Cell polarity underlies key processes in all cells, including growth, differentiation and division. In the bacterium Myxococcus xanthus, front-rear polarity is crucial for motility. Notably, this ...polarity can be inverted, independent of the cell-cycle, by chemotactic signaling. However, a precise understanding of the protein network that establishes polarity and allows for its inversion has remained elusive. Here, we use a combination of quantitative experiments and data-driven theory to unravel the complex interplay between the three key components of the M. xanthus polarity module. By studying each of these components in isolation and their effects as we systematically reconstruct the system, we deduce the network of effective interactions between the polarity proteins. RomR lies at the root of this network, promoting polar localization of the other components, while polarity arises from interconnected negative and positive feedbacks mediated by the small GTPase MglA and its cognate GAP MglB, respectively. We rationalize this network topology as operating as a spatial toggle switch, providing stable polarity for persistent cell movement whilst remaining responsive to chemotactic signaling and thus capable of polarity inversions. Our results have implications not only for the understanding of polarity and motility in M. xanthus but also, more broadly, for dynamic cell polarity.
•Tube hydroforming tests for characterization and validation of tubular material behavior.•Proposal of identification strategy to calibrate CB 2001 yield criterion based on reduced number of ...experimental tests.•Accurate validation of the proposed identification strategy by comparing experimental and finite element analysis results.
The present work focuses upon the use of tube hydroforming into square cross sectional-die as validation test for new constitutive parameter identification strategy. It presents how a developed identification startegy using a reduced set of experimental data in conjuction with some generated artificiel input data are proficient to identifiy the anisotropy parameters of an advanced Cazacu & Barlat yield criterion CB2001, which requires a large number of experimental data for its calibration. Two tubular materials are investigated, namely: mild steel S235 and AA6063 aluminum alloy, which manifest miscellaneous plastic behaviors. The concordance between numerical and experimental thickness distribution along a profile of the hydroformed part into cross sectional-die are the main facing challenges for the validation of the proposed calibration strategy. The analysis of the present findings reveals good agreement between numerical simulation and experimental results. Eventually, the proposed approach is a user friendly-identification strategy and effective method, which can be applied for the calibration of recent developed yield functions for better modeling anisotropic plastic behavior of sheet and tube metals and then could likely widespreadly used in research laboratories as well as in automative industry.
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•3D fracture loci of uncoupled ductile fracture models were calibrated for 2024-T351 aluminum alloy and DP600 steel.•The type and number of calibration tests has a marginal influence in the fracture ...locus and predictive ability of the models.•Quite different shapes of the fracture locus are observed for between both materials.•The models present different levels of prediction accuracy in the high range of stress triaxiality, for both materials.•It is difficult to select the most appropriate model based only on the objective function value.
The prediction of ductile failure is crucial for the progress of metal forming industries. Therefore, uncoupled fracture models have been proposed and continuously extended, trying to improve their forecasting abilities. However, without an assessment analysis of their predictive ability, it is difficult to establish the most suitable model, for describing the onset of failure under a wide range of loading conditions. Actually, a fair comparison of models’ predictive ability requires the use of an extensive experimental database and a similar calibration procedure. In this context, seven uncoupled fracture models are chosen and revisited to study the effect of the type and number of tests used for calibration on their predictive ability. Experimental datasets available in literature were considered for 2024-T351 aluminium alloy and for DP600 steel. For each material, the experimental dataset was split in two subsets. The first one includes tests that were carried out under plane stress conditions that were used in the calibration procedure. For the aluminium alloy, different groups of 6 tests, covering distinct stress states, were elicited from the experimental subset and applied in the calibration of the seven models. The remaining tests were used to assess the predictive ability and their sensibility regarding the group used in models’ calibration. Different trends of the fracture loci are observed, depending on the selected models and the tests used in their calibration. However, the analysis of the results indicates that a set of at least 6 experimental tests is appropriate to calibrate fracture models, providing that they enable covering a wide range for the stress triaxiality and Lode parameter. Finally, the conclusions provide some recommendations for the improvement of the calibration procedure.
This paper aims to identify the constitutive parameters of anisotropic tubular materials and to verify the accuracy of models׳ prediction. The identification of the constitutive parameters is based ...on information obtained from tensile tests, performed on samples cut from the tubes, and from the free tubular bulge test, using a home-developed bulge forming machine. Two tubular materials exhibiting different anisotropic behaviour and work hardening characteristics are investigated: a mild steel S235 seamed tube and an aluminium alloy AA6063 extruded tube. It is shown that advanced phenomenological yield functions, including a large number of anisotropy parameters, can accurately describe the plastic flow of highly anisotropic tubular materials during the tube hydroforming process. However, parameter identification procedure of advanced yield criteria requires a high number of experimental tests. Thus, in order to enable the parameter identification of these yield criteria when using a reduced set of experimental results, the present study develops a method that combines tensile tests with (i) a free bulge test, which is used to characterize the biaxial stress state experienced by the tube during the bulge testing, and (ii) some generated artificial input data. Finally, the proposed method shows an excellent agreement between numerical predictions and experimental results.
•Experimental characterization of tubular materials applied for tube hydroforming process.•Development of new strategy to calibrate several yield criteria using reduced set of experimental input data.•Successful validation of the proposed identification strategy used for Cazacu-Barlat′2001 yield criterion calibration by comparing experimental and FE results.
•Analysis of the influence of the number and type of experimental input data on the yield criteria prediction accuracy.•Identification of advanced yield criterion parameters using a reduced set of ...experimental input data.•Validation of the proposed identification strategies by comparing numerical with experimental results.
This work presents an investigation into the effect of the number and type of experimental input data used in parameter identification of Hill’48, Barlat’91 (Yld91) and Cazacu and Barlat’2001 (CB2001) yield criteria on the accuracy of the finite element simulation results. Different sets of experimental data are used to identify the anisotropy parameters of two metal sheets, exhibiting different anisotropic behaviour and hardening characteristics: a mild steel (DC06) and an aluminium alloy (AA6016-T4). Although it has been shown that the CB2001 yield criterion can lead to an accurate description of anisotropic behaviour of metallic sheets, its calibration requires a large set of experimental input data. A calibration procedure is proposed for CB2001 based on a reduced set of experimental data, i.e. where the results are limited to three uniaxial tensile tests, combined with artificial data obtained using the Barlat’91 yield criterion. Evaluation of the predictive capacity of the studied yield criteria, calibrated using different sets of experimental data, is made by comparing finite element simulation results with experimental results for the deep drawing of a cross-shaped part. A satisfying agreement is observed between experimental and numerical thickness distributions, with a negligible effect of the number and type of experimental data for the Hill’48 and Yld91 yield criteria. On the contrary, CB2001 calibration is quite sensitive to the experimental data available, particularly biaxial values. Nevertheless, CB2001 calibration based on the combination of effective and artificial experimental data achieves satisfying results, which in the worst case are similar to the ones obtained with the Yld91.
This work presents details concerning the strategies and algorithms adopted in the fully implicit FE solver DD3IMP to model the orthotropic behavior of metallic sheets and the procedure for ...anisotropy parameters identification. The work is focused on the yield criterion developed by Cazacu, Plunkett and Barlat, 2006 1, which accounts for both tension–compression asymmetry and orthotropic plastic behavior. The anisotropy parameters for a 2090-T3 aluminum alloy are identified accounting, or not, for the tension-compression asymmetry. The numerical simulation of a cup drawing is performed for this material, highlighting the importance of considering tension-compression asymmetry in the prediction of the earing profile, for materials with cubic structure, even if this phenomenon is relatively small.
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