PSI - Issue 18

9

Benjamin Möller et al. / Procedia Structural Integrity 18 (2019) 556–569 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Analogous to the adapter V1, the failure location of adapter V2 is at the first weld seams with respect to the steel sheet, i.e. the lower welds in the fatigue test and Fig. 8. As was the case for lap joints, cracks start at the root of the weld seam and propagate through the aluminium sheet.

Fig. 8. Fatigue failure of laser beam welded adapters V2 at load amplitudes of (a) F a = 4.0 kN, (b) F a = 5.0 kN and (c) F a = 6.0 kN as well as (d) a typical fatigue fracture surface In the case of explosive welded adapter specimens, just a small amount of specimens were available, so that fatigue test results give a rough estimation of the fatigue strength and Wöhler curve. However, polished flat specimens are close to characteristic base material values, since specimens merely failed due to plastification and necking of the unalloyed aluminium AlSi99, as shown by specimen Ex_05 and Ex_04 in Fig. 9. Failure due to crack initiation in the unalloyed aluminium (Ex_02) and in the conventional aluminium weld (Ex_01), which is necessary to produce the specimen, has also been found. The Wöhler curve on the basis of six fatigue test results is characterised by the knee point of F a,k ( N k = 2ꞏ10 6 ) = 6.03 kN, a slope k = 16.8 and a scatter T F = 1:1.13. Using the cross section of the unalloyed aluminium of 105.5 mm² for the calculation of the nominal stress amplitude, a fatigue strength at the knee point of  a,n,k ( N k = 2ꞏ10 6 ) = 56.9 MPa is found.

Fig. 9. Fatigue test results and evaluated Wöhler curves of explosive welded adapter specimens