•Measured monotonic tension, compression, and load reversals data for three steels are used to adjust parameters of the FE-EPSC model.•Geometrical shape changes after U-draw/bending forming are ...predicted using the FE-EPSC multi-level simulation framework.•Accounting for backstress fields is revealed as critical for the accurate predictions of part geometries upon U-draw/bending.•Hardening and carrying over residual stress fields are essential for predicting part shape changes involving pre-strained sheets.•Increase in the amount of springback with sheet strength is determined by simulating U-draw/bending of DP 590 and DP 1180.
This work is concerned with predicting geometrical shape changes in sheet metal forming using a multi-level simulation framework that considers the directionality of deformation mechanisms acting at the single-crystal level and microstructural evolution. The multi-level model is an elasto-plastic self-consistent (EPSC) homogenization of single-crystal behavior giving the constitutive response at each finite element (FE) material point. Numerical solution of a boundary value problem over geometry is then obtained using continuum finite elements at the macro-level. First, a set of model parameters for the evolution of slip resistance of ferrite and martensite and backstress are established by fitting a comprehensive set of mechanical data for dual-phase (DP) steels 590, 780, and 1180 using one-element model. Next, the potential of the FE-EPSC modeling framework is illustrated by carrying out a set of hat-shaped draw-bending simulations of the steel sheets. The evolution of geometry after hat-shaped draw-bending and springback is predicted and verified with experimental measurements for as-received DP 780. In doing so, the role of accounting for backstress is revealed as critical for the accurate prediction of the part geometry. The same process simulation involving a pre-strained sheet of DP 780 is compared with a corresponding experiment to reveal the role of strain hardening and residual stress on the subsequent part shape changes after the hat-shaped draw-bending test and springback. Finally, the same process simulations involving DP 590 and DP 1180 are performed to confirm the effect of strength on the geometrical shape changes of the sheets after springback.
Metal forming process is one of the oldest manufacturing techniques. It has witnessed the shift from conventional to integration of smart systems for manufacturing of highly complex components. Many ...mathematical, experimental and simulation software techniques are discussed. Servo press is the most indispensable machine used for the manufacturing of delicate parts of automobile, aviation industry with high accuracy. The main motive of replacing or modifying the prevailing conventional manufacturing techniques into modern, smart and sustainable manufacturing like industry 4.0 is to become more competitive and to adopt customization & sustainability. Integration of industrial internet of things (IIoT) with automated supply chain has given optimized productivity, quality, and economical feasibility. This manuscript throws some light on different metal forming process, servo press application in automobile, aviation industry and different components require to make metal forming smart and sustainable in term of industry 4.0.
Sheet metal forming is used to process a substantial percentage of automobile components, and the so-called springback behavior is of primary importance, in order to obtain the final part with an ...accurate geometry. This paper describes a springback research that employs three different materials often used in the automobile industry: DP780, HSLA420, and AA5754. The unconstrained cylindrical bending test (UCB test) will be utilized to assess the springback prediction for selected materials. In this study, experimental data is collected and numerical results are provided utilizing finite element techniques. Results show that UCB test is an adequate benchmark for analysis of springback behavior of sheet metallic materials and it has also been observed a close agreement between numerical results and experiments.
•Characterizing uniaxial tension, plane strain tension, and shear stress states of martensitic steel.•Adjusting yield function exponent and size of finite element model for calibration of fracture ...models.•Predicting hole expansion fracture of martensitic steel accurately with GTN-shear fracture model.•Predicting bending fracture of martensitic steel accurately with Hosford-Coulomb fracture model.
In this study, fracture of martensitic steel in hole expansion and stretch bending was predicted by finite element analysis with shell elements. Various mechanical experiments were conducted to characterize mechanical properties related to fracture as well as plasticity. Then, Swift-modified Voce and Yld2000-2d well-described plasticity properties of martensitic steel. For fracture modeling, Hosford-Coulomb (HC) and shear-modified Gurson-Tvergaard-Needleman (GTN-shear) models were selected and calibrated with load–displacement curves of three fracture tests. The hybrid numerical-experimental method was used for the HC model and inverse identification with finite element model updating was used for the GTN-shear model. In calibration, an exponent of yield function and mesh size were adjusted to match the strength of plane strain state and to maintain consistency of mesh size. After calibration, both fracture models were applied to numerical simulations of conical hole expansion and stretch bending tests. The GTN-shear model predicted well fracture in the conical hole expansion test but not in the stretch bending. The prediction results of HC model were vice versa. Through triaxiality analysis, these differences between the two models may result from a non-linear loading path and description of localized necking.
In this study, the recently developed distortional plasticity model (HAH20) was applied to EDDQ and TRIP steel sheets to account for hardening fluctuations induced by loading path changes. Previous ...non-linear loading path experiments, which were tension-compression, tension-tension, and tension-shear tests, revealed intricate latent hardening in EDDQ steel and a combination of latent hardening and cross loading contraction in TRIP steel. The HAH20 model was calibrated using tension-compression and 90° tension–45° tension tests with adjustment of setting parameters for accurate latent hardening prediction. Then, a comparison between the HAH20 model and the previous distortional plasticity model (HAH14) in the other independent experiments highlights the superiority of HAH20 model due to its description of latent hardening. Furthermore, for TRIP steel, the HAH20 and HAH14 models were applied to predict springback in a U-draw bending test featuring a novel curved blank subjected to reverse and cross loading states simultaneously. The simulation results show that the HAH20 model predicts springback more accurately than the HAH14 model; however, the main reason is the accurate description of reverse loading in the HAH20 model. This is due to the intricate interplay between cross loading contraction and latent hardening in springback.
Display omitted
•HAH20 model is firstly applied to the materials exhibiting latent hardening under cross loading conditions.•Performance of HAH20 model is better than HAH14 model in both latent hardening and reverse loadings for EDDQ and TRIP steels.•U-draw bending test with a different blank geometry is newly proposed to observe the effect of cross loadings on springback.
This study designed an asymmetric, interference-free and excellent heat dissipation performance CPU cooler. Due to the increasing size of the motherboard cooler, the heat pipes or aluminum fins of ...the CPU cooler may interfere with the motherboard or the graphics card, thus preventing smooth installation. The proposed tower-type cooler avoids this problem by offsetting the aluminum fins and bending the heat pipes away from the motherboard, ensuring compatibility with the motherboard, memory, graphics card, and other components. Combining the heat pipes, copper base, and aluminum base requires careful consideration of tolerance. The heat pipes are composed of copper tubes, copper powder, and pure water, then vacuum treated. The copper tubes are filled with copper powder and sintered (900 °C–1000 °C) to inject pure water and vacuum seal once more, then bent according to the design. The aluminum fins are stamped from sheet metal. After nickel plating, they facilitate welding between copper and aluminum materials. The CPU cooler developed in this study includes the design, drawing, fabrication, and assembly of each component (finning, tubing, soldering). It demonstrates successful installation on most commercial motherboards. Compared with commercially available coolers, the temperature of the cooler developed in this study is reduced by about 1∼2 °C.
Friction in sheet metal forming is largely determined by asperity flattening and the real contact area between sheet asperities and tool surface. This paper presents a new experimental test, which ...enables the investigation of asperity flattening under varying sub-surface strain ratios with or without the application of lubrication. The test is based on the Marciniak-Kuczynski test for inducing in-plane strains, while an asperity region in the centre is subjected to normal loading. The test was deployed to investigate model asperity flattening due to normal loading combined with controlled linear in-plane strain paths with and without the presence of liquid lubrication.
•A model is proposed to describe shear ductile fracture from shear to the balanced biaxial tension.•The stress invariant-based Drucker yield function is specified for BCC and FCC metals to the ...balanced biaxial tension.•The model is successfully employed to predict ductile fracture of AA6082 in wide loading conditions.•The model could also be used to describe ductile fracture under low and negative stress triaxiality with improved flexibility.
A ductile fracture model is proposed to describe shear fracture of sheet metals from shear to balanced biaxial tension via uniaxial and plane strain tension. The fracture criterion models plastic damage as strain-induced void nucleation, triaxiality-governed void enlargement, Lode-controlled void torsion, and shear-restrained coalescence of voids. Its flexibility is investigated by a parameter study of the ductile fracture model proposed. The fracture model is employed to describe ductile fracture behavior of an aluminum alloy AA6082 T6 (thickness: 1.0mm). Dogbone specimens are strained to characterize the strain hardening properties, while another four different specimens are tested to characterize fracture behavior in shear, uniaxial tension, plane strain tension and balanced biaxial tension. The loading processes are analyzed numerically with the stress invariant-based Drucker yield function which is for the first time specified for body-centered cubic and face-centered cubic metals. Fracture strains in various loading conditions are measured with a hybrid experimental-numerical approach. The measured fracture strains are then used to calibrate the ductile fracture model proposed. The ductile fracture model calibrated above is employed to predict the onset of ductile fracture for these four specimens. For the purpose of comparison, the predicted fracture strokes of these four loading conditions are compared with those predicted by the modified Mohr–Coulomb model (Bai and Wierzbicki, 2008), and two micromechanism-inspired criteria proposed recently (Lou et al., 2012, 2014). The comparison reveals that the proposed model predicts the fracture behavior in much better agreement compared with experimental results from shear to the balanced biaxial tension. Accordingly, the proposed ductile fracture criterion is recommended for the prediction of ductile fracture in sheet metal forming processes, optimization of forming parameters and design of tools for both solid elements and shell elements. Besides, the ductile fracture model proposed can also be applied in various bulk metal forming processes in case that the model is calibrated by proper sets of experiments.
PDF