The fatigue strength of steel welded joints has been obtained by tests in which the maximum applied stress, sigmamax, was kept constant and equal to the yield strength, sigmay, (which is equivalent to the tensile residual stress that exists in real welded structures) while the minimum stress was changed randomly. The equivalent range of applied stress, calculated by neglecting the stress cycles for which amplitudes were below the fatigue limit that was determined from constant amplitude tests, can be a useful design parameter. This is confirmed because Miner's rule applies for all the sigmamax=sigmay tests reported here and which simulate the actual stress condition of welded structures and gives the lowest S-N curve. The material used in this experiment was a JIS SPV50 steel with (in wt.%) 0,12 C, 0,23 Si, 1,23 Mn, 0,02 P, 0,005 S, 0,02 Ni, 0,01 Cr, 0,11 Mo and 0,02 V. The yield strength of this steel was 579 MPa, the tensile strength 628 MPa and the elongation 40 %. The Rayleigh spectrum was used for the random stress pattern. The following conclusions were obtained. In sigmamax=sigmay tests, the slope of the S-N relationship was 3, and the fatigue limit was 95 MPa for the constant amplitude sigmamax=sigmay tests. Miner's rule was valid for the sigmamax=sigmay test even when spike stresses were applied, this test simulating the actual stress condition of welded structures. That is, the fatigue limit under the random loading could be evaluated from constant amplitude tests. In R=0 tests, Miner's summation gave rather short predicted fatigue lives when spike stresses were not applied, and gave rather longer predicted fatigue lives when spike stresses were applied.
Fatigue strength of butt-welded joints under constant maximum stress and random minimum stress conditions
Ermüdungsfestigkeit von Stumpfschweißverbindungen bei konstanter Maximal- und unregelmäßiger Minimalspannung
Fatigue and Fracture of Engineering Materials and Structures ; 19 , 2/3 ; 265-275
1996
11 Seiten, 11 Bilder, 1 Tabelle, 15 Quellen
Article (Journal)
English
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