PSI - Issue 14

K. Shridhar et al. / Procedia Structural Integrity 14 (2019) 375–383

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K. Shridhar et al./ Structural Integrity Procedia 00 (2018) 000–000

rapidly for the next incremental crack lengths. From 8-24 mm average crack growth rate observed was 5Χ10 -5 mm/cycle. Radius ratio 3: From the data it was observed that crack growth rate is slow and gradually increasing when compared other two cases. Between 2 to 12 mm crack growth rate observed was 6Χ10 -6 mm/cycle. Further, from 12 to 32 mm crack growth rate was 1Χ10 -5 mm/cycle. From the fig 5 it is clear that for the given loading lug with radius ratio 3 has higher fatigue life and lug with radius ratio 1.5 has lesser fatigue life. From this it can be concluded that fatigue crack growth rate is higher in lugs with lesser radius ratios.

Fig 5. Crack length v/s Number of cycles

7. Conclusions In the present work, stress analysis has been carried out by MSC Patran/Nastran to analyze the stress distribution for a pin loaded lug and also identify the maximum tensile stress location which may be the prone region of developing fatigue cracks. The effect of lug geometry i.e. radius ratios and the direction of loading on the stress distribution were also studied. The SIF for progressive crack lengths has been determined for the different radius ratios of the lug geometry through analytical and numerical approaches. Further, fatigue crack growth life of the pin loaded lug joint with the crack emanating from the lug hole subjected to constant amplitude cyclic loading has been estimated by employing the Walker’s crack growth model. The following conclusions can be drawn from the present work:  As radius ratio increases, stress concentration factor reduces. A maximum SCF of4.2 was observed for radius ratio 1.5 and minimum SCF of 1.71 was observed for radius ratio 3.  Stress concentration is maximum at the location perpendicular to the loading direction and it shows exponential decay as we move along the net section towards the lug edge.  SIF values are more critical for lesser radius ratios and shows significant change for smaller changes in crack length.  The number of cycle to failure is as follows:  For the radius ratio =1.5, the maximum number of cycles to failure is seen to be 2, 94,910 cycles.  For the radius ratio= 2, the number of cycles to failure is 7, 76,180 cycles.