- South West Engineering Building, 1st Floor, Room 121, East Campus, Yale Road, Braamfontein, 2050, Johannesburg
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- Fatigue, Fracture Mechanics, Finite Element Analysis (Engineering), Laser Shock Peening, Additive Manufacturing, Titanium machining, and 4 moreCold Gas Dynamic Spraying, Friction Stir Welding, Residual Stress (Engineering), and Metallurgy and Materials Engineering(Cold Gas Dynamic Spraying, Friction Stir Welding, Residual Stress (Engineering), and Metallurgy and Materials Engineering)edit
- Professor Claudia Polese has a strong background in aeronautical metal structures and innovative aerospace technologi... moreProfessor Claudia Polese has a strong background in aeronautical metal structures and innovative aerospace technologies. She obtained her Masters and PhD at the Department of Aerospace Engineering of the University of Pisa, Italy. She worked as Research Engineer at the Institute of Materials Research of the German Aerospace Center (DLR) in Cologne, Germany, and in two European Framework Programs focused on advanced structural concepts. In 2009 she was appointed Associate Professor in Aerospace Manufacturing and Design at the School of Mechanical, Industrial and Aeronautical Engineering of the University of the Witwatersrand, Johannesburg, South Africa, and Advisory Aerospace Research Director of the National Aerospace Centre. A National Research Foundation rated researcher from 2011 and a Fellow of the Royal Aeronautical Society, Prof. Polese is also deeply involved in the activities of the DSI-NRF Centre of Excellence in Strong Materials, and she is currently Head of the Aeronautical Engineering Stream in the School.
Prof. Polese has significantly strengthened the South African research in the area of advanced manufacturing processes, e.g. Friction Stir Welding, Titanium Machining, Additive Manufacturing, Cold Spray, and in particular Laser Shock Peening in collaboration with the National Laser Centre of the Council for Scientific and Industrial Research, Airbus, and several international institutions.(Professor Claudia Polese has a strong background in aeronautical metal structures and innovative aerospace technologies. She obtained her Masters and PhD at the Department of Aerospace Engineering of the University of Pisa, Italy. She worked as Research Engineer at the Institute of Materials Research of the German Aerospace Center (DLR) in Cologne, Germany, and in two European Framework Programs focused on advanced structural concepts. In 2009 she was appointed Associate Professor in Aerospace Manufacturing and Design at the School of Mechanical, Industrial and Aeronautical Engineering of the University of the Witwatersrand, Johannesburg, South Africa, and Advisory Aerospace Research Director of the National Aerospace Centre. A National Research Foundation rated researcher from 2011 and a Fellow of the Royal Aeronautical Society, Prof. Polese is also deeply involved in the activities of the DSI-NRF Centre of Excellence in Strong Materials, and she is currently Head of the Aeronautical Engineering Stream in the School. <br />Prof. Polese has significantly strengthened the South African research in the area of advanced manufacturing processes, e.g. Friction Stir Welding, Titanium Machining, Additive Manufacturing, Cold Spray, and in particular Laser Shock Peening in collaboration with the National Laser Centre of the Council for Scientific and Industrial Research, Airbus, and several international institutions.)edit
Laser powder bed fusion (L-PBF) has the potential to be applied in the production of titanium aircraft components with good mechanical properties, provided the technology has been qualified and accepted in the aviation industry. To... more
Laser powder bed fusion (L-PBF) has the potential to be applied in the production of titanium aircraft components with good mechanical properties, provided the technology has been qualified and accepted in the aviation industry. To achieve acceptance of the L-PBF technology in the aircraft industry, mechanical property data needed for the qualification process must be generated according to accepted testing standards. The impact toughness of Ti6Al4V extra low interstitial (ELI) specimens, produced through L-PBF followed by annealing, was investigated in this study. Charpy impact testing complying with American Standard Test Method (ASTM) E23 was performed with specimens annealed and conditioned at low temperature. On average, the toughness recorded for the specimens with 3D-printed and machined V-notches was 28 J and 31 J, respectively. These results are higher than the 24 J required in the aerospace industry. Finally, fractographic analyses of the fracture surfaces of the specimens were performed to determine the fracture mechanism of the Ti6Al4V(ELI) impact specimens.
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ABSTRACT Laser Shock Peening (LSP) is a material enhancement process used to introduce compressive residual stresses in metallic components. This investigation explored the effects of different combinations of LSP parameters, such as... more
ABSTRACT Laser Shock Peening (LSP) is a material enhancement process used to introduce compressive residual stresses in metallic components. This investigation explored the effects of different combinations of LSP parameters, such as irradiance (GW/cm(2)) and laser pulse density (spots/mm(2)), on 3.2 mm thick AA6056-T4 samples, for integral airframe applications. The most significant effects that are introduced by LSP without a protective coating include residual stress and surface roughness, since each laser pulse vaporizes the surface layer of the target. Each of these effects was quantified, whereby residual stress analysis was performed using X-ray diffraction with synchrotron radiation. A series of fully reversed bending fatigue tests was conducted, in order to evaluate fatigue performance enhancements with the aim of identifying LSP parameter influence. Improvement in fatigue life was demonstrated, and failure of samples at the boundary of the LSP treatment was attributed to a balancing tensile residual stress.
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Friction Stir Welding (FSW) has become the most important evolving welding technology for the proposed integral aluminium structures for the aerospace fuselage to avoid high cost, excessive weight. The fatigue performances of FSW parts... more
Friction Stir Welding (FSW) has become the most important evolving welding technology for the proposed integral aluminium structures for the aerospace fuselage to avoid high cost, excessive weight. The fatigue performances of FSW parts are superior to riveting. FSW entails a non-onsumable rotating cylindrical tool, consisting of a shoulder and pin, being pushed in to induce heat to plasticize the material and then traversed along the abutting surfaces of the two plates to be welded. Several factors influence the resulting microstructure and mechanical characteristics, and tool transverse and rotational speed are the most significant.<br><br>Characterization of selected pioneering FSW components is presented. AA5083-H111 was selected because of its superplasticity, formability, weldability, high strength and corrosion resistance. It has been the preferred material for the manufacturing of pressure vessels for aircraft<br>and spaceships, and vehicle bodies’ structure...
The present PhD Thesis was developed in the framework of several Research Programs in which the Department of Aerospace Engineering at University of Pisa was directly involved, with the general aim to characterized the fatigue behavior of... more
The present PhD Thesis was developed in the framework of several Research Programs in which the Department of Aerospace Engineering at University of Pisa was directly involved, with the general aim to characterized the fatigue behavior of conventional and innovative joints typically employed in the production of aeronautical and aerospace structures. Correct predictions could obviously improve design of optimized structures, maintaining or increasing actual safety levels: but the separate or synergic effects of several parameters must be considered to correctly reproduce structure in-service behavior. The logic-flow adopted for each aspect analyzed in the present research had his origin on a consistent database of experimental data, ranging from general mechanical properties material characterization to strain gauge evaluations of associated stress fields, moving toward a more comprehensive description of the faced problem by means of Finite Elements simulations, to finally reach, b...
Friction Stir Welding (FSW) is a solid state process that utilizes a rotating tool, comprising a shoulder and pin, pushed in to stir the material while the tool moves along the jointline. Better mechanical properties, environmental... more
Friction Stir Welding (FSW) is a solid state process that utilizes a rotating tool, comprising a shoulder and pin, pushed in to stir the material while the tool moves along the jointline. Better mechanical properties, environmental friendliness and lower cost make it the fastest evolving welding technology . AA5083 was selected owing to its enhanced superplasticity, high strength and superior corrosion resistance, making it particularly effective for manufacturing ship and automobile bodies, and pressure vessels of space ships and aircraft . This work examined the role of defects and microstructure on the fast fracture mechanism in welded 5083-H111 aluminum alloy. The sample was welded at 400rpm tool rotation speed and 50mm/minute transverse speed. Optical microscopy images across the weld were taken. The sample was subjected to tensile test and the fracture surfaces were viewed with the SEM in SE mode. (did fast fracture occur during the welding pass or was it mechanically tested p...
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NbC was studied as the major carbide phase with Ni and Co binders, produced by both spark plasma sintering (SPS) and liquid phase sintering (LPS), and tested as cutting inserts during dry and MQL (Minimum quantity lubrication)... more
NbC was studied as the major carbide phase with Ni and Co binders, produced by both spark plasma sintering (SPS) and liquid phase sintering (LPS), and tested as cutting inserts during dry and MQL (Minimum quantity lubrication) face-milling of grey cast iron (GCI) (BS 1452, Grade 17).
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Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implemented in the transport industry today. Fracture surfaces of AA5083-H111 specimens, which were friction-stir-welded using different parameters,... more
Friction Stir Welding (FSW) is one of the fastest developing welding technologies being implemented in the transport industry today. Fracture surfaces of AA5083-H111 specimens, which were friction-stir-welded using different parameters, were studied with a scanning electron microscope (SEM). The changes in the microstructure of the weld, the location and type of defects that accompanied each stirring process determined the magnitude of reduction in strength and soundness of joints for flawed samples. The paths of crack propagation and modes of fast fracture under static loads were also determined. The sharp edges of the defects were stress concentrators, and so aided crack initiation. Understanding of the effect of microstructure and defect on failure of FSW joints will aid optimization of the process variables, tool design, weld quality assurance and decision making. On the long run, it will boost the confidence of medium scale manufacturers in the adoption and implementation this fairly new technology.
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Research Interests: Materials Engineering, Materials Science, Metallurgy, TIC, NBC, and 2 moreFlank Wear and Face Milling(Flank Wear and Face Milling)
(Flank Wear and Face Milling)
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Abstract Comparative fatigue tests were carried out on Friction Stir Welded specimens of a 2195-T8 aluminum–lithium alloy that differed significantly in width. The width of the larger specimens was over thirteen times greater than that of... more
Abstract Comparative fatigue tests were carried out on Friction Stir Welded specimens of a 2195-T8 aluminum–lithium alloy that differed significantly in width. The width of the larger specimens was over thirteen times greater than that of the small specimens. Fatigue results showed a clear “size effect”, i.e. fatigue life of large specimens was about 40% of the corresponding value of small specimens. The Equivalent Initial Flaw Size methodology was adopted to correlate the two sets of results. Fatigue crack initiation life was disregarded with respect to crack propagation life, and fatigue life was evaluated only as propagation of a small pre-existing defect. Following this methodology, test results of small specimens were used to evaluate the initial equivalent flaw contained in each specimen. It was assumed that this data followed a normal distribution. The equivalent initial flaw in larger specimens was evaluated by simple geometrical considerations. A very good assessment of mean fatigue life and scatter in the fatigue results of large specimens was obtained by simulating the propagation of these defects. Calculations were carried out by taking also welding residual stresses into account, but the results demonstrated that this effect was not significant.
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... Also, the authors would like to express immense gratitude to Dr. Andrea Lausi and Dr. Jasper Plaisier from Elettra Trieste Synchrotron ... 34, 327–337 (2000) [3] Heckenberger, U., Hombergsmeier, E., Holzinger, V., von Bestenbostel,... more
... Also, the authors would like to express immense gratitude to Dr. Andrea Lausi and Dr. Jasper Plaisier from Elettra Trieste Synchrotron ... 34, 327–337 (2000) [3] Heckenberger, U., Hombergsmeier, E., Holzinger, V., von Bestenbostel, W.: Advances in Laser Shock Peening theory ...
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The current paper describes a destructive, sectioning method for measuring residual stress in welded panels, using electric strain gauges. Since this method is carried out rather simply, it has a wide range of possible applications. For... more
The current paper describes a destructive, sectioning method for measuring residual stress in welded panels, using electric strain gauges. Since this method is carried out rather simply, it has a wide range of possible applications. For this reason, a more thorough analysis of the method is performed. The potential limits of its application are investigated, together with the parameters that can influence the obtained results. The sectioning method is verified by determining residual stress in welded panels numerically. The results show it is possible to estimate the residual stress field in a welded structure rapidly and accurately, by using reasonably priced equipment.
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ABSTRACT Fatigue and crack propagation tests are carried out on 7075-T73 open hole aluminium alloy specimens. A remarkable increment of fatigue life due to the Split Sleeve Cold Expansion (TM) process is observed, further improved by... more
ABSTRACT Fatigue and crack propagation tests are carried out on 7075-T73 open hole aluminium alloy specimens. A remarkable increment of fatigue life due to the Split Sleeve Cold Expansion (TM) process is observed, further improved by applying the process twice on the same hole. Comparable increments are obtained by using the StressWave (TM) method. Specific tests are performed in order to point out a possible relaxation of the residual stresses due to fatigue loading. The results obtained reveal no relaxation phenomena in the tested specimens. The compressive residual stress around cold expanded holes is numerically evaluated. Dedicated experiments based on the Sachs method are conducted to confirm the residual stress prediction.
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... The authors gratefully acknowledge the contribution given by the students Paola Apruzzese,Nicola Pasquale and Ing. ... 10 Poussard, CGC, Pavier, MJ and Smith, DJ (1994) Prediction of residual stresses in cold-worked fastener holes... more
... The authors gratefully acknowledge the contribution given by the students Paola Apruzzese,Nicola Pasquale and Ing. ... 10 Poussard, CGC, Pavier, MJ and Smith, DJ (1994) Prediction of residual stresses in cold-worked fastener holes using the finite element method. ...
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The use of steam turbines is the primary method of power extraction for most power plants. The corrosion resistant steel blades bear significant centrifugal loads in a wet steam environment making them susceptible to stress corrosion... more
The use of steam turbines is the primary method of power extraction for most power plants. The corrosion resistant steel blades bear significant centrifugal loads in a wet steam environment making them susceptible to stress corrosion cracking and fatigue. A surface technique known as Laser Shock Peening (LSP) can be used to generate beneficial Compressive Residual Stresses (CRS) at the highly stressed blade root in order to resist crack initiation. Achieving a consistent stress field around a complex component such as a low pressure steam turbine blade, therefore requires significant insight into the geometric effects on LSP processing. Conventional residual stress measurements can be hindered by the geometry and are specific to that location. The full field strain neutron imaging at IMAT offers the ideal technique to reveal the effectiveness of the LSP process around complex geometries.
Laser Shock Peening (LSP) is an advanced manufacturing process capable of introducing compressive residual stress within a component. Cracks in aeronautical structures can grow undetected between inspection periods. The move towards... more
Laser Shock Peening (LSP) is an advanced manufacturing process capable of introducing compressive residual stress within a component. Cracks in aeronautical structures can grow undetected between inspection periods. The move towards large, integral structures is making this issue more critical as these structures contain fewer natural crack-stopping features. LSP can address this issue by engineering unique residual-stress-guided crack propagation pathways. This effective combined stress state would then cause a deviation of the typical crack trajectory. Complex coupling of residual stresses and fracture mechanics is an extremely difficult problem to simulate. Hence we would like to investigate this interaction by neutron diffraction as it will allow for the characterisation of the stress field in a non-destructive fashion whilst allowing for full crack growth of the specimens.
Laser powder bed fusion (L-PBF) has the potential to be applied in the production of titanium aircraft components with good mechanical properties, provided the technology has been qualified and accepted in the aviation industry. To... more
Laser powder bed fusion (L-PBF) has the potential to be applied in the production of titanium aircraft components with good mechanical properties, provided the technology has been qualified and accepted in the aviation industry. To achieve acceptance of the L-PBF technology in the aircraft industry, mechanical property data needed for the qualification process must be generated according to accepted testing standards. The impact toughness of Ti6Al4V extra low interstitial (ELI) specimens, produced through L-PBF followed by annealing, was investigated in this study. Charpy impact testing complying with American Standard Test Method (ASTM) E23 was performed with specimens annealed and conditioned at low temperature. On average, the toughness recorded for the specimens with 3D-printed and machined V-notches was 28 J and 31 J, respectively. These results are higher than the 24 J required in the aerospace industry. Finally, fractographic analyses of the fracture surfaces of the specimens...
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Abstract Since Friction Stir Welding has been identified as a key technology for primary aerospace structures, fatigue crack growth testing and modelling is required. However, there is still a complete lack of information regarding the... more
Abstract Since Friction Stir Welding has been identified as a key technology for primary aerospace structures, fatigue crack growth testing and modelling is required. However, there is still a complete lack of information regarding the fatigue crack propagation in friction stir welds under variable amplitude loading and flight loading conditions. Experimental investigations have been performed on centre cracked 4 mm thick AA2024-T3 base metal and FSW specimens: regarding the FSW samples, the crack was placed 5 mm out of the weld centre, in the most critical part of the joint: the coupons have been tested under simple variable amplitude load sequences, and under a standardized flight-simulation load history, Falstaff. The fatigue crack propagation was then predicted using widespread aerospace fracture mechanics software packages. Interaction effects and internal residual stresses were firstly separately simulated and than combined in order to evaluate the ability to predict the fatigue crack propagation on FSW welded structures under service loading conditions.
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Abstract The effects of rapid sintering by pulse electric current sintering (PECS), variation in starting WC size (0.1–0.8 μm), Ni as a Co binder substitute and TiC, NbC and Mo 2 C additions on the microstructure, abrasion wear, thermal... more
Abstract The effects of rapid sintering by pulse electric current sintering (PECS), variation in starting WC size (0.1–0.8 μm), Ni as a Co binder substitute and TiC, NbC and Mo 2 C additions on the microstructure, abrasion wear, thermal shock and impact resistance of WC–Co and WC–Ni alloys were studied. Abrasion wear tests were done using a ball-on-disk tribometer, with 100Cr6 steel and silicon nitride balls. Use of PECS gave finer microstructures with poorly distributed binder pools than similar liquid phase sintered (LPS) samples, although large angular WC grains of up to 1 μm occurred in the nano (0.1 μm) and ultrafine (0.4 μm) grades. Addition of 5 wt.% NbC to WC–10Co (wt.%) had negligible effect on the WC grain size, while 5 wt.% Mo 2 C to WC–6.25TiC–9.3Ni significantly improved WC grain growth inhibition, leading to increased hardness (from ~ 13 to > 21 GPa) and reduced wear rate (from 2.73 × 10 − 4 to − 5 mm 3 ·N − 1 ·m − 1 ), compared to the LPS WC–9.3Ni. Thermal shock and impact resistance were measured using a thermal imaging camera and force gauges while testing the samples as cutting tools on Ti–6Al–4V under aggressive interrupted milling conditions. The LPS samples had better thermal shock and impact resistance, due to their higher fracture toughness (> 12.5 MPa·m 0.5 ) and B3B transverse rupture strength (> 2100 MPa), as a result of the larger and better binder pool distribution.