PSI - Issue 38

Benaouda Abdellaoui et al. / Procedia Structural Integrity 38 (2022) 116–131 Benaouda Abdellaoui et al / Structural Integrity Procedia 00 (2021) 000 – 000

127

12

The Fig. 10 presents the mean strain during the static test. There is a slight local plasticization at the hot spots because the mean strain of Fig. 10 do not come back to 0.

Fig. 10. Mean strain

The result of all the pivots is presented in the Table 7 below. They have been tested up to 10 6 cycles at 2,5KN in 2 directions. No failure has been detected. It has been decided to continue the fatigue test following by locati method [9] on the first two pivot to determine the endurance limit to reach 10 6 cycles. This method is based on Miner's assumption, which considers the cumulative damage to be linear and proportional to the number of cycles. The test consists of subjecting the part to stages of increasing loads until failure. The first level of loading corresponds to 2.5KN in each direction with 10 5 cycles at each level and a constant difference of 0.25 KN between the loading levels. We chose to take this value as the first level because it is the value of force representing the action of the centrifugal force due to the weight of the pulleys mounted on the axes and the weight of the pivot. This value was determined by estimation at the start and confirmed by finite element calculations. In terms of cycling, for the original pivot, it was based on a lifetime of 20 years of operation corresponding to 109 500 cycles. This method rests on the assumption of Minor, which considers the office plurality of the damage like linear and proportional to the number of cycles.

Table 7. Pivots tests results

Last step

Continuation in Locati method [9] step of 0,25 KN level of 100 000 cycles step of 0,25 KN level of 100 000 cycles

Part

Effort (KN)

lifecycle

Locati method [9] results

Effort (KN)

lifecycle

Failure after 14 stages at N = 2 281 000 cycles

Pivot 2

2.5

1 000 000

5.75

81 000

Failure after 11 stages at N = 1 956 153 cycles

Pivot 3

2.5

1 000 000

5

56 153

step of 1KN

Failure after 2 stages at N = 1 065 500 cycles

Pivot 4

4

1 000 000

5

65 500

level of 100 000 cycles

The S-N curve hypothesis corresponds to a Basquin model with slope coefficient m = 10 and associated with a fatigue limit of 10 6 cycles. The calculation of the coefficient C of the Basquin model: = − (7)