No abstract

Duplex and super-duplex stainless steels are increasingly used in applications where good fatigue strength is demanded in addition to corrosion resistance. In this research work, the fatigue strength of duplex and super-duplex steels was investigated experimentally, using standard fatigue strength assessment methods, and theoretically, using conventional design methods and a novel effective notch stress based procedure, the 4R method. The experimental tests included testing of welded joints with and without post-weld treatment. The experimental results were compared with the 4R method. The test results indicated good fatigue strength properties for both materials in the as-welded (ASW) condition, and postweld treatment by high-frequency impact (HFMI)-treatment improved the fatigue resistance at low stress ratios. No improvement, however, was found in the case of high mean stress of the applied load. The results obtained by the theoretical investigation agreed quite well with the experimental results.

No abstract

This study investigated the residual strength of a precracked cold‐formed rectangular hollow section made of novel ultra‐high‐strength steel. The primary goal was to experimentally discover the residual strength of the structure when used in low temperature service conditions. The secondary goal was to predict the residual strength by using a J‐integral approach with nonlinear finite element calculations and to compare these predictions with measured results. The experimental tests were carried out with a beam in four‐point bending loading. The test specimens were taken from a cold‐formed rectangular hollow section fabricated from direct quenched (untempered) ultra‐high‐strength steel S960 QC omitting the annealing in the fabrication process. The tests for final failure were carried out at −40 °C, with the exception of the first pilot test. There were two kinds of tests: (1) the beam was cyclically loaded until the final fracture or the fatigue precrack was first introduced and (2) the specimen was then subjected to a quasistatic bending loading condition until it failed. The new experimental results matched well with our predictions, and both confirmed the high toughness of ultra‐high‐strength steel in beam construction studied, even at a low ambient temperature.

Kasvavan taivutusjännitysosuuden (degree of bending, DOB) on ajateltu parantavan merkittävästi väsymiskestävyyttä perinteisessä jännitys-kestoikä (S-N) laskennassa. Tässä tutkimuksessa tarkasteltiin hitsattujen liitosten väsymistä kalvo- ja taivutuskuormituksessa tehollisen lovijännityksen menetelmällä ja lineaarielastisella murtumismekaniikalla. Tutkimuksen tuloksena saatiin selville, että liitoksen symmetrisyydestä määräytyen ulkoisen kuormituksen taivutusjännitys voi aiheuttaa merkittävästi korkeampia lovijännityksiä hitsin rajaviivalle kuin vastaavansuuruinen kalvojännitys.