Gottfried Laschet

Homogenization of the thermal properties of transpiration cooled multi-layer plates

To predict the aerothermal behaviour of transpiration cooled plates, a multi-scale approach based on the homogenization method of periodic material structures is presented. This method allows to calculate effective equivalent thermophysical properties either for each layer or for the multi-layer of superalloy, bondcoat and thermal barrier coating. Its variational formulation and finite element discretization are then presented. From the 3-D conjugate flow and heat transfer analysis, the stationary state is extracted and transferred to the micro-scale unit cell discretized by finite elements. The effect of the different cooling designs on the effective orthotropic conductivities are then discussed. Finally, the influence of the FE discretization and the position of unit cell on these effective thermal properties is investigated.

Towards integrative computational materials engineering of steel components

This article outlines on-going activities at the RWTH Aachen University aiming at a standardized, modular, extendable and open simulation platform for materials processing. This platform on the one hand facilitates the information exchange between different simulation tools and thus strongly reduces the effort to design/re-design production processes. On the other hand, tracking of simulation results along the entire production chain provides new insights into mechanisms, which cannot be explained on the basis of individual simulations. Respective simulation chains provide e.g. the basis for the determination of materials and component properties, like e.g. distortions, for an improved product quality, for more efficient and more reliable production processes and many further aspects. After a short introduction to the platform concept, actual examples for different test case scenarios will be presented and discussed.

Development of an integrative simulation method to predict the microstructural influence on the mechanical behaviour of semi-crystalline thermoplastic parts

Abstract The mechanical properties of injection moulded plastic parts depend on the morphology, the degree of crystallinity and the molecular orientation of the formed microstructure. In order to take the variation of the microstructure into account in a structural analysis, a novel multi-scale, integrated simulation approach is presented here. At first, a coupled mould filling and heat transfer analysis is achieved at the macroscale and its temperature field is transferred to the micromodel. Based on the concept of cellular automata, a 3-D microstructure evolution model is developed. It specifies the nucleation of the spherulite germs and describes their expansion rate. To evaluate the effective mechanical properties of the simulated microstructures, the homogenisation method is applied directly to the spherulites, assembled in few classes according to their crystallinity degree. These local properties are then introduced into a new multilinear material model for structural analysis of thermoplastics. Finally, the influence of the microstructure on macroscopic behaviour is outlined for a polypropylene tensile bar, extracted from an injection moulded plate.

Thermo-mechanical analysis of cast/mould interaction in casting processes

Abstract The numerical analysis of the thermo-mechanical interaction between the cast part and mould in casting processes requires a strong coupling between the thermal and mechanical simulation. This includes a 3-D frictionless contact algorithm and a model to describe the local heat transfer between part and mould as a function of the contact pressure or the formation of a local gap between both domains. Several features suitable for the analysis of solidification processes have been introduced in the classical master/slave contact algorithm like a temperature-dependent penalty factor and implemented in the software package CASTS. Benchmark tests and two industrial casting applications illustrate the correctness of the developed thermo-mechanical program and the ability to simulate complex cast parts.

Towards a metadata scheme for the description of materials – the description of microstructures

Abstract The property of any material is essentially determined by its microstructure. Numerical models are increasingly the focus of modern engineering as helpful tools for tailoring and optimization of custom-designed microstructures by suitable processing and alloy design. A huge variety of software tools is available to predict various microstructural aspects for different materials. In the general frame of an integrated computational materials engineering (ICME) approach, these microstructure models provide the link between models operating at the atomistic or electronic scales, and models operating on the macroscopic scale of the component and its processing. In view of an improved interoperability of all these different tools it is highly desirable to establish a standardized nomenclature and methodology for the exchange of microstructure data. The scope of this article is to provide a comprehensive system of metadata descriptors for the description of a 3D microstructure. The presented descriptors are limited to a mere geometric description of a static microstructure and have to be complemented by further descriptors, e.g. for properties, numerical representations, kinetic data, and others in the future. Further attributes to each descriptor, e.g. on data origin, data uncertainty, and data validity range are being defined in ongoing work. The proposed descriptors are intended to be independent of any specific numerical representation. The descriptors defined in this article may serve as a first basis for standardization and will simplify the data exchange between different numerical models, as well as promote the integration of experimental data into numerical models of microstructures. An HDF5 template data file for a simple, three phase Al-Cu microstructure being based on the defined descriptors complements this article.

Virtual Production Systems

The use of simulation systems is of significant importance for companies in high-wage countries as the requirements of product- and process quality are generally higher than in low-wage countries due to conditions of the market. Since the implementation of simulation tools is not value-adding in the first place, the performance of virtual product development chain must therefore be continuously increased in terms of greater planning efficiency. Research in the field of virtual production systems therefore addresses the following issue.

On a Class of Thermo-visco-plastic Constitutive Equations for Semi-solid Alloys

The behavior of semi-solid alloys is quite different in tension, compression and shear and depends strongly on the morphology of the micro-structure. This article outlines a generalized viscoplastic material model for semi-solid alloys which reflects this complex viscoplastic behavior. From the generalized model a number of well known yield functions and viscoplastic material models for semi-solid and solid materials can be reproduces. The general model is applied to describe the behavior of the semi-solid A356 alloy below the coherency temperature during equiaxed solidification.

Integrated Computational Materials and Production Engineering (ICMPE)

The research area “Integrative Computational Materials and Production Engineering” is based on the partial integration of individual models areas within separated simulation platforms with the objective of further development and integration into a single comprehensive ICMPE (Integrative Computational Materials and Production Engineering) platform that combines materials and machining simulation with factory and production planning. In order to realize an operational platform concept, the AixViPMaP has been implemented. AixViPMaP serves as a technology platform for the knowledge-driven design, implementation and improvement of complicated process chains for materials in high-value components. This allows manufacturing related influences to be considered during production in order to optimize process performance and materials properties. The extension and application of the AixViPMaP platform towards production modeling in the sense of an ICMPE based on one holistic system integrates production related models with all material-related models into a single, unified concept. Advanced test cases are under examination to validate and assess this new integrated approach (e.g., new alloys for large gears for the wind industry).