Multi-scale friction modeling for manufacturing processes: The boundary layer regime

This paper presents a multi-scale friction model for largescale forming simulations. A friction framework has been developed including the effect of surface changes due to normal loading and straining the underlying bulk material. A fast and efficient translation from micro to macro modeling, based on stochastic methods, is incorporated to reduce the computational effort. Adhesion and ploughing effects have been accounted for to characterize friction conditions on the micro scale. A discrete model has been adopted which accounts for the formation of contact patches ploughing through the contacting material. To simulate metal forming processes a coupling has been made with an implicit Finite Element code. Simulations on a typical metal formed product shows a distribution of friction values. The modest increase in simulation time, compared to a standard Coulomb-based FE simulation, proves the numerical feasibility of the proposed method

Inverse form finding with h-adaptivity and an application to a notch stamping process

The aim is to determine the optimized semi-finished workpiece geometry to its given target geometry after a forming process. Hereby, a novel approach for inverse form finding, a type of a shape optimization, is applied to a notch stamping process. As a special feature, h-adaptive mesh refinement is considered within the iteratively performed forming simulation

Identification of nonlinear kinematic hardening parameters for sheet metal from biaxial loading tests

In this work an anisotropic material model at finite strains with nonlinear mixed (isotropic and kinematic) hardening is used for the identification of the hardening parameters of sheet steel. The algorithmic system is thereby reduced to a single equation return mapping. For the identification, a cruciform specimen is loaded biaxially in an alternating shear test to provoke the kinematic hardening behavior and prevent the sheet from buckling. The material parameters are found through an optimization strategy by comparing the deformation field from the experiment to that from a finite element (FE) simulation. The resulting cost function is minimized by means of a gradient-based method

The forming of mild steel plates with a 2.5 kW high power diode laser

Bending of 07 M20 mild steel sheets to various degrees using a contemporary 2.5 kW high power diode laser (HPDL) has been successfully demonstrated for the first time. The experimental results revealed that the HPDL induced bending angle increased with an increasing number of irradiations and high laser powers, yet decreased as the traverse speed was increased. It was also apparent from the experimental results that the laser bending angle was only linearly proportional to the number of irradiations when the latter was small. It is believed that the absence of linearity observed when the number of irradiations was high is due to local material thickening along the bend edge. From graphical results and the employment of an analytical model, the laser line energy range in which accurate control of the HPDL bending of the 07 M20 mild steel sheets could be exercised was found to be between 138 J mm-1 and 260 J mm-1

Dirac points with giant spin-orbit splitting in the electronic structure of two-dimensional transition-metal carbides

Two-dimensional (2D) materials, especially their most prominent member, graphene, have greatly influenced many scientific areas. Moreover, they have become a base for investigating the relativistic properties of condensed matter within the emerging field of Dirac physics. This has ignited an intense search for new materials where charge carriers behave as massless or massive Dirac fermions. Here, we theoretically show the existence of Dirac electrons in a series of 2D transition-metal carbides, known as MXenes. They possess twelve conical crossings in the 1st Brillouin zone with giant spin-orbit splitting. Our findings indicate that the 2D band structure of MXenes is protected against external perturbations and preserved even in multilayer phases. These results, together with the broad possibilities to engineer the properties of these materials phases, make Dirac MXenes a potential candidate for studying and developing novel Dirac-physics-based technologies.Comment: 4 figures and supplementar

Comparison of gurson and lemaitre model in the context of blanking simulation of a high strength steel

The process of blanking takes place in a short band with high accumulated strain undergoing various stress triaxialities. Enhanced implementations for shear and compressive loads of Gurson’s and Lemaitre’s model are directly compared for the same blanking setup. For a dual phase steel DP600 the Lemaitre parameters are identified completely by an inverse strategy, while the parameters of the Gurson’s porous plasticity model are predominantly gained from analysis with a scanning electron microscopy (SEM). The models are validated by comparison of force-displacement curves, time point and location of crack initiation. Advantages and disadvantages of both approaches are discussed with respect to prediction accuracy and costs of parameter identification. Both of the models deliver an exact prediction for the location of the crack and a good prediction of the punch displacement at the onset of cracking