A METHOD TO IDENTIFY THE CRACK CLOSURE AND OPENING IN CYCLIC TEARING TESTS ON FRACTURE MECHANICS SPECIMENS

ABSTRACT To measure crack propagation in compact tension specimen, many methods can be used. The electric drop potential measurement is one of them and allows the detection of crack initiation. In our case, CT specimens, which have been taken from a carbon steel pipe (Tu42C) used in the secondary circuit of French PWR, are employed for cyclic tearing test. The detection of crack closure and crack opening should provide information for energetic analysis. However, the electric signal is unusable due to the cyclic loading. Indeed, because of the clearance between the pin and the specimen, each direction loading change causes a discontinuity in the signal. The roughness of the lips surface or the crack closure during compression loading returns also an unusual signal. Moreover, local measurement is required and there is high strain level around the crack tips, so strain gages are not suitable. Thus, displacement field are measured with digital image correlation and a specific image acquisition is employed. These methods allow a direct measurement of strain fields on the surface of the specimen. Thereby an interpretation of the previous electric signal and the crack opening and closure detection is realizable. Then, F.E. simulation, with non-linear kinematic hardening and node release method, are performed. These simulations allow the check of crack opening and closure detection through the specimen thickness. INTRODUCTION Currently, the analysis and the evaluation of the component integrity are realized by a cyclic J-integral in case of seismic loadings for nuclear application. This integral is calculated with the envelop curve of Load vs CMOD The calculation of the energy dissipated by the fracture for each cycle is our objective in this work. This is the reason why the identification of the different condition of the crack tip is essential in our work. In a first time, we tried the use of classical measurements: the electrical drop potential and strai

Contribution of the introduction of artificial defects by additive manufacturing to the determination of the Kitagawa diagram of Al-Si alloys

International audienceDespite the continuous progress in the additive manufacturing (AM) technologies to improve the quality of the produced parts, the presence of defects induced by the process remains a critical issue for the design of industrial components with respect to fatigue damage. Analytical models such as Kitagawa diagrams represent easy to use tools to predict fatigue strength accounting for the detrimental influence of the defects. They are therefore of great interest from an industrial point of view. The aim of the present work is to evaluate whether artificial defects obtained by placing holes directly into the CAD files of fatigue specimens can be used to establish Kitagawa diagrams, despite some differences in terms of shapes and morphologies between the natural and artificial defects. Two artificial defect geometries with a similar size were studied. For each of these geometries, the experimental fatigue strengths and the real sizes of the critical defects measured from the fracture surfaces were used to determine the parameters of the El-Haddad model. For one of the geometries, the obtained model was able to predict the fatigue strength corresponding to the natural defects, and the associated parameters were found consistent with the literature. The fatigue tests results also highlighted the influence of the defect shape

Chemotherapy may be delivered based on an integrated view of tumour dynamics.

International audienceThe aim here was to explore the potential of pharmacokinetic (PK)/pharmacodynamic (PD) and physiopathological parameters in explaining the primary effects of an anti-cancer treatment that targets cells in a specific cell cycle phase. The authors applied a theoretical multi-scale disease model of tumour growth that integrates cancer processes at the cellular and tissue scales. The mathematical model at the cell level relies on a dynamic description of cell cycle regulation while the model at the tissue level is based on fluid mechanics considerations. Simulations show that the number of target cells oscillates as the tumour grows after a first cycle of chemotherapy. Both treatment effect and tumour growth processes drive these oscillations. Nonetheless, results indicate that parameters related to physiopathological processes may have greater relevance than classical drug-related parameters in determining the efficacy of a chemotherapy treatment protocol. Physiopathological parameters, in particular those related to cell cycle regulation, may be integrated in PK/PD models aimed at optimising the delivery of phase-specific cytotoxic treatments

Anti-factor Xa activity of enoxaparin administered at prophylactic dosage to patients over 75 years old.

International audienceAIMS: Major bleeding complications with low-molecular-weight heparin (LMWH) treatment have been reported both in clinical studies and during postmarketing surveillance. Monitoring of antifactor Xa (anti-Xa) activities is therefore recommended in special populations often predisposed to renal impairment. The PROPHRE.75 study was conducted to estimate the distribution parameters of anti-Xa activity in the elderly. METHODS: PROPHRE.75 was a prospective study of a cohort of consecutive patients aged >75 years and treated with 4000 IU of enoxaparin once daily for venous thromboembolism prophylaxis. Dosing history and measurements of anti-Xa activity in sparse samples were recorded throughout treatment. The covariates included weight, gender, age, renal function, medical history and concomitant medication. Population parameters and interindividual variability were estimated using NONMEM V software. RESULTS: Anti-Xa activity was studied in 189 patients (mean age 82 +/- 5 years, 22% weighing 1.0 IU ml(-1), but this group did not include the sole patient experiencing a major bleed (0.53%). CONCLUSIONS: Systematic monitoring of anti-Xa activity in elderly patients treated with enoxaparin at prophylactic doses does not seem to be necessary to prevent the occurrence of major bleeding