Study of Al2O3 coatings on AISI 316 stainless steel obtained by controlled atmosphere plasma spraying (CAPS)

The tribological behaviour of Al₂O₃ coatings on AISI 316 stainless steel, obtained by the process of controlled atmosphere plasma spraying (CAPS), is studied in this work. Atmospheric plasma spraying (APS) and high pressure plasma spraying (HPPS) were applied in order to produce these coatings. The APS coatings exhibited lower microhardness values compared to the values of HPPS coatings. Regarding the HPPS coatings it was found that plasma composition, through its heat capacity, does influence the heat transfer to particles, and, consequently, their flattening and densification process, which govern coating properties. It was revealed that tribological behaviour of coatings was influenced by the applied spraying method too. Coatings from HPPS under high-enthalpy conditions led to worst wear behaviour. In general, properties, such as microstructure, microhardness, coefficient of friction and wear resistance depended on the processing conditions such as pressure and composition of the spraying chamber atmosphere.     

Rust morphology characterization of polyurethane and acrylic-based marine antifouling paints after salt spray test on scribed specimens

A newly developed, polyurethane-based, marine antifouling coating, containing 2% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was performed with XRD, Raman spectroscopy, SEM, and EDS methods. The absence of paint deformation during the experiment led to the formation of compact corrosion products, firmly adherent to the substrate, allowing transformation to more protective forms, such as oxides (hematite, maghemite, magnetite) and the least harmful of the oxyhydroxides (goethite, feroxyhyte), found in the mixture, ensuring sufficient corrosion protection. The unscratched part of the paint served as a barrier to corrosion product expansion beyond the scribed areas. An acrylic-based antifouling system was also examined for reasons of comparison. The experimental formulation exhibited superior anticorrosion performance overall, since the acrylic system presented extended material loss, blistering, checking, and extensive substrate rust coverage beneath the multilayer coat, implying unsatisfactory corrosion protection.     

Cavitation effects on textured compression rings in mixed lubrication

Thin lubricant films and cavitation to ring–bore contact have a directly correlation between wear and emissions output of internal combustion engines. Thus, there is a need to develop innovate engineering solutions such as surface texturing. In particular, micro textures are manufactured in order to keep more lubricant in weakly lubricated contact. An isothermal mixed‐hydrodynamic analysis was developed for textured compression rings, which utilised the effects of two‐phase flow using Navier–Stokes equations, vapour transport and asperity interaction. Realistic boundary conditions are used from a real motorbike engine. This paper employs a computational model including multiphase flow of the ring–bore conjunction in order to predict the effects of surface texturing of the barrel face ring around the dead centres. The model is validated using numerical and experimental results from the literature. Additionally, flow simulations have been performed, on how micro‐dimples shape and depth on the ring liner affect on the total friction and minimum lubricant film. Copyright © 2016 John Wiley & Sons, Ltd.     

Improving brain tumor characterization on MRI by probabilistic neural networks and non-linear transformation of textural features

The aim of the present study was to design, implement and evaluate a software system for discriminating between metastatic and primary brain tumors (gliomas and meningiomas) on MRI, employing textural features from routinely taken T1 post-contrast images. The proposed classifier is a modified probabilistic neural network (PNN), incorporating a non-linear least squares features transformation (LSFT) into the PNN classifier. Thirty-six textural features were extracted from each one of 67 T1-weighted post-contrast MR images (21 metastases, 19 meningiomas and 27 gliomas). LSFT enhanced the performance of the PNN, achieving classification accuracies of 95.24% for discriminating between metastatic and primary tumors and 93.48% for distinguishing gliomas from meningiomas. To improve the generalization of the proposed classification system, the external cross-validation method was also used, resulting in 71.43% and 81.25% accuracies in distinguishing metastatic from primary tumors and gliomas from meningiomas, respectively. LSFT improved PNN performance, increased class separability and resulted in dimensionality reduction.     

Dissimilar Friction Stir Welding Between 5083 and 6082 Al Alloys Reinforced With TiC Nanoparticles

Dissimilar friction stir welding between aluminum alloys thick plates reinforced with TiC nanoparticles was conducted. The defect-free welds are characterized by good mechanical mixing between the joined materials as well as by good nanoparticle distribution and further grain refinement in comparison with the unreinforced weld. The local mechanical behavior of the produced metal matrix composites was studied and compared with their bulk counterparts and parent materials. Specifically, the measured mechanical properties in microscale and nanoscale (namely hardness and elastic modulus) are correlated with microstructure and the presence of fillers. The hardness, elastic modulus, ultimate tensile strength, percentage of elongation, and yield values increase with the presence of TiC nanoparticles.     

Multimodal genetic algorithms-based algorithm for automatic point correspondence

In this paper, the problem of automatic determination of point correspondence between two images is formulated as a multimodal function optimization and the usefulness of genetic algorithms (GAs) as a multimodal optimizer is explored. Initially, a number of variations of GAs, capable of simultaneously discovering multiple extremes of an objective function are evaluated on a mathematical benchmark objective function with multiple unequal maxima. The variation of the GAs that performs best on the benchmark function, in terms of the number of maxima discovered, is selected for the determination of automatic point correspondence between two images. The selected variation of the GAs involves an iterative procedure for the formation of a genetic population of individuals (or chromosomes). Each individual encodes the position of a point of interest on one of the available images as well as parameters of a local transformation that generates the position of the corresponding point on the other image. The proposed algorithm aims to discover individuals that corresponds to local maxima of an objective function that measures the similarity between patches of the two images. When the GAs-based multimodal optimization algorithm terminates, pairs of corresponding points between the two images are obtained that can be used for the generation of a dense deformation field by means of the thin plate splines model.The proposed algorithm is applied to 2D medical images (dental and retinal images) under known transformations (similarity and elastic transformation) and is also assessed on medical images with unknown transformations (computer tomography transverse slices). The proposed algorithm is compared against the iterative closest point (ICP) algorithm, and a well-known non-rigid registration algorithm, based on free-form deformations (FFD) using various quantitative criteria. The obtained results indicate that in case of known similarity transformations, the proposed multimodal GAs-based algorithm and the ICP algorithm present equivalent performance, whereas the FFD algorithm is clearly outperformed. In the case of known sinousoidal deformations, the proposed multimodal GAs-based and the FFD algorithm achieve equivalent performance and clearly outperform the ICP algorithm. Finally, in the case of unknown elastic deformations, the proposed GAs-based algorithm appears to perform marginally better than the FFD algorithm, whereas it clearly outperforms the ICP algorithm.     

A biomimetic approach to inverse kinematics for a redundant robot arm

Redundant robots have received increased attention during the last decades, since they provide solutions to problems investigated for years in the robotic community, e.g. task-space tracking, obstacle avoidance etc. However, robot redundancy may arise problems of kinematic control, since robot joint motion is not uniquely determined. In this paper, a biomimetic approach is proposed for solving the problem of redundancy resolution. First, the kinematics of the human upper limb while performing random arm motion are investigated and modeled. The dependencies among the human joint angles are described using a Bayesian network. Then, an objective function, built using this model, is used in a closed-loop inverse kinematic algorithm for a redundant robot arm. Using this algorithm, the robot arm end-effector can be positioned in the three dimensional (3D) space using human-like joint configurations. Through real experiments using an anthropomorphic robot arm, it is proved that the proposed algorithm is computationally fast, while it results to human-like configurations compared to previously proposed inverse kinematics algorithms. The latter makes the proposed algorithm a strong candidate for applications where anthropomorphism is required, e.g. in humanoids or generally in cases where robotic arms interact with humans.     

Pin-on-disc testing of PE-CVD diamond-like carbon coatings on tool steel substrates

The present study deals with the tribological behaviour and the wear mechanisms of 2-μm thick diamond-like carbon coatings. The examined coatings were deposited by plasma-enhanced chemical vapour deposition (PE-CVD) on three tool steel substrates, of different hardnesses. Tribological studies against alumina were performed using a pin-on-disc apparatus under various normal loads (2–20 N) and sliding speeds (0.1–0.3 m s⁻¹), while the relative humidity of the environment was kept constant, equal to 25%. The influence of the testing parameters (normal load and sliding speed) and the mechanical properties of the substrate on the wear lifetime of the coatings was determined and the involving wear mechanisms were identified. It was found that both the sliding conditions and the hardness of the substrate affect strongly the wear rate and the wear lifetime, but have no significant influence on the value of the friction coefficient, which was found to be lower than 0.15 for all the testing parameters.     

An intelligent powered wheelchair to enable mobility of cognitively impaired older adults: an anticollision system.

Older adults with cognitive impairments are generally prohibited from using powered wheelchairs, because of the high risk of collisions with people and objects. This paper describes and presents the preliminary results of a system that uses an infrared sensor to provide anticollision and a prompting system for a powered wheelchair that helps guide the user safely past obstacles. Trials with the prototyped system detected collisions and stopped the chair in 95% of trials with an object and generated no false alarms.