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Institute
Paper presents results of dynamic FSI simulation of unmanned aerial
vehicle, where for first case, a typical linear material was used, and for second case, a composite material was used. The simulations were performed with the objective of studying model reaction with forces indicated by flow which were defined by initial conditions. Secondary objective was to evaluate critical flutter speed. Simulations provided interesting results: for linear case, applied flow speed resulted with occurrence of flutter phenomena, while composite case exhibited damping of vibration in designated points along the wing. Presented
simulations were performed within an environment using loosely-coupled
approach. CFD simulations were carried out with use of parallel code DLR-Tau.
FSI computations were executed with applied modal approach for structural model and full data exchange between fluid and structure as well as mesh deformation.
This contribution presents an investigation of strain rate dependent behaviour for selective laser sintered polyamide 12. Two different cases are considered: a strain rate change within tensile loading and a relaxation test incorporating a strain rate change after each holding time section. For the simulation of material behaviour the material model of Bodner-Partom and Chaboche were used. The damage behaviour was considered by the Lemaitre crack model. Thereby it was determined which numerical model is more suitable to reproduce the strain rate-dependent behaviour. Tensile and relaxation tests at constant speeds served as the basis for these investigations.
The material and damage behaviour of additively manufactured polyamide 12 under cyclic loading was characterized by cyclic tests and microstructure analysis by using microscopy, X-ray refraction, and computed tomography. The results were used to determine parameters for the viscoplastic material model by Chaboche and a damage model by Gurson-Tvergaard-Needleman. The temperature was monitored during the experiments and the self-heating effect was observed. By including this effect, a higher accuracy could be achieved with the results of mechanical experiments.
In order to characterise the material and damage behaviour of additively manufactured polyamide 12 (PA12) under quasi-static load and to implement it in a numerical model, experiments under quasi-static load as well as microstructural investigations were carried out. Selective laser sintering (SLS) was used as the manufacturing process. For the classification of the material behaviour, quasi-static cyclic tests with holding times as well as tensile tests were performed. X-ray refraction and computed tomography (CT) were used to investigate the damage behaviour. The Chaboche model, which has already been applied for metallic materials under thermomechanical loading, served as the basis for the selection of the numerical material model. The same procedure was used for the selection of the damage model, where the Gurson–Tvergaard–Needleman (GTN) model was chosen, which was already used for porous metallic materials. The Chaboche model shows very good agreement with experimental results. Furthermore, the coupling with the GTN model allows a very good modelling of the damage behaviour. Finally, it could be shown that the selected models are suitable to simulate the material and damage behaviour of 3D printed PA12.
Thermo-viscoplastic material modelling for self-heating loads and its experimental verification
(2020)
The paper examines a modelling approach for thermomechanically coupled problems and an experimental concept for a material law validation and verification for self-heating with small to moderate temperature ranges. The study compares two different model formulations and is generally applicable to a variety of material classes. One model is based on a rheological network with an extension for dissipative deformation below the elastic limit. The other model operates without a yield condition. Both models are applied to published experimental data in terms of rate-independent behaviour and the evaluation is carried out on stress-strain-level, temperature evolution and the energy transformation ratio. Furthermore the two models are applied to a strain rate-dependent load case conducted at our institute discussing the same entities. It is pointed out, that the approach of a thermomechanical analysis is valuable and informative to assess the observed deformation processes and to describe the material behaviour with a thermodynamically valid parameter set.
Characterization and Simulation of Shear-Induced Damage in Selective-Laser-Sintered Polyamide 12
(2024)
This paper presents the characterisation of selective-laser-sintered (SLS) samples of polyamide 12 (PA12) under shear loading. PA12 is a semi-crystalline thermoplastic and is used in various industries. Its behaviour under shear stress, which is particularly important for product reliability, has not yet been sufficiently investigated. This research focuses on understanding the material and damage behaviour of PA12 under shear-induced stress conditions. The study included quasi-static experiments and numerical simulations. Samples were prepared via SLS and tested according to ASTM standards. Digital image correlation (DIC) was used for precise deformation measurements. The Chaboche material model was used for the viscoplastic behaviour in the numerical simulations. Due to existing material discontinuities in the form of voids, the material model was coupled with the Gurson–Tvergaard–Needleman (GTN) damage model. A modified approach of the GTN model was used to account for low stress triaxiality under shear loading. These models were implemented in MATLAB and integrated into Abaqus via a User Material (UMAT) subroutine. The results of the experiments and simulations showed a high degree of accuracy. An important finding was the significant influence of the shear factor kw on the damage behaviour, especially during failure. This factor proved to be essential for the accurate prediction of material behaviour under shear-induced stress conditions. The integration of the modified GTN model with the Chaboche material model in UMAT enables an accurate prediction of the material and damage behaviour and thus makes an important contribution to the understanding of the mechanical material behaviour of SLS PA12 specimens.