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The present paper focuses on the validation of on-going efforts made to develop more advanced 3D mathematical model for cold rolling strip process [8]. Following [2], the model uses the multi-slab strategy to deal with the differential reduction in the transverse direction due to roll deformation, and analytical solutions of roll bending and flattening discretized by the Influence Function Method (IFM). Furthermore, the model has been extended to incorporate elastic deformation of strip and to be fit for 6-high rolling mills with shiftable work roll (WR) or Intermediate Rolls (IR) as well as 4-high mills. Validation is performed by using FEM solutions (Abaqus® implicit) as references: a 2D quasi-static model to check the slab method under rigid work roll condition; a 3D FEM to discuss the assumption of small lateral flow of strip; a comparison of FEM and IFM with regard to 6-high roller stack deformation with intermediate roll shifting. All these steps are essential to gain more insight into the mechanism of cold rolling strip and to guide future development work of the mathematical model. [ABSTRACT FROM AUTHOR]

This work aims at a better understanding and modeling of the failure of carbonitrided pinions made out of 20MnB5 steel. Carbonitriding is a thermochemical treatment inducing high surface hardness while preserving significant core ductility. This results in graded microstructure and properties which makes the prediction of failure particularly complex: brittle external layer, ductile core material. A test bench was specifically designed to load one tooth of the studied pinions with a lateral force until complete failure. In situ observations were performed and the load-displacement curve recorded, showing a variety of behaviors as a function of the teeth engagement depth. The presence of the carbonitrided layer induces only a slight force and toughness increase. The main failure mechanism comes from shear failure of the ductile core material which will therefore be studied in this paper. Experimental tests with various stress states were conducted to measure plastic properties as well as to calibrate fracture criteria for the core steel. Von Mises plasticity and a simple strain hardening curve fit very well all these experiments. As fracture criteria from the literature were unable to predict failure correctly for all the mechanical tests, an adapted criterion has therefore been proposed as an outcome of this extensive mechanical testing campaign. Fracture simulations in LS Dyna were performed using the element erosion technique, the limitations of which are discussed. Comparison with the experimental tooth fracture allows evaluation of the proposed failure criteria, and enables to highlight and discuss the present limits of the simulation. [ABSTRACT FROM AUTHOR]

In cold strip rolling, the transverse gradient of thickness strain results in heterogeneous longitudinal stress σ xx . Whenever the latter is compressive in spite of strip tensions, an on-line manifested flatness defect may occur. It is of interest to determine the occurrence and geometric characteristics of such defects. To do this, a two-scale model based on the generalized continuum approach of Damil and Potier-Ferry (2006, 2008) is applied to this problem. It consists in developing the unknowns (in plane stress components and out-of-plane displacement) in Fourier series and solving von Karman equations of thin strip buckling, in an energetic formulation. For application to cold rolling, certain simplifications are made and commented. The potential of this method is analyzed using simple assumed stress fields via (i) parametric studies and (ii) comparison with other available studies: a semi-analytical solution and a more general FEM solution of sheet buckling by the Asymptotic-Numerical Method (ANM). [ABSTRACT FROM AUTHOR]

The purpose of the present paper is to show how and to what extent the introduction of refined, shear sensitive models improves on previous ones, based on triaxiality only, for the phenomenological description of ductile damage in bulk cold metal forming processes. Wire-drawing and wire rolling are taken as examples. A set of mechanical tests has been conducted: round bar tension, notched bar tension, plane strain tension, and torsion for pure shear deformation. Both constitutive and damage model parameters have been carefully identified, with back-computation of the laboratory tests for validation. Application of the models to the cold forming processes, described here, shows the superiority of the shear-enhanced models for locating maximum damage in flat wire rolling, where a significant amount of shear is present (“blacksmith's cross” deformation pattern). On the contrary, it proves unnecessary for low-shear processes such as wire-drawing. The cavity-growth Gurson-Tvergaard-Needleman model seems to be the best basis for damage prediction in patented high carbon steel, a very ductile material. [ABSTRACT FROM AUTHOR]

An accurate knowledge of the phenomenon is required to develop a predictive modeling of the electromigration failure. Thus, a hitherto unseen SEM in operando observation method is devised. The test structure with “high density” through silicon vias (TSV) is tested at 623 K with an injected current density of 1 MA/cm 2 . Regular shots of micrographs inform about the voids nucleation, forced in copper lines above the TSV, and about the scenario of their evolution. A clear relation is established between voids evolution and the one of the electrical resistance. The lack of impact of test conditions on the failure mechanism is demonstrated. Finally, the impact of microstructure on the depletion mechanism is discussed. Grain boundaries are preferential voids nucleation sites and influence the voids evolution. A probable effect of grain size and crystallographic orientation is revealed. [ABSTRACT FROM AUTHOR]