Characterization and modeling of void nucleation by interface decohesion in dual phase steels

International audienceIn situ tensile tests have been carried out during X-ray microtomography imaging of dual phase steels. Void nucleation has been quantified as a function of strain and triaxiality using the obtained three-dimensional images. The Argon criterion of decohesion has been used in a model for nucleation in the case where martensite plays the role of inclusions. This criterion has been modified to include the local stress field and the effect of kinematic hardening present in such a heterogeneous material

Comparison of Damage Evolution in Different Steels by Means of 3D X Ray Tomography

2nd International Conference on High Manganese Steels (HMnS), Aachen, GERMANY, 2014International audienceIn this paper, the damage behavior of three different steels is studied by the means of 3D X ray tomography in tension: a Fe22Mn0.6C austenitic TWIP steel, a 316 L austenitic stainless steel, and an interstitial-free (IF) ferritic one. The comparison gives a better insight into the damage of the twinning-induced plasticity steel (Fe22Mn0.6C), which is a promising one due its very high mechanical properties. It is shown that the damage process of this type of steel involves not only an important nucleation of small voids but also a large growth of the biggest cavities. This last conclusion is true even if a constant macroscopical triaxiality is observed

Experimental investigation of void coalescence in a dual phase steel using X-ray tomography

International audienceIn situ tensile tests were carried out during X-ray microtomography imaging of a smooth and a notched specimen of dual phase steel. The void coalescence was first qualitatively observed and quantitative data concerning this damage step was then acquired. The void coalescence criteria of Brown and Embury and of Thomason were then tested against the experimental data at both the macroscopic and local levels. Although macroscopic implementation of the criteria gave acceptable results, the local approach was probably closest to the real nature of void coalescence, because it takes into account local coalescence events observed experimentally before final fracture. The correlation between actual coalescing couples of cavities and local implementation of the two criteria showed that the Thomason criterion is probably the best adapted to predict the local coalescence events in the case of the material studied

Validation of void growth models using X-ray microtomography characterization of damage in dual phase steels

In situ tensile tests were carried out during X-ray microtomography imaging of three steels: a single phase ferritic steel, a dual phase steel and a fully martensitic steel. Cavity growth was first quantified in the different samples as a function of strain and triaxiality. The Rice and Tracey model, a version of this model corrected by Huang, and a third version accounting for the cavity shape were then used to predict void growth evolution. It was experimentally demonstrated that for steels Huang’s correction is a real improvement to the original Rice and Tracey model. Some differences in the void growth kinetic are discussed, accounting for the microstructure and the mechanical behavior of each steel

Non-destructive 3-D reconstruction of the martensitic phase in a dual-phase steel using synchrotron holotomography

International audienceThis paper presents the first non-destructive three-dimensional characterization of a dual-phase ferrite/martensite steel. The martensitic phase was imaged using the holotomography technique based on phase contrast. The visualization and the study of the volume distribution of the martensitic phase confirmed that the martensite forms a partial network around the ferritic grains. The simultaneous visualization of ductile damage induced by tensile deformation using the same technique was also performed, but proved to be more challenging

Outcome of anti-PL12 positive patients with antisynthetase syndrome.[Profil évolutif du syndrome des antisynthétases avec anticorps anti-PL12]

International audienceOBJECTIVES: The aim of the present study was to assess the outcome in anti-PL12 patients with antisynthetase syndrome (ASS). METHODS: The medical records of anti-PL12 (n=5) patients with ASS were retrospectively analyzed without prior selection. To exclude false-positive patients, we included patients who were successively tested positive for anti-PL12 antibody at least twice by immunodot and/or Western blot. RESULTS: Anti-PL12 patients experienced: myositis (n=2), Raynaud's phenomenon (n=2), mechanic's hands (n=1), joint impairment (n=4), digestive involvement (n=2), and interstitial lung disease (ILD) (n=4). The two patients with myositis exhibited deterioration of muscle manifestations despite therapy. As regards outcome of ILD, patients developed resolution (n=1), stabilization (n=1) or deterioration (n=2) of pulmonary status. One patient died of pyogenic pneumonia. CONCLUSION: Our series underscores that the presence of anti-PL12 antibody is associated with a particular phenotype of ASS characterized by: (1) less frequent although severe/steroid refractory myositis; (2) less common mechanic's hands and calcinosis cutis; (3) both frequent and severe ILD. Taken together, our findings suggest that PM/DM patients should routinely undergo the search for anti-PL12 antibody as this autoantibody appears to impact patients' prognosis. Furthermore, ILD patients with anti-PL12 antibody should routinely undergo clinical screening for underlying ASS

Application of an Advanced GTN Model

The present contribution consists of implementing an advanced GTN damage model as a "User Material subroutine" in the Abaqus FE code. This damage model is based on specific nucleation and growth laws.This model is applied to the prediction of the damage evolution and the stress state in notched specimens made of dual phase steel. By comparing numerical predictions with experimental results based on high-resolution X-ray absorption tomography, the numericalapproach was improved and validate

Numerical investigation and experimental validation of physically-based advanced GTN model for DP steels

This numerical investigation of an advanced Gurson-Tvergaard-Needleman (GTN) model is an extension of the original work of [Ben Bettaieb, M., Lemoine, X., Bouaziz, O., Habraken, A.-M., Duchêne, L., Numerical modeling of damage evolution of DP steels on the basis of X-ray tomography measurements, Mechanics of Materials 43 (2011) 139-156]. The current damage model extends the previous version by integrating the three damage mechanisms: nucleation, growth and coalescence of voids. Physically-based void nucleation and growth laws are considered, including an effect of the kinematic hardening