The Fraunhofer Institute for Mechanics of Materials IWM (German: Fraunhofer-Institut für Werkstoffmechanik) in Freiburg, Germany, is a division of the Fraunhofer-Gesellschaft which focuses upon application-oriented research. The Fraunhofer IWM is a research and development partner for both industry and public institutions whose themes include the safety, reliability, life expectancy and functionality of materials in components and manufacturing processes. The broad spectrum of services offered by the Fraunhofer IWM's business units aid their clients and project partners in the assessment and continuing development of highly stressed materials and components and in the optimization of production process. Established in 1971 in Freiburg in Breisgau, the institute expanded in 1992 to include a location in Halle (Saale). On 1 January 2016 the Halle division of the Fraunhofer IWM became the Fraunhofer Institute for Microstructure of materials and Systems IMWS.
Lubricant flow in nanoscale channels is complicated by various effects that are not considered in conventional thermo-elasto-hydrodynamic lubrication (TEHL) models, one of them being wall slip. The relationship between slip and thermal effects is intricate: some authors debate whether the friction reduction observed in experiments in the TEHL regime is due to slip or viscosity reduction in heated lubricants. To disentangle these mechanisms, a molecular dynamics study of the relationship between temperature and slip in the shear flow of 4 cSt polyalphaolefins (PAO4) in a nanoscale diamond-like carbon (DLC) channel is performed here. We derive a temperature- and pressure-dependent slip law and a pressure-dependent law for the interfacial thermal resistance between DLC and PAO4. These constitutive laws are employed in a continuum model that can answer questions about the competition of slip and thermal thinning of the lubricant. The model shows that slip is only relevant for thin lubricant films typical of boundary lubrication.
Directed Energy Deposition-Arc (DED-Arc) processes create residual stresses in the material due to their nonuniform thermal gradients. These residual stresses interact with the in-service loads and could negatively impact the material integrity. To understand and mitigate the negative effects of these stresses, in this study, a thin-walled structure out of a high strength low alloy (HSLA) steel was manufactured by DED-Arc process. The formation of residual stresses was studied with neutron diffraction at the centerline of the structure. To incorporate the effects of martensitic phase transformation on the residual stress formation, the microstructure of the material was studied using electron and optical microscopy. Also, the phase fractions were calculated using image segmentation methods. Furthermore, thermodynamics calculations were performed to understand the kinetics of the phase changes. The results show that the structure follows a tensile-compressive-tensile-compressive residual stress regime in the travel direction by moving from the lower side of the substrate to the top side of the thin-walled structure. The main influencing factors in the formation of these stresses are the volume expansion due to martensitic and bainitic phase transformations, contraction due to cooling of the hot material, and bending of the structure due to the interaction between tensile and compressive stresses at different heights of the part.
Process control and optimization are important aspects of manufacturing processes. Surrogate models, i.e. data driven models obtained from numerical simulations, are often employed to predict the process outcome for given process parameters in real time. In this work, we investigate a Laplace-Beltrami shape-feature approach for constructing a surrogate model for cup drawing process simulations. The resulting surrogate model captures local changes in deformations and field quantities on mesh geometries more accurately than standard methods. However, comparing mesh distortions, especially local mesh qualities, is challenging. To address this, we introduce a measure of improvement of mesh distortion to analyse the obtained error distributions. We demonstrate the benefits of the proposed method in contrast to variance-based methods such as principal component analysis, which do not adequately model local variations.
Shear transformations are the elementary events of plasticity in glasses and underpin many mesoscopic models of plastic flow, yet their atomic origin and energetics remain difficult to establish. Here we use a machine-learned interatomic potential to show that, in amorphous carbon as a representative network glass, a shear transformation corresponds to the breaking or formation of a single covalent bond. The simplicity of the associated reaction coordinate, the bond length, enables us to extract energy landscapes and barriers. Despite the intrinsic structural disorder, we find that all energy landscapes collapse onto a universal barrier shape. What remains bond-specific is a single scale, the bond-jump distance, which fixes the barrier height through a cubic law. Combined with the activation statistics of shear transformations, this yields a model that predicts the plastic flow stress from independently determined bond-level quantities. Our results provide microscopic support for phenomenological models of plastic flow in glasses and suggest a route towards a quantitative description of amorphous plasticity.
Laser powder bed fusion of metals (PBF-LB/M) involves strongly coupled thermo-fluid dynamics and laser–material interaction, where melt pool stability and keyhole formation are sensitive to optical energy deposition. Most simulations assume constant absorptivity and neglect temperature- and wavelength-dependent optical properties.This work extends a Smoothed Particle Hydrodynamics (SPH)–ray tracing framework by incorporating a temperature- and wavelength-dependent complex refractive index. Reflection and volumetric absorption are computed via Fresnel relations and Lambert–Beer attenuation.Validation against high-speed X-ray experiments reproduces keyhole scaling behavior. A wavelength study for Ti6Al4V at 1.06 µm and 10.6 µm shows reduced effective energy deposition and penetration depth at longer wavelength under identical nominal energy density.
