Deep Drawing Tests Research Articles

Failure prediction on steel sheet under different loading paths based on fully coupled ductile damage model

It is well known that the ductile damage evolution on sheet metal under complex loading conditions is highly dependent on the complexity of the applied loading path. In this study, a fully coupled ductile damage model including the effect of Lode angle and microcracks closure together with the mixed nonlinear isotropic and kinematic hardenings is used to simulate the fracture occurrence of the chosen low carbon steel. Various mechanical tests including the uniaxial tensile tests, the pre-notched tensile tests with four notched radii, the butterfly specimen tests under different loading paths, and deep drawing tests are performed on the chosen low carbon steel sheet to calibrate and validate the proposed model. The influence of the Lode angle on damage evolution is investigated throughout various numerical simulations. These results showed the wide capabilities of the proposed fully coupled damage model on the prediction of ductile fracture under the wide range of loading conditions.

Size effect on the yield behavior of metal foil under multiaxial stress states: Experimental investigation and modelling

In microforming process, the metal foil is often deformed under complex stress states and meanwhile affected by the scale effect. To explore the size effect on the yield behavior of metal foil under multiaxial stress states, the biaxial tensile tests of the annealed stainless steel SUS304 foils were performed. The experimentally determined yield loci evolve from rough ellipse to Tresca-like yield locus with the decrease of the ratio of foil thickness to grain size. The experimental result indicates that both size and shape of the yield locus are influenced by size effect and stress states. Four conventional yield criteria including von Mises, Hill’48, Barlat’89 and Yld2000-2d were utilized to evaluate their applicabilities at micro scale. It is found that the predicting accuracy of the macro-scaled yield criterion is worsened with the decreasing grain numbers across the thickness direction. According to the evolving trend of the experimental yield locus and the deviation analysis of the theoretical yield locus, a multiscale yield criterion was proposed by modeling the relationship between the exponent, anisotropy parameters and size effect. In the end, the developed criterion was verified by analyzing the earing profile of the cup from deep drawing test and Hall-Petch (HP) relationships under multiaxial stress states.

Mechanical Behavior of Embossed AA1050-O Sheets Subjected to Tension and Forming

In this paper, experimental characterization of embossed aluminum sheets is performed using extensive mechanical tests. Rotary embossing is performed on these sheets in order to obtain a periodic hill-and-valley structure. The experimental program consists of realizing mechanical tests such as tension, deep drawing, and hydraulic bulge tests using embossed samples in order to build a database that can be used for future finite element modeling tasks. The tensile tests are performed using digital images correlation (DIC) for total displacement measurements and for detailed strain maps. The hydraulic bulge and deep drawing tests are conducted on embossed circular samples to study their formability. A comparison was made with the plane (non-embossed) sheets to explain the contribution of the embossed structure either in both cases of uniaxial and multiaxial loadings.

Effect of coining on springback behaviour

Especially due to utilization of high strength steels in automotive parts, accurate prediction and reduction of springback have gained more importance in the recent years. One of the widely used approaches to reduce the springback in deep drawn parts especially in and around the bent regions is coining (restrike operation). In this method, the sheet material in the springback-relevant regions is compressed between two rigid tools having clearences less than the sheet thickness. By this way, compressive stresses and strains are superimposed and therefore the bending effects are reduced. During coining, plastic deformation occurs in the thickness direction. In order to predict this behavior in process planning numerical simulations should be capable of considering the effects of through-thickness compression. In order to analyze this effect, axisymmetrical deep drawing tests were performed. In a further step, the bottom surface or the radius region of the geometry was compressed between the punch and additional tools. To analyze the springback behaviour, drawn geometries were cut along the rolling direction, so that the residual stresses are released. The same procedure was also simulated with shell elements having enhanced formulation to account for through-thickness deformation. Experimental springback results show that the coining process influences the springback and this can be captured by the enhancements in the shell formulation.

Improvement of deep drawing conditions utilizing LDPE/Gr/MWCNT composite films

The main purpose of this work is reduction of friction coefficient in deep drawing die to improve the deep drawing conditions of St37 blank sheet. For this purpose, graphite (Gr) and multi wall carbon nanotube (MWCNT) were introduced into low density poly(ethylene) (LDPE), and blown composite films were prepared by co-rotating extruder. The composite films (LDPE/Gr, LDPE/MWCNT, and LDPE/Gr/MWCNT) were used as lubricants in deep drawing of St37 blanks. Gr was added in the content of 5, 10, 15, 20 and 25 wt%, and MWCNT was added in content of 0.1, 0.5, 1 and 2 wt%. The effect of filler content on drawing depth, forming force, and thinning of St37 blanks was investigated. The results of experiments indicated that MWCNT was more beneficial than Gr in improving the drawing depth, forming force, and thinning of St37 blanks when Gr and MWCNT were singly combined. Deep drawing tests using LDPE/Gr/MWCNT hybrid composite films revealed that hybrid composite films were more suitable in improvement of deep drawing conditions of St37 blanks. Minimum thinning (8.5%), forming force (49470 N), and maximum drawing depth (13.5 mm) were obtained using LDPE/15 wt% Gr/2 wt% MWCNT hybrid composite film.

Design of a reverse deep drawing experiment enhancing strain path changes

To evaluate a priori the amount of strain path changes in forming processes in order to adjust the complexity of constitutive equations, it is necessary to develop forming tests at the laboratory scale sensitive to strain paths changes. In this work, a micro-forming experiment is designed in order to perform reverse deep drawing tests on ultra-thin metallic sheets, typically 0.1mm-thick copper alloys. This experiment is supposed to be set on a Zwick-Roell BUP 200 device. The work presents the design of the device and the evolution of strain path changes occurring during both stages of the process. The experimental results obtained after both stages (force-displacement, thickness) are presented. Finally, a sensitivity analysis of a strain path change indicator is proposed through the numerical simulation of the reverse deep drawing test by varying the geometry of the tools.

Prediction of earing defect and deep drawing behavior of commercially pure titanium sheets using CPB06 anisotropy yield theory

Recently, sheet metal forming industries have shown interest in characterization of anisotropy properties, tension-compression strength differential and deep drawing behavior of commercially pure titanium (CP Ti) material for successful fabrication of lightweight components. In present work, the formability of 1.0 mm thick CP Ti sheet metal was studied using a laboratory scale deep drawing test set-up, and the limiting drawing ratio (LDR) was found to be 2.143. Four ears were observed in the LDR cup with maximum cup height along diagonal direction (DD) and troughs along both rolling direction (RD) and transverse direction (TD), and the earing height was approximately 13.7% of the total cup height. Tensile and stack compression tests were carried out along different orientations to evaluate the anisotropy properties and tension-compression strength differential, and these data were used to develop the CPB06 constitutive yield model. Also, the developed CPB06 anisotropy plasticity theory was implemented in an FE model to predict the non-uniform material flow, earing defect and thickness distribution successfully. In order to reduce earing defect, a two-stage blank modification technique was proposed incorporating directionalities of both yield strength and plastic strain ratio. A significant 83% reduction in earing height was achieved through use of modified blank with simultaneous benefit of improvement in thickness distribution and reduction in peak load.

Identification strategy influence of elastoplastic behavior law parameters on Gurson–Tvergaard–Needleman damage parameters: Application to DP980 steel

This work adopts elastic–plastic/damage coupling in order to describe tensile behavior with validation on the deep-drawing test of a DP980 Dual Phase steel sheet. The damage model used is the Gurson–Tvergaard–Needleman (GTN model). The hardening laws used are those of Swift (non-saturating law), Voce (saturating law), Hockett-Sherby (saturating law) and the two combined laws Swift/Hockett-Sherby and Swift/Voce. An identifying method for elastic–plastic parameters and GTN damage model parameters is presented using the software modeFRONTIER. This method based on the inverse analysis is also proposed for the identification of weighting coefficient α of the Swift/Hockett-Sherby combined hardening law. Finally, a parametric study was carried out to show that the plastic modulus can be considered as another criterion for the choice of a hardening law. Dependence of the damage model parameters to the hardening law is clearly established. The different behavior laws are introduced via a VUHARD type subroutine in the calculation code Abaqus.

Effects of Cryogenic Treatment after Annealing of Ti-6Al-4V Alloy Sheet on Its Formability at Room Temperature

In this article, the effects of cryogenic treatment after annealing on the formability of Ti-6Al-4V alloy sheet were experimentally studied. The Ti-6Al-4V titanium alloy was treated by cryogenic treatment after annealing (ACT). Tensile tests were carried out using a universal machine at room temperature. The microstructure evolution of Ti-6Al-4V subjected to ACT was also investigated using an optical microscope (OM). Both the shearing performance and drawing formability were analyzed by punch shearing tests and deep drawing tests, respectively. Results showed that after ACT, the tendency of the β phase can be apparently changing into stable β’ and α’ phases. The elastic modulus is lower than that of the untreated material. It was found that both the yield strength and tensile strength are declined slightly, whereas the ductility is increased significantly. The shear strength in punch shearing is decreased at room temperature and cryogenic temperature. The ratio of smooth zone on the section after ACT3 is much larger than the others. The rollover diameters are not obviously greater than those of the untreated. Additionally, the height of the burr shows a decreasing trend after ACT. During deep drawing, drawing depth is deeper than that of the untreated material, the drawing load after ACT is reduced, and the decreasing tendency of the drawing load slows down. It is noted that the micro-cracks occur at the bottom of the sample.

Hot Roll Bonding of Aluminum to Twin-Roll Cast (TRC) Magnesium and Its Subsequent Deformation Behavior

In an experiment in which twin-roll cast AZ31 magnesium alloy and commercial purity aluminum (AA 1050) sheets were bonded by hot rolling as Al/Mg/Al laminate composites, it was found that increasing the preheating temperatures up to 400 °C enhances the bonding strength of composites. Further increases in the preheating temperatures accelerate the magnesium oxide growth and thus reduce the bonding strength. The influence of the reduction ratio on the bonding properties was also studied, whereby it was observed that increasing the rolling reduction led to an increase in the bonding strength. The experimental results show that the optimum bonding strength can be obtained at rolling temperatures of 375-400 °C with a 50-60% reduction in thickness. On the other hand, the subsequent deformation behavior of composite was assessed using plane strain compression and deep drawing tests. We demonstrate that the composites produced using the optimum roll bonding conditions exhibited sufficient bonding during subsequent deformation and did not reveal any debonding at the bonding interface.

Numerical Predictions of the Occurrence of Necking in Deep Drawing Processes

In this work, three numerical necking criteria based on finite element (FE) simulations are proposed for the prediction of forming limit diagrams (FLDs) for sheet metals. An elastic–plastic constitutive model coupled with the Lemaitre continuum damage theory has been implemented into the ABAQUS/Explicit software to simulate simple sheet stretching tests as well as Erichsen deep drawing tests with various sheet specimen geometries. Three numerical criteria have been investigated in order to establish an appropriate necking criterion for the prediction of formability limits. The first numerical criterion is based on the analysis of the thickness strain evolution in the central part of the specimens. The second numerical criterion is based on the analysis of the second time derivative of the thickness strain. As to the third numerical criterion, it relies on a damage threshold associated with the occurrence of necking. The FLDs thus predicted by numerical simulation of simple sheet stretching with various specimen geometries and Erichsen deep drawing tests are compared with the experimental results.

AW-7075-T6 sheet for shock heat treatment forming process

Abstract The forming behaviour of AW-7075-T6 sheet was studied across a range of shock heat treatment (SHT) temperatures of 200-480 °C. After SHT, formability of the samples was investigated by tension and deep drawing tests at room temperature. Differential scanning calorimetry (DSC) was used to study the precipitation states of the AW-7075 sheet in the as-received and shock heat treated conditions. Formability was started to improve with increasing shock heat treatment temperature from 300 °C onwards. Strain hardening resulted from the dissolution of η′ precipitates and the coarsening of remaining precipitates were found to contribute to the increase in formability at room temperature. Re-precipitation and coarsening of the precipitates were responsible for the post-paint baking strength of SHT samples.

Superplasticity and Micro-arrayed Deep-Drawing Behavior of Ni-Co/GO Nanocomposite

In this article, Ni-Co/GO nanocomposite was fabricated by AC pulse electrodeposition method. The room temperature strength tests and the superplasticity of the nanocomposite were investigated by the tensile tests. A 5 × 5 micro-arrayed deep-drawing die was designed to explore the feasibility of micro-forming. The as-deposited material has a narrow grain size distribution with a mean grain size of 50 nm. The addition of GO as a reinforcing phase can effectively enhance the room temperature tensile strength of the nanocomposite, but reduce the plasticity. When adding GO to the plating bath, a maximum elongation of 467% was observed for the specimen with a GO content of 0.01 g/L at 773 K and a strain rate of 1.67 × 10−3 s−1 by tensile tests. Micro-arrayed deep-drawing tests were subsequently performed with male die diameter of 0.58 mm and female die diameter of 0.8 mm. The experimental relative drawing height values were measured and compared with the deep-drawing parts without GO additive. It is found that the micro-arrayed deep-drawing with rigid male die at high temperature was feasible and forming parts with good shape could be got. The thickness distribution analysis of the deep-drawing parts showed that wall thickness changed ranging from 53 to 95 μm, and the thickness reduction at the punch fillet is the most obvious.

Evaluation of Uniaxial Tensile Behavior under Pulsed Current for Electrically Assisted Warm Forming of Light Weight Alloys

In this study, the electric current effects in the deformation of light weight alloys are investigated to improve the formability. To begin with, a test system is built up to carry out the tensile test with heavy electric current flowing through the specimen. The evolutions of the flow stresses and failure elongations were obtained using this test system. The thermal and athermal effect such as electro-plastic effect of metallic materials induced by high density current make significant reduction of the flow stress, which is beneficial to the forming process of less formable metal. From the uniaxial test results, pulse current-assisted deep drawing test were conducted. The experimental results demonstrate that electrically assisted warm forming provides lower energy consumption and higher efficiency.

Hydrogen-Induced Delayed Cracking in TRIP-Aided Lean-Alloyed Ferritic-Austenitic Stainless Steels.

Susceptibility of three lean-alloyed ferritic-austenitic stainless steels to hydrogen-induced delayed cracking was examined, concentrating on internal hydrogen contained in the materials after production operations. The aim was to study the role of strain-induced austenite to martensite transformation in the delayed cracking susceptibility. According to the conducted deep drawing tests and constant load tensile testing, the studied materials seem not to be particularly susceptible to delayed cracking. Delayed cracks were only occasionally initiated in two of the materials at high local stress levels. However, if a delayed crack initiated in a highly stressed location, strain-induced martensite transformation decreased the crack arrest tendency of the austenite phase in a duplex microstructure. According to electron microscopy examination and electron backscattering diffraction analysis, the fracture mode was predominantly cleavage, and cracks propagated along the body-centered cubic (BCC) phases ferrite and α’-martensite. The BCC crystal structure enables fast diffusion of hydrogen to the crack tip area. No delayed cracking was observed in the stainless steel that had high austenite stability. Thus, it can be concluded that the presence of α’-martensite increases the hydrogen-induced cracking susceptibility.

Influence of different rolling routes on mechanical anisotropy and formability of commercially pure titanium sheet

Influence of three different rolling routes on mechanical anisotropy and formability of commercially pure titanium sheet was investigated. Route A and Route B are unidirectional rolling (UR) where the rolling direction is along initial rolling direction (RD) and transverse direction (TD), respectively. Route C is cross rolling (CR) where the rolling direction is changed by 90° after each rolling pass. The microstructure and texture, tensile mechanical properties including strength and elongation, and also the anisotropy of the UR and CR sheets were investigated at room temperature. The XRD results indicate that the texture intensity of rolled samples gradually weakens from Route A to Route C. Compared with Route A and Route B rolled samples, the Route C rolled samples show a smaller planar anisotropy. The deep drawing tests reveal that cross rolling can avoid the occurrence of earing. Erichsen tests indicate that rolling routes have an effect on stretch formability of pure titanium sheet.

Deep drawing of aluminum alloy 7075 using hot stamping

In this paper, simulations of deep drawing tests at elevated temperatures were carried out with experimental validation. The aim of this work was to study the effect of process parameters on formability and mechanical properties of aluminum alloy 7075 in hot stamping process. Process parameters, including blank temperature, stamping speed, blank holder force and friction coefficient, were studied. Stamping tests were conducted at temperatures between 350 and 500 °C, blank holder force between 0 and 10 kN, stamping speed between 50 and 150 mm·s−1, and friction coefficient between 0.1 and 0.3. Based on the analysis, it is shown that thickness homogeneity could be improved when the blank is formed at lower temperature, lower blank holder force and lower friction coefficient. Formability could be improved when the blank was well lubricated at about 400 °C. Formability at stamping speed 50 mm·s−1 is far better than those at other speeds. The mechanical property analysis shows that the hot stamping process could make the formed part to obtain high quality.

Calculation method and experimental study of coulomb friction coefficient in sheet metal forming

Friction is one of the important factors influencing the formability of sheet metal and improving the forming quality. According to the relationship between the drawing force and the stroke, the linear fitting algorithm of the friction coefficient is given based on the least squares method. Based on the drawing die of the cylindrical parts, a friction coefficient measuring apparatus is developed, which has fixed calculation program. Through a series of deep drawing tests, the friction coefficients and force-stroke curves are measured for different combinations of sheet metal and lubricant. What’s more,the drawing process of the cylindrical part with different specifications is carried out to examine the application of the measured friction coefficient. The results show that the friction coefficient calculated by the linear fitting algorithm can accurately reflect the friction state of the whole drawing process; the measurement of the friction coefficient is not limited by the size of the mould; the established test system, can be used for the measurement of friction coefficient in sheet metal forming.

An investigation into the flexural and drawing behaviors of GFRP-based fiber–metal laminate

ABSTRACTFiber–metal laminates (FMLs) are advanced composite materials that consist of bonded thin metal sheets and fiber-reinforced composite layers. In this article, mechanical behavior of a thermoplastic-based FML is investigated, which is composed of glass-fiber-reinforced polypropylene (GFRP) laminate and aluminum AA1200-O as the core and skin layers, respectively. Engineering constants of the composite laminate were achieved using Timoshenko's beam theory, flexural and tensile test results. Finite element simulations of the GFRP-based FML were performed to predict the behavior of this material in three-point bending and deep drawing tests. Some experimental verification tests were conducted to prove the reliability of results in the FE analysis of the FML. Comparison of the results shows an excellent correlation between the FE analysis and experimental tests.

Reverse deep drawing process: Material anisotropy and work-hardening effects

The present work aims to study the constitutive models’ influence on the reverse deep drawing simulation of cylindrical cups. Several constitutive laws were considered to predict the combined effects of anisotropy as well as the changes in strain path direction of the stainless steel. To this end, a number of models were used, worth mentioning among which are the isotropic with nonlinear kinematic hardening laws, along with the isotropic von Mises and anisotropic Hill’48 yield criteria. For the models’ parameters identification, uniaxial tensile and shear tests at several orientations to the rolling direction as well as reversed shear tests were carried out. Then, a subsequent comparison between experimental data and numerical simulations of reverse deep drawing tests were performed, using the finite element code Abaqus/Explicit. On the basis of the major reached results, it has been found that for the first stage, whatever the yield criteria used and for all the hardening models, the numerical punch-force evolution correlates well with the experimental one. For the second stage, the punch-force evolution was found to be remarkably more influenced by the yield criteria than by the kinematic laws. The major strain distribution greatly depends on the yield criteria. Meanwhile, it was slightly linked to the work hardening.