Time to failure prediction in rubber components subjected to thermal ageing: A combined approach based upon the intrinsic defect concept and the fracture mechanics

In this contribution, we attempt to derive a tool allowing the prediction of the stretch ratioat failure in rubber components subjected to thermal ageing. To achieve this goal, the mainidea is to combine the fracture mechanics approach and the intrinsic defect concept. Using an accelerated ageing procedure for an Ethylene–Propylene–Diene Monomer (EPDM), it is first shown that the average molar mass of the elastically active chains (i.e. between crosslinks) can be used as the main indicator of the macromolecular network degradation. Byintroducing the time–temperature equivalence principle, a shift factor obeying to an Arrhenius law is derived, and master curves are built as well for the average molar mass as for the ultimate mechanical properties. Fracture mechanics tests are also achieved and the square root dependence of the fracture energy with the average molar mass is pointed out. Moreover, it is shown that the mechanical response could be approximated by the phantom network theory, which allows to relate the strain energy density function to the average molar mass. Assuming that the fracture of a smooth specimen is the consequence of a virtual intrinsic defect whose the size can be easily estimated, the stretch ratio at break can be therefore computed for any thermal ageing condition. The estimated values are found in a very nice agreement with EPDM experimental data, making this approach a useful tool when designing rubber components for moderate to high temperature environments

On Ternary FF-manifold Algebras and their Representations

We introduce a notion of ternary $F$-manifold algebras which is a generalization of $F$-manifold algebras. We study representation theory of ternary $F$-manifold algebras. In particular, we introduce a notion of dual representation which requires additional conditions similar to the binary case. We then establish a notion of a coherence ternary $F$-manifold algebra. Moreover, we investigate the construction of ternary $F$-manifold algebras using $F$-manifold algebras. Furthermore, we introduce and investigate a notion of a relative Rota-Baxter operator with respect to a representation and use it to construct ternary pre-$F$-manifold algebras.Comment: Comments are welcome. arXiv admin note: text overlap with arXiv:2102.05595; text overlap with arXiv:2002.10238 by other author

La conductivité électro-magnétique : application au suivi de la salinité des sols des périmètres irrigués de Tunisie

Le but de la mission était de présenter une méthode d'évaluation de la salinité des sols par conductivimétrie électromagnétique et de tester dans les conditions de la Tunisie son application à la cartographie de la salure des périmètres irrigués du territoire. La présentation de l'appareillage a d'abord fait l'objet d'un séminaire à Sidi Thabet, organisé par la Direction des Sols. Puis quatre études de cas représentatifs ont été réalisées sur le terrain avec la collaboration des ingénieurs des laboratoires d'arrondissements de la Direction des Sols : périmètre de Sidi Saad (Kairouan), périmètre de Zelba (Mahdia), périmètre de Hazeg (Sfax), périmètre de Sebala ben Amar (Tunis). Au total plus de 700 mesures ont été réalisées au cours de la tournée soit sur la totalité de chaque périmètre, soit sur des parcelles représentatives (cf rapport technique). La facilité de mise en oeuvre de l'appareillage par rapport aux mesures habituelles avec prélèvements, la rapidité de la mesure qui est immédiate, la sensibilité de l'appareil même aux faibles salinités, l'appréhension d'une salinité globale permettant de s'affranchir du problème de variabilité spatiale, font de cette méthodologie une technique bien adaptée au suivi simultané d'un grand nombre de périmètres irrigués dans le cadre d'un réseau national de surveillance de la salinité des sols. (Résumé d'auteur

Reperfusion therapy in renal dysfunction patients presenting with STEMI: Which is better in the Tunisian context?

BackgroundPatients with renal insufficiency experience worse prognosis after STEMI. Current guidelines do not clearly draw specific strategies for renal dysfunction (RD) patients, and most clinical trials exclude them from the study population.Aim of the studyTo compare primary PCI (PPCI) and thrombolysis (using Strepokinase) results as well as in-hospital mortality after successful reperfusion between patients with or without RD.MethodsFrom January 1995 to October 2011, 1388 patients admitted for STEMI were enrolled in the MIRAMI (MonastIR’s Acute Myocardial Infarction) registry. Two reperfusion groups were identified: PPCI (315 patients) and thrombolysis (379 patients). Patients who underwent rescue PCI were excluded. Due to lacking clearance data, we used a serum creatinine level >130μmol/l to define RD patients. We compared in each reperfusion group: (1) The success of revascularization (TIMI III flow restoring with <20% residual stenosis after PPCI, pain relief with ST regression >50% 60min after thrombolysis) and (2) the in-hospital mortality rate after reperfusion success between the RD patients (RD+) and normal renal function patients (RD−).ResultsNinety patients (13%) had RD, 50% of which underwent PPCI, and 50% received thrombolytics. Among RD+ and RD- groups, baseline characteristics were similar between the two reperfusion groups.In the PPCI group, although TIMI flow was similar before angioplasty (p=0.82), TIMI III restoring was significantly lower in the RD+ group (78.6% vs 91.8%, p=0.013). Suboptimal result was also higher in the RD+ group (13.6% vs 2.7%, p<0.001), but ST regression after TIMI III achievement was similar in the 2 groups (p=0.43) reflecting probably no microvascular damage.In the thrombolysis group, successful reperfusion was also significantly lower when RD exists (58% vs 74%, p=0.03).After successful reperfusion, in-hospital mortality is higher among RD+ patients in the PPCI group (33.3% vs 4.3%, p<0.001), whereas it is similar after successful thrombolysis (2.6% vs 0%, p=0.42).ConclusionRD reduces either PPCI or thrombolysis success, with no proven microvascular damage after PPCI. In-hospital prognosis is however worse in RD group only after successful PPCI, but not after successful Streptokinase thrombolysis

Micromechanical based model for predicting aged rubber fracture properties

Environmental aging induces a slow and irreversible alteration of the rubber material’s macromolecular network. This alteration is triggered by two mechanisms which act at the microscale: crosslinking and chain scission. While crosslinking induces an early hardening of the material, chain scission leads to the occurrence of dangling chains responsible of the damage at the macromolecular scale. Consequently, the mechanical behavior as well as the fracture properties are affected. In this work, the effect of aging on the mechanical behavior up to fracture of elastomeric materials and the evolution of their fracture properties are first experimentally investigated. Further, a modeling attempt using an approach based upon a micro-mechanical but physical description of the aging mechanisms is proposed to predict the mechanical and fracture properties evolution of aged elastomeric materials. The proposed micro-mechanical model incorporates the concepts of residual stretch associated with the crosslinking mechanism and a so-called “healthy” elastic active chain (EAC) density associated with chain scission mechanism. The validity of the proposed approach is assessed using a wide set of experimental data either generated by the authors or available in the literature

Association entre la dégénérescence maculaire liée à l’âge et les parodontites

Purpose: To evaluate the association between age-related macular degeneration (AMD) and periodontal disease, two frequent conditions in the elderly, with some risk factors in common. Methods: Single center, pilot, case-control study performed in a center specialized in the diagnosis and management of AMD. Periodontal status was evaluated in 43 AMD patients and 19 controls. Fundus examination and a complete periodontal examination were performed in all subjects. Results: AMD patients have a greater percentage of 3–4 mm clinical attachment loss compared to controls (47% vs. 38%, [P = 0.039]). However, no significant difference was found between the groups with regard to the prevalence of severe periodontitis. Conclusions: These results suggest an association between AMD and attachment loss characteristic of periodontal disease and support the need for larger prospective studies to elucidate the relationships between these 2 highly prevalent and potentially severe diseases

Monitoring and lifetime prediction of pvc cables: methodology by multiscale and multidisciplinary approach

Monitoring of the PVC cables as well as the prediction of their residual lifetime are important issues for the maintenance of the French nuclear power plants (NPPs). To date, the unanimously end of life criterion admitted for these cables is a 50% value of elongation at break and, to our knowledge, only destructive tests give access to this parameter. This study reports a relationship between elongation at break of the PVC and their plasticizer content. This correlation opens the door to a monitoring directly on site or by micro sampling since all classic laboratory techniques able to measure this content become ways to judge the condition of the PVC sheaths and insulators. In addition, this study demonstrates the feasibility of prediction of industrial PVC behavior changes. This model, adapted to the case of thin films, involved tools of chemical kinetics and the implementation of a constitutive model

Sensitivity of Melt Pool Dimensions and Keyhole to Laser Beam Diameter

The laser powder bed fusion process has witnessed a huge interest in recent years since it has the potential to produce challenging shapes in a broad range of applications. The process parameters have a considerable effect on melt pool size and on the development of defect porosity. This paper predicts numerically the effect of a large range of laser beam diameters on melt pool dimensions and on the occurrence of porosity defects such as keyhole. A series of single beads of Inconel IN625 was made using various combinations of beam diameters, scan speeds, and laser powers. The use of a large diameter was more suitable rather than a small diameter as it ensures a large and shallow heat affected zone, thus decreasing the development of the keyhole defect. Our numerical results correlate satisfactorily with experimental finding from literature