PSI - Issue 19

Jan Presse et al. / Procedia Structural Integrity 19 (2019) 423–432 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

431

9

For this reason, an additional shell layer with the same material properties as the solid adhesive elements is created on the free area of the solid elements. Fig 6 shows the additionally modeled shell layer. Since the failure of the adhesive initiates on the edge of the adhesive, the maximum of major principal stress of this additional shell layer is considered as the main cause for the crack initiation of the adhesive layer. Fig 7 shows the regression through the calculated stress values for the loads from the fatigue tests of adhesively bonded connections and the related number of cycles. The resulting scatter of the reference SN-curve is  = 1 ∶ 1.22 which leads to an accurate estimation of fatigue life for this adhesive within the tested configurations. The extension in the FE-simulation of shell layers on the free areas of the solid-element modeled adhesives and the extraction of the maximum stresses represents a minor additional effort. Therefore, the final assessment of comparing the stresses to the reference SN-curve is performant and easy to use, compared to existing approaches for fatigue life estimation. For this approach, in the FE-simulation no detailed models of the adhesive with fine mesh are necessary which improves the calculation performance.

100

LS-DP600 LS-DP600-EN AW-6016 LS-EN AW-6016 CP-DP600 CP-DP600-EN AW-6016 CP-EN AW-6016

T  =1:1.22

N50% N90% N10%

Stress  1,o [MPa]

k=9.47

10

1,0E+03

1,0E+04

1,0E+05

1,0E+06

1,0E+07

Cycles to failure N [-]

Fig 7. Fatigue parameters for adhesive and reference SN-curve.

6. Conclusion

In this study, the behavior of multi-material thin sheet connections joined by self-piercing rivets and adhesive under quasi-static and cyclic loads has been investigated. With the insights from the experiments, a new approach for fatigue life estimation of adhesively bonded connections has been developed. Following the main conclusion can be drawn: • Under quasi-static and cyclic loads on hybrid joined thin sheet multi-material connections adhesive bears most of the shear loads. The loads that are applied to the hybrid joined lap shear configuration are much higher than for self-piercing riveted connections while the load range for adhesively bonded connections is similar. The use of a smaller rivet leads to higher static and fatigue strength. A bigger rivet may have negative effects on the strength values under shear loads. For the LS configuration, an estimation of the fatigue life of the structural adhesive should lead to an accurate estimation for the hybrid joined connections as well.