Hydrogen - Plasticity interactions : modelling and experiments in hydrogenated nickel alloys

International audienceThe effect of hydrogen on tensile tests of nickel and binary nickel - 16 wt. % chromium is analysed in terms of solute drag phenomenon. Static Strain Ageing experiments are used to measure the saturated dislocation pinning force as a function of the H concentration. First order hydrogen - dislocation interactions causes a shielding of the pair interactions between edge dislocations. The influence of this screening effect is analytically evaluated on the selfenergy and line tension of curved dislocations, the critical force for the expansion of a dislocation loop and the dissociation mechanism. These results are used to interpret experimental results on the plastic flow of hydrogen-charged nickel single crystals oriented for easy glide. This study illustrates the mechanisms of H - dislocation interactions and their consequences on the different contributions of hydrogen to the flow stress of nickel

Experimental and numerical analysis of hydrogen interaction with plastic strain in a high strength steel

8 pagesInternational audienceCyclic loading tests were performed on micro-notched samples of high-strength steel S690QT in air and under cathodic polarisation in a saline solution. These specimens were modelled and their behaviour simulated by finite elements calculations with a combined nonlinear isotropic-kinematic hardening constitutive law. This model can simulate cyclic softening and ratcheting effect of the high-strength steel. Stress and strain fields in the vicinity of the notch-tip were calculated. Results show that a strong dependence of the crack initiation with plastic strain accumulation. Hydrogen assisted cracking mechanism is discussed based on arrangements of dislocations structures

Effects of Cyclic Plastic Strain on Hydrogen Environment Assisted Cracking in High-Strength Steel

8 pagesInternational audienceCyclic loading tests were performed on micro-notched samples of high-strength steel S690QL (standard EN 10137-2) in air and under cathodic polarization in a saline solution. These specimens were modeled and their behavior simulated by finite elements calculations with a combined nonlinear isotropic-kinematic hardening constitutive law. This model can simulate cyclic softening and ratcheting effect of the high-strength steel. Stress and strain fields in the vicinity of the notch-tip were calculated. Results show a strong dependence of the crack initiation with plastic strain accumulation. Hydrogen assisted cracking mechanism is discussed based on arrangements of dislocations structures

Experimental investigations of internal and effective stresses during fatigue loading of high-strength steel

International audienceLow cycle fatigue tests are performed on a high strength tempered martensitic steel at different plastic strain amplitudes at room temperature. Internal and effective components of the flow stress are analyzed using Handfield and Dickson's method. The internal stress is affected by the plastic strain amplitude. Conversely, the evolution of the athermal component of the effective stress with the number of cycles is independent of the plastic strain amplitude. The thermal part of the effective stress increases with the plastic strain amplitude, but remains constant with plastic strain accumulation. Microstructural changes in the cyclically deformed material are investigated by means of transmission electronic mycroscopy and X-Ray characterizations. Internal and effective stress evolutions are discussed based on these observation