Fretting is a small oscillatory motion between two contact surfaces, which may cause wear or fatigue damage. Many parameters may affect fretting wear including normal load, applied displacement, ...material properties, surface roughness of the contact surfaces, frequency, etc. The design of engineering components subjected to fretting wear, such as couplings and splines, jointed structures, is still a challenge to engineers. This is because of the continuous change in the contact surfaces of component during fretting wear cycles. Therefore, a predictive technique that takes into account the wear progress during life cycle is desirable. Analytical solutions of wear problems are very difficult and limited to simple 2D configuration steady-state analysis. In contrast, numerical modelling techniques such as Finite Element Analysis (FEA) can be used for any type of structures in 3D configuration with many complicated details such as large deformation, material non-linearity, changes in geometry and time integration effect. In this article, we use FEA to find whether or not there exists a stress singularity at cylinder on flat contact according to different variables, such as applied displacement, coefficient of friction (COF) and fretting wear cycles. Based on a stress singularity signature method, it is found that stress singularity has close relation with fretting regime. There is no stress singularity neither in partial slip nor gross sliding after one-fourth of a fretting wear cycle for lower COF, but it exits for higher COF, in which condition the contact interface is almost stick. After 20,000 cycles, stress singularity exists in partial slip, while there is no stress singularity for gloss sliding condition, when COF is 0.8. Results reveal that more attention should be paid to the mesh size at contact interface, when the contact condition is under partial slip regime.
•Finite element analysis of fretting wear.•Stress singularity in partial slip and gross sliding regimes.•Effect of contact regime on stress singularity.•Effect of COF on stress singularity.•Effect of wear cycles on stress singularity.
•Damage detection in structures by applying using artificial neural network (ANN) and cuckoo search (CS) algorithm.•Structural damage localization and quantification in bridges and beam-like ...structures.•Improve ANN training parameters using CS.•ANN combined with CS (ANN-CS) is accurate and cost effective.
This paper presents a new approach for damage detection in structures by applying a flexible combination based on an artificial neural network (ANN) and cuckoo search (CS) algorithm. ANN has become one of the most powerful tools employing computational intelligence techniques to tackle complex problems in numerous fields. However, due to the application of backpropagation algorithms based on gradient descent, a major drawback of ANN is the common problem of local minima that acts as a great hindrance to the search for the best solution. To overcome this disadvantage, we propose to combine ANN with evolutionary algorithms based on global search techniques. This paper employs CS to improve ANN training parameters (weight and bias) by minimizing the difference between real and desired outputs and then using these parameters to generate the network. Two numerical models, comprising a steel beam calibrated using experimental measurements and a large-scale truss bridge, are used to assess the robustness of the proposed approach. The results demonstrate that ANN combined with CS (ANN-CS) is accurate and requires a lower computational time than ANN, and evolutionary algorithm (EA) alone in terms of structural damage localization and quantification.
Fretting occurs when two loaded contacting surfaces are exposed to oscillatory relative movement of small amplitude. Depending on conditions such as surface finishing, coefficient of friction, normal ...load and slip amplitude, fretting may reduce the service life of a component by fretting wear. The effect of surface roughness on the fretting wear profile is still uncertain and may be significant. However, most of the finite element (FE) models that are used to predict fretting wear do not take it into consideration. In this paper, we propose a multiscale procedure to study roughness effect on fretting wear using FE models. In order to do that, we treat the problem in two scales: a) micro scale to analyse the effect of roughness on the contact pressure for frictionless conditions, and b) macro scale to estimate the wear profile evolution for a cylinder on plane contact configuration.
•Multiscale procedure to study roughness effect on fretting wear using FE models.•Micro scale model to analyse the effect of roughness on contact pressure.•A cylinder on plane contact configuration.•Roughness has a minor effect in gross sliding condition.
Summary
Actinomycetes are a rich source for secondary metabolites with a diverse array of biological activities. Among the various genera of actinomycetes, the genus Saccharopolyspora has long been ...recognized as a potential source for antibiotics and other therapeutic leads that belong to diverse classes of natural products. Members of the genus Saccharopolyspora have been widely reported from several natural sources including both terrestrial and marine environments. A plethora of this genus has been chemically investigated for the production of novel natural products with interesting pharmacological effects. Therefore, Saccharopolyspora is considered one of the pharmaceutical important genera that could provide further chemical diversity with potential lead compounds. In this review, the literature from 1976 until December 2018 was covered, providing a comprehensive survey of all natural products derived from this genus and their semi‐synthetic derivatives along with their biological activities, whenever applicable. Moreover, the biological diversity of Saccharopolyspora species and their habitats were also discussed.
Vibration-based structural health monitoring (SHM) for long-span bridges has become a dominant research topic in recent years. The Nam O Railway Bridge is a large-scale steel truss bridge located on ...the unique main rail track from the north to the south of Vietnam. An extensive vibration measurement campaign and model updating are extremely necessary to build a reliable model for health condition assessment and operational safety management of the bridge. The experimental measurements are carried out under ambient vibrations using piezoelectric sensors, and a finite element (FE) model is created in MATLAB to represent the physical behavior of the structure. By model updating, the discrepancies between the experimental and the numerical results are minimized. For the success of the model updating, the efficiency of the optimization algorithm is essential. Particle swarm optimization (PSO) algorithm and genetic algorithm (GA) are employed to update the unknown model parameters. The result shows that PSO not only provides a better accuracy between the numerical model and measurements, but also reduces the computational cost compared to GA. This study focuses on the stiffness conditions of typical joints of truss structures. According to the results, the assumption of semi-rigid joints (using rotational springs) can most accurately represent the dynamic characteristics of the truss bridge considered.
This study was designed to evaluate the role of multiparametric magnetic resonance imaging (MRI) for differentiation of parotid gland neoplasms.
Prospective study was conducted upon 52 consecutive ...patients (30 men, 22 women; aged 24–78 years; mean, 51 years) with parotid tumours that underwent multiparametric MRI using combined static MRI, dynamic contrast enhanced (DCE) MRI, and diffusion-weighted imaging (DWI). The static MRI parameter, time signal intensity curves (TIC) derived from DCE-MRI, and apparent diffusion coefficient (ADC) values of parotid tumours were correlated with histopathological findings.
Static MRI revealed a significant difference between both benign and malignant lesions in regards to margin definition (P < .001) and T2 hypointensity (P < .013), with a diagnostic accuracy 95% and 78.33% respectively. Study of the TIC type on DCE-MRI revealed statistically significant difference between benign and malignant lesions (P < .001) and diagnostic accuracy 96.55%. There was no statistically significant difference (P = .181) between the ADC values of benign and malignant lesions. ROC curve analysis revealed that by using ADC cut-off value of 1 × 10−3 mm2/s had accuracy of 84.62% respectively for differentiating Warthin from malignant tumours that could be modified to higher value (94.28%) by excluding lymphoma from malignant lesions. By using cutoff value of 1.3 × 10−3 mm2/s to differentiate pleomorphic adenoma from malignancy, ROC curve analysis had high accuracy of 97.06%.
Multiparametric MRI can be used for differentiation of malignant from benign parotid tumours and characterization of some benign parotid tumours.
Cette étude a été conçue pour évaluer le rôle de l'imagerie par résonance magnétique (IRM) multiparamétrique pour la différenciation des néoplasmes de la glande parotide.
Une analyse prospective a été conduite sur 52 patients consécutifs (30 hommes et 22 femmes âgés de 24 à 78 ans; âge moyen de 51 ans) présentant des tumeurs parotidiennes et s’étant soumis à une IRM multiparamétrique par l'utilisation combinée d’IRM statique, d’IRM dynamique rehaussée par produit de contraste (DPC) et d'imagerie pondérée en diffusion (IPD). Les paramètres de l’IRM statique, les courbes d'intensité de signal en fonction du temps (CIT) dérivées des IRM-DPC et le coefficient de diffusion apparent (CDA) des tumeurs parotidiennes coïncidaient avec les résultats histopathologiques.
L’IRM statique a conduit à une différence significative entre les lésions à la fois bénignes et malignes concernant la définition de la marge (P < 0,001) et un hyposignal en T2 (P < 0,013), avec une exactitude diagnostique de 95 % et 78,33 % respectivement. L’étude des types de CIT obtenues par IRM-DPC a révélé une différence statistiquement significative entre les lésions bénignes et malignes (P < 0,001) et une exactitude diagnostique de 96,55 %. Aucune différence statistiquement significative (P = 0,181) n'a été obtenue entre les lésions bénignes et malignes au niveau du coefficient de diffusion apparent. L'analyse de la courbe ROC a permis de démontrer que l'utilisation d'une valeur seuil de 1 × 10−3 mm2/s pour le CDA avait une exactitude de 84,62 % pour la différenciation des tumeurs de Warthin des tumeurs malignes pouvant être haussée à une valeur supérieure (94,28 %) en excluant les lymphomes des lésions malignes. Avec une valeur seuil établie à 1,3 × 10−3 mm2/s afin de différencier les adénomes pléomorphes de la malignité, l'analyse de la courbe ROC a adopté une exactitude supérieure (de 97,06 %).
L’IRM multiparamétrique peut être utilisée pour différencier les tumeurs parotidiennes malignes des tumeurs bénignes et pour caractériser certaines tumeurs parotidiennes bénignes.
•A new damage indicator, Modified Cornwell Indicator (MCI).•MCI performs more efficient then Cornwell Indicator (CI).•MCI is combined with Genetic Algorithm (GA), MCI-GA.•MCI-GA provides more ...accurate and efficient results than other techniques in the literature.
This paper presents a new methodology for damage identification and quantification in two- and three-dimensional structures. The application of the proposed methodology is investigated numerically using Finite Element Method (FEM) and Matlab program. We propose a Modified Cornwell Indicator (MCI) that performs more efficient in damage detection than the standard Cornwell Indicator (CI). Furthermore, MCI is combined with Genetic Algorithm (GA) for further quantification of the detected damage. In GA, MCI, is used as an objective function to compare between measured and calculated indicators. The results of the analysis show that the proposed technique is accurate and efficient, when compared with other techniques in the literature, to estimate the severity of structural damage.
•Rice husk, palm leaf, and water hyacinth are efficient absorbers for metals.•Rice husk is the most efficient biosorbent for Cu(II), Co(II) and Fe(III).•Adsorption of metals follows Langmuir ...adsorption isotherm.•Metals adsorption by the biosorbents follows pseudo-second order model.•Chemical structure of the biosorbents affects their adsorption efficiency.
Biosorption of Cu(II), Co(II) and Fe(III) ions from aqueous solutions by rice husk, palm leaf and water hyacinth was investigated as a function of initial pH, initial heavy metal ions concentration and treatment time. The adsorption process was examined by two adsorption isotherms: Langmuir and Freundlich isotherms. The experimental data of biosorption process were analyzed using pseudo-first order, pseudo-second order kinetic models. The equilibrium biosorption isotherms showed that the three studied biosorbents possess high affinity and sorption capacity for Cu(II), Co(II) and Fe(III) ions. Rice husk showed more efficiency than palm leaf and water hyacinth. Adsorption of Cu(II) and Co(II) was more efficient in alkaline medium (pH 9) than neutral medium due to the high solubility of metal ion complexes. The metal removal efficiency of each biosorbent was correlated to its chemical structure. DTA studies showed formation of metal complex between the biosorbents and the metal ions. The obtained results showed that the tested biosorbents are efficient and alternate low-cost biosorbent for removal of heavy metal ions from aqueous media.
In our paper, we have synthesized modified PEA and alkyd resin by replacing the new source of polyol (SDEA) which was confirmed by different analyses such as IR, and 1HNMR spectra. A series of ...conformal, novel, low-cost, and eco-friendly hyperbranched modified alkyd and PEA resins were fabricated with bio ZnO, CuO/ZnO) NPs through an ex-situ method for mechanical and anticorrosive coatings. The synthesized biometal oxides NPs and its composite modified alkyd and PEA were confirmed by FTIR, SEM with EDEX, TEM, and TGA, and can be stably dispersed into modified alkyd and PEA resins at a low weight fraction of 1%. The nanocomposite coating was also subjected to various tests to determine their surface adhesion, which ranged from (4B-5B), physico-mechanical characteristics such as scratch hardness, which improved from < 1.5 to > 2 kg, gloss (100-135) Specific gravity (0.92-0.96) and also chemical resistance test which passed for water, acid, and solvent except alkali, was poor because of the hydrolyzable ester group in the alkyd and PEA resins. The anti-corrosive features of the nanocomposites were investigated through salt spray tests in 5 wt % NaCl. The results indicate that well-dispersed bio ZnO and CuO/ZnO) NPs (1.0%) in the interior of the hyperbranched alkyd and PEA matrix improve the durability and anticorrosive attributes of the composites, such as degree of rusting, which ranged from 5 to 9, blistering size ranged from 6 to 9, and finally, scribe failure, which ranged from 6 to 9 mm. Thus, they exhibit potential applications in eco- friendly surface coatings. The anticorrosion mechanisms of the nanocomposite alkyd and PEA coating were attributed to the synergistic effect of bio ZnO and (CuO/ZnO) NPs and the prepared modified resins are highly rich in nitrogen elements, which might be regarded as a physical barrier layer for steel substrates.
Over the past decades, many numerical procedures aiming to predict the life of components subjected to fretting fatigue have been developed. Most procedures combine estimates of crack initiation and ...propagation lives in order to obtain total lifetime. Nevertheless, crack initiation life estimates are generally not easy to define. An alternative is to consider the failure in a cycle-by-cycle analysis using cyclic cohesive zone model (CCZM), accounting for loading and unloading damage accumulation at crack front. However, a cycle-by-cycle analysis is extremely computational demanding. To overcome this issue, we propose an extrapolation procedure in junction with CCZM for the crack propagation modelling, which is substantially faster than a complete cycle-by-cycle analysis. This approach is compared, in terms of accuracy of life estimates, to traditional linear elastic fracture mechanics and experimental data.
•Cyclic cohesive zone model (CCZM).•Crack propagation lifetime prediction.•Taking into account loading and unloading damage accumulation at crack front.•Extrapolation procedure in junction with CCZM for the crack propagation modelling.
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