The Experts below are selected from a list of 147 Experts worldwide ranked by ideXlab platform
Paul E Krajewski - One of the best experts on this subject based on the ideXlab platform.
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high temperature Forming of a vehicle closure component in fine grained aluminum alloy aa5083 finite element simulations and experiments
Key Engineering Materials, 2010Co-Authors: Louis G Hector, Paul E Krajewski, Eric M. Taleff, Jon T CarterAbstract:Fine-grained AA5083 aluminum-magnesium alloy sheet can be formed into complex closure components with the Quick Plastic Forming process at high temperature (450oC). Material models that account for both the deformation mechanisms active during Forming and the effect of stress state on material response are required to accurately predict final sheet thickness profiles, the locations of potential Forming defects and Forming cycle time. This study compares Finite Element (FE) predictions for Forming of an automobile decklid inner panel in fine-grained AA5083 using two different material models. These are: the no-threshold, two-mechanism (NTTM) model and the Zhao. The effect of sheet/die friction is evaluated with five different sheet/die friction coefficients. Comparisons of predicted sheet thickness profiles with those obtained from a formed AA5083 panel shows that the NTTM model provides the most accurate predictions.
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Dynamic Recrystallization of AA5083 at 450 °C: the Effects of Strain Rate and Particle Size
Metallurgical and Materials Transactions A, 2008Co-Authors: S. Agarwal, Paul E Krajewski, C.l. BriantAbstract:This article presents a study of the dynamic recrystallization that occurs when AA5083 is deformed at elevated temperatures and strain rates typical of those observed in Quick Plastic Forming (QPF). Strain rates between 0.0005 and 0.3/s were used for these tests, which were performed with the samples at 450 °C. The results showed that for strain rates at or below 0.01/s, no recrystallization occurred. At higher strain rates, recrystallization did occur in the most highly strained regions of the sample. The recrystallized grain size was smallest at the highly-strained fracture point and increased in size as one moved away from the fracture end toward the grip of the sample. Below a critical strain, no further recrystallization was observed. This critical strain decreased with increasing strain rate and with an increase in the diameter of the largest constituent particles in the sample. Analysis of the results showed that both a critical strain rate and critical strain were required to achieve dynamic recrystallization. Humphrey’s model for critical strain rate gave qualitative agreement with experimental results, but the fact that the strain rate in the necked region of the sample increases above the nominal strain rate made a more detailed comparison with the model difficult.
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Characteristics of the Transition from Grain-Boundary Sliding to Solute Drag Creep in SuperPlastic AA5083
Metallurgical and Materials Transactions A, 2008Co-Authors: Terry R. Mcnelley, Paul E Krajewski, Keiichiro Oh-ishi, Alexander P. Zhilyaev, Srinivasan Swaminathan, Eric M. TaleffAbstract:SuperPlastic tensile ductility has been attained when specially-processed AA5083 materials are strained in tension at relatively high strain rates, in the range of the transition from grain-boundary sliding (GBS) to solute drag creep (SDC) control of deformation. Quick Plastic Forming (QPF) technology involves deformation at such strain rates, and the relative contributions of GBS and SDC to the strain during deformation in this strain rate regime have been examined in this investigation. The additive, independent contributions of GBS and SDC to the elevated temperature deformation of fine-grained materials are reviewed. The transition from GBS to SDC in grain-refined AA5083 materials was evaluated by several methods, including the assessment of initial transients during straining and of transients during strain-rate change tests; the strain-rate dependence of the flow stress; the dependence of ductility on strain rate; flow localization behavior and fracture mode; cavitation growth; the evolution of microstructure and microtexture during deformation; and comparison with phenomenological models for the GBS-to-SDC transition.
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Forming Limit Diagrams for AA5083 under SPF and QPF Conditions
Materials Science Forum, 2007Co-Authors: Mary Anne Kulas, Paul E Krajewski, John R. Bradley, Eric M. TaleffAbstract:Forming Limit Diagrams (FLD’s) for AA5083 aluminum sheet were established under both SuperPlastic Forming (SPF) and Quick Plastic Forming (QPF) conditions. SPF conditions consisted of a strain rate of 0.0001/s at 500°C, while QPF conditions consisted of a strain rate of 0.01/s at 450°C. The Forming limit diagrams were generated using uniaxial tension, biaxial bulge, and plane strain bulge testing. Forming limits were defined using two criteria: (1) macroscopic fracture and (2) greater than 2% cavitation. Very little difference was observed between the plane strain limits in the SPF and QPF conditions indicating comparable formability between the two processes with a commercial grade AA5083 material.
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overview of Quick Plastic Forming technology
Materials Science Forum, 2007Co-Authors: Paul E Krajewski, James G SchrothAbstract:General Motors has developed Quick Plastic Forming (QPF) as a hot blow Forming process capable of producing aluminum closure panels at high volumes. This technology has been successfully implemented for automotive liftgates and decklids with complex shapes. This talk will review key elements of the QPF process, describe some of the technical achievements realized in this process, and identify areas for future research in process, material, and lubricant development.
Eric M. Taleff - One of the best experts on this subject based on the ideXlab platform.
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high temperature Forming of a vehicle closure component in fine grained aluminum alloy aa5083 finite element simulations and experiments
Key Engineering Materials, 2010Co-Authors: Louis G Hector, Paul E Krajewski, Eric M. Taleff, Jon T CarterAbstract:Fine-grained AA5083 aluminum-magnesium alloy sheet can be formed into complex closure components with the Quick Plastic Forming process at high temperature (450oC). Material models that account for both the deformation mechanisms active during Forming and the effect of stress state on material response are required to accurately predict final sheet thickness profiles, the locations of potential Forming defects and Forming cycle time. This study compares Finite Element (FE) predictions for Forming of an automobile decklid inner panel in fine-grained AA5083 using two different material models. These are: the no-threshold, two-mechanism (NTTM) model and the Zhao. The effect of sheet/die friction is evaluated with five different sheet/die friction coefficients. Comparisons of predicted sheet thickness profiles with those obtained from a formed AA5083 panel shows that the NTTM model provides the most accurate predictions.
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Characteristics of the Transition from Grain-Boundary Sliding to Solute Drag Creep in SuperPlastic AA5083
Metallurgical and Materials Transactions A, 2008Co-Authors: Terry R. Mcnelley, Paul E Krajewski, Keiichiro Oh-ishi, Alexander P. Zhilyaev, Srinivasan Swaminathan, Eric M. TaleffAbstract:SuperPlastic tensile ductility has been attained when specially-processed AA5083 materials are strained in tension at relatively high strain rates, in the range of the transition from grain-boundary sliding (GBS) to solute drag creep (SDC) control of deformation. Quick Plastic Forming (QPF) technology involves deformation at such strain rates, and the relative contributions of GBS and SDC to the strain during deformation in this strain rate regime have been examined in this investigation. The additive, independent contributions of GBS and SDC to the elevated temperature deformation of fine-grained materials are reviewed. The transition from GBS to SDC in grain-refined AA5083 materials was evaluated by several methods, including the assessment of initial transients during straining and of transients during strain-rate change tests; the strain-rate dependence of the flow stress; the dependence of ductility on strain rate; flow localization behavior and fracture mode; cavitation growth; the evolution of microstructure and microtexture during deformation; and comparison with phenomenological models for the GBS-to-SDC transition.
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Forming Limit Diagrams for AA5083 under SPF and QPF Conditions
Materials Science Forum, 2007Co-Authors: Mary Anne Kulas, Paul E Krajewski, John R. Bradley, Eric M. TaleffAbstract:Forming Limit Diagrams (FLD’s) for AA5083 aluminum sheet were established under both SuperPlastic Forming (SPF) and Quick Plastic Forming (QPF) conditions. SPF conditions consisted of a strain rate of 0.0001/s at 500°C, while QPF conditions consisted of a strain rate of 0.01/s at 450°C. The Forming limit diagrams were generated using uniaxial tension, biaxial bulge, and plane strain bulge testing. Forming limits were defined using two criteria: (1) macroscopic fracture and (2) greater than 2% cavitation. Very little difference was observed between the plane strain limits in the SPF and QPF conditions indicating comparable formability between the two processes with a commercial grade AA5083 material.
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Forming-Limit Diagrams for Hot-Forming of AA5083 Aluminum Sheet: Continuously Cast Material
Journal of Materials Engineering and Performance, 2007Co-Authors: Mary Anne Kulas, Paul E Krajewski, John R. Bradley, Eric M. TaleffAbstract:Fine-grained AA5083 aluminum sheet is used for hot-Forming automotive body panels with gas pressure in the superPlastic Forming (SPF) and Quick Plastic Forming (QPF) processes. Deformation under QPF conditions is controlled by two fundamental creep mechanisms, grain-boundary-sliding (GBS) and solute-drag (SD) creep. The failure mechanisms of AA5083 materials under QPF conditions depend strongly on these deformation mechanisms and on the applied stress state. Failure can be controlled by flow localization, cavitation development or a combination of both. There is interest in using continuously cast (CC) AA5083 materials instead of direct-chill cast (DC) materials in QPF operations as a means of reducing material cost. However, CC and DC AA5083 materials can produce significantly different ductilities under hot Forming. Rupture-based Forming-limit diagrams (FLDs) have been constructed for a CC AA5083 sheet material under hot-Forming conditions. Forming limits are shown to be related to the controlling deformation mechanisms. Differences between FLDs from DC and CC AA5083 materials are investigated. The differences in FLDs between these materials are related to differences in cavitation development.
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Failure mechanisms in superPlastic AA5083 materials
Metallurgical and Materials Transactions A, 2006Co-Authors: Mary Anne Kulas, Paul E Krajewski, Eric M. Taleff, W. Paul Green, Terry R. McnelleyAbstract:The mechanisms of tensile failure in four 5083 aluminum sheet materials are evaluated under conditions of interest for superPlastic and Quick-Plastic Forming. Two mechanisms are shown to control failure of the AA5083 materials under uniaxial tension at elevated temperatures: cavitation and flow localization ( i.e. , necking). Conditions for which failure is controlled by cavitation correspond to those under which deformation is primarily by grain-boundary-sliding creep. Conditions for which failure is controlled by flow localization correspond to those under which deformation is primarily by solutedrag creep. A geometric parameter, Q , is used to determine whether final failure is controlled by cavitation or by flow localization. Differences in elongations to failure between the different AA5083 materials at high temperatures and slow strain rates are the result of differences in cavitation behaviors. The rate of cavitation growth with strain is nearly constant between the AA5083 materials for identical testing conditions, but materials with less tensile ductility evidence initial cavitation development at lower strain levels. The rate of cavitation growth with strain is shown to depend on the governing deformation mechanism; grain-boundary-sliding creep produces a faster cavitation growth rate than does solute-drag creep. A correlation is found between the early development of cavitation and the intermetallic particle-size population densities of the AA5083 materials. Fine filaments, oriented along the tensile axis, are observed on fracture surfaces and within surface cavities of specimens deformed primarily under grain-boundary-sliding creep. As deformation transitions to control by solute-drag creep, the density of these filaments dramatically decreases.
Mary Anne Kulas - One of the best experts on this subject based on the ideXlab platform.
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Forming Limit Diagrams for AA5083 under SPF and QPF Conditions
Materials Science Forum, 2007Co-Authors: Mary Anne Kulas, Paul E Krajewski, John R. Bradley, Eric M. TaleffAbstract:Forming Limit Diagrams (FLD’s) for AA5083 aluminum sheet were established under both SuperPlastic Forming (SPF) and Quick Plastic Forming (QPF) conditions. SPF conditions consisted of a strain rate of 0.0001/s at 500°C, while QPF conditions consisted of a strain rate of 0.01/s at 450°C. The Forming limit diagrams were generated using uniaxial tension, biaxial bulge, and plane strain bulge testing. Forming limits were defined using two criteria: (1) macroscopic fracture and (2) greater than 2% cavitation. Very little difference was observed between the plane strain limits in the SPF and QPF conditions indicating comparable formability between the two processes with a commercial grade AA5083 material.
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Forming-Limit Diagrams for Hot-Forming of AA5083 Aluminum Sheet: Continuously Cast Material
Journal of Materials Engineering and Performance, 2007Co-Authors: Mary Anne Kulas, Paul E Krajewski, John R. Bradley, Eric M. TaleffAbstract:Fine-grained AA5083 aluminum sheet is used for hot-Forming automotive body panels with gas pressure in the superPlastic Forming (SPF) and Quick Plastic Forming (QPF) processes. Deformation under QPF conditions is controlled by two fundamental creep mechanisms, grain-boundary-sliding (GBS) and solute-drag (SD) creep. The failure mechanisms of AA5083 materials under QPF conditions depend strongly on these deformation mechanisms and on the applied stress state. Failure can be controlled by flow localization, cavitation development or a combination of both. There is interest in using continuously cast (CC) AA5083 materials instead of direct-chill cast (DC) materials in QPF operations as a means of reducing material cost. However, CC and DC AA5083 materials can produce significantly different ductilities under hot Forming. Rupture-based Forming-limit diagrams (FLDs) have been constructed for a CC AA5083 sheet material under hot-Forming conditions. Forming limits are shown to be related to the controlling deformation mechanisms. Differences between FLDs from DC and CC AA5083 materials are investigated. The differences in FLDs between these materials are related to differences in cavitation development.
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Failure mechanisms in superPlastic AA5083 materials
Metallurgical and Materials Transactions A, 2006Co-Authors: Mary Anne Kulas, Paul E Krajewski, Eric M. Taleff, W. Paul Green, Terry R. McnelleyAbstract:The mechanisms of tensile failure in four 5083 aluminum sheet materials are evaluated under conditions of interest for superPlastic and Quick-Plastic Forming. Two mechanisms are shown to control failure of the AA5083 materials under uniaxial tension at elevated temperatures: cavitation and flow localization ( i.e. , necking). Conditions for which failure is controlled by cavitation correspond to those under which deformation is primarily by grain-boundary-sliding creep. Conditions for which failure is controlled by flow localization correspond to those under which deformation is primarily by solutedrag creep. A geometric parameter, Q , is used to determine whether final failure is controlled by cavitation or by flow localization. Differences in elongations to failure between the different AA5083 materials at high temperatures and slow strain rates are the result of differences in cavitation behaviors. The rate of cavitation growth with strain is nearly constant between the AA5083 materials for identical testing conditions, but materials with less tensile ductility evidence initial cavitation development at lower strain levels. The rate of cavitation growth with strain is shown to depend on the governing deformation mechanism; grain-boundary-sliding creep produces a faster cavitation growth rate than does solute-drag creep. A correlation is found between the early development of cavitation and the intermetallic particle-size population densities of the AA5083 materials. Fine filaments, oriented along the tensile axis, are observed on fracture surfaces and within surface cavities of specimens deformed primarily under grain-boundary-sliding creep. As deformation transitions to control by solute-drag creep, the density of these filaments dramatically decreases.
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Deformation mechanisms in superPlastic AA5083 materials
Metallurgical and Materials Transactions A, 2005Co-Authors: Mary Anne Kulas, Paul E Krajewski, Eric M. Taleff, W. Paul Green, Terry R. McnelleyAbstract:The Plastic deformation of seven 5083 commercial aluminum materials, produced from five different alloy heats, are evaluated under conditions of interest for superPlastic and Quick-Plastic Forming. Two mechanisms are shown to govern Plastic deformation in AA5083 over the strain rates, strains, and temperatures of interest for these Forming technologies: grain-boundary-sliding (GBS) creep and solutedrag (SD) creep. Quantitative analysis of stress transients following rate changes clearly differentiates between GBS and SD creep and offers conclusive proof that SD creep dominates deformation at fast strain rates and low temperature. Furthermore, stress transients following strain-rate changes under SD creep are observed to decay exponentially with strain. A new graphical construction is proposed for the analysis and prediction of creep transients. This construction predicts the relative size of creep transients under SD creep from the relative size of changes in an applied strain rate or stress. This construction reveals the relative size of creep transients under SD creep to be independent of temperature; temperature dependence resides in the “steady-state” creep behavior to which transients are related.
Vjekoslav Franetovic - One of the best experts on this subject based on the ideXlab platform.
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A New Technique for the Investigation of Tribological Behavior of Sliding Pairs Used in Hot Forming Processes
STLE ASME 2008 International Joint Tribology Conference, 2008Co-Authors: Vjekoslav FranetovicAbstract:Hot Forming of aluminum sheet is highly influenced by the tribological behavior of the interacting surfaces of sliding pairs. Here we describe a new technique to investigate tribo-pair candidates for Quick Plastic Forming (QPF) and warm Forming processes. This technique represents a bench type simulation of the real Forming process where the sheet and tool interact by sliding against each other in a single motion (slide/stroke).Copyright © 2008 by General Motors Corporation
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Improved Tribological Performance of Tribo-Pairs by Optimization of Sliding Speed: Implications for Hot Forming Processes
STLE ASME 2008 International Joint Tribology Conference, 2008Co-Authors: Vjekoslav FranetovicAbstract:The tribology of hot Forming processes is highly critical for the quality of formed aluminum panels and the cost-effectiveness of hot Forming. In this report a flat-on-flat experimental technique for tribological evaluation of a single stroke was used to investigate the effect of sliding speed on the operative friction coefficient (FC) and tribological failure of the tribo-pairs used in Quick Plastic Forming (QPF) and warm Forming processes.Copyright © 2008 by General Motors Corporation
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The Effect of Boron Nitride Lubricant Thickness and Steel Surface Condition on Tribological Behavior of P20 Steel/5083 Aluminum Sliding Pairs at High Temperature
STLE ASME 2008 International Joint Tribology Conference, 2008Co-Authors: M. David Hanna, Vjekoslav FranetovicAbstract:The tribological behavior of AA5083 aluminum sheet sliding against tool steel impacts the quality of components manufactured with the Quick Plastic Forming (QPF) process. The effect of boron nitride lubricant thickness on the tribological performance of different coated steel/AA5083 pairs utilizing a recently developed reciprocating flat-on-flat tribological test technique was investigated. In most cases of coated and uncoated steel, the time-to-contact increased by a factor of ten when the BN thickness was increased from 8.4 μm to 14.5 μm. The tribological tests with a low sliding speed method (0.1 Hz) confirmed the previous observations conducted at 0.5 Hz in which nitrocarburizing of the tool surface decreased adhesion of aluminum to the steel during sliding contact.
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Improved Hot Aluminum Forming Tribology by Anodization
ASME STLE 2007 International Joint Tribology Conference Parts A and B, 2007Co-Authors: Vjekoslav Franetovic, James G SchrothAbstract:The process of Quick Plastic Forming (QPF) developed by General Motors involves hot aluminum Forming at ∼450°C, and has formability advantages over conventional stamping of aluminum or steel. However, there are still no fully satisfactory solutions for the problem of local interaction/sticking between the aluminum blank and the tool, and the eventual transfer of some aluminum to the steel tool after repeated Forming cycles. In this paper we show that the process of anodizing aluminum prior to Forming greatly diminishes the interaction of aluminum with steel at QPF Forming temperatures. Significantly improved tribological behavior of the aluminum surface after anodization as compared to lubricated aluminum was shown on a laboratory scale with flat-on-flat reciprocating experiments.Copyright © 2007 by General Motors
Arianna T. Morales - One of the best experts on this subject based on the ideXlab platform.
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Tribological issues during Quick Plastic Forming
Journal of Materials Engineering and Performance, 2004Co-Authors: Paul E Krajewski, Arianna T. MoralesAbstract:Quick Plastic Forming (QPF) was developed as a high-volume, hot blow Forming process for automobile components, enabling larger volume applications than traditional superPlastic Forming (SPF). One critical aspect of the process is the tribological interaction between the Forming tool and the aluminum blank, as this impacts formability, surface quality, and tool durability. While QPF has been successfully implemented for automobile components, many opportunities exist for improving the tribological condition during the process, including the die coating or treatment, the lubricant, and the fundamental understanding of aluminum/iron adhesion under QPF conditions (450 °C). This work reviews key tribological issues affecting QPF and identifies areas where additional research is required.
