Jan Teßmer

German Aerospace Center (DLR) | DLR · Windenergy-Research

By the end of 2015, wind turbine power plants with a total output of 430 GW were installed worldwide, more than 43 GW in Germany accounting for roughly 14% of its national gross electricity generation. Essential advantages of wind energy are low electricity generation costs, global applicability and good controllability (especially concerning syste...

The full set of information on the study "Flexibility concepts for the German power supply in 2050. Ensuring stability in the age of renewable energies" can be found on http://www.acatech.de/de/aktuelles-presse/dossiers/dossier-stromversorgung-2050.html and the main document with the study in English is available on http://www.acatech.de/de/publika...

Im Beitrag werden vier wichtige Innovationsfelder der Windenergie beschrieben werden, die wichtige Herausforderungen und Trends aufgreifen: Kostendegression, Anlagengröße, Offshore-Windenergie und Netzintegration

The discrepancy between the analytically determined buckling load of perfect cylindrical shells and experimental test results is traced back to imperfections. The most frequently used guideline for design of cylindrical shells, NASA SP-8007, proposes a deterministic calculation of a knockdown factor with respect to the ratio of radius and wall thic...

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. Structural weight reduction by exploitation of structural reserves in composite aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis of real s...

In this paper a simulation strategy for composite structures will be presented taking into account all thermal aspects, which may occure from manufacturing to in-service. Focus herein is laid on the thermo-elastic simulation of the spring-in effect on large airframe structures based on the FEmethod. Besides the identification of curing parameters v...

Sandwich structures are of great importance for aircraft structures due to their high specific bending stiffness, bending strength and functional integrability. However, impact damage can provoke a significant strength and stability reduction. Computational methods for rapid and reliable design are presented together with advanced non destructive t...

Aerospace industry strives for significantly reduced development and operating costs. Reduction of structural weight at safe design is one possibility to reach this objective. Another one is the use of reliable simulation methods in order to minimize expensive and time consuming experimental design studies. DLR has developed improved concepts and t...

Textile and thick composites show growing importance for cost efficient manufacturing and need a proper out-of-plane failure analysis for safe performance of modern aircrafts. Both important types of composites show complex 3D mechanical behaviour. The paper presents: 1. A new testing device accounting for combined out-of-plane loading. 2. An effic...

Thin-walled shell structures like circular cylindrical shells are prone to buckling. Imperfections, which are defined as deviations from perfect shape and perfect loading distributions, can reduce the buckling load drastically compared to that of the perfect shell. Design criteria monographs like NASA-SP 8007 recommend that the buckling load of the...

Fiber-composite materials are increasingly used for airframe structures. This is due to their superior mechanical and mass characteristics compared to conventional materials, besides other advantages. Special methods for predicting manufacturing problems of “as-built ” fibercomposite structures are required, since chemical matrix material reactions...

For efficiently simulating the damage resistance of sandwich panels subjected to low-velocity impacts, the finite element based damage tolerance tool CODAC has been enhanced. While sandwich structures are very weight efficient and provide integrated acoustic and thermal insulation, impact damage can provoke a significant strength and stability redu...

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. Contributions to this aim are provided by the completed project POSICOSS and the running follow-up project COCOMAT, both supported by the European Commission. As an important contribution to cost reduction a decre...

Anisotropic textile composites show nonlinear deformation and complex fai- lure behaviour. In particular three-dimensional reinforced textile composites are characterised by an orthotropic material behaviour. To achieve the full po- tential of textile composites the material and especially the failure behaviour has to be analysed particularly for r...

Generally it is well known that the performance of fibre reinforced composite structures is mainly dependent on the in-plane material behaviour. Non Crimp Fabric (NCF) composites provide the potential to increase the out-of-plane material performance by introducing full through thickness re

Aerospace industry demands for significantly reduced development and operating costs. Reduction of structural weight at safe design is one avenue to achieve this objective. The running ESA (European Space Agency) study Probabilistic Aspects of Buckling Knock Down Factor acts on this route. It concentrates on thin-walled circular cylindrical CFRP sh...

The finite element based design tool, CODAC, has been developed for efficiently simulating the impact behavior of sandwich structures consisting of two composite face sheets and a compliant core. To achieve a rapid and accurate stress analysis, three-layered finite shell elements are used. A number of macromechanical damage models are implemented t...

Anisotropic textile composites show nonlinear deformation and complex failure behaviour. In particular three-dimensional reinforced textile composites are characterised by an orthotropic material behaviour. To improve the erformance of Non Crimp Fabrics (NCF) for lightweight structures the material and failure behaviour has to be analysed especiall...

A new four-node bilinear shell element with full piezoelectric coupling is presented. It can be used for the analysis of light-weight smart structures (adaptive structures), i.e. laminated composite structures with piezoelectric patches attached to its surface or embedded within the laminated layers. The piezoelectric patches can be both passive (s...

Overview on Structural Mechanic Aspects of CFRP Fuselage Structures. Focus lies on numerical and experimental investigations and their comparison (validation)

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. Contributions to this aim are provided by the completed project POSICOSS and the running follow-up project COCOMAT, both supported by the European Commission. As an important contribution to cost reduction a decre...

One key objective of the ITOOL project is to improve failure and impact modelling of textile composites and establish validated Finite Element (FE) tools for the analysis of 2D and 3D textile composites on a macro- scale. Furthermore, these tools are to be linked to the data exchange software being developed within the project so that information m...

Current industrial demands for fibre composite primary structures in the area of aeronautics require innovative, experimentally validated simulation methods and tools, to support a cost and weight efficient design and to reduce their time-to-market. Reliable application of numerical analysis in upfront design challenges not only verification (“sol...

Aircraft design calls for weight efficient shell constructions. Composite sandwich structures satisfy this demand by the combination of two thin, stiff face sheets and an intermediate lightweight core. Furthermore, the outer face sheet can act as an impact detector while the core provides damping and insulation. Thus, sandwich structures are increa...

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. Structural weight reduction by exploitation of structural reserves in composite aerospace structures contributes to this aim, however, it requires accurate and experimentally validated stability analysis of real s...

A strategy for accurate, ef cient and economic thermal investigation of hybrid composite structures by means of the Finite Element Method (FEM) will be presented. It includes test prediction, validation tests, validation analysis, and an industrial application. Drawbacks of commercial software codes are identi ed and current research work for the s...

The allowable load bearing capacity of undamaged thin-walled stringer stiffened carbon fibre reinforced plastic (CFRP) panels loaded in compression is currently limited by its buckling load. The extension to a novel stability design scenario - to permit postbuckling under ultimate load (1, 2) or even more progressive to move ultimate load close to...

The paper focuses on the topic of smart and adaptive structures using embedded piezoelectric sensors and actuators. A new high-performance degenerated continuum based solid piezoelectric shell element is developed herein. It is an isoparametric 4-noded quadrilateral layered element based on the Reissner-Mindlin theory of plates with piezoelectric c...

A fast semi-analytical model for the post-buckling analysis of stiffened cylindrical panels is presented. The panel is comprised of a skin (shell) and stiffeners in both longitudinal (stringers) and circumferential direction (frames). Local buckling modes are considered where the skin may buckle within a bay and may induce rotation of the stiffener...

The finite element based damage tolerance tool, CODAC, has been developed for efficiently simulating the damage resistance of sandwich structures subjected to low-velocity impacts. The considered double shell structures consist of two thin composite face sheets separated by a lightweight core. Due to their high mass specific stiffness and strength,...

For the prediction of composite strengths with representative volume elements (RVE) a thorough understanding of the ongoing failure mechanisms is needed. This again is influenced by the manufacturing process. Therefore, a brief overview on fabrication, material characteristics and failure mechanisms for Prepreg and textile composites is given in th...

The finite element based tool, CODAC, has been developed for efficiently simulating the damage tolerance of composite structures subjected to low-velocity impacts. It is applicable to monolithic and also sandwich based structural concepts. The considered sandwich shell structures consist of two thin composite face sheets separated by a lightweight...

Industrialised infusion processes enable a cost-effective possibility to produce textile composite structures compared to pre-impregnated composite systems (Prepregs). Particularly with regards to high performance structures one has to be familiar with the material behaviour and the failure characteristic to apply fibre reinforced composites profit...

The allowable load bearing capacity of undamaged thin-walled stringer stiffened carbon fibre reinforced plastic (CFRP) panels loaded in compression is currently limited by its buckling load. The extension to a novel stability design scenario - to permit postbuckling under ultimate load - requires validated simulation procedures for this highly nonl...

In order to make modern aeroplane design more competitive the use of CFRP, which under cost and technical aspects proves to be highly effective, is enlarged with every new aircraft generation. Among the new problems that have to be tackled finds the thermal behaviour of the poorly heat conducting composite materials. This report gives the descripti...

This paper presents two new design tools for lightweight aerospace structures. The first tool is the Tailored Fibre Placement (TFP) design tool TACO. It is used to optimize the fibre orientations of structures made of Carbon Fibre Reinforcement Plastics (CFRP). The optimization concept is explained and results are given for a horizontal tail plane...

Hybrid structures, for example metallic multiwall thermal protection systems, sandwiches or hot structures, consist of layers with different thermal conductivity. In addition, radiation and convection can occur within these layers. Analysis of these internal heat transfer mechanisms and the design of hybrid structures require three-dimensional mode...

An overview of DLR's current research activities and results in the fields of heat transfer, thermal stresses, and thermally induced buckling in composite aerospace structures is given. Novel theories and finite element formulations are presented, realistic modeling of boundary conditions and junction areas is highlighted, experimental validation i...

Virtual Testing of Aircraft Structures, considering Postcritical and Thermal Behavior

Fiber Metal Laminates (FML) are well suited for high performance structures, e.g. in aeronautics. Despite their great mechanical potential, they already suffer a decrease of material strength at temperatures that are likely to occur on a standard flight profile. Therefore, an accurate thermal analysis is important, if dimensioning load cases occur...

In the case of composite structures 3D finite elements or finite difference methods are commonly used for the evaluation of the temperature fields. This leads to a high effort on discretization and computation, especially for transient load cases. Therefore, 2D finite elements have been developed based on a layerwise theory to calculate the full 3D...

Strong international competition in the civil aircraft market requires a continuous effort of the aircraft manufacturers to improving structural performance and reducing production costs of their products. A key step forward with great potential for achieving both goals is the application of composite materials to primary aircraft structures. Howev...

Three-dimensional (3D) finite element formulations are usually applied for the analysis of temperature fields for hybrid and conventional composite structures. This leads to a high effort with respect to discretisation and computation time, especially for transient calculations. Using a new formulation basing on a two-dimensional (2D) finite elemen...

The terms ‘Right First Time’ and ‘First Right Time’ stand for the actual demands to the product development process, and the they characterize Concurrent/Integrated Engineering as development procedure: The right design has be to obtained already at the first time when a prototype is manufactured, and the duration of the whole process has to be min...

Following the theoretical and numerical aspects given in [10] the formulation for the multidirector shell element is extended for the description of failure, especially the onset and propagation of delaminations in thin-walled composite structures. Therefore, stress based failure criteria are presented as a necessary condition for initiation of del...

An hierarchical concept for the analysis of thin-walled composite shells is presented within the finite element method for nonlinear deformation of thin-walled composite structures. For non-disturbed subdomains of the structure an effective 4-node shell element with 5 or 6 d.o.f. per node is used for the whole laminate. For the analysis of 3D-stres...

This chapter presents a numerical method for the nonlinear analysis of thin-walled composite structures within the finite element method. Composites are typically used for light weight structures. They are employed in many engineering fields. Because anisotropy and stacking sequences of laminates, i.e. heterogeneities, the material shows rather com...