PSI - Issue 39

Jesús Toribio et al. / Procedia Structural Integrity 39 (2022) 730–734 Author name / Procedia Structural Integrity 00 (2021) 000–000

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1. Introduction The knowledge of the stress intensity factor (SIF or K ) solution is a basic requirement in fracture mechanics, damage tolerance or structural integrity analyses. With regard to cracked bolts, there is a scarcity of published solutions: Reibaldi(1984), Nord and Chung (1986), Springfield and Jung (1988) and James and Mills (1988), the two latter papers presenting reviews of K -solutions applicable to crack in bolts.. In the matter of crack paths and fatigue crack growth evolution in bolts, previous research works are also scarce, although some published papers can be found (Mackay and Alperin, 1985). This paper provides closed-form SIF solutions for a cracked bolt loaded directly by the nut, providing analytical solutions useful for analysis of crack path evolution during fatigue or stress corrosion cracking. 2. Problem statement: geometry and loading conditions The geometry consists of an ISO M8 x 1.0 bolt with an elliptical surface crack and the following dimensions: Maximum diameter: 8 mm Minimum diameter: 6.77 mm Root radius: 0.125 mm Pitch: 1 mm Thread angle: 60º The bolt was modeled in parallel jointed threads, without taking into account the helical shape. A semi-elliptical surface crack was considered (Fig. 1) with three aspect ratios: Slightly-curved (SC) crack: a/b = 0.2 Intermediate (I) crack: a/b = 0.6 Circular (C) crack: a/b = 1.0 Two loading conditions were considered (see Fig. 2): (a) Tension loading, consisting of a uniform stress distribution applied far enough from the crack. (b) Nut loading. In this case the load, due to the nut, was directly applied on the thread flank.

Fig. 1. Crack geometry