Comparison of Constitutive Models for predicting the formability of SS 304 by tubular hydroforming process

Finite Element (FE) simulation of sheet/tube forming precision depends mainly on the accuracy of the constitutive modeling. The present paper aim is to compare the constitutive models to fit the stress-strain curves. The accurate deformation behavior of the SS 304 tubes depends on the constitutive modeling of hardening behavior. Deformation data of the tensile specimens cut from tubular sample were collected by conducting Uniaxial tensile tests (UTT) at three different rolling directions. Five constitutive relationships were then recognized by fitting the true stress and strain data with the constitutive models of Hollomon, Power, Krupowsky, Voce and Ghosh, and the fitting accuracy were analyzed and compared. Effects of hardening models on Forming Limit Curves (FLC), pressure loading and bulge height of the hydroformed tube were then studied. The obtained FLC from the simulations were compared with experimental FLC to predict the accuracy of the hardening models.

Insight into the Influence of Punch Velocity and Thickness on Forming Limit Diagrams of AA 6061 Sheets—Numerical and Experimental Analyses

In this article, the forming limit diagram (FLD) for aluminum 6061 sheets of thicknesses of 1 mm and 3 mm was determined numerically and experimentally, considering different punch velocities. The punch velocity was adjusted in the range of 20 mm/min to 200 mm/min during the Nakazima test. A finite element (FE) simulation was carried out by applying the Johnson–Cook material model into the ABAQUSTM FE software. In addition, a comparison between the simulation and the experimental results was made. It was observed that by increasing the punch velocity, the FLD also increased for both thicknesses, but the degree of the improvement was different. Based on these results, we found a good agreement between numerical and experimental analyses (about 10% error). Moreover, by increasing the punch velocity from 20 mm/min to 100 mm/min in 1 mm-thick specimens, the corresponding FLD increased by 3.8%, while for 3 mm-thick specimens, this increase was 5.2%; by increasing the punch velocity from 20 mm/min to 200 mm/min in the 3 mm-thick sheets, the corresponding FLD increased by 9.3%.

Localized forming limit analysis of substrate-supported metals: Influence of yield-dependent necking bound angle

In this paper, the influence of functional elastomeric substrate-supported layers for enhancing potential resistance capability against localized plastic failure of advanced high strength steels is considered based on a localized necking model of vertex theory. Application of this structure leads to postponing the plastic instability of the metallic part. By defining diffuse and localized modes of deformation in a general framework, the theoretical models are developed to predict necking limits at several stress states. In addition, the results of the Hookean and neo-Hookean elastomers are compared in terms of strain hardening with the anisotropy parameter of Hill’s yield criteria. Since necking band angle (NBA) is a principal factor for the necking prediction, its effect on bifurcation events is evaluated specifically for different ratios of stress rate, and quadratic and non-quadratic yield criteria. This analysis is performed by proposing a supported and yield-dependent necking bound angle (YD-NBA). All considerations are done by providing equilibrium conditions governed over the NBA. Finally, obtained results indicate good agreements between several theoretical considerations and experimental data.

Theoretical predictions of dynamic necking formability of ductile metallic sheets with evolving plastic anisotropy and tension-compression asymmetry

In this paper, we have investigated necking formability of anisotropic and tension-compression asymmetric metallic sheets subjected to in-plane loading paths ranging from plane strain tension to equibiaxial tension. For that purpose, we have used three different approaches: a linear stability analysis, a nonlinear two-zone model and unit-cell finite element calculations. We have considered three materials –AZ31-Mg alloy, high purity α-titanium and OFHC copper– whose mechanical behavior is described with an elastic-plastic constitutive model with yielding defined by the CPB06 criterion [10] which includes specific features to account for the evolution of plastic orthotropy and strength differential effect with accumulated plastic deformation [37]. From a methodological standpoint, the main novelty of this paper with respect to the recent work of N’souglo et al. [32] –which investigated materials with yielding described by the orthotropic criterion of Hill [19]– is the extension of both stability analysis and nonlinear two-zone model to consider anisotropic and tension-compression asymmetric materials with distortional hardening. The results obtained with the stability analysis and the nonlinear two-zone model show reasonable qualitative and quantitative agreement with forming limit diagrams calculated with the finite element simulations, for the three materials considered, and for a wide range of loading rates varying from quasi-static loading up to 40000 s−1, which makes apparent the capacity of the theoretical models to capture the mechanisms which control necking formability of metallic materials with complex plastic behavior. Special mention deserves the nonlinear two-zone model, as it does not need prior calibration –unlike the stability analysis– and it yields accurate predictions that rarely deviate more than 10% from the results obtained with the unit-cell calculations

Research on the Secondary Forgeability of High Volume Fraction Whisker Reinforced Aluminum Matrix Composites of Original Squeeze Casting

The poor formability of high volume fraction whisker reinforced aluminum matrix composites of original squeeze casting is an important factor restricting its further development and application. Currently, there are no reports on the secondary forgeability of aluminum matrix composites of original squeeze casting, although some papers on its first forgeability are published. The secondary forgeability is very important for most metals. This study aims to investigate the secondary forgeability of aluminum matrix composites. In this study, the secondary upsetting experiments of 20 vol% SiCw + Al18B4O33w/2024Al composites, treated by the original squeeze casting and extrusion, were carried out. The first upsetting deformation is close to the forming limit, the secondary upsetting deformation under the same deformation conditions was carried out to investigate the secondary forgeability. The experimental results show that, unlike aluminum alloys, the 20 vol% SiCw + Al18B4O33w/2024Al composites at the original squeeze casting and extrusion states have no secondary forgeability due to the whisker rotating and breaking during the secondary upsetting. The high volume fraction whisker reinforced aluminum matrix composites of original squeeze casting cannot be formed by the multiple-forging method since the cavities and cracks caused by whisker fracture continue to expand during secondary processing, which leads to further extension of macroscopic cracks.

Prediction of load requirement and instabilities during end forming of friction stir processed AA 6063-T6 thin-walled tubes

PurposeThe current work aims to propose a finite element (FE) simulation methodology to predict the formability of friction stir processed (FSPed) tubes by end forming. Moreover, a strain mapping method is also presented to predict the end forming instabilities.Design/methodology/approachIn this work, FE simulation of end forming of raw tubes and FSPed AA6063-T6 tubes are done using Abaqus (explicit) incorporating anisotropic properties of the raw tube and FSPed zone. Actual thickness of the FSPed zone is also implemented. Expansion, reduction and beading are the end forming operations considered. Load requirement and instabilities are predicted. A new method “strain mapping method” is followed to predict the failure instabilities in expansion and beading, while during reduction, wrinkling is predicted by FE simulations. Lab scale experiments on FSP and end forming are done for validation at various rotational speeds.FindingsResults reveal that in the case of expansion and reduction of FSPed tubes, forming load predictions are accurate, while in beading, after initiation of bead, predictions are not accurate. Experimental observation on the type of instability is consistently predicted during numerical simulations. Prediction of displacement at failure by strain mapping method is encouraging in most of the cases including those that are FSPed. Hence, it is suggested that the method can be utilized to evaluate the onset of failure during tube expansion and beading.Originality/valueFE simulation methodology including anisotropic properties of raw tube and FSPed tubes is proposed, which is not attempted until now even for normal tubes. Strain mapping method is easy to implement for instability predictions, which is done usually by failure theories and forming limit diagram.

Effect of Frictional Conditions in Deep Drawing on Formability

This study investigated the stress and strain behavior caused in the forming process via simulation analysis using the finite element method, for suppressing punch shoulder and head plate thickness reduction die shoulder stress concentration by controlling the friction conditions. The following findings were obtained: The thickness of the blank head and punch shoulder decreased with the forming process. Due to the increase in the coefficient of friction with the punch side, the plate thickness reduction ratio decreases, and is the lowest when it is close to non-lubrication; Stress concentration occurs at the die shoulder with forming processing. With the increase in the friction coefficient value, forming limit parameter (FLP) increases slightly, but as it does not reach the limit value of 1, the forming process can be safely performed without mechanical damage; When the formability is comprehensively evaluated using the plate thickness reduction ratio and FLP, the friction coefficient μ = 0.4 to 0.5 is reasonable.