PSI - Issue 75

6

Fabrice Deleau et al. / Procedia Structural Integrity 75 (2025) 392–418 Deleau Fabrice, Emmanuel Persent, Guillaume Coudouel, Guillaume Perrin/ Structural Integrity Procedia (2025)

397

, A n

Parameters of the Basquin’s model for the S -N curve

, ,       Eigen stress ranges (i.e. eigenvalues of

  )

I

II

III

max  )

max F (i.e. eigenvalues of

Principal stresses at

max , ,    max

max

I

II

III

min  )

min F in the direction of

Normal stress acting at

max I  (not an eigenvalue of

min

I 

max 

Principal directions of

max max ma I II II x I ,

, n n n

2. Fatigue design An elastic material is not the best choice to analyse the hot spot of the i-Clip connector, as its maximum principal stress or von Mises stress may exceed the yield strength. The calculation of peak stress should be carried out considering elastic-plastic material behaviour, in which case the stress state requires one or several cycles to stabilize while the material adapts. 2.1. Stress analysis of the numerical cyclic simulations on small-size model The analysis of the evolution of the stress state provides information on the assumptions that must be considered for fatigue calculations, such as the choice of the definition of the stress amplitude. The octahedral shear stress (better known as Von Mises’s stress), defined as VM 2 3 ( ) J   = is interesting for fatigue analysis, because the shear intensity is the reason for cracks initiation (Lemaitre et al., 2020) and (Lu, 2002). Fig. 5 shows the Von Mises’s stress of the two extreme times during the loading cycle on a small-sized configuration, i.e. where the tension reaches its maximum and minimum values, respectively max F and min F . We observe that its value is higher at maximum tension and lower at minimum tension throughout the grooves of the connector lug.

Fig. 5 : Von Mises’s stress at maximum load (a), and minimum load (b).

We can also examine the hydrostatic stress (or normal octahedral stress) as presented in Fig.6. Its positive values are higher at the instant of maximum load, so the tension acting on octahedral plane increases with load.