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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Fig. 4. SIF variation along the crack front for SC-cracks (left) and for C-cracks (right), The values for remote tension (*) are also represented. Nut loading strongly increases the SIF for the shortest cracks, the effect being higher at the crack surface and decreasing with the crack depth. The nut effect (intensification) is even more pronounced at the surface points of shallow circular cracks. For the deepest circular cracks, however, nut loading relaxes the K -value, as shown in the right-hand plot of Fig. 3. In relation to the SIF variation along the crack line (Fig. 4), the K -value increases in the vicinity of the bolt surface, due to the nut load directly applied on the thread. This effect is more important in shallow cracks, and less in deep cracks. The trend is opposite for deep circular cracks. 5. Closed-form SIF solutions for nut loading An interpolation was performed with the results, to have closed-form SIF solutions valid for any crack geometry: Y ( a / b , a/d ) = A 0 ( a / b ) + A 1 ( a / b )*( a / d ) + A 2 ( a / b )*( a / d ) 2 CENTER: A 0 = –1.002 + 17.495 ( a / b ) – 14.575 ( a / b ) 2 A 1 = 34.1171 – 157.8175 ( a / b ) + 121.7594 ( a / b ) 2 A 2 = – 54.9303 + 239.635 ( a / b ) – 183.9188 ( a / b ) 2 SURFACE: A 0 = 1.7625 + 15.17 ( a / b ) – 1.5125 ( a / b ) 2 A 1 = 15.6175 – 117.625 ( a / b ) + 20.9375 ( a / b ) 2 A 2 = – 35.525 + 190.05 ( a / b ) – 49.625 ( a / b ) 2 These expressions may be used to predict fatigue crack paths in the form of aspect ratio evolution. 6. Conclusions Nut loading increases the SIF for the shortest cracks, mainly at the crack surface, due to the direct load on the thread by the nut. This effect decreases as the crack growths. The trend of SIF variation with nut direct loading is the opposite for the deepest circular crack, because in this case the SIF values are higher for remote tension loading. The worst effect of the nut is related to the next three conditions: (i) short cracks; (ii) points next to the free surface; (iii) circular cracks. In Memoriam: A Tribute to Agustín de Betancourt The paper is a heartfelt tribute to the memory of the prominent Spanish engineer Agustín de Betancourt. References

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