The test method for KIc is well known to produce size dependent fracture toughness values where toughness increases with specimen size, especially for high toughness materials. This revision to E399 proposes to introduce a new analysis method for the standard force-displacement data collected as part of the standard E399 test method. The new method is believed to produce approximately size insensitive, linear-elastic plane-strain fracture toughness. The new nomenclature is KIsi that is, Mode-I, size insensitive toughness. The approach taken to integrate the new method into E399 is to add an appendix to E399 with the new method. Appendix information is non-mandatory. The intent is that for an E399 test, the user will always produce a KIc data analysis and can optionally produce the KIsi data analysis. A key difference between the KIc data analysis and the KIsi data analysis is that the KIc data analysis is based on a 95% secant offset from the linear region of the data test record, which corresponds to 2% crack growth. As a result, when specimen size increases, the amount of crack growth at which KIc is evaluated also increases, leading to the possibility of an R-curve effect for a data set with increasing specimen size. In contrast, the KIsi data analysis is based on a fixed amount of crack growth independent of specimen size. As a result, for fixed crack growth the compliance offset is variable, and equations are provided to calculate the appropriate compliance offset as a function of remaining ligament for each of the specimens in the annexes. There are a number of concerns for this first subcommittee ballot. Among them is the approach to integrating the new analysis method into the standard. There are significant apparatus, specimen configuration, and test procedure commonalities between the two methods to warrant merging the new test method into E399. However, the colloquial terminology E399 has essentially become synonymous with KIc. As a result, we are especially interested in a clear integration of the new method that minimizes possibility of confusion for the many existing users of E399. It was decided that the non-mandatory appendix provides a reasonable balance between opportunity to continue evaluation of this new test method with minimal disruption of the existing commercial user base that relies on E399 for testing specifications. The only part of the standard that is open for ballot is the new appendix and the specific changes highlighted in the remainder of the standard. The bulk of the standard is being provided for information only. The proposed revision is significant and the task group believed that having the bulk of the standard available for context was beneficial. Only comments on the highlighted revisions will be addressed. This is not a ballot for the full text of E399.
Draft Under Development