The influence of grain size distribution on strain hardening behavior for dual phase steels using statistica ly informed artificial microstructure model and crystal plasticity

Dual phase steels are well suited to the automotive application. Their microstructures comprise constituents of strong distinction in mechanical properties. As a result, dual phase steels exhibit remarkably high-energy absorption as well as an excellent combination of strength and ductility. Various deformation mechanisms can be observed on the microscale owing to their heterogeneous composition. A reliable microstructure-based simulation approach for describing these deformations is hence needed. Therefore, the approach to generate artificial dual phase microstructure models based on the quantitative results of metallographic microstructure analysis and their statistical representation is developed. This method captures several microstructural features such as microstructure morphology and thus enables a simulation-based analysis of the influence of these features on the meso- and macroscopic material behavior. The algorithm input contains representative information about individual phase grain size and orientation distributions. The statistical parameters to represent the grain size distribution function are then input into a multiplicatively weighted Voronoi tessellation based algorithm to generate artificial microstructure geometry models that are applicable to bimodal distribution and with which microstructure deformation (finite element) simulations can be performed. By implementation of the phenomenological based crystal plasticity model to the generated artificial microstructure model, the influence of grain size distribution on the strain hardening behavior can be investigated

Failure analysis based on microvoid growth for sheet metal during uniaxial and biaxial tensile tests

The aim of the presented investigations is to perform an analysis of fracture and instability during simple and complex load testing by addressing the influence of ductile damage evolution in necking processes. In this context, an improved experimental methodology was developed and successfully used to evaluate localization of deformation during uniaxial and biaxial tensile tests. The biaxial tensile tests are carried out using cruciform specimen loaded using a biaxial testing machine. In this experimental investigation, Stereo-Image Correlation technique has is used to produce the heterogeneous deformations map within the specimen surface. Scanning electron microscope is used to evaluate the fracture mechanism and the micro-voids growth. A finite element model of uniaxial and biaxial tensile tests are developed, where a ductile damage model Gurson-Tvergaard-Needleman (GTN) is used to describe material deformation involving d`amage evolution. Comparison between the experimental and the simulation results show the accuracy of the finite element model to predict the instability phenomenon. The advanced measurement techniques contribute to understand better the ductile fracture mechanism

Apolipoprotein D is involved in the mechanisms regulating protection from oxidative stress

Producción CientíficaMany nervous system pathologies are associated with increased levels of apolipoprotein D (ApoD), a lipocalin also expressed during normal development and aging. An ApoD homologous gene in Drosophila , Glial Lazarillo, regulates resistance to stress, and neurodegeneration in the aging brain. Here we study for the first time the protective potential of ApoD in a vertebrate model organism. Loss of mouse ApoD function increases the sensitivity to oxidative stress and the levels of brain lipid peroxidation, and impairs locomotor and learning abilities. Human ApoD overexpression in the mouse brain produces opposite effects, increasing survival and preventing the raise of brain lipid peroxides after oxidant treatment. These observations, together with its transcriptional up-regulation in the brain upon oxidative insult, identify ApoD as an acute response protein with a protective and therefore beneficial function mediated by the control of peroxidated lipids. Key words: learning, lipid peroxidation, lipocalin, locomotor behavior, paraquat, oxidative stress

Інженерна комп’ютерна графіка

Розглянуто відомості про систему тривимірного моделювання КОМПАС-3D при виконанні практичних завдань, побудову тривимірних моделей деталей і складальних одиниць машин та обладнання, будівельних споруд, а також про випуск асоціативних креслеників, розробку специфікацій, експлікацій, інших текстових документів

Modelling the Cold Formability of Dualphase Steels on Different Length Scales

Modern multiphase steels contain constituents of distinctive mechanical properties, so that they develop strong gradients in the local strain distribution during forming operations and this strongly promotes the microstructural damage evolution. Consequently, the material’ resistance against ductile crack initiation sets the limits of cold formability and these can even be reached without any macroscopic necking phenomena. The modified Bai Wierzbicki (MBW) model has been proven the capability of providing an impressive accuracy of simulation results when applied to stretch forming tests as it describes ductile crack initiation and propagation. The consideration of the third invariant of the stress deviator on plasticity and ductile failure is a key factor for the model’ high accuracy, but due to its phenomenological character its applicability for materials design is currently not given. Furthermore, the quantity of material parameters is so high that an industrial application of this model cannot be expected. Therefore the paper presents an alternative approach for parameter calibration relying on virtual experiments on representative volume elements, where the plastic strain localization theory is applied without any other damage model