PSI - Issue 19

Helen Bartsch et al. / Procedia Structural Integrity 19 (2019) 395–404 Helen Bartsch, Benno Hoffmeister, Markus Feldmann / Structural Integrity Procedia 00 (2019) 000 – 000

400

6

outlining the high amount auf bending in the bolts in these kind of specimens.

200

1000

Bending Tension

150

100 Stress range ∆σ [ N/mm²]

100

50

Small-scale tests LA Regression line m = 3 Deisgn S-N-curve m = 3

0

10

0 25 Stress increase in bolt [MPa]

50

75

100

1.E+07 ∙ 10 7

1.E+04 ∙ 1 4

1.E+05

1.E+06

1 ∙ 10 6

1 ∙ 10 5

Tension force on specimen [kN]

Number of cycles to failure N [-]

Fig. 5. Test results and design S-N curves of series LA and bolt stress diagram of one bolt in an LA specimen (from left to right)

4. Numerical simulations of experimental investigations In order to verify the numerical models for the investigation of influencing parameters, the experimental tests have been recalculated using the FE software A BAQUS , version 6.14. For the application of the effective notch stress concept the submodel technique is used. A global model is used to recalculate the connection and a far smaller submodel only depicts the relevant areas for fatigue failure in the welds, allowing for a finer discretization. In both models, linear 3D-elements with reduced integration (C3D8R) have been applied in a discretization which becomes continuously finer in relevant areas. The IIW recommendations for sizes of linear elements along and across the notch surface are smaller than r ref / 6 in filleted areas. For a reference radius r ref = 1 mm as used in the present study, mesh sizes of less than 0.16 mm have been applied (Hobbacher, 2008). Fig. 6 presents the satisfactory accordance between experimentally and numerically obtained stress ranges measured by strain gauges (SG) in the beam (SG2), the end plate (SG3 and SG4) and in two prestressed bolts in the tension area of the connection (SG5 and SG6).

600

20 40 60

SG5 SG6

550

SG5-FE SG6-FE

-60 -40 -20 0 Stress range ∆σ [MPa]

500

SG2 SG3 SG4

450

SG2-FE SG3-FE SG4-FE

Stress in bolt [MPa]

400

0

0.0282 ,5

0.0564 1,0

0

0.0285 0,5

0.057 1,0

Cycles [-]

Cycles [-]

Fig. 6. Comparison of experimental and numerical stress ranges in endplate, beam and bolts by strain gauges on one B specimens

Additionally to the comparison of stresses by means of the global model, Fig. 7 presents the failure location of test and simulation of large-scale specimen B2. The left hand side presents the effective notch stress ranges at the four