Issue 9

C. M. Sonsino, Frattura ed Integrità Strutturale, 9 (2009) 3-12; DOI: 10.3221/IGF-ESIS.09.01 9 CA: Constant amplitude loading, VA Variable amplitude loading *) retested run-out (brace 1), **) retested run-out (brace 2) No. Load  F [MN] Measured hot- spot stress  hs [MPa] Local stress r f = 1 mm  loc,v.Mises = 3.14  hs [MPa] N 1 (a  1 mm, 2l  20mm) N 3 (break- through) Site of crack initiation  (°) Brace Calculated  hs [MPa] Calculated  loc,v.Mises [MPa] 6, CA 1.5 150 471 1.60 10 5 3.95 10 5 90 95 1 163.5 514 7 * ) , CA 1.0 108 339 6.00 10 5 1.92 10 6 105 1 109 343 7 **) , CA 1.0 97 305 8.05 10 5 1.92 10 6 270 1 109 343 1, VA 3.0 346 1086 5.93 10 5 2.22 10 6 90 2 327 1028 10, VA 3.0 294 920 8.00 10 5 3.96 10 6 225 1 327 1028 13, VA 1.7 218 685 7.42 10 6 1.46 10 7 120 235 1 185 583 3, VA 2.0 208 653 2.82 10 6 1.29 10 7 120 135 1, 2 218 685 2, VA 2.0 205 644 1.20 10 6 6.30 10 6 90 1 218 685 Table 2 : Test and calculation results obtained with welded K-nodes. Assuming the soundness of quality of the welds, of the fatigue data and of the calculated local stresses provided, the comparison of the calculated and experimental fatigue lives will reveal the accuracy and reliability of the three concepts. C OMPARISON OF CALCULATIONS WITH EXPERIMENTS ACCORDING TO SELECTED CONCEPTS he assessments are carried out with calculated hot-spot and local notch stresses. As the differences between the real and calculated stresses are tolerable, the consideration of the real stresses (which are not known in the design stage) will not change the results, which will be discussed in the following. The assessment by the hot-spot concept is displayed in Fig. 14 and by the notch stress concept in Fig. 15. The calculated fatigue life curves for both concepts, which are valid for the failure criterion total rupture and P s = 97.7 %, cover all results for the comparable failure criterion break-through. Even the results for the criterion crack initiation of a crack with the depth of a  1.00 mm are on the safe side with one exception. The curves with P s = 97.7 % for the experimental results are derived from the experimental mean curves with P s = 50 % using the factor j = 1.37 as explained in Fig. 8. As the insertion of the particular experimental curves with P s = 97.7 % into the Figs. 14 and 15 would overload them, they are not presented here but used later for the comparison of the calculated fatigue lives with the experimental ones. Figure 14 : Application of the hot-spot concept for the evaluation of welded K-nodes. T