1,720,967 research outputs found
A novel approach for detecting undercuts within surface textures generated by Electrochemical Jet Machining (ECJM)
No full textThe present study proposes a novel method for detecting micrometric undercuts (UCs) generated by electrochemical machining for the production of surfaces with tailored functionality. Two different algorithms for the detection of UCs based on two-dimensional topographic maps are tested. The first is a traditional approach based on definition of UCs in terms of surface orientation with respect to a reference direction. The second is an innovative alternative approach designed to reduce sensitivity to numerical effects that potentially lead to overestimation of the number of detected UCs. Electrochemical Jet Machining (ECJM) is used to texture SUS 316L specimens with the aim of producing a measurable surface with a representative number of micrometric UCs. Generated surface textures, comprising craters with diameters ranging from a few microns to tens of microns, are crosssectioned and inspected with Scanning Electron Microscopy. The extracted profiles allow the novel method for detection of UCs to be efficiently tested and compared with the traditional approach. The number of UCs is found to decrease with increasing electrolyte jet scanning speed, while remarkable differences are revealed between the two calculation approaches at scanning speeds below 2mms-1
Laser texturing of Li-ion battery electrode current collectors for improved active layer interface adhesion
No full textNanosecond laser processing (NLP) is performed on aluminium and copper Li-ion battery (LIB) current collectors to improve the interface adhesion with active materials. The developed area ratio, Sdr, void volume, Vv, and maximum crater depth, h, are introduced to quantify the effectiveness and feasibility of NLP over a range of process parameters. By limiting the crater depth to half the foil thickness, increases in surface area of 20% and 13% are achieved on aluminium and copper foils of thickness 30 μm and 10 μm with a fluence of 24.8 J/cm2 and 49.5 J/cm2, respectively. The adhesion ratio of intact active material following peel-off tests on complete electrodes with textured current collectors is approximately 30% higher than with untreated current collectors
Influence of ns laser texturing of AISI 316L surfaces for reducing bacterial adhesion
Full text linkNanosecond pulsed laser texturing has been performed on stainless steel with the objective of developing surface treatments to reduce bacterial adhesion on mechanical components in food handling machinery. The adhesion of Escherichia coli (E. coli) on four distinct textures has been investigated with standardised protocols for measurement of antibacterial performance. Surface morphology has been studied in detail for each texture to ascertain the presence of hierarchical structures and determine the role of topography in reducing bacterial adhesion. Despite the absence of sub-micrometric features comparable with bacterial size, this work highlights the crucial role that nanosecond pulsed laser irradiation plays in promoting a thin layer of iron oxide that reduces E. coli adhesion through local repulsive electrostatic interactions
High precision feature detection in laser texturing
No full textThe present work seeks to develop a novel and systematic approach to quantifying the repeatability of textured surfaces, a relevant property for several technological fields. Specifically, aluminum alloy and stainless steel specimens were subject to nanosecond pulsed laser texturing to produce arrays of ablation craters in a typical configuration employed to improve wettability and tribological performance. Feature repeatability was firstly assessed in terms of crater volume and interfacial area, after which an additional parameter was developed based on the Pearson's Correlation Coefficient (PCC). Within the tested laser parameter range, the crater volume exhibited highest repeatability in the high energy dose regime on aluminum alloy specimens, while the crater volume was more repeatable in the low energy dose regime on stainless steel specimens. This difference was attributed to the development of an oxide ring surrounding the craters on stainless steel at high energy dose. This outcome was confirmed through analysis of the point-to-point repeatability, where process repeatability was determined for different portions of the ablation craters
Nanostructure patterns on stainless-steel upon ultrafast laser ablation with circular polarization
Full text linkRipple-like nanostructure patterns are known to occur in ultrafast laser ablation with linearly polarized radiation. The observation of similar features at the bottom of grooves produced during laser ablation of stainless-steel with circular polarization is reported here. A comprehensive morphological analysis of the machined surfaces, carried out by electron and scanning probe microscopes, reveals a marked dependence of feature shape on process parameters, in particular on the scanning velocity of the laser spot. Such a dependence is interpreted based on the occurrence of an inclined surface during the ablation and on the consequent differential absorption of s- and p-polarized components of the laser radiation by stainless-steel. The resulting anisotropy of the absorbed energy mimics irradiation with elliptical polarization that can drive formation of ripple-like, elongated nanostructures
Molecular dynamics model for the antibactericity of textured surfaces
Full text linkAn original model has been developed for the initial stage of bacterial adhesion on textured surfaces. Based on molecular dynamics, the model describes contact between individual bacterial cells in a planktonic state and a surface, accounting for both the mechanical properties of the cells and the physico-chemical mechanisms governing interaction with the substrate. Feasibility of the model is assessed via comparison with experimental results of bacterial growth on stainless steel substrates textured with ultrashort laser pulses. Simulations are performed for two different bacterial species, Staphylococcus aureus and Escherichia coli, on two distinct surface types characterised by elongated ripples and isolated nanopillars, respectively. Calculated results are in agreement with experiment outcomes and highlight the role of mechanical stresses within the cell wall due to deformation upon interaction with the substrate, creating unfavourable conditions for bacteria during the initial phases of adhesion. Furthermore, the flexibility of the model provides insight into the intricate interplay between topography and the physico-chemical properties of the substrate, pointing to a unified picture of the mechanisms underlying bacterial affinity to a textured surface
Systematic Repeatability Analysis of Nanosecond Pulsed Laser Texturing
No full textThe fabrication of specific surface features requires an adequate level of repeatability to be applied in industrial production environments. Although reference is frequently made to repeatability as a strength of many micro-machining techniques, few works in the literature have been dedicated to systematic and quantitative study of this parameter. The purpose of this work was therefore to quantitatively analyze the repeatability of textured surfaces with an original approach. Aluminum alloy substrates were textured with nanosecond laser pulses to produce micro-dimple arrays. Such features are widely employed to enhance wettability and tribological behavior, for which analysis was performed in terms of interfacial area and void volume. To give the work a more general character, two other parameters based on the definition of the Pearson’s Correlation Coefficient were also tested and compared to find the most suitable parameter for assessing repeatability for a given application. Finally, a study of the point-to-point repeatability of single surface features was conducted to detect variations in process repeatability in different portions of the same processed area. For the specific laser texturing process considered, it was found that an increase in total energy dose led to improved process repeatability
Molecular dynamics model for the antibactericity of textured surfaces
No full textAn original model has been developed for the initial stage of bacterial adhesion on textured surfaces. Based on molecular dynamics, the model describes contact between individual bacterial cells in a planktonic state and a surface, accounting for both the mechanical properties of the cells and the physico-chemical mechanisms governing interaction with the substrate. Feasibility of the model is assessed via comparison with experimental results of bacterial growth on stainless steel substrates textured with ultrashort laser pulses. Simulations are performed for two different bacterial species, Staphylococcus aureus and Escherichia coli, on two distinct surface types characterised by elongated ripples and isolated nanopillars, respectively. Calculated results are in agreement with experiment outcomes and highlight the role of mechanical stresses within the cell wall due to deformation upon interaction with the substrate, creating unfavourable conditions for bacteria during the initial phases of adhesion. Furthermore, the flexibility of the model provides insight into the intricate interplay between topography and the physico-chemical properties of the substrate, pointing to a unified picture of the mechanisms underlying bacterial affinity to a textured surface
Modelling the interaction between bacterial cells and laser-textured surfaces
Full text linkThe influence of surface topography resulting from ultrashort pulsed laser texturing on bacterial cell adhesion is studied as a method for preventing contamination on stainless steel components. The initial adhesion of a single spherical cell on a rough surface prior to the onset of any chemical or biological effect is simulated with a numerical approach including non-covalent interactions between the cell and textured substrate. The study demonstrates that when asperities are large enough to allow the cell to occupy valleys between two adjacent protrusions, the cell is protected from hydrodynamic turbulence and is therefore more prone to adhere to the substrate. Results pave the way to validating, in quantitative terms, hypotheses relating to the influence of surface topography on bacterial growth. Two different levels of anisotropy are taken into account to contrast the high adaptability of spherical cells, demonstrating that laser texturing can invoke a specific biological response
Influence of skin-layer microstructure in ultrafast laser surface treatment
Full text linkIn this work, the morphology of AISI 316L stainless steel surfaces, textured with ultrafast laser machining, was studied by scanning probe microscopy. In particular, correlations between the morphology and the polycrystalline microstructure of the material were searched. Topographic maps of the treated surfaces revealed a transition from small-sized to larger size and rather irregular features, driven by increase in laser fluence and depending on process parameters. In addition, a metrological analysis of the material grains demonstrated a shape and size similarity with laser-induced features attained for certain process parameters, suggesting that surface texture turns influenced by the microstructure of the skin-layer
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