Forming limit predictions for single-point incremental sheet metal forming

peer reviewedA characteristic of incremental sheet metal forming is that much higher deformations can be achieved than conventional forming limits. In this paper it is investigated to which extent the highly non-monotonic strain paths during such a process may be responsible for this high formability. A Marciniak-Kuczynski (MK) model is used to predict the onset of necking of a sheet subjected to the strain paths obtained by finite-element simulations. The predicted forming limits are considerably higher than for monotonic loading, but still lower than the experimental ones. This discrepancy is attributed to the strain gradient over the sheet thickness, which is not taken into account in the currently used MK model

Comparison of solvate ionic liquids and DMSO as an in vivo delivery and storage media for small molecular therapeutics

BACKGROUND: Solvate ionic liquids (SILs) are a new class of ionic liquids that are equimolar solutions of lithium bistrifluoromethanesulfonimide in either triglyme or tetraglyme, referred to as G3LiTFSA and G4LiTFSA, respectively. SILs play a role in energy storage lithium batteries, and have been proposed as potential alternatives to traditional organic solvents such as DMSO. G3TFSA and G4TFSA have been shown to exhibit no toxicity in vivo up to 0.5% (v/v), and solubilize small compounds (N,N-diethylaminobenzaldehyde) with full penetrance, similar to DMSO delivered DEAB. Herein, we compare the effects of storage (either at room temperature or - 20 °C) on DEAB solubilized in either DMSO, G3TFSA or G4TFSA to investigate compound degradation and efficacy. RESULTS: The findings show that DEAB stored at room temperature (RT) for 4 months solubilized in either G3TFSA, G4TFSA or DMSO displayed no loss of penetrance. The same was observed with stock solutions stored at - 20 °C for 4 months; however G4TFSA remained in a liquid state compared to both G3TFSA and DMSO. Moreover, we examined the ability of G3TFSA and G4TFSA to solubilize another small molecular therapeutic, the FGFR antagonist SU5402. G4TFSA, unlike G3TFSA solubilized SU5402 and displayed similar phenotypic characteristics and reduced dlx2a expression as reported and shown with SU5402 in DMSO; albeit more penetrative. CONCLUSION: This study validates the use of these ionic liquids as a potential replacement for DMSO in vivo as organic solubilizing agents

Evaluation of strain and stress states in the single point incremental forming process

Single point incremental forming (SPIF) is a promising manufacturing process suitable for small batch production. Furthermore, the material formability is enhanced in comparison with the conventional sheet metal forming processes, resulting from the small plastic zone and the incremental nature. Nevertheless, the further development of the SPIF process requires the full understanding of the material deformation mechanism, which is of great importance for the effective process optimization. In this study, a comprehensive finite element model has been developed to analyse the state of strain and stress in the vicinity of the contact area, where the plastic deformation increases by means of the forming tool action. The numerical model is firstly validated with experimental results from a simple truncated cone of AA7075-O aluminium alloy, namely, the forming force evolution, the final thickness and the plastic strain distributions. In order to evaluate accurately the through-thickness gradients, the blank is modelled with solid finite elements. The small contact area between the forming tool and the sheet produces a negative mean stress under the tool, postponing the ductile fracture occurrence. On the other hand, the residual stresses in both circumferential and meridional directions are positive in the inner skin of the cone and negative in the outer skin. They arise predominantly along the circumferential direction due to the geometrical restrictions in this direction.The authors would like to gratefully acknowledge the financial support from the Portuguese Foundation for Science and Technology (FCT) under project PTDC/EMS-TEC/1805/2012. The first author is also grateful to the FCT for the postdoctoral grant SFRH/BPD/101334/2014.info:eu-repo/semantics/publishedVersio

Differential hardening in IF steel - Experimental results and a crystal plasticity based model

Work hardening in metals is commonly described by isotropic hardening, especially for monotonically increasing proportional loading. The relation between different stress states in this case is determined by equivalent stress and strain definitions, based on equal plastic dissipation. However, experiments for IF steel under uniaxial and equibiaxial conditions show that this is not an accurate description. In this work, the determination of the equibiaxial stress–strain relation with 3 different tests will be elaborated: a stack compression test, a cruciform tensile test and a bulge test. A consistent shape of the hardening curve is obtained which deviates from that of a uniaxial tensile test. Several physical explanations based on crystal plasticity are considered, including texture evolution, strain inhomogeneity and glide system hardening models. Texture evolution changes the shape of the yield surface and hence causes differential hardening, however, the observed differences at low strains cannot be explained by texture evolution. Accounting for the strain heterogeneity in the polycrystal, with equilibrium of forces over grain boundaries, improves the prediction of differential hardening considerably, even with a simplified interaction model (Alamel) and simple hardening laws for the glide systems. The presentation is based on a recently published paper by the authors [1]

Comparison of the tests chosen for material parameter identification to predict single point incremental forming forces

peer reviewedSingle Point Incremental Forming is a sheet forming process that uses a smooth-ended tool following a specific tool path and thus eliminates the need for dedicated die sets. Using this method, the material can reach a very high deformation level. A wide variety of shapes can be obtained without specific and costly equipment. To be able to optimize the process, a model and its material parameters are required. The inverse method has been used to provide material data by modeling experiments directly performed on a SPIF set-up and comparing them to the experimental measurements. The tests chosen for this study can generate heterogeneous stress and strain fields. They are performed with the production machine itself and are appropriate for the inverse method since their simulation times are not too high

The Application of Crystal Plasticity Material Files in Stamping Simulations

© 2018 Institute of Physics Publishing. All rights reserved. Representative material data are inevitable to execute accurate stamping simulations. These material data are generally generated by performing extensive mechanical material tests. In this research the generation and application of material data from a crystal plasticity-based multiscale model have been studied. The crystal plasticity model enables to generate detailed material properties which can be applied in various yield locus models. The evolution of the anisotropic properties during deformation can be readily taken into account with the crystal plasticity model. The generated material data have been applied in deep drawing simulations of a cross-die. The thickness distribution of the simulation has been compared with experiments. Results showed that crystal plasticity models are a viable alternative for material data generation, having as main advantage that extensive mechanical experiments are avoided.status: publishe