The NSF Public Access Repository (PAR) system and access will be unavailable from 11:00 PM ET on Friday, December 13 until 2:00 AM ET on Saturday, December 14 due to maintenance. We apologize for the inconvenience.
Explore Research Products in the PAR It may take a few hours for recently added research products to appear in PAR search results.
Title: Effect of pre-strain on springback behavior after bending in AA 6016-T4: Experiments and crystal plasticity modeling
Modeling springback in sheet materials is challenging in aluminum alloys, especially when a complex strain path is applied. This paper presents results from pure bending experiments on AA 6016-T4 sheet material, where various plastic pre-strains were first applied prior to bending. A crystal plasticity based elasto-plastic selfconsistent (EPSC) model that includes the effect of backstress in the hardening law was used to predict final part shape after unloading. The backstress term in the model was calibrated using geometrically necessary dislocation (GND) content, measured experimentally by high resolution electron backscattered diffraction (HREBSD). The EPSC model predicted springforward angles for unstrained 1 mm AA 6016-T4 sheet with an error of 0.4% (0.3◦) in the worst case, while the J2 plasticity isotropic model overpredicted springforward angles by as much as 2.4% (2◦). For cases where uniaxial, plane-strain, and biaxial pre-strains were first imparted to the sheets before bending, the EPSC model with backstress accurately predicted the transition from springforward to springback, while the EPSC model without backstress did not. Backstress influence on model accuracy, which increased with greater pre-strain levels, appears to be correlated to the statistically stored dislocation (SSD) density computed by the model at the end of each pre-strain step. more »« less
Automotive stampings undergo complex strain paths during drawing, stretching, and bending operations which develop large plastic strain gradients within the material. Aluminum sheet alloys are increasingly used for vehicle structure lightweighting, but limited formability and high levels of springback present challenges to the manufacturing and assembly processes. The current work explores the springback levels in AA6016-T4 sheet after pure bending operations. Finite element modeling is performed using both isotropic and elasto-plastic self-consistent (EPSC) crystal plasticity approaches. The EPSC model incorporates backstresses informed by GND content, as measured via high-resolution EBSD. Its predictions are shown to be more accurate than those of the isotropic model. The benefits and limitations of the current EPSC model are discussed.
Lee, Jinwoo; Bong, Hyuk Jong; Ha, Jinjin; Kim, Daeyong(
, Journal of Materials Research and Technology)
In this study, the ductile damage responses of high-strength 7000 series aluminum alloy (AA), AA 7075-T6 sheet samples, subjected to the plane strain deformation mode were investigated using finite element (FE) simulations. In the experiments, uniaxial tension (UT) and plane strain tension (PST) tests were conducted to characterize the plasticity and ductile damage behavior of the AA 7075-T6 sheet samples. The limiting dome height (LDH) and V-die air bending tests were conducted to evaluate the ductility of the material subjected to plastic deformation and friction between the tools, and the corresponding fractured samples were qualitatively analyzed in terms of dimples using fractography. FE simulations were performed to predict the ductility of the AA 7075-T6 sheet samples under plane strain deformation using an enhanced Gurson−Tvergaard−Needleman (GTN) model, namely the GTN-shear model. The model was improved by adding the shear dimple effect to the original GTN model. The predicted results in terms of the load–displacement curves and displacements at the onset of failure were in good agreement with experimental data from the aforementioned tests. Furthermore, virtual roll forming simulations were conducted using the GTN-shear model to determine the effect of the prediction on ductile behavior for industrial applications.
Sharma, Rishabh; Poulin, Camille M.; Knezevic, Marko; Miles, Michael P.; Fullwood, David T.(
, Materials science engineering)
null
(Ed.)
Continuous bending under tension (CBT) is known to achieve elongation-to-failure well above that achieved under a conventional uniaxial simple tension (ST) strain path. However, the detailed mechanism for supplying this increased ductility has not been fully understood. It is clear that the necking that occurs in a typical ST specimen is avoided by constantly moving the region of plastic deformation during the CBT process. The volume
of material in which the flow stress is greatest is limited to a moving line where the rollers contact the sheet and superimpose bending stress on the applied tensile load. Hence the condition of a large volume of material experiencing stress greater than the material flow stress, leading to strain localization during ST, is avoided. However, the magnitude of the contribution of this phenomenon to the overall increase in elongation is unclear.
In the current set of experiments, an elongation to fracture (ETF) of 4.56x and 3.7x higher than ST was achieved by fine-tuning CBT forming parameters for Q&P 1180 and TBF 1180, respectively. A comparison of maximum local strains near the final point of fracture in ST and CBT sheets via digital image correlation revealed that avoidance of localization of plastic strain during CBT accounts for less than half of the increased elongation in the
CBT specimens for two steels containing different amounts of retained austenite (RA). Geometrically necessary dislocation evolution is monitored using high-resolution EBSD (HREBSD) for both strain paths, indicating a lower hardening rate in the CBT samples in the bulk of the sheet, potentially relating to the cyclical nature of the stress
in the outer layers of the sheet. Interestingly, the GND evolution in the center of the sheet, which does not experience the same amplitude of cyclic stress, follows the ST behavior more closely than the sheet edges. This appears to contribute to a precipitous drop in residual ductility for the specimens that are pulled in ST after partial CBT processing. The rate of transformation of RA is also tracked in the steels, with a significantly lower
rate of transformation during CBT, compared to ST. This suggests that a slower transformation rate achieved under CBT also contributed to higher strain-to-failure levels.
Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. We introduce rough diamond anvils to reach maximum friction equal to yield strength in shear and perform the first in-situ study of the evolution of the pressure-dependent yield strength and nanostructural parameters for severely pre-deformed Zr. ω-Zr behaves like perfectly plastic, isotropic, and strain-path-independent. This is related to reaching steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states for α-Zr obtained with smooth and rough anvils are different, which causes major challenge in plasticity theory.
Lin, Feng; Levitas, Valery I.; Pandey, Krishan K.; Yesudhas, Sorb; Park, Changyong(
, Materials Research Letters)
Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. Rough diamond anvils are introduced to reach maximum friction equal to yield strength in shear and the first in-situ study of the evolution of the pressure-dependent yield strength and radial distribution of nano structural parameters are performed for severely pre-deformed Zr.ω-Zr behaves like perfectly plastic, isotropic, and strain-path-independent and reaches steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states forα-Zr obtained with smooth and rough anvils are different, causing major challenge in plasticity theory.
Sargeant, Dane, Sarkar, Md Zahidul, Sharma, Rishabh, Knezevic, Marko, Fullwood, David T., and Miles, Michael P. Effect of pre-strain on springback behavior after bending in AA 6016-T4: Experiments and crystal plasticity modeling. Retrieved from https://par.nsf.gov/biblio/10487144. International Journal of Solids and Structures 283.C Web. doi:10.1016/j.ijsolstr.2023.112485.
Sargeant, Dane, Sarkar, Md Zahidul, Sharma, Rishabh, Knezevic, Marko, Fullwood, David T., & Miles, Michael P. Effect of pre-strain on springback behavior after bending in AA 6016-T4: Experiments and crystal plasticity modeling. International Journal of Solids and Structures, 283 (C). Retrieved from https://par.nsf.gov/biblio/10487144. https://doi.org/10.1016/j.ijsolstr.2023.112485
Sargeant, Dane, Sarkar, Md Zahidul, Sharma, Rishabh, Knezevic, Marko, Fullwood, David T., and Miles, Michael P.
"Effect of pre-strain on springback behavior after bending in AA 6016-T4: Experiments and crystal plasticity modeling". International Journal of Solids and Structures 283 (C). Country unknown/Code not available: Elsevier. https://doi.org/10.1016/j.ijsolstr.2023.112485.https://par.nsf.gov/biblio/10487144.
@article{osti_10487144,
place = {Country unknown/Code not available},
title = {Effect of pre-strain on springback behavior after bending in AA 6016-T4: Experiments and crystal plasticity modeling},
url = {https://par.nsf.gov/biblio/10487144},
DOI = {10.1016/j.ijsolstr.2023.112485},
abstractNote = {Modeling springback in sheet materials is challenging in aluminum alloys, especially when a complex strain path is applied. This paper presents results from pure bending experiments on AA 6016-T4 sheet material, where various plastic pre-strains were first applied prior to bending. A crystal plasticity based elasto-plastic selfconsistent (EPSC) model that includes the effect of backstress in the hardening law was used to predict final part shape after unloading. The backstress term in the model was calibrated using geometrically necessary dislocation (GND) content, measured experimentally by high resolution electron backscattered diffraction (HREBSD). The EPSC model predicted springforward angles for unstrained 1 mm AA 6016-T4 sheet with an error of 0.4% (0.3◦) in the worst case, while the J2 plasticity isotropic model overpredicted springforward angles by as much as 2.4% (2◦). For cases where uniaxial, plane-strain, and biaxial pre-strains were first imparted to the sheets before bending, the EPSC model with backstress accurately predicted the transition from springforward to springback, while the EPSC model without backstress did not. Backstress influence on model accuracy, which increased with greater pre-strain levels, appears to be correlated to the statistically stored dislocation (SSD) density computed by the model at the end of each pre-strain step.},
journal = {International Journal of Solids and Structures},
volume = {283},
number = {C},
publisher = {Elsevier},
author = {Sargeant, Dane and Sarkar, Md Zahidul and Sharma, Rishabh and Knezevic, Marko and Fullwood, David T. and Miles, Michael P.},
}
Warning: Leaving National Science Foundation Website
You are now leaving the National Science Foundation website to go to a non-government website.
Website:
NSF takes no responsibility for and exercises no control over the views expressed or the accuracy of
the information contained on this site. Also be aware that NSF's privacy policy does not apply to this site.
