{"id":132,"date":"2024-05-17T15:16:02","date_gmt":"2024-05-17T06:16:02","guid":{"rendered":"https:\/\/wps.itc.kansai-u.ac.jp\/strength-e\/?page_id=132"},"modified":"2024-05-18T13:36:53","modified_gmt":"2024-05-18T04:36:53","slug":"fatcr","status":"publish","type":"page","link":"https:\/\/wps.itc.kansai-u.ac.jp\/strength-e\/fatcr\/","title":{"rendered":"Fatigue\/Creep"},"content":{"rendered":"\n

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\u25c6Fatigue fracture problem<\/h2>\n\n\n\n

The stress-life (S-N) diagrams of non-ferrous alloys do not usually exhibit distinct knee-points (fatigue limit or endurance limit) unlike those of carbon steels. Such a character necessitates us to use a fatigue strength at finite cycles (e.g. 10^7cycle stress) instead of a cycle-independent threshold stress value. Here we raise a question: can we change such an inconvenient character of conventional alloys through a simple metallurgical modification?
\u3000We then focused on the possible relation between fatigue limit and strain-aging in carbon steels suggested many decades ago. We employed a conventional A6061-T6 (a typical precipitation-hardened Al alloy) as a base metal and added small amount of strain-aging inducer, i.e. magnesium (Mg). What we encountered was a distinct fatigue limit and, moreover, a clear coaxing effect!<\/p>\n\n\n\n

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For more detail, see:

Y. Takahashi, T. Shikama, R. Nakamichi, Y. Kawata, N. Kasagi, H. Nishioka, S. Kita, M. Takuma, H. Noguchi, Effect of additional magnesium on mechanical and high-cycle fatigue properties of 6061-T6 alloy, Materials Science & Engineering A641, 2015, pp. 263\u2013273 (https:\/\/doi.org\/10.1016\/j.msea.2015.06.051<\/a>)

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Related studies:

T. Shikama, Y. Takahashi, L. Zeng, S. Yoshihara, T. Aiura, K. Higashida, H. Noguchi, Distinct fatigue crack propagation limit of new precipitation-hardened aluminium alloy, Scripta Materialia, Vol. 67, 2012, pp. 49\u201352 (https:\/\/doi.org\/10.1016\/j.scriptamat.2012.03.018<\/a>)<\/p>\n\n\n\n

Y. Takahashi, T. Shikama, S. Yoshihara, T. Aiura, H. Noguchi, Study on dominant mechanism of high-cycle fatigue life in 6061-T6 aluminum alloy through micro-analyses of microstructurally small cracks, Acta Materialia, Vol. 60, 2012, pp. 2554-2567 (https:\/\/doi.org\/10.1016\/j.actamat.2012.01.023<\/a>)<\/p>\n\n\n\n

Y. Takahashi, H. Yoshitake, R. Nakamichi, T. Wada, M. Takuma, T. Shikama, H. Noguchi, Fatigue limit investigation of 6061-T6 aluminium alloy in giga-cycle regime, Materials Science & Engineering A, Vol. 614, 2014, pp. 243-249.
(https:\/\/doi.org\/10.1016\/j.msea.2014.07.039<\/a>)<\/p>\n\n\n\n

Y. Takahashi, R. Kuriki, J. Kurihara, T. Kozawa, T. Shikama, H. Noguchi, Distinct fatigue limit of a 6XXX series aluminum alloy in relation to crack tip strain-aging, Materials Science & Engineering A, Vol. 785, 2020, 139378 (https:\/\/doi.org\/10.1016\/j.msea.2020.139378<\/a>).<\/p>\n\n\n\n

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\u25c6 Creep fracture problem<\/h2>\n\n\n\n

Structural components like butt joints and LSI packages contain metal\/polymer interfaces. Polymers, unlike metals having high melting temperature, are subjected to time-dependent plasticity (creep) even at room temperature. The fracture nucleation from a free-edge, where the interface meets a free surface, is quantified by the fracture mechanics concept for time-independent problems. The validity of the concept for time-dependent case, however, remains unknown.
\u3000We pulled Epoxy\/SUS butt joints under various sustained loads and found a clear stress-life (S-T) tendency regarding fracture nucleation. Near-edge stress analysis by the FEM revealed that the event was controlled by a unique relation of two time-dependent parameters (K; stress intensity factor, lambda: stress singularity). This marks the first example demonstrating the validity of the so-called \u201cK-lambda criterion\u201d in the time domain.<\/p>\n\n\n\n

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For more detail, see\uff1a<\/p>\n\n\n\n

Y. Takahashi, K. Inoue, M. Takuma, K. Saitoh, T. Sato, Fracture mechanics criterion of time-dependent crack initiation from interface free-edge in adhesively bonded butt joints, Engineering Fracture Mechanics, Vol. 186, 2017, pp. 368\u2013377 (https:\/\/doi.org\/10.1016\/j.engfracmech.2017.08.017<\/a>)<\/p>\n\n\n\n

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Related studies:<\/p>\n\n\n\n

H. Hirakata, T. Hirako, Y. Takahashi, Y. Matsuoka, T. Kitamura, Creep crack initiation at a free edge of an interface between submicron thick elements, Engineering Fracture Mechanics, Vol. 75, 2008, pp. 2907\u20132920 (https:\/\/doi.org\/10.1016\/j.engfracmech.2008.01.007<\/a>)<\/p>\n\n\n\n

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