PSI - Issue 14

L. Chikmath et al. / Procedia Structural Integrity 14 (2019) 922–929 Author name / Structural Integrity Procedia 00 (2018) 000–000

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(i) Cold working � = 0, � = 2 � � , �� = 0 … (4) (iii) At the far end of the lug for Pin load = − , � = − � , �� = 0 … (6)

(ii) Pure interference � = 0, � = 2 � �� = 0 … (5) (iv) Load equilibrium (pin load): = � � � � � � � … (7)

(iv) In the region of separation: � = 0, �� = 0, inequality constraints: � ≥ 0 … (8) (v) On the region of contact: � = 2 � , �� = 0, inequality constraints: � ≤ 0 . (9) (vi) On all the free edges: � = 0, �� = 0, n and s are normal and running co − ordinates on the edges … (10)

Fig 7: Boundary conditions on the lug joint for different conditions

3. Results and discussions 3.1 Stress analysis

The lug joint with fastener is cold worked with a mandrel size (λ c ) varying between 0.3% to 0.5% higher than that of hole radius (R i ). Later, the hole is filled with an interference fit with misfit parameter (λ) of 0.2% higher than hoe radius (R i ). The stress ( σ ) - strain (ε) relation of the lug material (T-6061) used in current analysis is elasto-plastic in nature and is shown in Fig.8. Through the FE stress analysis, critical locations of fatigue crack initiation are identified to be (±90 0 ) at the interface of pin-hole in the lug geometry. The results are concentrated on the maximum tensile hoop stress where the fatigue crack is likely to initiate. The tangential (hoop) stress vary linearly and go beyond the yield limit of the material when a pin is inserted (pure interference) which is higher than the hole radius by 0.4%. (Fig.9). The hole is cold worked by introducing a mandrel which is just causing the material to yield and removed, further a interference fit is inserted. This would cause a initial negative hoop stress and with increase in the misfit value ( λ ), the hoop stress vary linearly to a positive value. Due to the cold working, there is a consequential drop in the hoop stress which is shown in the same Fig.9 (points C and D)