4th Workshop on Structural Analysis of Lightweight Structures
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- Session 1
- Session 2
- Session 3
Session 1: Markets & Products
Time: 9:45 - 12:00
The use of structural design optimization to ascertain optimal topology of structures under transient nonlinear behavior, exemplified by automotive crash, remains a challenge. This is due to both computational effort of the simulation and handing of the system responses. Developments in efficient optimization algorithms as well as increased computer speed and capacity has now enabled the examination of optimal topology of structures undergoing crash and impact. Different methods are currently be investigated for varying loading and degrees of nonlinear behavior. These can be categorized in two general families:
- efficient optimization algorithms to reduce the number of nonlinear simulations needed
- single or multiple linear elastostatic replacement loads to approximate the true system
In this presentation, methods being analyzed and expanded at the Associate Professorship of Computational Mechanics (Prof. Duddeck) of the Technical University of Munich will be shown. For the former, structural design optimization using hybrid cellular automata will be introduced and results shown. For the latter, three methods to represent a transient nonlinear structural model with a linear elastostatic model and their application in topology optimization will be addressed: single replacement loads, multiple replacement loads and multiple replacement loads with updating. To conclude, a comparison will be drawn in addition to providing an outlook to these methods.
The benefits of incorporating finer-scale information into material modeling are threefold:
- Chemical and physical processes within the material can be considered at the scale of their occurance, enabling a more realistic description of the underlying processes.
- As the finer-scale information is linked to the macroscopic material behaviour via homogenization techniques, quantification of the effect of the aforementioned chemical and physical processes on macroscopic properties becomes accessible.
- Finally, with this link between finer scales and the macroscale being established, goal-oriented optimization of materials and structural members becomes possible.
The basis of this so-called multiscale approach in material modeling is the proper characterization of material properties at various length scales. The respective experimental results may either serve as input data describing the behaviour of material phases at finer length scales or provide experimental data for validation of underlying homogenization schemes. Accordingly, the first part of this presentation is devoted to the NanoLab at University of Innsbruck, installed as Core Facility of the University of Innsbruck in 2008, exclusively serving the purpose of multiscale characterization. Within this presentation, available experimental equipment and techniques will be addressed.
Within the second part of the presentation, a recently started joint research project on the optimization of FRC components is presented. This project, covering several lenght scales in material modeling strongly benefits from the available infrastructure at the NanoLab. This presentation will provide first insight into the obtained research results as regards both experimental characterization and multiscale modeling & simulation of FRC.
Advanced models account for viscoplastic deformations including isotropic and kinematic hardening, recovery and ratcheting. However, the models contain a relatively large number of temperature dependent material properties that must be determined on the basis of data of material tests. The determination of the properties is a non-trivial task because it is not clear which loading history must be applied in the tests for a certain material to obtain stable and robust (i.e. objective) material properties. Thus, methods for the assessment of the stability and robustness of the properties are presented and results obtained in a project funded by the European Space Agency ESA are shown for material data of copper in the temperature range from 300 to 700 Kelvin.
Session 2: Optimization & Robustness
Time: 13:30 - 15:30
Starting from simple optimization of framework structures up to the optimization of shapes with the use of topography optimization approaches and the optimization of volume structures with the help of topology optimization. Beyond that, the mathematical models that are embedded in the optimization procedures have developed, so that nowadays it is possible to identify the optimum design for defined multiple loading situations in terms of more than one target parameter. Especially topology optimization is an appropriate procedure, because it can handle a wide range of different optimization problems.
One special topology optimization approach is the bionic topology optimization. Another trend in the field of engineering is the analysis of the behavior of the nature, that has advanced structures, such as trees, for thousands of years and to deduce ideas for the optimization of mechanical structures. One outcome is the local adaption of mass of a component to reach the optimization target like weight. These ideas and the topology optimization approach is combined to the bionic topology optimization. For this approach components are optimized concerning weight and additional targets like a constant stiffness of the part. Based on this procedure various components, form interior elements up to engine cases have already been optimized respecting the determined optimization target.
The practical requirements of cranes with increasing hoisting heights and maximum load capacities require a realignment in the rope and crane design. In several years of cooperation Liebherr and the Austrian rope manufacturer Teufelberger have devel- oped a new high strength fiber rope for hoisting applications. Through the use of the fiber rope, with a weight saving of approximately 80% compared to the steel rope, the payloads of the crane can be increased considerably. In addition, advantages in life time, transport weights as well as the elimination of maintenance intervals will be achieved.
In this presentation, a so-called Bayesian model updating procedure will be employed for parameter fitting. As opposed to classical optimization algorithms, which are geared towards the identification of one optimal solution, the employed approach provides a set of solutions together with their probability. Hence, Bayesian model updating allows for the consideration of uncertainties and also information with respect to the uniqueness of the obtained solution can be gathered.
The approach will be applied to a viscoplastic material model including isotropic and kinematic hardening, recovery and ratcheting, where material data of copper in the temperature range from 300 to 700 K are used.
The approach is done by a top down method. Instead of solving the direct problem, one uses Stochastic Fourier Integral Operators to model both the propagation and the material properties.
A theoretical model needs quality assessment to verify its robustness and accuracy. For that purpose two approaches are proposed. First a Kriging predictor is used to compare experimental with theoretical values obtained from the model. Secondly a Monte-Carlo based sensitivity analysis is adopted to see how small disturbances in the input affect the output. The methods are applied to a static test model of a winglet, developed by INTALES.
Session 3: Stochastic structural analysis & computational aspects
Time: 16:00 - 17:15
The development, certification and production of modern aircraft components generate large datasets that need to be managed and maintained. Intales GmbH has developed a framework to manage this data and act as a centerpiece between the design, stress and production departments. An SQL database acts as the data container whereas the toolbox Aletheia provides a wide range of supporting functions linking design model, FEM and strength analysis. Some of the main advantages are:
- Fast and robust flow from CAD model to strength results.
- Making efficient use of computational capacity.
- Increased traceability of results.
The toolbox Aletheia has been created for the development of Airbus's A350XWB Wingtip/Winglet at FACC. By using this as an industrial example, the advantages of Aletheia will be shown.
A new linear sandwich shell element is presented, based on the third order shear deformation theory from Reddy in combination with the zigzag model. In addition to the in-plane stresses, the element can calculate the out-of-plane shear stresses. Following from a set of benchmark tests, the sandwich element shows good correlation with 3D FEM models and analytical solutions and shows superior performance compared to the Abaqus S4 shell element, especially for soft cores. A facesheet wrinkling criterion is implemented into the element, which is compared to results of a four-point-bending experiment on sandwich panels. Based on the results of the wrinkling analysis, an attempt is made to predict the effect of facesheet wrinkling on the response of the sandwich structure by penalizing the stiffness of elements which have wrinkled. The method shows good potential in predicting possible growth of the wrinkled area and the redistribution of loads.