Modeling of Damage Interaction in Fatigue Relaxation for Long-Term Life Prediction. Case of Alloy 800 Grade 2 Study at 550°C

Prediction of fatigue life in creep-fatigue at a temperature of 550°C has been made for an Inconel alloy with the help of 3 models of damage evolution: the Chaboche model, the Levaillant model, and a new model of creep fatigue relaxation. The main advantages of the new model are that it requires only few constants and provides a high accuracy of the fatigue life prediction.Прогнозирование усталостной долговечности в условиях ползучести при температуре 550°С выполнено для жаропрочного и жаростойкого сплава на никелевой основе (Inconel). Представлены модели эволюции повреждения Шабоша (Chaboche) и Леваяна (Levaillant), а также новая модель релаксации при совместном действии ползучести и усталости. Предложенная модель позволяет осуществлять долгосрочное прогнозирование без использования большого количества постоянных.Прогнозування утомної довговічності в умовах повзучості при температурі 550°С виконано для жароміцного і жаростійкого сплаву на нікелевій основі (Inconel). Представлено методи еволюції пошкодження Шабоша (Chaboche) і Леваяна (Levaillant), а також нову модель релаксації при сумісній дії повзучості й утоми. За допомогою запропонованої моделі можна проводити довготермінове прогнозування без використання великої кількості сталих

Brittle Mixed-Mode (I+II) Fracture: Application of the Equivalent Notch Stress Intensity Factor to the Cracks Emanating From Notches

In the present paper, crack initiation in mixed-mode (I+II) fracture has been studied using notched circular ring specimens. A new criterion of brittle mixed-mode (I+II) fracture based on the notch tangential stress and the volumetric approach has been developed. The critical value of the equivalent notch stressintensity factor has been considered as fracture toughness in mixed-mode (I+II) fracture.Исследуется зарождение трещины по смешанному механизму разрушения (типа I+II) в образцах кольцевого типа с внутренним надрезом. Предложен новый критерий для описания хрупкого разрушения смешанного типа I+II, в основу которого положен объемный подход, а базовым параметром служит касательное напряжение в надрезе. Предлагается в качестве параметра вязкости разрушения для смешанного механизма разрушения по типу I+II использовать предельное значение эквивалентного коэффициента интенсивности напряжений в надрезе.Досліджується зародження тріщини за змішаним механізмом руйнування (типу І+ІІ) в зразках кільцевого типу з внутрішнім надрізом. Запропоновано новий критерій для описання крихкого руйнування змішаного типу І+ІІ, в основу якого покладено об’ємний підхід, а базовим параметром є дотичне напруження у надрізі. За параметр в ’язкості руйнування для змішаного механізму руйнування за типом І+ІІ пропонується використовувати граничне значення еквівалентного коефіцієнта інтенсивності напружень у надрізі

Etude analytique et numérique de la réponse en vibration à hautes fréquences d'éprouvettes de fatigue vibratoire des métaux. Application aux aciers

In the present paper, the so-called " ultrasonic fatigue " or fatigue at very high frequency has been studied in the materials elastic behaviour case while neglecting the thermal effects that influence the mechanical fields. The determination of mechanical fields and specimen resonance length has been done both analytically and numerically. The numerical method used for this calculation is the finite element method (FEM). Martensitic steel " Soleil A2 " and austenitic steel " ICL 472 BC " have been considered in order to compare the two methods (analytical and numerical). It is shown that a perfect convergence is obtained between the two solutions.Dans le présent travail, la fatigue vibratoire a été étudiée dans le cas du comportement élastique des matériaux en négligeant les effets thermiques pouvant influencer les champs mécaniques. La détermination de ces champs et de la longueur de résonance des éprouvettes de fatigue a été faite analytiquement et numériquement. Le calcul numérique effectué se base sur la méthode des éléments finis. Dans le but d'une comparaison des solutions analytiques et numériques, deux aciers ont été considérés : un acier martensitique (Soleil A2) et un acier austénitique de type 18-10 (ICL 472 BC). Une parfaite convergence est obtenue entre les deux solutions

Environmental control of the recruitment of sardines (Sardina pilchardus) over the western Saharan shelf between 1995 and 2002 : a coupled physical/biogeochemical modelling experiment

Fisheries constitute an important economic sector for Morocco, where the species Sardina pilchardus represents the main landings. In acoustic evaluations conducted along the Moroccan coast since 1995, the absence of juveniles in 1996 and 1998 and the collapse of the sardine stock between 1996 and 1997 represent the main events until 2002. Sardines are known to be microphageous planktivores and thus are sensitive to environmental variability. A biogeochemical model coupled to a hydrodynamic model (ROMS) was run over the Canary Current System (1991-2002) to investigate the environmental factors that could have played a role in the variability of the sardine spawning. A grid refinement (1/12 degrees) centred on the Saharan Bank (SB) region was built to study the main spawning ground of sardines off northwest Africa. The volume of the potential spawning habitat (PSH) of sardines was defined as a function of depth, temperature and salinity, which are included in the ranges 0-200 m, 15-21 degrees C and 35.8-36.8, respectively. Our modelling frame was able to reproduce the seasonal cycle of temperature, phytoplankton concentration and PSH over the SB. It also captured the warming associated with the negative index of the North Atlantic Oscillation of 1995-1997 and allowed a description of the inter-annual variability of the PSH. Our experiment shows that the volume of PSH was much reduced in 1996 compared to the other years. The results suggest that the delay between high abundance of plankton and favourable spawning conditions is a good proxy for determining the recruitment failure of sardine in this oceanic region

Improving rheological and mechanical properties of non-plastic clay soil from Bensmim region (Morocco) using bentonite additions: Suitability for building application

The present study aims to develop an innovative scientific methodology for adjusting the phys-icochemical composition of any clay soil to make it appropriate for construction applications. The realized research was carried out on unexploited clayey soil extracted from Bensmim village (Morocco). Another clay sample from "Extrabrick" brick manufactory was also used as a reference since it is used to produce high-quality bricks. Raw materials physicochemical and geotechnical properties were determined. Results demonstrated that the studied clay is an unsuitable raw material for clay bricks production. This is due to its low plasticity resulting from its significant sand content, low clay fraction, and absence of swelling clay. Therefore, improving the plasticity of our clay was taken as a critical factor to enhance the properties of this clay. Different per-centages of bentonite, which is known for its high plasticity, ranging from 0 to 10%, were added to study the effect of this addition on the characteristics of the studied clay. The rheological and mechanical analysis showed that increasing the percentage of bentonite has a beneficial effect on the properties of the studied clay bricks. In fact, the addition of 10% bentonite showed an increase in the yield stress, viscosity, and the mixture exhibited a rheological behavior very close to the reference sample. The founded results were fitted to Herschel-Bulkley classical. The findings suggest that the addition of bentonite decreases the flow index value and increases the consis-tency index of the studied clay. Furthermore, compressive strength went from 5.3 MPa for the studied clay without additive to 19.33 MPa after 10% of bentonite addition. This value of compressive strength is very close to the compressive strength of the reference brick 23.83 MPa. These results confirmed that rheology could be a powerful tool to tune the formulation of con-struction materials

Sub-regional ecosystem variability in the Canary current upwelling

15 páginas, 2 tablas, 5 figurasThe Canary Current upwelling ecosystem (CanC) constitutes one of the four main eastern boundary upwelling ecosystems (EBUEs) of the world, thus hosting high productivity and fisheries. Recent observations indicate that the CanC region as a whole has been experiencing a progressive warming and a decrease in productivity over the last decades. This overall trend is however not directly reflected in the fisheries of the region. Here we update recent results and previous reviews on the CanC, covering aspects from the physical environment to fish populations and fisheries on a range of time scales. We approach these topics, when possible, through a comparative exploration of the biogeographical characteristics of different sub-regions comprising this ecosystem. This review shows that variability in coastline configuration, shelf width, coastal upwelling, nutrient fertilization, productivity, or retentive vs. dispersive physical mechanisms, among other factors, may help explain sub-regional differences in fish distributions and abundances in the CanC. Nevertheless, the lack of systematic information on the regional variability of physical and biological processes hampers an integrated understanding of the relative contribution of natural vs. human-induced variability in the populations of at least small-pelagic fishes and their associated fisheriesThis work was partly funded by the Spanish projects ZOTRACOS (REN2003- 06633-C03-02/MAR), RODA (CTM2004-06842-C03/MAR) and CAIBEX (CTM2007- 66408-C02/MAR), and the French IRD Program ECO-UP (UR097). EDB, XAA-S and FGF were partially supported by project CRIA (PDIGIT05RMA40201PR) from the Xunta de Galicia.Peer reviewe

Canary Current upwelling: does geographical diversity make the difference?

Eastern boundary upwelling ecosystems: integrative and comparative approaches, 2-6 June 2008, Las Palmas, Gran Canaria, SpainThe Large Marine Ecosystem of the Canary Current (CC) is one of the four major eastern boundary upwelling systems of the world ocean, and thus an area of intensive fisheries activity. The coastline is separated into two distinct areas -the Iberian coast and the NW African coast- at the Strait of Gibraltar, where the Mediterranean Sea and the Atlantic Ocean exchange water. The two areas share similarities in local oceanography, productivity and fisheries, but also exhibit their own particularities. In the northern most Iberian region, the Rías Baixas represent a unique ecosystem, strongly interacting with the coastal upwelling and amplifying its signal. Although seasonality in the Trade wind regime is more pronounced in the northern and southern extremes of the CC, the whole region exhibits high annual productivity and fish population yield. Nevertheless, a large fraction of the productivity is presumably lost to the open ocean. In particular, the NW African shelf between Cape Guir (32 N) and Cape Blanc (21 N) exhibits numerous upwelling filaments. These appear topographically generated in general and those arising south of 28 N result largely from the interplay of the coastal jet with eddies shed downstream the Canaries Archipelago. Filaments facilitate nearshore-offshore exchange of water parcels and properties and a net productivity loss. In recent years, considerable information has been gathered from these coastal ecosystems, and several review papers have been published on plankton biology, biogeochemistry or regional fisheries. Here, we present an updated global review of the CC, covering aspects ranging from hydrography, through biogeochemistry to trophic interactions and fisheries, all of which are affected by processes occurring on distances from mesoscale to large scale and over periods from days to decades. The synthesis will highlight recent major advances in experimental studies, both over the coastal shelf and in the open-ocean transition zone, as well as in modelling exercises. Ongoing numerical models range from large-scale and regional circulation off Iberia and NW Africa to coupled physical-biological models looking at plankton productivity or fish population dynamicsN