Détermination de la ténacité de matériaux fragiles ou ductiles à partir de l’essai d’indentation

Les différentes méthodes qui utilisent l’essai d’indentation pour estimer la ténacité sont revues et commentées. Pour les matériaux fragiles, les formules sont principalement basées sur la mesure des fissures formées par l’indenteur ou, si l’essai est instrumenté, sur les décrochements (pop-in) observés sur la courbe charge-déplacement. D’autres méthodes moins connues peuvent utiliser la mesure de l’ouverture en fond de fissure, une équivalence entre la longueur de fissure formée et l’accroissement de pénétration de l’indenteur ou le clivage provoqué par une indentation proche du bord du matériau étudié. Pour les matériaux ductiles aucune fissure n’est visible à la surface, même pour les fortes charges appliquées. Dans ce cas la ténacité est reliée par la mécanique continue du dommage à un dommage critique mis en évidence par la diminution du module d’élasticité avec l’augmentation de la profondeur d’indentation. Toutes ces méthodes permettent de calculer la ténacité avec une incertitude pouvant aller au maximum à 50 %

Drones: Innovative Technology for Use in Precision Pest Management.

Arthropod pest outbreaks are unpredictable and not uniformly distributed within fields. Early outbreak detection and treatment application are inherent to effective pest management, allowing management decisions to be implemented before pests are well-established and crop losses accrue. Pest monitoring is time-consuming and may be hampered by lack of reliable or cost-effective sampling techniques. Thus, we argue that an important research challenge associated with enhanced sustainability of pest management in modern agriculture is developing and promoting improved crop monitoring procedures. Biotic stress, such as herbivory by arthropod pests, elicits physiological defense responses in plants, leading to changes in leaf reflectance. Advanced imaging technologies can detect such changes, and can, therefore, be used as noninvasive crop monitoring methods. Furthermore, novel methods of treatment precision application are required. Both sensing and actuation technologies can be mounted on equipment moving through fields (e.g., irrigation equipment), on (un)manned driving vehicles, and on small drones. In this review, we focus specifically on use of small unmanned aerial robots, or small drones, in agricultural systems. Acquired and processed canopy reflectance data obtained with sensing drones could potentially be transmitted as a digital map to guide a second type of drone, actuation drones, to deliver solutions to the identified pest hotspots, such as precision releases of natural enemies and/or precision-sprays of pesticides. We emphasize how sustainable pest management in 21st-century agriculture will depend heavily on novel technologies, and how this trend will lead to a growing need for multi-disciplinary research collaborations between agronomists, ecologists, software programmers, and engineers

Analysis of indentation size effect in copper and its alloys

For describing the indentation size effect (ISE), numerous models, which relate the load or hardness to the indent dimensions, have been proposed. Unfortunately, it is still difficult to associate the different parameters involved in such relationships with physical or mechanical properties of the material. This is an unsolved problem since the ISE can be associated with various causes such as workhardening, roughness, piling-up, sinking-in, indenter tip geometry, surface energy, varying composition and crystal anisotropy. For interpreting the change in hardness with indent size, an original approach is proposed on the basis of composite hardness modelling together with the use of a simple model, which allows the determination of the hardness–depth profile. Applied to copper and copper alloys, it is shown that it is possible to determine the maximum hardness value reached at the outer surface of the material and the distance over which both the ISE and the workhardening take place

Efeito da radiação UV-B na germinação de conídios de Trichoderma obtidos de produtos comerciais.

Resumo: O efeito da radiação UV-B foi avaliada na germinação de conídios de Trichoderma spp. obtidos de produtos comerciais (Trichodermil® - Itaforte Bioprodutos; Trichodermax® SP – Turfal; Quality® WG – Laboratório de Biocontrole Farroupilha). Uma alíquota de 20 ?L de suspensões de conídios (105 conídios/ml), de cada produto, foi plaqueada em triplicata em meio BDA + oxgall e imediatamente expostas à radiação UV-B por 1, 2, 3, 4 e 5 h. Placas controle foram envoltas em papel alumínio e mantidas na câmara durante toda a exposição. Após a exposição, as placas foram mantidas no escuro a 25°C± 1. A germinação foi avaliada após 16 h e 24 h para a testemunha e para os conídios irradiados, respectivamente. De cada placa foram avaliados 300 conídios e a porcentagem de germinação foi calculada comparando-se com o controle. O aumento da radiação UV-B reduziu a germinação de conídios para todos os isolados de Trichoderma. Para os três isolados, a média de germinação dos conídios para o controle foi de 91,3%. Para os irradiados por 1, 2, 3, 4 e 5 h as médias de germinação foram de 78,1%, 47,6%, 38,4%, 28,0% e 17,4%, respectivamente. Todos os isolados apresentaram a mesma sensibilidade à radiação UV-B. Esses resultados demonstram a sensibilidade de isolados de Trichoderma ao UV-B e sugerem a necessidade de formulações com protetores anti-UV-B ou recomendação de aplicação em períodos ou condições adequadas

A contact area function for Berkovich nanoindentation : Application to hardness determination of a TiHfCN thin film

In nanoindentation, especially at very low indenter displacements, the indenter/material contact area must be defined in the best possible way in order to accurately determine the mechanical properties of the material. One of the best methodologies for the computation of the contact area has been proposed by Oliver and Pharr [W.C.Oliver, G.M.Pharr, J.Mater. Res. 7 (1992) 1564], which involves a complex phenomenological area function. Unfortunately, this formulation is only valid when the continuous stiffness measurement mode is employed. For other conditions of indentation, different contact area functions, which take into account the effective truncation length or the radius of the rounded indentertip, as well as some fitting parameters, have been proposed. However, most of these functions require a calibration procedure due to the presence of such parameters. To avoid such a calibration, in the present communication a contact area function only related to the truncation length representative of the indenter tip defect, which can be previously estimated with high resolution microscopy, has been proposed. This model allows the determination of consistent indentation data from indenter displacements of only few nanometers indepth. When this proposed contact area function is applied to the mechanical characterization of a TiHfCN film of 2.6 μm in thickness deposited onto a tool steel substrate, the direct determination of the hardness and elastic modulus of the film leads to values of 35.5±2 GPa and 490±50 GPa, respectively

Cr2C3–NiCr VPS thermal spray coatings as candidate for chromium replacement

The present investigation has been carried out with the aim of determining the tribological behavior of a VPS chromium carbide coating both in the as-deposited and heat-treated conditions. A commercial powder of Cr2C3–25% NiCr was sprayed employing a VPS system (Medicoat AG, Switzerland) onto plain low carbon steel coupons. The samples were subsequently annealed for 2 h at 600 °C, 800 °C and 900 °C in Ar. The microstructural characterization was carried out by using SEM and XRD before and after the heat treatment of the samples. SEM observations were employed for determining the degradation mechanisms that took place during the wear tests. When the coated systems rubbed against alumina under a 5 N normal load in air, a progressive change in the mechanism, from a mixed adhesive and abrasive, to a predominant abrasive was observed, as the heat treatment temperature increased. The wear constants were found to be of the order of approximately 10− 6 mm3/N.m, which indicates a wear resistance of nearly 4 times higher in comparison with the wear results reported in the literature for similar coating systems obtained by employing HVOF deposition. However, the heat treatment carried out at 900 °C brought about only 20% increase in the sliding wear resistance of the coated system

Sliding wear of a-C:H coatings against alumina in corrosive media

This paper reports the results obtained from the study of friction and sliding wear in two corrosive solutions of an a-C:H coating deposited on 316L stainless against an alumina ball, employed as static counter part. Calculations of the values of the von Mises stresses developed at the coating–substrate interface, as soon as the ball touches the coated sample, and how this state of stress influences the response of the coated system under the corrosion environment, are presented and discussed. The results obtained from these calculations, as well as from the experiments conducted in the present research, are compared with other experiments published in the literature, where a-C:H coatings deposited on different substrates and with different coating architectures were tested in similar corrosive media. It has been determined that in those systems, where the von Mises stress in the coating, found in the vicinity of the interface, exceeds the threshold value of approximately 370MPa, coating failure with spallation will take place, regardless of the substrate nature on which this coating has been deposited. From this analysis it has been concluded that the coating yield strength is of utmost importance in conferring the a-C:H coated system there quired stability in a corrosive solution

On the detection of corrosion pit interactions using two-dimensional spectral analysis

A particular thanks to Professor Maxence Bigerelle (UTC, Compiègne, France) and to research and development engineer Dr. Benjamin Fournier (CEA, Saclay, France) for their interesting discussions and useful advices about the scientific problem of pitting corrosion.A statistical methodology for detecting pits interactions based on a two-dimensional spectral analysis is presented. This method can be used as a tool for the exploratory analysis of spatial point patterns and can be advanced as an alternative of classical methods based on distance. One of the major advantages of the spectral analysis approach over the use of classical methods is its ability to reveal more details about the spatial structure like the scale for which pits corrosion can be considered as independent. Furthermore, directional components of pattern can be investigated. The method is validated in a first time using numerical simulations on random, regular and aggregated structures. The density of pits, used in the numerical simulations, corresponds to that assessed from a corroded aluminium sheet. In a second time, this method is applied to verify the independence of the corrosion pits observed on the aforementioned aluminium sheet before applying the Gumbel theory to determine the maximum pit depth. Indeed, the property of independence is a prerequisite of the Gumbel theory which is one of the most frequently used in the field of safety and reliability.International audienceA statistical methodology for detecting pits interactions based on a two-dimensional spectral analysis is presented. This method can be used as a tool for the exploratory analysis of spatial point patterns and can be advanced as an alternative of classical methods based on distance. One of the major advantages of the spectral analysis approach over the use of classical methods is its ability to reveal more details about the spatial structure like the scale for which pits corrosion can be considered as independent. Furthermore, directional components of pattern can be investigated. The method is validated in a first time using numerical simulations on random, regular and aggregated structures. The density of pits, used in the numerical simulations, corresponds to that assessed from a corroded aluminium sheet. In a second time, this method is applied to verify the independence of the corrosion pits observed on the aforementioned aluminium sheet before applying the Gumbel theory to determine the maximum pit depth. Indeed, the property of independence is a prerequisite of the Gumbel theory which is one of the most frequently used in the field of safety and reliability

Association between cognitive impairment and criteria for frailty syndrome among older adults

OBJECTIVE: The association between cognitive impairment and physical frailty has been studied in older adults. The criteria degree of frailty may be keys to associated cognitive impairment. To analyze the association between cognitive impairment and the criteria for frailty. METHODS: We cross-sectionally examined data from 667 older adults (≥60 years of age) from a study entitled 'Variables associated to cognition in elderly caregivers' involving patients in an urban and rural primary healthcare center. We defined cognitive impairment based on different groups of scores on the Mini Mental State Examination, and defined frailty and prefrailty using the criteria by the Cardiovascular Health Study. We performed multinomial regression models to analyze the association between levels of frailty and cognitive impairment. RESULTS: Similar proportions of women (54.8%) and men (45.2%) participated in the study (mean age: 71 years old). We found cognitive impairment, prefrailty and frailty in 34, 54, and 24% of the participants, respectively. Concomitant cognitive impairment and frailty was found in 13% of them. The chances of cognitive impairment increased up to 330% (Odds Ratio [OR]: 4.3; 95% confidence interval [95%CI] 2.4‒7.7; p<0.001) among frail individuals, and 70% (OR: 1.7; 95%CI 1.0‒2.8; p=0.033) among prefrail individuals compared to robust/non-frail individuals. After controlling for age, education, place of residence and functional dependence, slowness and fatigue criteria were significantly associated with cognitive impairment. CONCLUSION: Older adults with frailty have a greater likelihood of concomitant cognitive impairment than prefrail and robust older adults. The prevalence of cognitive impairment and frailty is consistent with data reported in literature. The present findings contribute to the investigation of cognitive frailty