Mechanical cyclic behaviour of 316L welded joint

To take into account the reduced fatigue strength of welded joints, a reduction factor on the fatigue curves was introduced into the RCC-MR French nuclear design and construction code. To better assess this factor, a previous work on large plates showed that the mechanical behaviour of a welded assembly is influenced by the geometry of the weld and by the interaction of the different cyclic plastic behaviour of the two materials: base metal (BM) and weld metal (WM). A new program was performed consisting in tests on butt welded pipe connections (4 points bending), fatigue tests on uniaxial specimens (uniaxial tensile-compressive load) and finite elements calculations. The uniaxial fatigue tests have been carried out on specimens extracted form a butt welded pipe connection manly at 600 °C. Some tests have been carried out at ambient temperature and have permit to realise some ESPI measurements to have a better knowledge of the strain gradients at some stage of the fatigue tests. But the use of ESPI sensor requires some experimental conditions which are hardly adaptable to real fatigue test conditions. Nevertheless, by using concurrently some classic extensometers sensors, new observations can be done on the fatigue specimens behaviour.