Advanced models for the prediction of forming limit curves

edition: 2ndstatus: publishe

An evolving plane stress yield criterion based on crystal plasticity virtual experiments

This paper presents a new hierarchical multi-scale framework that allows taking into account evolution of the plastic anisotropy during sheet forming processes. The evolution of crystallographic texture, which is identified as the main source of the plastic anisotropy, is predicted by the ALAMEL crystal plasticity model. An extension to the phenomenological anisotropic plane-stress yield criterion BBC2008 is proposed, which provides adaptive updates of the local anisotropy in the integration points of the macroscopic finite element model. To this end, the BBC2008 is systematically recalibrated to data provided by the crystal plasticity virtual experiment framework (VEF). An enhanced identification algorithm is proposed. The new algorithm exploits comprehensive material characterization delivered by the VEF. The deep drawing of cylindrical cups is used as a benchmark case. An industrial-grade aluminium alloy AA6016 is chosen for the test case. The experimental part of the study includes X-ray diffraction measurements of the texture as well as mechanical testing, which comprises uniaxial tensile tests, a bulge test and the deep drawing of cylindrical cups. A noticeable through-thickness gradient in terms of both the texture and the plastic anisotropy is identified in the initial material. This issue is taken into consideration in the study. Three groups of simulations have been performed, in which (i) the BBC2008 was calibrated by means of the mechanical tests, (ii) the BBC2008 was calibrated by means of the VEF based on the initial texture, but kept constant throughout the simulation, and (iii) the BBC2008 was systematically recalibrated by means of the VEF to reflect the effects of texture evolution. The earing profiles measured in the experimentally drawn cups are compared to the ones predicted by the simulations. It is found that the cup profile predictions by (i) are clearly inferior compared to both (ii) and (iii). However, in the considered process (iii) provides only a moderate improvement over the results of (ii). The explanation of this limited impact of the anisotropy evolution is based on the analysis of the evolved texture and associated plastic anisotropy.publisher: Elsevier articletitle: An evolving plane stress yield criterion based on crystal plasticity virtual experiments journaltitle: International Journal of Plasticity articlelink: http://dx.doi.org/10.1016/j.ijplas.2015.02.011 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved.status: publishe

Microwave ablation in the treatment of liver tumors. A better tool or simply more power?

It has been a long time since tumor ablation was first tested in patients with liver cancer, especially hepatocellular carcinoma. Since than it has become a first line treatment modality for hepatocellular carcinoma. Over the years, the indications of thermal ablation have expanded to colorectal cancer liver metastases and intrahepatic cholangiocarcinoma as well. Together with the new indication for ablation, new ablation devices have been developed as well. Among them microwave ablation shows potential in replacing radiofrequency ablation as the preferred method of thermal ablation in liver cancer. The debate whether radiofrequency or microwave ablation should be the preferred method of treatment in patients with liver cancer remains open. The main purpose of this review is to offer some answers to the question: Microwave ablation in liver tumors: a better tool or simply more power? Various clinical scenarios will be analyzed including small, medium, and intermediate size hepatocellular carcinoma, colorectal cancer liver metastases and intrahepatic cholangiocarcinoma. Furthermore, the advantages, limitations, and technical considerations of MWA treatment will be provided also