Limiting Dome Height Research Articles

Warm forming behavior of high strength aluminum alloy AA7075

The formability of aluminum alloy AA7075 at elevated temperature was investigated through experiment. Stress–strain relationship at different temperatures and forming speeds were investigated through tensile testing. Deep drawing and stretch formability were also tested through limiting drawing ratio (LDR) and limiting dome height (LDH) tests. Finally, post forming mechanical property testing was conducted to investigate the effects of exposure to warm forming temperatures on the mechanical properties. Results show that deep drawing and stretch formability of AA7075 can be significantly improved when the blank is heated to 140–220°C. At temperature over 260°C, formability and post forming mechanical properties begin to decrease due to the effect of the heating and forming processes on the material's temper.

보론강 용접 맞춤 판재의 고온 에릭슨 커핑 평가

The combination of tailor welded blank (TWB) and hot stamping often offers improved crash-worthiness and reduced mass of stamped parts in the automobile body. To investigate the formability of laser TWB and the reliability of weld line, the present study used 22MnB5 boron steel sheet of the same thickness and used the Erichsen cupping test at elevated temperatures. The effects of laser direction, die temperature, weld line positions and forming speed on formability(the limiting dome height) were studied and the results were compared with the formability of the base material.

Formability Evaluation of FSW Blanks Made of Aluminum Sheet: Influence of Welding Speed and Tool Rotation Speed

The main aim of the work is to analyze the influence of welding speed and tool rotation speed on the forming behavior of FSW blanks. The FSW blanks are made of 6061 Al sheet of 2.1 mm thickness. The welded sheets are made at two different optimized levels of welding speed (90 and 100mm/min) and tool rotation speed (1300 and 1400 rpm). The effect of FSW parameters on the forming limit curve (FLC) and thickness distribution was analyzed by performing limit dome height (LDH) tests at few pre-defined stretching strain paths. It is observed that FSW blanks exhibit more formability as compared to un-welded sheets. The forming limit is found to improve with increase in tool rotation speed and it decreases with increase in welding speed. An attempt has been made to relate the thinning gradient developed during necking with the forming limit at different welding conditions.

Weld zone representation during the formability prediction of friction stir welded blanks with similar thickness sheets

During formability prediction of friction stir welded (FSW) blanks, it is necessary to incorporate nugget zone and heat-affected zone (HAZ) properties separately for better accuracy. In general, it is observed that the weld zone is represented as a single entity, in which only global weld zone properties are implemented. In this work, it is proposed that there is a domain of weld conditions in which the single-zone assumption (nugget and HAZ are modelled without incorporating their individual properties) breaks down and the double-zone assumption (nugget zone and HAZ are represented separately) should be followed. During limiting dome height simulations, a representative base material is considered from the literature with changing nugget zone and HAZ properties. The punch displacement at failure and maximum load are compared between FSW blanks modelled with single- and double-zone assumptions. It is observed that modelling FSW blanks with double-zone assumption plays a vital role for accurate formability prediction. The single-zone assumption is not valid for all the FSW conditions. Both in transverse and longitudinal weld orientations, there are possibilities of multiple domains in which the double-zone assumption is valid. It is found that there exists a relationship between the thickness distribution and availability of single-zone or double-zone models. Whenever the thickness distribution of a particular double zone is closer to the reference case modelled with single zone, it is sufficient to model that weld zone case with a single zone. Double-zone representation is required in cases when the thickness distribution is very different. The domains for weld zone modelling in FSW blanks are sensitive to failure location. Put simply, it is advisable to model HAZ separately, when failure occurs in it. But this is not always the case. It depends on a compromise between the accuracy and availability of HAZ properties.

Statistical modeling of laser welding of DP/TRIP steel sheets

In this research work, a statistical analysis of the CO 2 laser beam welding of dual phase (DP600)/transformation induced plasticity (TRIP700) steel sheets was done using response surface methodology. The analysis considered the effect of laser power (2–2.2 kW), welding speed (40–50 mm/s) and focus position (−1 to 0 mm) on the heat input, the weld bead geometry, uniaxial tensile strength, formability limited dome height and welding operation cost. The experimental design was based on Box–Behnken design using linear and quadratic polynomial equations for predicting the mathematical models. The results indicate that the proposed models predict the responses adequately within the limits of welding parameters being used and the welding speed is the most significant parameter during the welding process.

Development of Experimental Method to Improve Sheet Metal Formability by Transverse Normal Stress

To make full use of the promotion potential of hydrostatic stress on the formability of sheet metal, several foundational questions met in practical application of double-sided pressure forming technique are studied in this paper. The theoretical analysis of sheet metal deformation during the double-sided pressure bulging process is carried out, and an analytical approximation for normal pressure loading path that secures out-of-plane stress ratio, γ, continuously increasing (dγ ≥ 0 holds) is presented. Utilization of the relationship between the theoretical approximation for normal pressure load and material hardening properties, a novel double-sided pressure forming method is proposed—the viscous pressure bulging (VPB) of the overlapping sheet metals, in which a highly viscous but flowable semi-solid medium is used as the soft die and the target sheet metal is deformed under the constraints from viscous medium on one side and overlapping sheet on another side. To confirm the efficiency of the proposed method, the VPB test of overlapping sheet metals is simulated by DEFORM-2D, and the experimental tests are also carried out. The results show that σ3 provided by overlapping sheet can overcome the diminishing of γ value caused by evolving strain-hardening and geometric softening effect in the post-diffuse necking stage. The experimental obtained increase of the limit dome height (LDH) of double-sided pressure bulging specimen is 12.6% compared with that of single-sided pressure bulging specimens.

Effect of the Thickness Ratio on the Failure Modes of Tailor Welded Blanks

Tailor welded blanks (TWBs) offer several notable benefits including decreased part weight, reduced manufacturing costs, increased environmental friendliness, and improved dimensional consistency. To take full advantage of these benefits, however, one needs to overcome the reduced formability of TWBs and be able to accurately predict the failure modes depending on the thickness ratio between the thicker and thinner sheets of a tailor welded blank with similar base materials early in the design process. In this paper, we studied the effect of the thickness ratio on the limit dome height of TWBs by using finite element method and experiments, analyzed the effect of TR on the failure mode of TWBs. A concept of the critical thickness ratio was presented to predict the failure modes of TWBs. The results show that the rapture originates on the weld of TWBs when the thickness ratio is less than the critical thickness ratio and on the thinner side when the thickness ratio exceeds the critical thickness ratio.

Strain Mode Dependence of Deformation Texture Developments: Microstructural Origin

Fully recrystallized commercial-purity aluminum sheets were deformed by limiting dome height tests, the following strain modes: uniaxial tension (US), near plane strain tension (PS), and equibiaxial tension (BS) were identified using standard procedure. The deformation texture developments differed significantly depending on the strain mode. Although the full constraints Taylor (FCT) model captured the texture developments in US, it failed to reproduce deformation textures in PS and especially in BS. The Advanced LAMEL (ALAMEL) model and the crystal plasticity finite element method (CPFEM) were, however, successful with respect to all three strain modes. Microtexture data brought out interesting observations of orientation gradients. First, the orientation gradients increased from US to PS to BS. Second, such gradients were mostly around initial (or prior deformation) grain boundary regions. A simple algorithm, and an associated computer program, was developed to demarcate such near boundary gradient zones (NBGZs). The area fraction and severity of NBGZ seemed to affect the texture development; FCT was reasonably successful at low NBGZ, whereas high NBGZ required the ALAMEL and the CPFEM models that are capable of addressing strain heterogeneity and grain interactions.

Microstructures and tensile properties of a twin roll cast and heat-treated Mg–2.4Zn–0.1Ag–0.1Ca–0.1Zr alloy

An Mg–2.4Zn–0.1Ag–0.1Ca–0.1Zr alloy sheet, with a tensile yield strength of 316 MPa, an ultimate tensile strength of 342 MPa and an elongation of 17%, has been processed by twin roll casting (TRC), hot rolling and heat treatment. The high yield strength has been attributed to a uniform distribution of fine rod-like precipitates of MgZn2 phase. The TRC and hot-rolled sheet also showed an exceptionally high stretch formability with a limiting dome height much larger than those of other Mg alloys.

Forming Limit of Holed Dome in Two-Stage Stretch Forming

This paper deals with the accurate prediction of forming limit of a dome with a circular hole in two-stage stretch forming. Since this two-stage forming is a process of non-proportional deformation, a fracture criterion, which is capable to predict fracture limit of sheet metal under non-proportional strain path, is introduced. The limit dome height of steel blank is predicted by utilizing numerical optimization technique, in which the fracture criterion is used as a constraint function to avoid sheet breakage. The calculated result and the corresponding experimental result show that the fracture criterion can successfully predict the limit dome height in the two-stage forming while the classical forming limit diagram (FLD) overestimates it.

Effect of Loading Location of Viscous Medium on Sheet Deformation in Viscous Pressure Bulge (VPB) Test

Viscous pressure forming (VPF) uses a highly viscous but flowable material as pressure-carrying medium (PCM). Due to the relative low flowability of viscous medium compared with fluid, nonuniform pressure distribution in viscous medium can be used to control and regulate the deformation sequence of the workpiece through controlling the loading mode of viscous medium. In the present study, viscous pressure bulge (VPB) tests with three kinds of loading location of viscous medium (central zone, corner zone and the whole deformation zone) are conducted and the influences of loading location of viscous medium on sheet deformation behavior are investigated via numerical simulations and experiments. It is found that changing the loading location of viscous medium can greatly affect the deformation behavior of sheet metal. When the viscous medium is injected from the die corner zone, a local high pressure formed at the corner zone of sheet metal and a higher limiting dome height and strains are obtained.

Effect of Weld Location, Orientation, and Strain Path on Forming Behavior of AHSS Tailor Welded Blanks

Use of multiple advanced high strength steel sheets for fabrication of tailor welded blanks (TWBs) is one of the current interests for automotive and steel industries as it reduces manufacturing cost and weight of the vehicle, and also improves the quality of the component. As the varieties of TWB applications are increasing, the effects of the difference in material properties, weld, and its orientation on blank formability have become important both in deep drawing and stretch forming. In this work, high strength low alloy (HSLA) grade steels were laser welded with two different dual phase steels having 980 MPa (DP980) and 600 MPa (DP600) tensile strengths to fabricate two different material combination TWBs (DP980-HSLA and DP600-HSLA). Formability of these two types of TWBs has been studied experimentally both in biaxial and plane strain stretch forming modes by performing limiting dome height (LDH) tests using a 101.6 mm diameter hemispherical punch. Five different weld locations during biaxial-stretch forming mode, and the effect of weld orientation with respect to major principal strain in plane strain stretch forming mode, have been studied. It was found that formability LDH and failure location depended on weld location, and LDH increased when weld line was positioned at the extreme positions away from the center due to more uniform strain distribution on the deformed dome. The welded blanks had lower formability in plane strain deformation mode compared with biaxial-stretch forming mode. However, influence of weld orientation on the formability depended on material combination. Changes in the fracture mode were confirmed from fractography analysis of biaxial, transverse plane strain, and longitudinal plane strain stretch formed samples.

Influence of Yield Criteria in the Prediction of Strain Distribution and Residual Stress Distribution in Sheet Metal Formability Analysis for a Commercial Steel

In this study, Hill 48 and Barlat 89 yield criteria are evaluated by simulating the Limiting Dome Height test of the Numisheet 96 benchmark problem [1] for a commercial D-grade steel and the results are validated with experimental data. Three strain modes, viz. biaxial, plane strain, and uniaxial strain modes, are used in the simulation studies. The yield criteria are evaluated based on the strain distribution in forming and residual stress distribution after springback. The results show that the Hill 48 and Barlat 89 yield criteria do not show a good match with predicted results of strain distribution in the plane strain mode. The difference between predicted results and experiments can be attributed to the combined influence of friction coefficient and draw bead boundary condition. The prediction of residual stress distribution differed considerably with the yield criteria. The residual stress predicted is validated for selected locations using X-ray diffraction techniques.

Thermal forming of light-weight alloys under a multi-stage forming process

This article presents an experimental investigation aimed to obtain the optimum formability of light-weight alloys under the multi-stage forming process. Titanium alloy sheets (Ti-6Al-4V) and aluminium alloy sheets (AA5052) of thickness 1 mm with different widths (i.e. 20, 90, and 110 mm) are selected as forming specimens. In order to carry out the multi-stage forming process, a special fixture with a heating system for the pre-straining process is designed and manufactured. The limit dome heights of both titanium alloys and aluminium alloys are measured and recorded. The experimental results reveal that both of the light-weight alloys yielded enhanced ductility at higher working temperatures, because of a decrease in the yield strength. The formability of selected materials is found to be sensitive to the forming temperatures and multi-stage forming processes.

Biaxial Stretching Behavior of a Copper-Alloyed Interstitial-Free Steel by Bulge Test

Biaxial stretching behavior of a promising high-strength copper-alloyed interstitial-free (IF) steel has been investigated under various processing conditions using bulge tests. Hill theory and von Mises yield criterion have been used to analyze the results. It is revealed that copper-alloyed IF steel in continuous-annealed (CA) condition exhibits the highest equivalent strain at fracture and largest limiting dome height (LDH) among all the processing conditions. However, these values are lower in copper-alloyed interstitial steel than in traditional interstitial-free–high-strength (IF-HS) steels due to the presence of solute copper and copper precipitates in the former.

Formability of Friction Stir Welded AZ31 Magnesium Alloy Sheets

The formability of friction stir welded AZ31 magnesium alloy sheets was investigated by means of uniaxial tensile and hemispherical punch tests performed under different process conditions. The results of the tensile tests were analysed in terms of flow stress and ductility at different temperature and strain rate; the hemispherical punch tests, carried out at different temperatures, provided the limiting dome height. The formability of FSW-ed blanks was compared to the one exhibited by the base material in order to evaluate the quality of the welded joints.

Warm-Forming of Light-Weight Alloys under Multi-Stage Forming Process

This paper aims at presenting an experimental investigation to obtain the optimum formability of light-weight alloys under the multi-stage forming process. Titanium alloy sheets (Ti-6Al-4V) and aluminium alloy sheets (AA5052) are selected as forming specimens. The special fixture with heating device is applied in order to carry out the prestraining process. The swift forming test at warm-forming condition is performed for measuring the limit dome heights after the multi-stage formign process. The outcomes of this investigation are valuable for engineers to design and fabricate high-quality light-weight components efficiently.

Experimental and numerical studies on the forming behavior of tailor welded steel sheets in biaxial stretch forming

Stretch forming is an important process in making complex stampings for autobody components. In the present work formability of three different types of tailor welded blanks (TWBs) in biaxial stretch forming modes has been studied by conducting limiting dome height (LDH) tests. The TWBs are laser-welded samples of low carbon and ultra low carbon steel sheets with difference in thickness, grade and surface conditions. In TWBs with difference in thickness, the LDH decreases as the thickness ratio increases and the thickness of the thinner side is also crucial. A high thickness ratio causes two major strain peaks on thinner side and fracture takes place due to strain localization at the peak close to the pole. The weld ductility and the extent of difference in properties are the two crucial parameters for formability in TWBs with difference in properties. In both these TWBs, the fracture takes place perpendicular to the weld line and propagates towards the stronger side. Significant weld line movement occurs towards the thicker/stronger side in biaxial stretch forming. The maximum weld line movement occurs at the pole and it increases with increase in thickness ratio and becomes constant beyond a certain thickness ratio. The peak load required to deform the TWB specimens is less compared to the corresponding parent sheets. In case of TWBs with difference in thickness, as the thickness ratio increases, the peak load reduces due to decreasing punch-blank contact area.

7110 Efficacy and safety of AMG 102 in patients with advanced renal cell carcinoma (RCC)

Transformation induced plasticity (TRIP) steel provides enormous potential for auto-body construction in the automotive sector, owing to its enhanced mechanical behavior. In this work, Si-alloyed TRIP steel is joined by employing laser beam welding (LBW) and by utilizing two arc welding processes: gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) in order to assess the effect of the net heat input on the microstructure, the uniaxial tensile properties and the forming response. Results indicate that in spite of the Si content in TRIP steel; precipitation and growth of carbides (tempering) are observed in both: the martensite islands and the retained austenite phase, thus leading to the measurable softening at the sub-critical heat affected zone (SC-HAZ) of the arc welded samples. Although the failure location was predominantly found at the sub-critical heat affected zone of the GMAW samples, the maximum stress and elongation was basically controlled by the total extension of the weldment including fusion zone and heat affected zone. While the limiting dome height upon tension-tension (T-T) and tension-compression (T-C) depended primarily on the fusion zone hardness, weld width and geometry of the sample; the fracture location was outside the weld for T-C, whereas the fracture initiated at the weld in T-T samples. LBW specimens showed optimum forming performance.

Modeling of anisotropic plastic behavior of ferritic stainless steel sheet

Modeling of anisotropic plastic behavior of ferritic stainless steel sheet (Type 409) was investigated using the three yield functions of Hill [A theory of the yielding and plastic flow of anisotropic metals. Proceedings of Royal Society of London, Series A 1948;193:281–97.], Barlat and Lian [Plastic behavior and stretchability of sheet metals. Part I: A yield function for orthotropic sheets under plane stress conditions. International Journal of Plasticity 1989;5:51–66] and Barlat et al. [Plane stress yield function for aluminum alloy sheet. Part I: Theory. International Journal of Plasticity 2003;19:1297–319.] (referred to as Yld2000-2d) criteria. Mechanical behaviors were characterized based on uniaxial tension, balanced biaxial bulge, and disk compression tests. Directionalities of yield stresses and r values were predicted from the three criteria and compared with experimental results. In order to verify the modeling accuracy of the three functions under complex loading conditions, cylindrical cup drawing and limiting dome height tests were carried out numerically and experimentally. It has been demonstrated that the result from Yld2000-2d criterion exhibits good agreement with experimental data. The effects of anisotropic hardening on earing and necking were also investigated based on the different levels of plastic work.