Life cycle analysis of engineering polymer joining methods using adhesive bonding: Fatigue performance and environmental implications

Traditional assembly processes such as screw fastening and riveting are increasingly being replaced by new processes such as adhesive bonding. Life cycle performance including fatigue and durability are critical, for which surface activation techniques are often used with the aim of improving both mechanical and life cycle performance. Within this context, the present paper aims to investigate the life cycle performance of adhesive bonding in relation to engineering polymers considering four surface pre-treatments: mechanical, chemical, plasma, and laser activation. The work focuses on two key aspects: (i) mechanical characterization of fatigue performance by assessing the useful life of joints, and (ii) environmental analysis through Life Cycle Assessment (LCA). The outcome of this study provides important insight into the development of laser and plasma technologies as sustainable surface activation methods for polymer joining methods. The substitution of traditional joining methods (i.e., bolting, riveting) with adhesive bonding will allow reductions in overall product weight to be achieved

As‐built surface quality and fatigue resistance of Inconel 718 obtained by additive manufacturing

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Influence of ns laser texturing of AISI 316L surfaces for reducing bacterial adhesion

Nanosecond 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

Molecular dynamics model for the antibactericity of textured surfaces

An 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

LCA of laser surface activation and traditional pre-treatments for adhesive bonding of engineering polymers

The use of engineering polymers for mechanical applications has seen increasing uptake due to properties such as low density, flexibility, ease of manufacturing and cost effectiveness. Despite these advantages, joining and assembly methods for these types of materials is still an open issue. Traditional assembly processes such as screw fastening and riveting are increasingly being replaced by new processes such as adhesive bonding. Engineering polymers, however, are difficult to bond using adhesives due to their low surface energy and low wettability. For this reason, surface chemical activation techniques with primers are often used. The utilization of various chemicals associated with such pre-treatments has a significant environmental impact. Within this context, the present paper aims to compare the environmental performance of four adhesive bonding pre-treatments: (i) mechanical (i.e., abrasion), (ii) chemical (i.e., primer), (iii) plasma and (iv) laser activation. The work was performed in three phases: (i) setup of the surface activation processes, (ii) mechanical characterization of bonded joints (static tests) and (iii) LCA analysis to evaluate and compare the different pre-treatments. The outcome of this study provides important insight into the development of laser and plasma technologies as sustainable surface activation methods for polymers through the creation of models correlating process parameters to the type of surface and joint strength

Modelling of the surface morphology and size effects on fatigue strength of L-PBF Inconel 718 by comparing different testing specimens

The aim of this study was to investigate the impact of surface roughness and size effect on the uniaxial fatigue strength of aged specimens made of Inconel 718, obtained by laser-powder bed fusion (L-PBF) both under as-built and machined surface conditions. The surface profiles were scanned with a 3D optical profilometer, and then modelled and filtered by the fast Fourier transform. This latter allowed to obtain the relevant parameters to calculate the term sqrt(area) in the Murakami model to account for the effect of surface roughness on fatigue strength prediction. Two additional terms were added to the standard Murakami formula: one to account for the size effect and the other to consider the nonzero value of the average stress. A cylindrical plain and a miniaturized plain specimens, in the as-built condition, were employed to calibrate the proposed model, while a machined plain cylindrical and a miniaturized notched specimens were used as validators with low prediction errors

Modelling of Thin-Film Single and Multi-Layer Nanosecond Pulsed Laser ProcessingVolume 1: Processing

A complete model of nanosecond pulsed laser scribing of arbitrary thin multi-layer structures is presented. The chain of events is separated according to time-scale; an initial simulation considers material response during the pulse; another combines this result with the much slower effects of heat flow away from the laser axis. The former considers heating, vaporisation and phase explosion of metals in the course of a single pulse, accounting for variations in thermal conductivity and optical absorption as the material becomes superheated and approaches its critical temperature. The latter calculates the bidimensional heat flow in a complete multi-layer structure over the course of a scribing operation, combining material properties and considering removal by both short-pulse ablation and long-term heating of the work piece. Simulation results for the single pulse ablation of an aluminium target align well with published experimental data both in terms of phase explosion threshold and ablation depth as a function of fluence. Bidimensional heat flow simulations of a polypropylene–aluminium–polypropylene triplex structure reveal the progression of events towards steady state behaviour; aluminium ejected due to short-pulse ablation and plastic removed due to conduction.</jats:p

An improved model for nanosecond pulsed laser ablation of metals

A model is presented for the ablation of metals by nanosecond laser pulses, based on one-dimensional heat flow with temperature dependent material properties. A numerical optical calculation is introduced to account for laser beam absorption in the target, utilizing established matrix methods for electromagnetic plane wave propagation in multi-layered media. By including the effects of reflection from the dielectric-metal interface, the fall in reflectivity of aluminum during nanosecond laser pulses above the phase explosion threshold is found to be approximately twice that calculated in previous works. A simulated shielding coefficient is introduced to account for reflection and absorption of the incident laser beam by the ablation products. With these additions to foregoing models, good agreement between calculated and published experimental ablation data is attained for aluminum, both in terms of ablation threshold and depth. An investigation is subsequently carried out into the effects of laser wavelength, pulse duration and target thickness on the phase explosion threshold of aluminum. © 2013 AIP Publishing LLC

Modeling of thin-film single and multilayer nanosecond pulsed laser processing

A complete model of nanosecond pulsed laser scribing of arbitrary thin multilayer structures is presented. The chain of events is separated according to time-scale; an initial simulation considers material response during the pulse; another combines this result with the much slower effects of heat flow away from the laser axis. The former considers heating, vaporization and phase explosion of metals in the course of a single pulse, accounting for variations in thermal conductivity and optical absorption as the material becomes superheated and approaches its critical temperature. The latter calculates the bidimensional heat flow in a complete multilayer structure over the course of a scribing operation, combining material properties and considering removal by both short-pulse ablation and long-term heating of the work piece. Simulation results for the single pulse ablation of an aluminum target align well with published experimental data both in terms of phase-explosion threshold and ablation depth as a function of fluence. Bidimensional heat flow simulations of a polypropylene-aluminum-polypropylene triplex structure reveal the progression of events toward steady state behavior; aluminum ejected due to short-pulse ablation and plastic removed due to conduction. Copyright © 2013 by ASME