Issue 38

J. Papuga et al., Frattura ed Integrità Strutturale, 38 (2016) 106-113; DOI: 10.3221/IGF-ESIS.38.14 110 Bennebach (Ben – [22]), Palin-Luc (PaL – [23]) As usually in the case of tests realized at ENSAM in Bordeaux, staircase philosophy was adopted for fatigue limit determination for these both cases. Because the first international publication of the test set was found in the paper by Morel and Palin-Luc [24], test sets were originally marked MPC and MPB in [1]. Bennebach’s PhD thesis [22] allows the reader to define just two fatigue limits. Such a low number differs from the MPC set, where four items are available. One more fatigue limit can be traced back to Palin-Luc [23], where unfortunately no information is present, whether the same lot of material was used. The origin of the last item in MPC test set has not been found yet. Findley (Fin – [25]) Papuga reported in [1] this test set three times, because he defined three different S-N curve section cuts at 10 6 , 10 7 and 10 8 cycles in order to increase the number of experiments realized on aluminum alloys. Though the same strategy was accepted e.g. in [26], this simple multiplication of the same data set is not consequent, because it was not adopted while processing the other data sets. Gough and Pollard (GPx – [27-28]), Gough (Ggh – [29]) Gough and Pollard published in the 30 th of the 20 th century several papers (see e.g. [27-28]) describing results of their multiaxial tests on bar specimens manufactured from various steels and cast irons. The combination of plane bending and torsion without any phase shift and without any mean stress can be found in all data sets. Apparently, the focus of their effort was mostly devoted to covering of various materials extensively, than to determining the fatigue limits precisely. Therefore, many of these experiments do not conform to the lowest standards defined here before, and big scatter of data in some curves can be found in many cases. As a result of such practice, one half of the defined multiaxial fatigue limit items could be included into the validation data set at maximum. After the WWII, Gough published further papers (e.g. [29]), mostly devoted to more complex testing on S65A steel. Nevertheless, no information on the way the reported fatigue limits were set can be found in any of his papers from that period, and only his personal classification describing the reliability of the outputs is available. Rotvel (Rot – [30]) Rotvel’s data were used for a validation study even recently [31], though Papuga wrote in [1], that the experiments miss the case of pure torsion loading. This value has to be estimated, if the test set should be admitted for validation purposes, and this is apparently the method of determination used in [31]. Bhongbhibhat (BhO, BhA – [32]) These tests realized on specimens on large hollow specimens manufactured from 42CrMo4 (BhO) and St35 (BhA) are affected by substantially different cross-sections of specimens used for uniaxial and multiaxial fatigue tests. Additionally, the lifetime regions of individual curves in these data groups differ so substantially, that only small intersections can be found. Issler (Iss – [33]) Issler’s data set suffer from the doubtful way the fatigue limits were determined. No clue is provided by the author, but based on an analysis of his results, it seems that he either used the section cut at 2 000 000 cycles or the stress level of the last finished experiment with the longest lifetime. Section cuts at lower number of cycles are recommended to avoid potential extrapolations. The S-N curves for multiaxial load combinations are described by graphs with data points only. Unfortunately, the uniaxial fatigue curves are not present at all, and the fatigue limits derived by the author are provided solely. Because of the way the fatigue limits were determined in other cases, it cannot be anticipated how precise these values are. Baier (BaB, Bai, BaG – [34]) The data on both steels (BaB – Ck35, Bai – 34CrMo4) are very interesting for validation purposes. The tests were realized as S-N curve tests on sufficient numbers of hollow specimens in most cases. Anyhow, the tests on GG30 cast iron (BaG test set), for which any fully reversed torsion tests are missing, should not be used.