Mechanical behavior of recrystallized Zircaloy-4 under monotonic loading at room temperature: Tests and simplified anisotropic modeling

Mechanical behavior of recrystallized Zircaloy-4 was studied at room temperature in the rolling-transverse plane of a thin sheet. Uniaxial constant elongation rate tests (CERTs) were performed along with creep tests, over a wide range of strain rates. Based on a simplified formulation, different sets of parameters for an anisotropic viscoplastic model were found to fit the stress–strain curves. Notched specimen tensile tests were carried out with a digital image correlation (DIC) technique in order to determine the strain field evolution. From these measurements and the determination of Lankford coefficients, the most consistent model was selected and simulated data were successfully compared with the experimental observations

Simulation of the MANDREL Test

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Expansion due to compression tests for RIA situtations

International audienceThis paper presents new experimental thermo-mechanical tests recently developed in order to understand the behaviour of fuel clads under anisothermal conditions. The experimental setups permitted material testing in complex conditions representative of real RIA loading (high strain and heating rates) coupling simultaneous mechanical and thermal loading. Mechanical properties are studied and compared to isothermal ones. Results showed a clear history effect at low strain rates, this effect seems to disappear at high strain rates due to rapid mechanical loading which limits heating before failure. 2D and 3D FEM are illustrated with applied thermo-mechanical loadings. These numerical simulations allowed us to evaluate the history effect during anisothermal tensile tests using a constitutive law identified on isothermal uniaxial tests

Expansion Due To Compression Tests With Rapid Heating Rate For RIA Situations

International audienceThis paper presents an assessment of the thermo-mechanical behavior of non-irradiated Cold-Worked Stress Relieved (CWSR) Zircaloy-4 nuclear fuel cladding, the first of the three containment barriers for the radioactive matter, under thermo-mechanical loading conditions representative of the first phase of a Reactivity Initiated Accident (RIA) in a nuclear power reactor. During this type of accident, the zirconium alloy fuel cladding tubes may be subjected to Pellet-Cladding Mechanical Interaction (PCMI) due to the thermal expansion of the pellet. Experimental data from past research reactor programs simulating RIAs have shown that the cladding experiences a strain rate of more than 1 s-1 , a heating rate of up to 1000 °C.s-1 , and a variable multiaxial load path. In this study, different kinds of Expansion Due to Compression (EDC) tests with varying strain biaxiality (εzz/εθθ) conditions have been performed in order to study the evolution of the hoop strain at failure. The cladding was heated by a Joule effect heating method in order to produce heating rates greater than 150 °C.s-1. The heating method consists of passing an electric current through a heating element inside a ductile metallic pellet, which in turn is inserted inside the cladding. The electric current heats the pellet, which then heats the cladding via conduction. Once the temperature of the cladding reaches 500°C, the heating element and the pellet are compressed by two rigid pistons. As the pellet is compressed and expands in diameter, a hoop strain is imposed on the cladding specimen. To vary the biaxiality, the ends of the sample are either free or fixed. During the tests, the strain field in the sample is measured using a Digital Image Correlation (DIC) technique, and the temperature field is characterized using a thermal camera and thermocouples

Biaxial expansion due to compression experiments for measuring the failure strain of tubular samples

Abstract The failure strain of a tube is a function of the biaxial strain ratio (axial strain/hoop strain) to which it is subjected. The relationship between failure strain and the strain ratio can be determined experimentally using expansion due to compression tests with a tensile load (EDCT), in which a ductile pellet placed inside the tube is compressed axially so it expands in diameter and imposes a hoop strain on the tube. At the same time, a tensile load on the ends of the tube creates an axial strain. This study investigates the capabilities and limitations of EDCT tests using two devices that allow experiments to be performed on a standard tensile testing machine. The first device applies an axial force on the ends of the sample, and the second device applies an axial displacement. Tests on zirconium alloy tubes confirmed that the failure strain is dependent on the strain ratio and the metallurgical state of the material. EDCT tests can produce a range of strain ratios, but there is an upper limit on the strain ratio that can be obtained, and it is dependent on the plastic behaviour of the sample and the friction conditions between the components

Testing and Modelling Iodine-induced Stress Corrosion Cracking (I-SCC) in Zircaloy alloys

International audienceThe I-SCC behavior of cold-worked stress-relieved (CWSR) Zircaloy-4 was investigated by means of internal pressure tests in both inert and gaseous iodine environments. I-SCC susceptibility was derived from tests on both un-irradiated and neutron-irradiated claddings tubes. Crack propagation rates were obtained from tests on pre-cracked tubes. The internal pressure tests conducted on un-irradiated cold-worked stress-relieved Zircaloy-4 cladding tubes in an iodine vapor environment were used to investigate the influence of loading mode (either constant pressure tests, constant circumferential strain rate tests, or constant circumferential strain tests) and test temperature (320DC to 488DC) on the I-SCC process. The experimental results obtained with different loading modes indicated that there is an apparent threshold hoop stress, below which I-SCC does not occur.The tests were simulated by finite element models using a specific viscoplastic constitutive equation. The I-SCC initiation and time-to-failure predictions were modelled by a Kachanov's damage law written with a hoop stress threshold. In the simulations, the Kachanov's law can be used in post-treatment of calculations or coupled with the viscoplastic constitutive equation for the cladding in order to simulate the initiation and the propagation of the I-SCC crack. The coupling was implemented in the finite-element code CAST3M

Social Validation of Solutions in the Context of Online Communities

Part 4: Computational Intelligence: Machine LearningInternational audienceOnline Communities are considered as a new organizational structure that allows individuals and groups of persons to collaborate and share their knowledge and experiences. These members need technological support in order to facilitate their learning activities (e.g. during a problem solving process).We address in this paper the problem of social validation, our aim being to support members of Online Communities of Learners to validate the proposed solutions. Our approach is based on the members’ evaluations: we apply three machine learning techniques, namely a Genetic Algorithm, Artificial Neural Networks and the Naïve Bayes approach. The main objective is to determine a validity rating of a given solution. A preliminary experimentation of our approach within a Community of Learners whose main objective is to collaboratively learn the Java language shows that Neural Networks represent the most suitable approach in this context

High level of soluble programmed cell death ligand 1 in blood impacts overall survival in aggressive diffuse large B-Cell lymphoma: results from a french multicenter clinical trial.

International audienceThe dosage of soluble programmed cell death ligand 1 (sPD-L1) protein in the blood of adults with cancer has never been performed in a prospective patient cohort. We evaluated the clinical impact of sPD-L1 level measured at the time of diagnosis for newly diagnosed DLBCL. Soluble PD-L1 was measured in the plasma of 288 patients enrolled in a multicenter, randomized phase III trial that compared R-high-dose chemotherapy to R-CHOP. The median follow-up was 41.4 months. A cut-off of 1.52 ng/ml of PD-L1 level was determined and related to overall survival (OS). Patients with elevated sPD-L1 experienced a poorer prognosis with a three-year OS of 76% versus 89% (P<0.001). Considering clinical characteristics, the multivariate analysis retained this biomarker besides bone marrow involvement and abnormal lymphocyte-monocyte score as independently related to poor outcome. sPD-L1 was detectable in the plasma and not in the serum, found elevated in patients at diagnosis compared to healthy subjects and its level dropped back to normal value after CR. The intention-to-treat analysis showed that elevated sPD-L1 was associated with a poorer prognosis for patients randomized within the R-CHOP arm (P<0.001). Plasma PD-L1 protein is a potent predicting biomarker in DLBCL and may indicate usefulness of alternative therapeutic strategies using PD1 axis inhibitors

Point-Cloud Shape Retrieval of Non-Rigid Toys

In this paper, we present the results of the SHREC'17 Track: Point-Cloud Shape Retrieval of Non-Rigid Toys. The aim of this track is to create a fair benchmark to evaluate the performance of methods on the non-rigid point-cloud shape retrieval problem. The database used in this task contains 100 3D point-cloud models which are classified into 10 different categories. All point clouds were generated by scanning each one of the models in their final poses using a 3D scanner, i.e., all models have been articulated before scanned. The retrieval performance is evaluated using seven commonly-used statistics (PR-plot, NN, FT, ST, E-measure, DCG, mAP). In total, there are 8 groups and 31 submissions taking part of this contest. The evaluation results shown by this work suggest that researchers are in the right way towards shape descriptors which can capture the main characteristics of 3D models, however, more tests still need to be made, since this is the first time we compare non-rigid signatures for point-cloud shape retrieval