Papers by John Lewandowski
Journal of Composite Materials, 1991
The aim of this investigation was to determine the fracture behavior of a particulate reinforced ... more The aim of this investigation was to determine the fracture behavior of a particulate reinforced aluminum alloy composite under combined mode I-mode III loading conditions. A modified three point bend specimen was used to carry out these tests. It was found that the mode I loading condition was energetically most favorable. Addition of mode III components to the system seems to increase the amount of redundant work during fracture without affecting the critical fracture criterion.
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Journal of Materials Science Letters, 1989
ABSTRACT 2oo attention in recent years due to the need for highstrength materials in various stru... more ABSTRACT 2oo attention in recent years due to the need for highstrength materials in various structural applications. The addition of a fairly strong and brittle reinforcement to a metal serves to improve the strength and stiffness, but the ductility of the composite is typically lower than that of the unreinforced matrix [1, 2]. This is consistent with observations of reduced ductility accompanying increased volume fractions of reinforcements or inclusions in ductile matrices [3]. The superimposition of compressive hydrostatic stresses provides increased ductility in these materials [4, 5], and approximates the stress state obtained in various material-forming applications. Furthermore, the relatively low ductiles of these composites complicates the detailed study of the damage events leading to catastrophic fracture. The enhancement of ductility provided by superimposing hydrostatic pressure during deformation provides an improved means of studying the fracture micromechanisms in these materials. There has been relatively little work on the effects of superimposed hydrostatic pressure on the deformation behaviour of composites. Recent work on aluminium alloy composites [4-6] and on A1-Ni composites [6] has revealed a significant effect of superimposed hydrostatic pressure on the ductility of these materials~ Previous studies have not, however, focused on the effects of the matrix alloy composition and ageing condition on the pressure-induced ductility response of these materials. Composites based on three different matrix compositions were studied in this investigation. The first composite material studied was a powder metallurgy 2XXX series aluminium alloy, designated MB-85, containing (in wt %) 3.5 copper, 1.5 magnesium, 0.4 zirconium, 0.21 manganese, balance aluminium, rein100 forced with 15 vol % SiC particulate (average size 13/~m). Processing details are summarized elsewhere 80
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Acta Metallurgica et Materialia, 1990
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Applied Physics Letters, 2006
Dynamic crack propagation in a model brittle bulk metallic glass (BMG) is studied. Contrary to ot... more Dynamic crack propagation in a model brittle bulk metallic glass (BMG) is studied. Contrary to other brittle glassy materials, the authors find nanometer scale out-of-plane periodic corrugations along the crack surface of the BMG. The nanoscale periodicity remains nearly constant at different loading rates. An interpretation is presented to explain the evolution and the periodic coalescence of the nanometer scale cavities along the crack surface. The observation sheds light on the origin of dynamic fracture surface roughening in brittle materials and could be generally applicable to brittle materials.
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Parameter optimization for metal powders in Selective Laser Melting (SLM) is usually carried out ... more Parameter optimization for metal powders in Selective Laser Melting (SLM) is usually carried out by experimental investigations of the influence of significant parameters (such as laser power, scan speed, hatch spacing, layer thickness, scan pattern, etc.) on microstructure and/or mechanical properties. This type of experimental optimization is extremely time- and cost-consuming. In order to accelerate the optimization process, a study was undertaken to develop a method for rapid optimization of parameters based on melt pool characterizations. These characterizations began with investigations of SLM single bead experiments. Pre-alloyed Ti-6Al-4V powder was used for single bead fabrication with multiple laser power and scan speed combinations. Surface morphology and dimensions of single beads were characterized. Geometrical features of melt pools were measured after polishing and etching of the cross section of each single bead. It was found that melt pool characteristics provide sig...
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Vickers micro-hardness, tension tests, notch and fatigue precrack toughness tests, as well as con... more Vickers micro-hardness, tension tests, notch and fatigue precrack toughness tests, as well as controlled monotonic and cyclic strain experiments via bending over mandrels of different diameter have been performed on two different chemistries of Fe-based (Fe-Si-B) metallic glass ribbons. Tensile strengths of Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 were 2000 ±100 MPa and 1640 ±35 MPa for Fe 78 Si 9 B 13 , consistent with the microhardness trends. High notch toughnesses (e.g. 89 ±0.9 MPam 1/2 Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ; 94.5 ±5.5 MPam 1/2 - Fe 78 Si 9 B 13 ) and fatigue precracked toughness of 76 MPam 1/2 for the Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 and 80 MPam 1/2 for the Fe 78 Si 9 B 13 were obtained. Flex bending cyclic fatigue tests revealed a fatigue limit of 385 MPa for Fe 78 Si 9 B 13 ribbons, while the more brittle behavior of the Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 ribbons prevented generation of flex bending fatigue data. SEM examination was used to characterize all fracture surface details. Th...
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Continued advancements in medicine, biomedical device design, and a drive to minimally invasive s... more Continued advancements in medicine, biomedical device design, and a drive to minimally invasive surgeries have combined to create a stronger demand for increasingly smaller medical devices and surgical tools. In many of these applications, the components or subcomponents of the devices are fine wires. Stents, filters, staples, clips, catheters, needles, and orthodontic braces represent a sampling of the devices used in cardiology, orthopaedics, surgical instruments, and dentistry, with wire diameters ranging from the tens to hundreds of micrometers [1-3]. Miniaturization of these devices and/or subcomponents requires increased performance from less material, and therefore necessitates investigation of the connection between material processing and performance. Moreover, it is imperative to understand how impurities that result from processing affect the lifetime performance of that material. Research on the material purity of fine Nitinol wires and its effect on fatigue performance ...
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In situ alloying of elemental Cu, Cr, and Nb to form GRCop-42 (Cu-4at.% Cr-2at.% Nb) using laser ... more In situ alloying of elemental Cu, Cr, and Nb to form GRCop-42 (Cu-4at.% Cr-2at.% Nb) using laser powder bed fusion (LPBF) additive manufacturing (AM) was successful. Evaluation of the in situ alloyed GRCop-42 (ISGRCop-42) was conducted using phase extraction to explore the effects of AM process conditions on the formation of Cr2Nb precipitates from elemental powders. It was found that ISGRCop-42 successfully and repeatedly formed Cr2Nb at a yield as high as 89% of potential Cr2Nb content. Initial work shows that powder preparation was the most influential factor in alloying success, followed by laser power.
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Science China Technological Sciences, 2017
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Journal of Nuclear Materials, 2017
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JOM, 2016
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The Journal of Rehabilitation Research and Development
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Materials Science and Technology, 2006
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Scripta Materialia, 2009
Atomized amorphous Al 89 Ni 3 Gd 7 Fe 1 powders were extruded inside an aluminum can to create a ... more Atomized amorphous Al 89 Ni 3 Gd 7 Fe 1 powders were extruded inside an aluminum can to create a composite with nanosized intermetallic particles in a nominally pure Al matrix, surrounded by the aluminum can. The extruded rods were machined into beams to produce either bi- or trilayer laminates containing the nanocomposite and the aluminum layer(s). The bend ductility and fracture toughness of the laminates were obtained in both crack divider and crack arrester orientations, and were compared to the fracture behavior of the nanostructured composite.
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Metallurgical and Materials Transactions A, 1995
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Papers by John Lewandowski