25.4 by 25.4-mm cantilever beam (CB) specimens in a 3.5% sodium chloride solution of distilled water.

The results of the round robin test programs showed some informations to standardize the K_ISCC testing procedure. For valid K_ISCC values to be obtained, the test must last 7000 h for a WOL specimen and 4000 h for a CB specimen. In the WOL tests, the final crack length and width ratio a_f/W of a specimen must be smaller than 0.8. An elastic bolt analysis of WOL specimens was recommended to obtain the valid K_ISCC values and the good relationship between da/dt and K_I. In the CB tests, the estimated K_ISCC value coincided well with that in the WOL tests when at least six CB specimens were used. Slight effect of crack front curvature, test temperature, and pH of the solution on the variance of the K_If values was observed.

With these test results, the K_ISCC testing procedure was standardized by the Committee and entitled “Standard Test Method for Threshold Stress Intensity Factor K_ISCC in Stress Corrosion Cracking.”