Fatigue Equivalent Stress State Approach Validation in Non-conservative Criteria: a Comparative Study

Abstract This paper is concerned with the fatigue prediction models for estimating the multiaxial fatigue limit. An equivalent loading approach with zero out-of-phase angles intended for fatigue limit evaluation under multiaxial loading is used. Based on experimental data found in literatures, the equivalent stress is validated in Crossland and Sines criteria and predictions compared to the predictions of existing multiaxial fatigue; results over 87 experimental items show that the equivalent stress approach is very efficient

Identification des paramètres d'anisotropie des tôles d'aluminium 1200 et 1050 produites au Cameroun

L'anisotropie des tôles d'aluminium est induite par le procédé de laminage, elle entraîne des défauts lors de l'opération de mise en forme de pièces par emboutissage. Le travail présenté dans cet article est une étude phénoménologique de cette anisotropie sur des tôles d'aluminium produites à SOCATRAL, au Cameroun. L'objectif est de mettre en évidence l'influence des différents paramètres en vue de mieux contrôler l'évolution de l'anisotropie. Au cours du laminage de l'aluminium, tous les paramètres susceptibles d'avoir une incidence sur la répartition des constituants insolubles dans le métal et sur la déformation des grains du métal ont un effet considérable sur l'anisotropie. Deux nuances d'aluminium (1200 et 1050) ont fait l'objet de cette étude pour laquelle tous les paramètres sont étudiés en utilisant une méthode statistique (SPC) à partir des banques de données de fabrication. Pour chaque paramètre identifié, les courbes de l'évolution de l'anisotropie sont présentées pour différentes épaisseurs de tôle. Les résultats obtenus permettront par la suite d'optimiser l'indice d'anisotropie afin de réduire les défauts à l'emboutissage

Multivariate Statistical and Hydrochemical Analysis of Drinking Water Resources in Northern Cameroon Watersheds

Watershed pollution by natural and anthropogenic activities remains a global challenge that requires careful and prompt attention. So, identifying possible pollution sources and studying the hydrochemistry of water resources would positively affect human health, especially in resource-limited communities and their economy. Water samples were collected during the rainy season in the North (R-NO) and Adamawa (R-AD) Region communities of Cameroon and assessed for physicochemical parameters using standard methods. The data were analysed using multivariate statistical and hydrochemical methods. Principal component analysis (PCA) retained seven and six principal components explaining 77.65% (R-NO) and 72.24% (R-AD) of the total variance, respectively. The drinking water sources assessed were highly, moderately, and lightly contaminated with turbidity, PO43−, Al3+, Fe2+, Mn2+, NH4+, NO3−, NO2−, and electrical conductivity (EC) from surface runoff and soil erosion sources. PCA and factor analysis (PCA/FA) revealed two main groups, distinguished by natural and anthropogenic sources, responsible for water quality variations. Hierarchical cluster analysis (HCA) grouped sampling sites into three clusters: low, moderate, and high pollution areas in the R-NO and unpolluted, low, and moderate pollution areas in the R-AD. The order of dominant cations was Mg2+ > Ca2+ > K+ and HCO3− > Cl− > SO42− for anions. Based on Piper diagram classification, watersheds studied were predominated by the Mg-Ca-HCO3 water type in 85% (R-NO) and 79% (R-AD) of water samples. The chemical composition of shallow and deep water was dominantly controlled by the dissolution of silicates and carbonate, reverse ion exchange, and precipitation of calcite. These results reveal that diffuse pollution predominantly impacted the study sites during the rainy season, and this should be the focus of policymakers when planning and implementing measures to protect drinking water sources, human health, and reduce water treatment costs

Antiproliferative and cytotoxic secondary metabolites from fruits of <i>Leplaea mayombensis</i>

<p>Two new <i>seco</i>-lanostane-type triterpenes, named mayomlactones A (<b>1</b>) and B (<b>2</b>) were isolated from the fruits of <i>Leplaea mayombensis</i> together with 10 known compounds (<b>3</b>–<b>12</b>). Structures of the new compounds were elucidated by extensive spectroscopic studies. Except compounds <b>11</b> and <b>12</b>, all the other chemical compounds are newly reported from <i>Leplaea</i> genus. From the results of this investigation, compounds <b>1</b>–<b>10</b> were examined for antiproliferative activity against HeLa cells as well as cytotoxicity against 3T3 cell line. Compounds <b>3</b> and <b>4</b> showed moderate antiproliferative activity with IC₅₀ values of 10.4 ± 0.1 and 18.6 ± 0.2 μM, respectively. On the other hand, compounds <b>1</b>, <b>4</b> and <b>9</b> showed weak cytotoxicity with IC₅₀ values 44.1 ± 0.5, 55.8 ± 0.7 and 55.1 ± 0.5 μM. Overall, none of the tested compounds showed good selectivity (SI ranging from 0.51 to 3.06) but high toxicity against the 3T3 cell line.</p