Browsing by Author "Martina, Filomeno"
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Item Open Access Analysis of fracture toughness properties of wire + arc additive manufactured high strength low alloy structural steel components(Elsevier, 2020-08-14) Dirisu, Philip; Ganguly, Supriyo; Mehmanparast, Ali; Martina, Filomeno; Williams, Stewart W.The uncertainty surrounding the fracture behaviour of CMT-WAAM deposited steel, in terms of crack tip condition (J and CTOD) needed to cause crack tip extension, has made this manufacturing technique unpopular to date. Fracture toughness parameters are crucial in the structural integrity assessment of components and structures in various industries for assessing the suitability of a manufacturing process and material. In the offshore wind industry, the EN-GJS-400-18-LT ductile cast grade for the mainframe and hub has lower fracture toughness resistance for its high strength grade. Its high weight level affects the Eigen frequency of the tower and imposes high installation cost incurred from heavy lifting equipment usage. Poor fracture toughness is currently a challenge for wind turbine manufacturers in the quest for a cleaner and cheaper energy in the form of offshore wind. In this study, CMT-WAAM is used in depositing steel components with an oscillatory and single pass deposition strategy. The effects of microstructural variation, as a result of layer by layer deposition and the layer band spacing, on the fracture resistance in the build and welding direction was shown here. The fracture mechanics and failure mode of the WAAM deposited parts were investigated. The microstructural variation, again as a result of the layer by layer deposition and the layer band spacing, are the key parameters that control the fracture toughness of WAAM steel. Anisotropic behaviour in the values was observed between both fracture orientations. The constructive transformation mechanism of the WAAM oscillatory process made way for intragranular nucleation of acicular ferrite on the Ti containing inclusion, thereby improving the toughness of the ER70S-6 deposit with a unique microstructure and Jq value of 640kJ/m2.Item Open Access Analytical process model for wire + arc additive manufacturing(Elsevier, 2018-04-03) Sergio, Rios; Colegrove, Paul A.; Martina, Filomeno; Williams, Stewart W.An analytical process model for predicting the layer height and wall width from the process parameters was developed for wire + arc additive manufacture of Ti-6Al-4V, which includes inter-pass temperature and material properties. Capillarity theory predicted that cylindrical deposits were produced where the wall width was less than 12 mm (radius <6 mm) due to the large value of the surface tension. Power was predicted with an accuracy of ±20% for a wide range of conditions for pulsed TIG and plasma deposition. Interesting differences in the power requirements were observed where a surface depression was produced with the plasma process due to differences in melting efficiency and/or convection effects. Finally, it was estimated the impact of controlling the workpiece temperature on the accuracy of the deposit geometry.Item Open Access Analytical process model for wire + arc additive manufacturing(Elsevier, 2018-04-03) Ríos, Sergio; Colegrove, Paul A.; Martina, Filomeno; Williams, Stewart W.An analytical process model for predicting the layer height and wall width from the process parameters was developed for wire + arc additive manufacture of Ti-6Al-4V, which includes inter-pass temperature and material properties. Capillarity theory predicted that cylindrical deposits were produced where the wall width was less than 12 mm (radius <6 mm) due to the large value of the surface tension. Power was predicted with an accuracy of ±20% for a wide range of conditions for pulsed TIG and plasma deposition. Interesting differences in the power requirements were observed where a surface depression was produced with the plasma process due to differences in melting efficiency and/or convection effects. Finally, it was estimated the impact of controlling the workpiece temperature on the accuracy of the deposit geometry.Item Open Access Application of bulk deformation methods for microstructural and material property improvement and residual stress and distortion control in additively manufactured components(Elsevier, 2016-11-08) Colegrove, Paul A.; Donoghue, J.; Martina, Filomeno; Gu, Jianglong; Prangnell, P. B.; Honnige, JanMany additively manufactured (AM) materials have properties that are inferior to their wrought counterparts, which impedes industrial implementation of the technology. Bulk deformation methods, such as rolling, applied in-process during AM can provide significant benefits including reducing residual stresses and distortion, and grain refinement. The latter is particularly beneficial for titanium alloys where the normally seen large prior β grains are converted to a fine equiaxed structure – giving isotropic mechanical properties that can be better than the wrought material. The technique is also beneficial for aluminium alloys where it enables a dramatic reduction in porosity and improved ductility.Item Open Access A comparative study of additive manufacturing techniques: Residual stress and microstructural analysis of CLAD and WAAM printed Ti-6Al-4V components(Elsevier, 2015-09-28) Szost, Blanka A.; Terzi, Sofiane; Martina, Filomeno; Boisselier, Didier; Prytuliak, Anastasiia A.; Pirling, Thilo; Hofmann, Michael; Jarvis, David JohnNowadays, there is a great manufacturing trend in producing higher quality net-shape components of challenging geometries. One of the major challenges faced by additive manufacturing (AM) is the residual stresses generated during AM part fabrication often leading to unacceptable distortions and degradation of mechanical properties. Therefore, gaining insight into residual strain/stress distribution is essential for ensuring acceptable quality and performance of high-tech AM parts. This research is aimed at comparing microstructure and residual stress built-up in Ti–6Al–4V AM components produced by Wire + Arc Additive Manufacturing (WAAM) and by laser cladding process (CLAD).Item Open Access Compression behaviour of wire+ arc additive manufactured structures(MDPI, 2021-05-27) Abbaszadeh, Masoud; Ventzke, Volker; Neto, Leonor; Riekehr, Stefan; Martina, Filomeno; Kashaev, Nikolai; Hönnige, Jan; Williams, Stewart; Klusemann, BenjaminIncreasing demand for producing large-scale metal components via additive manufacturing requires relatively high building rate processes, such as wire + arc additive manufacturing (WAAM). For the industrial implementation of this technology, a throughout understanding of material behaviour is needed. In the present work, structures of Ti-6Al-4V, AA2319 and S355JR steel fabricated by means of WAAM were investigated and compared with respect to their mechanical and microstructural properties, in particular under compression loading. The microstructure of WAAM specimens is assessed by scanning electron microscopy, electron back-scatter diffraction, and optical microscopy. In Ti-6Al-4V, the results show that the presence of the basal and prismatic crystal planes in normal direction lead to an anisotropic behaviour under compression. Although AA2319 shows initially an isotropic plastic behaviour, the directional porosity distribution leads to an anisotropic behaviour at final stages of the compression tests before failure. In S355JR steel, isotropic mechanical behaviour is observed due to the presence of a relatively homogeneous microstructure. Microhardness is related to grain morphology variations, where higher hardness near the inter-layer grain boundaries for Ti-6Al-4V and AA2319 as well as within the refined regions in S355JR steel is observed. In summary, this study analyzes and compares the behaviour of three different materials fabricated by WAAM under compression loading, an important loading condition in mechanical post-processing techniques of WAAM structures, such as rolling. In this regard, the data can also be utilized for future modelling activities in this direction.Item Open Access Data for paper entitled "Laser stabilization of GMAW additive manufacturing of Ti-6Al-4V components"(Cranfield University, 2019-05-09 12:07) Rodrigues Pardal, Goncalo; Martina, Filomeno; Williams, StewartData used in paper "Laser stabilization of GMAW additive manufacturing of Ti-6Al-4V components"Item Open Access Defining next-generation additive manufacturing applications for the Ministry of Defence (MoD)(Elsevier, 2016-11-02) Busachi, Alessandro; Erkoyuncu, John Ahmet; Colegrove, Paul A.; Drake, Richard; Watts, Chris; Martina, Filomeno“Additive Manufacturing” (AM) is an emerging, highly promising and disruptive technology which is catching the attention of the Defence sector due to the versatility it is offering. Through the combination of design freedom, technology compactness and high deposition rates, technology stakeholders can potentially exploit rapid, delocalized and flexible production. Having the capability to produce highly tailored, fully dense, potentially optimized products, on demand and next to the point of use makes this emerging and immature technology a game changer in the “Defence Support Service” (DS2) sector. Furthermore, if the technology is exploited for the Royal Navy, featured with extended and disrupted supply chains, the benefits are very promising. While most of the AM research and efforts are focusing on the manufacturing/process and design opportunities/topology optimization, this paper aims to provide a creative but educated and validated forecast on what AM can do for the Royal Navy in the future. This paper aims to define the most promising next generation Additive Manufacturing applications for the Royal Navy in the 2025 – 2035 decade. A multidisciplinary methodology has been developed to structure this exploratory applied research study. Moreover, different experts of the UK Defence Value Chain have been involved for primary research and for verification/validation purposes. While major concerns have been raised on process/product qualification and current AM capabilities, the results show that there is a strong confidence on the disruptive potential of AM to be applied in front-end of DS2 systems to support “Complex Engineering Systems” in the future. While this paper provides only next-generation AM applications for RN, substantial conceptual development work has to be carried out to define an AM based system which is able to, firstly satisfy the “spares demands” of a platform and secondly is able to perform in critical environments such as at sea.Item Open Access Design for additive manufacturing: Trends, opportunities, considerations, and constraints(Elsevier, 2016-06-25) Thompson, Mary Kathryn; Moroni, Giovanni; Vaneker, Tom; Fadel, Georges; Campbell, R. Ian; Gibson, Ian; Bernard, Alain; Schulz, Joachim; Graf, Patricia; Ahuja, Bhrigu; Martina, FilomenoThe past few decades have seen substantial growth in Additive Manufacturing (AM) technologies. However, this growth has mainly been process-driven. The evolution of engineering design to take advantage of the possibilities afforded by AM and to manage the constraints associated with the technology has lagged behind. This paper presents the major opportunities, constraints, and economic considerations for Design for Additive Manufacturing. It explores issues related to design and redesign for direct and indirect AM production. It also highlights key industrial applications, outlines future challenges, and identifies promising directions for research and the exploitation of AM's full potential in industry.Item Open Access Design for wire + arc additive manufacture: design rules and build orientation selection(Taylor & Francis, 2017-08-20) Lockett, Helen L.; Ding, Jialuo; Williams, Stewart W.; Martina, FilomenoWire + Arc Additive Manufacture (WAAM) is an additive manufacturing technology that can produce near net-shape parts layer by layer in an automated manner using welding technology controlled by a robot or CNC machine. WAAM has been shown to produce parts with good structural integrity in a range of materials including titanium, steel and aluminium and has the potential to produce high value structural parts at lower cost with much less waste material and shorter lead times that conventional manufacturing processes. This paper provides an initial set of design rules for WAAM and presents a methodology for build orientation selection for WAAM parts. The paper begins with a comparison between the design requirements and capabilities of WAAM and other additive manufacturing technologies, design guidelines for WAAM are then presented based on experimental work. A methodology to select the most appropriate build orientation for WAAM parts is then presented using a multi attribute decision matrix approach to compare different design alternatives. Two aerospace case study parts are provided to illustrate the methodology.Item Open Access Design of an empirical process model and algorithm for the Tungsten Inert Gas wire+arc additive manufacture of TI-6AL-4V components(University of Texas, 2013-08-31) Martina, Filomeno; Williams, Stewart W.; Colegrove, Paul A.In the wire+arc additive manufacture process parameters can be varied to achieve a wide range of deposit widths, as well as layer heights. Pulsed Tungsten Inert Gas was chosen as the deposition process. A working envelope was developed, which ensures unfeasible parameters combinations are excluded from the algorithm. Thanks to an extensive use of a statistically designed experiment, it was possible to produce process equations through linear regression, for both wall width and layer height. These equations are extremely useful for automating the process and reducing the buy-to-fly ratio. For a given layer height process parameters can be selected to achieve the required layer width while maximising productivity.Item Open Access Designing a WAAM based manufacturing system for defence applications(Elsevier, 2015-10-09) Busachi, Alessandro; Erkoyuncu, John Ahmet; Colegrove, Paul A.; Martina, Filomeno; Ding, JialuoCurrent developments in “Wire+Arc Additive Manufacturing” (WAAM) have demonstrated the suitability of the technology for rapid, delocalized and flexible manufacturing. Providing a defence platform with the ability of on-board WAAM capability, would give the platform unique advantages such as improved availability of its systems and ability to recover its capability after being subject to shock. This paper aims to investigate WAAM technology and define a WAAM based manufacturing system for In-platform applications.Item Open Access Development of Wire + Arc additive manufacture for the production of large-scale unalloyed tungsten components(Elsevier, 2019-05-11) Marinelli, Gianrocco; Martina, Filomeno; Ganguly, Supriyo; Williams, Stewart W.The manufacturing of refractory-metals components presents some limitations induced by the materials' characteristic low-temperature brittleness and high susceptibility to oxidation. Powder metallurgy is typically the manufacturing process of choice. Recently, Wire + Arc Additive Manufacture has proven capable to produce fully-dense large-scale metal parts at relatively low cost, by using high-quality wire as feedstock. In this study, this technique has been used for the production of large-scale tungsten linear structures. The orientation of the wire feeding has been studied and optimised to obtain defect-free tungsten deposits. In particular, front wire feeding eliminated the occurrence of pores and micro-cracks, when compared to side wire feeding. The microstructure, the occurrence of defects and their relationship with the deposition process have also been discussed. Despite the repetitive thermal cycles and the inherent brittleness of the material, the as-deposited structures were free from internal cracks and the layer dimensions were stable during the entire deposition process. This enabled the production of a relatively large-scale component, with the dimension of 210 × 75 × 12 mm. This study has demonstrated that Wire + Arc Additive Manufacture can be used to produce large-scale parts in unalloyed tungsten by complete fusion, presenting a potential alternative to the powder metallurgy manufacturing route.Item Open Access Effect of deposition strategies on fatigue crack growth behaviour of wire+ arc additive manufactured titanium alloy Ti-6Al-4V(Elsevier, 2021-04-03) Syed, Abdul Khadar; Zhang, Xiang; Davis, Alec E.; Kennedy, Jacob R.; Martina, Filomeno; Ding, Jialuo; Williams, Stewart; Prangnell, Philip B.The influence of three deposition strategies on the fatigue crack growth behaviour of Wire + Arc Additive Manufactured (WAAM) Ti–6Al–4V has been investigated in the as-built condition. Test samples were prepared using single pass, parallel pass, and oscillation deposition strategies and tested with cracks propagating parallel and normal to the plane of deposition. Due to the higher local heat input, the oscillation build exhibited a significantly coarser columnar β grain structure as well as a coarser transformation microstructure, compared to the single pass and parallel pass builds, which were very similar. Among the three build methods, the lowest crack growth rates were found with the oscillation build. The crack growth data was found to broadly fall between that of a recrystallized α (mill-annealed) and β annealed wrought material, with the oscillation strategy build behaving more similarly to a β annealed microstructure. The fatigue crack growth rate was lower when cracks were propagated perpendicular to the build layers. For each build strategy, a greater microstructural influence on crack growth rate was found at lower levels of stress intensity factor range (<25 MPa m1/2). However, the anisotropy and scatter in the data was much more significant in the case of the oscillation build. These differences have been attributed to the stronger α microtexture heterogeneity present in the oscillation build, which led to a greater crack deflection and bifurcation, giving rise to lower crack growth rates and a higher sensitivity to the anisotropy caused by the directional β grain structure.Item Open Access The effect of loading direction on strain localisation in wire arc additively manufactured Ti–6Al–4V(Elsevier, 2020-05-21) Lunt, David; Ho, Alistair; Davis, Alec E.; Harte, Allan; Martina, Filomeno; da Fonseca, João Quinta; Prangnell, PhilipTi–6Al–4V microstructures produced by high deposition rate Wire Arc Additive Manufacturing (WAAM) can be both heterogeneous and anisotropic. Key features of the as-built microstructures include; large columnar ß grains, an α transformation texture inherited from the β solidification texture, grain boundary (GB) α colonies, and Heat Affected Zone (HAZ) banding. The effect of this heterogeneity on the local strain distribution has been investigated using Digital Image Correlation (DIC) in samples loaded in tension; parallel (WD), perpendicular (ND) and at 45° (45ND) to the deposited layers. Full-field surface strain maps were correlated to the underlying local texture. It is shown that loading perpendicular to the columnar β grains leads to a diffuse heterogeneous deformation distribution, due to the presence of regions containing hard, and soft, α microtextures within different parent β grains. The ‘soft’ regions correlated to multi-variant α colonies that did not contain a hard α variant unfavourably orientated for basal or prismatic slip. Far more severe strain localisation was seen in 45° ND loading at ‘soft’ β grain boundaries, where single variant α GB colonies favourably orientated for slip had developed during transformation. In comparison, when loaded parallel to the columnar ß grains, the strain distribution was relatively homogeneous and the HAZ bands did not show any obvious influence on strain localisation at the deposit layer-scale. However, when using high-resolution DIC, as well as more intense shear bands being resolved at the β grain boundaries during 45° ND loading, microscale strain localisation was observed in HAZ bands below the yield point within the thin white-etching α colony layer.Item Open Access Effect of shielding gas composition and welding speed on autogenous welds of unalloyed tungsten plates(Elsevier, 2019-07-30) Marinelli, Gianrocco; Martina, Filomeno; Ganguly, Supriyo; Williams, Stewart W.Tungsten usually exhibits poor weldability and marked brittleness at room temperature. This causes tungsten welds to be affected by the evolution of cracks along the weld bead, which can be eliminated by using a pre-heating step to reduce thermal straining. In this study, based on the tungsten inert gas welding process, a working envelope, focussed on varying welding speed and five different shielding gas mixtures of argon and helium, has been defined with the view of producing crack-free autogenous welds. The bead appearance and the microstructure of the different welds were correlated to the welding parameters, whose main effects have been analysed. Welding defects such as humping occurred when using gas mixtures with relatively low content of helium, and when using relatively high welding speeds. Crack-free autogenous welds have been produced without pre-heating when using a high content of helium and relatively low welding speeds. Thus, this study has demonstrated that a helium-rich shielding gas is required for welding thick tungsten plates. Moreover, the low thermal shock induced by the process, coupled with the purity of the tungsten plates used, strongly contributed to avoid the occurrence of any crack.Item Open Access The effectiveness of combining rolling deformation with wire-arc additive manufacture on β-Grain refinement and texture modification in Ti-6Al-4V(Elsevier, 2016-02-08) Donoghue, J.; Anthonysamy, A. A.; Martina, Filomeno; Colegrove, Paul A.; Williams, Stewart W.; Prangnell, P. B.In Additive Manufacture (AM), with the widely used titanium alloy Ti–6Al–4V, the solidification conditions typically result in undesirable, coarse-columnar, primary β grain structures. This can result in a strong texture and mechanical anisotropy in AM components. Here, we have investigated the efficacy of a new approach to promote β grain refinement in Wire–Arc Additive Manufacture (WAAM) of large scale parts, which combines a rolling step sequentially with layer deposition. It has been found that when applied in-process, to each added layer, only a surprisingly low level of deformation is required to greatly reduce the β grain size. From EBSD analysis of the rolling strain distribution in each layer and reconstruction of the prior β grain structure, it has been demonstrated that the normally coarse centimetre scale columnar β grain structure could be refined down to < 100 μm. Moreover, in the process both the β and α phase textures were substantially weakened to close to random. It is postulated that the deformation step causes new β orientations to develop, through local heterogeneities in the deformation structure, which act as nuclei during the α → β transformation that occurs as each layer is re-heated by the subsequent deposition pass.Item Open Access Fatigue crack growth in additive manufactured titanium: residual stress control and life evaluation method development(VTT Information Service, 2017-06-09) Zhang, Xiang; Martina, Filomeno; Syed, Abdul Khadar; Wang, Xueyuan; Ding, Jialuo; Williams, Stewart W.This paper presents fatigue crack growth behaviour in titanium alloy Ti-6Al-4V built by the Wire + Arc Additive Manufacture (WAAM®) process. Process induced residual stress and stress relief by cold working were measured by neutron diffraction and contour methods. Residual stress retained in the compact tension test specimens was evaluated by the finite element method based on the measured stresses in the WAAM wall. Fatigue crack growth rate in as-built and stress relieved conditions are discussed with respect of the effects of material build orientation, residual stress, and microstructure characteristics. Key conclusions are: (a) residual stresses arising from the WAAM process can be controlled and reduced significantly by cold working. Residual stress retained in compact tension specimens is low, resulting in low residual stress intensity factor. (b) Microstructure affects fatigue crack growth rate in twodifferent material’s build orientations. (c) Fatigue crack growth rate in WAAM Ti-6Al-4V is lower than that in traditional wrought plate, with and without the residual stress relief. Therefore, WAAM is a viable additive manufacture process to produce aerospace titanium alloys for damage tolerance design.Item Open Access Fracture toughness and fatigue crack growth rate properties in wire + arc additive manufactured Ti-6Al-4V(Wiley, 2016-11-29) Zhang, Xiang; Martina, Filomeno; Ding, Jialuo; Wang, X.; Williams, Stewart W.This paper presents an experimental investigation of the fracture and fatigue crack growth properties of Ti-6Al-4V produced by the Wire + Arc Additive Manufacture (WAAM) process. First, fracture toughness was measured for two different orientations with respect to the build direction; the effect of wire oxygen content and build strategy were also evaluated in the light of microstructure examination. Second, fatigue crack growth rates were measured for fully additive manufactured samples, as well as for samples containing an interface between WAAM and wrought materials. The latter category covers five different scenarios of crack location and orientation with respect to the interface. Fatigue crack growth rates are compared with that of the wrought or WAAM alone conditions. Crack growth trajectory of these tests is discussed in relation to the microstructure characteristicsItem Open Access Functionally graded structures of refractory metals by Wire Arc Additive Manufacturing(Maney Publishing, 2019-03-11) Marinelli, Gianrocco; Martina, Filomeno; Ganguly, Supriyo; Williams, Stewart W.; Lewtas, Heather; Hancock, DavidFunctionally graded components are usually preferred for severe and critical service conditions, thanks to the possibility of achieving different complementary material properties within the same structure. Wire + Arc Additive Manufacturing is an emerging technology which lends itself well to the production of sound graded structures. In this study, an integral structure of two functional gradients, namely tantalum to molybdenum, and molybdenum to tungsten, was successfully deposited. A linear gradient was observed in both composition and hardness. Microstructure, elemental composition and hardness were characterised as a function of position, and discussed. The study demonstrates that WAAM has the potential to successfully deposit functionally graded structures of refractory metals, obtaining controlled properties
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