
Denis P DowlingUniversity College Dublin | UCD · School of Mechanical and Materials Engineering
Denis P Dowling
PhD MIE, CEng, FIMF, MICI
About
358
Publications
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Introduction
Denis P Dowling directs the Science Foundation Ireland funded I-Form Advanced Manufacturing Research Centre. This Centre combined a focus on materials processing and the use of digital technology in manufacturing. Denis is based at the School of Mechanical and Materials Engineering, University College Dublin. My core research work is focused on Surface Engineering and Additive Manufacturing. Application areas include medical devices, engineering composites and solar energy. My initial research work was on the deposition and characterisation of nano and micron thick coatings deposited using plasma processes. Increasingly I am applying this 'surface' expertise to tailor the properties of particles and fibres used in the fabrication of components by additive manufacturing.
Additional affiliations
December 2008 - present
Publications
Publications (358)
The study brings together in a single publication the phase-space projection analysis of microwave-assisted synthesis of transition monometallic (palladium, silver, platinum, and gold), binary zinc oxide, and metals supported on carbon framework nanostructures. It is shown for a database of fifty microwave-assisted syntheses, a two-variable power-l...
The evolution of laser powder bed fusion (L-PBF) has provided increased design flexibility in the fabrication of a range of parts, including aerospace components and medical devices. The presence of overhangs in metal alloy print structures, however, can give rise to enhanced levels of print defects such as porosity. This is associated with overhea...
This study investigates the printability limitations of 3D-printed continuous 316L stainless steel fibre-reinforced polymer composites obtained using the Materials Extrusion (MEX) technique. The objective was to better understand the geometric printing limitations of composites fabricated using continuous steel fibres, based on a combination of ben...
This study investigates the influence of processing parameters, specifically laser power and scan speed, on the melt pool characteristics of Ti-6Al-4V alloy during Powder Bed Fusion–Laser Beam (PBF-LB) printing. The objective is to provide a deeper understanding of the melt pool based on in-process melt pool monitoring data obtained from a producti...
This study investigates the feasibility of 3D printing continuous stainless steel fibre-reinforced polymer composites. The printing study was carried out using 316L stainless steel fibre (SSF) bundles with an approximate diameter of 0.15 mm. This bundle was composed of 90 fibres with a 14 μm diameter. This fibre bundle was first coated with polylac...
Enhanced levels of alloy print defects such as porosity are associated with the printing of overhang structures by laser powder bed fusion (L-PBF). This study compared the microstructure and porosity of Ti-6Al-4V overhang structures, with that observed for the bulk alloy. It was observed in the region around the overhang structure that the microstr...
Geometrically complex features, such as overhang structures, can be a challenge in laser powder bed fusion (L-PBF), as they can be associated with print defects, such as porosity. In this study, Ti-6Al-4V alloy overhang structures were fabricated using an L-PBF system. Differences were observed in the microstructure in the region around the overhan...
This study investigated the print homogeneity of Ti-6Al-4 V alloy parts, when printed over a large build area of 250 × 250 × 170 mm3, using a production scale laser powder bed additive manufacturing system. The effect of part location across this large build area was investigated based on printed part porosity, microstructure, hardness, and tensile...
The objective of this study is to develop an operation that can conduct separations based on diafiltration using semipermeable nanofiltration or ultrafiltration membranes in a fully continuous manner in a single stage configuration.
BACKGROUND
COVID-19 continues to present challenges to both patient management and the protection of the airway management team involved, in particular in resource-constrained low-income countries. Among the most concerning complications in affected patients is rapid hypoxemic respiratory failure requiring tracheal intubation and mechanical ventila...
This paper discusses diverse data management approaches and proposes a comprehensive information model that is built from voxelated data from across the Additive Manufacturing and Computer Aided (AM – CAx) platforms workflow. The information model is developed using discretisation and data management techniques to provide a robust method of managin...
Additive manufacturing (AM) is widely used in the fabrication of metallic parts in sectors such as medical devices and aerospace. One key characteristic used to measure the quality of an AM produced part is the roughness of the printed alloy surface. Conventional methods for measuring roughness, such as the stylus and optical profilometer, have con...
This paper describes the use of log-linear energy phase-space projections to analyze microwave-assisted inactivation of bacteria and viruses under different fomite conditions within multimode microwave ovens. The ovens are operated at a cavity-magnetron frequency of 2.45 ± 01 GHz. Porous fomites (moist face towels, cotton swabs, kitchen sponges, an...
This presentation describes the use of energy phase-space projections to analyze microwave-assisted inactivation of bacteria and virus under different fomite conditions within multimode microwave ovens. Porous fomites (moist face towels, cotton swabs, kitchen sponges, and scrubbing pads, cigarette filters and N95-like respirators), along with non-p...
The first half of the twentieth century became the Golden Age of the dirigible airship. After the Hindenburg disaster, (1937), the dirigible use fell into rapid decline leaving the non-rigid airships to serve in maritime roles until the mid 1960s. Throughout dirigible and non-rigid use, violent storm systems have been associated with in-flight airs...
This study investigated the print homogeneity of Ti-6Al-4V alloy parts, when printed over a large build area of 250 Χ 250 Χ 170 mm ³ , using a production scale laser powder bed additive manufacturing system. The effect of part location across this large build area, was investigated based on printed part porosity, microstructure, hardness, and tensi...
This paper reviews three complex interactions between microwave energy and microorganisms (bacteria, fungi, and viruses). The first interaction comprises the detection of viruses within human blood using a 50-Ohm transmission-line vector net-analyzer (typically 0 to 10 dBm @ 2 to 8.5GHz) where the blood is placed within a test chamber that acts as...
This study investigated the difference between the properties of Ti-6Al-4V alloy parts printed using continuous wave (CW) and modulated wave (MW) laser emission modes, with equivalent input energy densities. Laser powers in this powder bed fusion process, were systematically altered to evaluate the effect of different input energies on the as-built...
The effect of furnace heat treatments to 850 °C, on the evolution of microstructureMicrostructurein Ti–6Al–4Ti-6Al-4VV alloy produced via selective laser melting (SLM), was studied using optical microscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Columnar prior-β grains in the build direction with lamellar α-martensite...
Since the beginning of recorded history Saint Elmo’s fire (SEF) has been observed and experienced by humans in and close to thunderstorms which are dissipating in strength, either at sea level or in mountainous regions. The systematic study of SEF in nature has proved difficult due to inadequate measurement equipment and the understanding of high-v...
This paper reviews the literature on the formation of carbon-based nanomaterials using converted domestic microwave oven plasma reactors. The carbon-based compounds range from single and multi-walled carbon nanotubes, to onion-like nanostructures, fullerene, and graphene sheets. The microwave plasma process is performed using in-liquid containing p...
Whether in the Hawaiian, Bluegrass, Rock ‘n’ roll, film sound track or animated cartoon genre, the swoop (glissando) sound made on a slide-guitar is one the most instantly recognizable in western music. This paper reports on the complex acoustical and perceptual glissando of the opening few seconds of Warner Brothers ‘Looney Tunes’ ascending glissa...
Dielectric volume heating of water inside a microwave oven, can generate steam which in-turn can be used for the decontamination of surfaces against bacteria and viruses. This microwave generated steam (MGS) has a number of potential applications, such as the decontamination of personal protective equipment. This paper focuses on the use of MGS for...
Since the beginning of recorded history Saint Elmo’s fire (SEF) has been observed and experienced by humans in and close to thunderstorms which are dissipating in strength, either at sea level or in mountainous regions. The systematic study of SEF in nature has proved difficult due to inadequate measurement equipment and the understanding of high-v...
This presentation brings new thermodynamic analysis* to MGS decontamination of respirators and masks
*V.J.Law and D.P. Dowling. Microwave generated steam decontamination of respirators: A thermodynamic analysis Global Journal of Research in Engineering & Computer Sciences
Volume 1(1), Sep-Oct, 2021.
During the two influenza pandemic’s (caused by H1N1 and SARS-Cov-2), over the past twenty years, the use of experimental microwave generated steam (MGS), has shown potential, for decontamination of single-use face respirators and surgical masks. Recent review articles of the decontamination of single-use respirator and face mask has been primarily...
The nanocomposites of nickel oxide (NiO) and zirconia (ZrO2) (NZNCs) are particularly effective photocathodic materials in p-type dye-sensitized solar cells (p-DSCs) and tandem DSCs (t-DSCs). The t-DSCs obtained from P1-sensitized NZNC as photocathode and nanostructured titania (TiO2) sensitized with squaraine VG10-C8 as photoanode display overall...
Multi Jet Fusion (MJF) is one of the newly developed additive manufacturing techniques, based on the use of powder bed fusion technology. It provides the opportunity to build up 3D, complex polymer geometries, without the need for support structures. This study evaluates the effect of build location across a 380 × 284 mm² build plate, on both the d...
MGS of decontamination of N954 respirators and face masks
In this study, a functionally graded material (FGM) was fabricated using a powder bed fusion additive manufacturing technique. The FGM evaluated was Ti–6Al–4V, due to its importance in the medical device and aerospace sectors. The microstructure at selected build locations was analysed using both scanning electron microscopy (SEM) and electron back...
This study investigates the use of a statistical anomaly detection method to analyse in-situ process monitoring data obtained during the Laser-Powder Bed Fusion of Ti-6Al-4V parts. The printing study was carried out on a Renishaw 500M Laser-Powder Bed Fusion system. A photodiode-based system called InfiniAM was used to monitor the melt-pool emissio...
The first half of the twentieth century became the Golden Age of the dirigible airship. After the Hindenburg disaster, (1937), the dirigible use fell into rapid decline leaving the non-rigid airships to serve in maritime roles until the mid 1960s. Throughout dirigible and non-rigid use, violent storm systems have been associated with in-flight airs...
Whether in the Hawaiian, Bluegrass, Rock’ n’ roll, film sound track or animated cartoon genre, the swoop (glissando) sound made on a slide-guitar is one the most instantly recognizable in western music. This paper reports on the complex acoustical and perceptual glissando of the opening few seconds of Warner Brothers ‘Looney Tunes’ ascending glissa...
Additively Manufactured (AM) titanium (Ti) components are routinely post-thermal heat treated (HT), to reduce internal stresses, as well as to obtain more desirable microstructural features, yielding improved mechanical performance. Currently, there is no consensus on the optimum HT method for AM Ti-6Al-4V, as the mechanism for the main phase trans...
COVID-19 continues to present challenges within the healthcare setting. COVID patients with rapid hypoxaemic respiratory failure require intubation supported by high-flow oxygen delivery and artificial respiration. However, intubation increases risk of exposure to aerosolized virus which is further compounded by concomitant oxygen delivery. As such...
Process monitoring and sensing is widely used across many industries for quality assurance, and for increasing machine uptime and reliability. Though still in the emergent stages, process monitoring is beginning to see strong adoption in the additive manufacturing community through the use of process sensors recording a wide range of optical, acous...
Additive manufacturing processes, such as Laser Powder Bed Fusion (L-PBF), facilitates the manufacture of porous biomaterials structures, which can be used for example to enhance bone tissue regeneration. In-situ process monitoring techniques such as meltpool emission monitoring are increasingly being applied for the monitoring of the l-PBF process...
The present work is concerned with adhesive bonding of thermoplastic composites used in general aerospace applications, including polyphenylene sulfide (PPS), polyetherimide (PEI) and polyetheretherketone (PEEK) carbon fibre composites. Three different surface treatments have been applied to the PEEK, PPS and PEI-based composites in order to enhanc...
This paper evaluates the mechanical properties of woven continuous carbon fibre composites printed by additive manufacturing (AM). Comparison mechanical test studies (tensile, flexural and fatigue) were carried out with two nonwoven AM printed composites (unidirectional and multidirectional fibres), along with those of both a woven composite, as we...
A low-cost, modular, robust, and easily customisable continuous liquid–liquid phase separator has been developed that uses a tubular membrane and annular channels to allow high fluidic throughputs while maintaining rapid, surface wetting dominated, phase separation.
The fourth industrial revolution (Industry 4.0) offers enhanced processing efficiencies and reduced downtime, however there is a lack of manufacturing training equipment for those seeking practical training in the key underpinning digital technologies. This paper reports on the development of a digital manufacturing training demonstrator, called th...
The present work investigates the effects of geometry and laser power on the porosity and melt pool formation for 316L stainless steel samples fabricated using the laser powder bed fusion (LPBF) technique. Both cylindrical and conical parts with the same heights were processed at a range of laser powers (60–70 W). An analytical model was used to se...
Additive Manufacturing (AM) is increasingly used for the fabrication of metallic components used in the medical device, aerospace and automotive industries. With the wider adoption of AM in these sectors, there is an increased demand for the in-situ process monitoring of the build process. This study investigates the performance of a photodiode bas...
Three-dimensional (3D) printing has been successfully applied for the fabrication of polymer components ranging from prototypes to final products. An issue, however, is that the resulting 3D printed parts exhibit inferior mechanical performance to parts fabricated using conventional polymer processing technologies, such as compression moulding. The...
This paper investigates the formation of process by-products during the laser processing of titanium alloy powders by Selective Laser Melting (SLM). The study was carried out during the printing of Ti6AL4V parts using a production scale SLM system (Renishaw RenAM500 M). By-product particles were obtained on the surface of powder removed from the ar...
This work studied the effects of adding short basalt fibers (BFs) and multi‐walled carbon nanotubes (MWCNTs), both separately and in combination, on the mechanical properties, fracture toughness, and electrical conductivity of an epoxy polymer. The surfaces of the short BFs were either treated using a silane coupling agent or further functionalized...
Since the beginning of recorded history Saint Elmo’s fire (SEF) has been observed and experienced by humans in and close to thunderstorms which are dissipating in strength, either at sea level or in mountainous regions. The systematic study of SEF in nature has proved difficult due to inadequate measurement equipment and the understanding of high-v...
This paper reviews the literature on the formation of carbon-based nanomaterials using converted domestic microwave oven plasma reactors. The carbon-based compounds range from single and multi-walled carbon nanotubes, to onion-like nanostructures, fullerene, and graphene sheets. The microwave plasma process is performed using in-liquid containing p...
Chemically resistant parts for flow chemistry, with integrated mixing elements have been produced using the 3D printing process of fused filament fabrication, from poly(etheretherketone). Poly(etheretherketone) has greater chemical resistance than common fused filament fabrication materials such as acrylonitrile butadiene styrene, polypropylene, or...
Selective Laser Melting allows for the creation of intricate porous structures, that possess favourable biological properties. These structures are known as porous biomaterials. The focus of this paper is to evaluate the use of an in-line photodiode based process monitoring system, for the monitoring of the operational behaviour of the laser, and t...
Additive manufacturing is being increasingly used in the fabrication of Ti-6Al-4V parts to combine excellent mechanical properties and biocompatibility with high precision. Unfortunately, due to the build-up of thermal residual stresses and the formation of martensitic structure across a wide range of typical processing conditions, it is generally...
The enhancement of photoelectrochemical conversion efficiency of p-type dye-sensitized solar cells (p-DSSCs) is necessary to build up effective tandem devices in which both anode and cathode are photoactive. The efficiency of a p-type device (2.5%) is roughly one order of magnitude lower than the n-type counterparts (13.1%), thus limiting the overa...
Over the last 20 years microwave power supplies in domestic microwave ovens have increasingly found applications in plasma reactors for processing of functional carbon-based nanostructures for engineering materials, electronics and biomedical applications. However, the packaged magnetrons used in the microwave ovens are known to suffer from moding...
This study investigated the effect of laser power on the properties of Ti-6Al-4V alloy parts produced by additive manufacturing. The printing study was carried out using the laser beam powder bed fusion (PBF-LB) technique (Renishaw RenAM 500M). The laser power was altered in the range of 100–400 W, in order to evaluate the effects of changing the i...
This study investigates the material and mechanical properties of both polyamide 12 (PA12) and reinforced glass bead PA12 composites, fabricated using a production scale additive manufacturing (AM) process. The printing studies were carried out using the production scale, Multi Jet Fusion powder bed fusion process. The study demonstrated that the c...
Tidal turbine applications will place composite materials such as glass-fibre-reinforced polymers (GFRPs) and carbon-fibre-reinforced polymers under surprisingly high pressure due to the significant water depths they operate in (to depths of 50 m). The technical reliability of tidal turbines must be guaranteed despite the high dynamic loads resulti...
Selective Laser Melting (SLM) facilitates the formation of complex, stochastic or non-stochastic, metallic cellular structures. There is a high level of interest in these structures recently, particularly due to their high strength to weight ratios and osteoconductive properties. While the ability to in-situ monitor the SLM process is of key import...
The objective of this study is to investigate the use of an air atmospheric plasma jet for the treatment of sized basalt fibers, used in the fabrication of continuous fiber‐reinforced polypropylene filaments. The plasma treatments were carried out both at a laboratory scale, as well as in‐line during the production of fiber‐reinforced filaments. Th...
Carbon–fibre epoxy composites are widely used for high-performance structural applications, where they are often exposed to harsh environments. The result of moisture ingress has been extensively studied, causing significant deterioration in the mechanical properties of these composites. This study evaluates the performance of five commercial hydro...
Continuous fiber‐reinforced polymer composites have found a wide range of applications in the automotive and aerospace industry due to their lightweight properties. Recently the use of additive manufacturing (AM) has been developed for the fabrication of these composites. This study investigates the use of both atmospheric and, for the first time,...