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This thesis presents a method for fast numerical calculation of warpage in laser sintering of semicrystalline thermoplastics. The developed model is based on the simulation of the thermal interaction in the building chamber, caused by different thermal boundary conditions. For that purpose, a finite element mesh of the whole building space is generated. The interaction of the thermal boundary conditions causes a time dependent temperature eld, which influences the crystallization progress and in consequence the volume shrinkage. Subsequently to the thermal calculation, that shrinkage strain is used as time-space dependent mechanical load in a sequence of static mechanical FEM-computations of the part distortion. The developed approach allows the prediction of part warpage caused by macroscopic boundary conditions of real parts for the first time and has been used to analyse several test samples as well as real industrial parts.

In this work an effcient method for the prediction of residual stresses and distortions of parts generated by the additive manufacturing process Laser Beam Melting (LBM) is presented. The method allows to calculate the LBM build-up process at least 100 times faster than state-of-the-art approaches for realistic macroscopic components based on a structural Finite Element Analysis. The developed approach is based on the fact, that remaining strains cause the residual stresses within the part. These inherent strains can be derived by complex thermo-mechanical simulations on microscale. Based on the known stress and strain distribution during the process, scanning trajectories were optimized with respect to the reduction of end deformations, plastic strains and stresses during the build-up process. Based on the calculated displacements after the release from the baseplate, distortions can further be minimized by at least factor ten for one iteration if inverted displacements are back-mapped to the computer aided design. The combination of these two simulation driven methods leads to a nearly zero distortion fabrication while process stability rises.

Porous sound-absorbing ceramics contribute to the passive damping of thermo-acoustic instabilities and sound dissipation. As ceramic liners, they must satisfy all requirements respecting mechanical strength and thermal resistance. Design and development of such ceramics concern various aspects like thermal shock resistance, crack behavior, fatigue limit, creep and erosion resistance. The aim of this work is to investigate the mechanical behavior of highly porous sound absorbing ceramics and to predict the brittle damage behavior considering the material microstructure. It studies the applicability of such ceramics as insulation liners for the combustion chambers and gives a clue to further material improvement in terms of mechanical strength. Experiments were performed in this work to characterize the mechanical strengths of a new developed sound absorbing ceramic for the application as ceramic heat shields for the combustion chambers of premixed gas turbines. Compressive tests at both room and high temperature as well as four-point bending tests at room temperature have been carried out. Furthermore, the fits of fracture strengths of the material to the Normal, Weibull and Type I extreme value distributions are investigated. The characterization was then expanded to other physical properties such as porosity, density, thermal conduction coefficients and thermal expansion coefficients. A non-multi-physic but multi-scale approach is applied in this work which predicts the influence of the microstructure on the macroscopic properties. The scale transition method is known as mean-field homogenization method, based on assumed relations between average values of micro-strain and -stress fields in each phase. This homogenization model is based on the Eshelby model and assumes the pores (or rather inclusions) to be ellipsoidal. Influence of the pore density, pore form and pore orientation on the strength of these porous sound absorbing ceramic are studied here. Depending on the loading condition higher strength by higher porosity values is achievable by for example aligning the pores on a desired direction or changing their form from spherical to ellipsoid with high aspect ratios. Furthermore, direct finite element simulations of a representative-volume element (RVE) are also implemented in this work to investigate the pure brittle damage of this sound absorbing ceramic. An effective-stress degradation model has been implemented in a predefined user-subroutine of ABAQUS. It is based on the three dimensional rupture criterion and describes the pure brittle damage under mechanical, thermomechanical, static and quasi-static loadings. Different RVE s have been generated and investigated in terms of damage considering different structural parameters. The present results demonstrate the application potential of these sound absorbing ceramic as liner in terms of mechanical strengths, predict their brittle damage behavior considering the microstructure and provide a base for further material developments and numerical investigations. The applicability of these ceramic to line the combustion chambers in terms of sound absorption is investigated on an experimental set-up at the Faculty of Combustion of the Center of Applied Space Technology and Microgravity (ZARM). The validation of the results from this chapter will be performed on this set-up.