Workshop

2018

5th Workshop on Structural Analysis of Lightweight Structures

Program

Morning Session

Time: 9:45 - 12:30

9:45 - 10:15
Design criteria for wind-loaded structures beyond Eurocode

Daniel Straub (TU Munich)

Eurocode provides the basis for the design of structures. It ensures a generally accepted level of safety throughout its domain of applicability. However, there are many instances of structures whose design is not fully covered by Eurocode; one example are lightweight structures subject to wind for which the simple load formulas given in Eurocode are not appropriate. When designing such structures, it is nevertheless desired that the overall safety of the structure is in accordance with Eurocode. In this talk, we address appropriate means to ensure this.
The lecture consists of two parts. First, we present a methodology for determining the relevant design parameters based on a limited set of response time-series from numerical simulations (or experiments). We show how the safety margin becomes a function of the amount of data available. This approach is demonstrated through application to a membrane structure analysed with fluid-structure interaction analysis.
The second part is looking at the issue that simple formulas given in Eurocode for establishing wind loads are based on conservative assumptions and parameter choices, i.e. the models contain “hidden safety”. As a consequence, even if advanced numerical models are more accurate than the Eurocode formulations, they can lead to reduced safety because they eliminate the conservative assumptions. To compensate, it can be necessary to employ additional safety factors. We make recommendations on these safety factors based on an analysis of a building portfolio.

 

10:25 - 10:55
3D-LightTrans – Large scale manufacturing technology for high-performance lightweight 3D multifunctional composites

Marianne Hörlesberger (Austrian Institute of Technology, Wien)

Textile reinforced polymer composites (TRPC) hold the promise for enhanced products featuring superior properties, such as light weight and high strength, with comparatively low material costs. This promising potential is nevertheless hindered by the lack of appropriate processing technologies to enable low-cost manufacturing of mass products with sufficient quality. The goal of the 3D-LightTrans project was to create a highly flexible manufacturing chain for low cost production of integral large scale 3D textile reinforced polymer composite parts and its integration in the complete supply chain. 3D-LightTrans manufacturing chains is based on hybrid yarn incorporating thermoplastic matrix material, processed to deep draped multilayer textiles and multifunctional 3D-textile constructions, which is fixed to dry pre-forms and finally, processed into composites by thermoforming. A model is presented for full automation (in nowadays mostly manually performed) complex handling operations.

 

11:05 - 11:35
Stochastic Fourier integral operators for parameter estimation and
damage detection

Martin Schwarz (University of Innsbruck)

This talk addresses a novel for wave propagation in material with spatially varying random properties. The target model is the linear elastic wave equation in solids. We construct a deterministic Fourier integral operator to solve the problem. For modelling the uncertainty we
use a new approach:
The randomness is included into the solution operator rather than in the coefficients of the model. The solution can be represented by stochastic Fourier integral operators (sFIO), which
have nice computational properties for (numerical) simulations. Our model predicts the fully time dependent dynamic response of the structure, and its stochastic properties. Calibrating the sFIO to measurements can be used for both parameter estimation and damage detection.

 

11:40 - 12:00
Multiscale model for braid-reinforced polymers. I: Elastic properties and application to coil springs
Marc Luger (University of Innsbruck)

Purposive custom-tailoring of laminated textile-reinforced polymers demands reliable simulative frameworks to predict the individual reinforcement layers’ structural response, yielding potential of optimization of structural components’ mechanical performance. Multiscale modeling is standardly employed to obtain the effective (homogenized) properties of composites, whereas both analytical and numerical upscaling methods are commonly applied. Whilst analytical methods of homogenization usually cause low computational expenses, the geometrical representation of the material is rather simplified and little information is gained concerning the local stress and strain situation. As regards numerical methods, FE-based unit cells are standardly employed to predict the behavior of composite materials.
Within the presented multiscale method, a modeling approach for braid-reinforced polymers employing 3D continuum models to overcome the aforementioned shortcomings is proposed. Hereby, attempting to reduce the number of parameters, idealized geometric properties are employed for the observation scales’ numerical representations. Starting from the definition of observation scales – such as the yarn, the braid, and the component scale – upscaling procedures are employed to obtain effective elastic properties at each scale, whereas the properties of the constituents, i.e. fiber and matrix, serve as input for multiscale modeling:
● At yarn scale, suitable geometric fiber arrays are employed within these FE-models to obtain effective elastic yarn properties. Besides the elastic properties of the aforementioned constituent materials, the fiber-volume-ratio is required.
● At braid scale, FE-based unit-cells are employed to obtain the effective elastic braid properties, applying the effective yarn properties, and matrix properties describing the resin pockets. The influence of geometric braid properties such as braid angles, braid patterns, and yarn undulations is reflected within the geometric arrangement of the FE model.
● Finally, at component scale, the effective braid properties are employed within structural simulations to assess the component’s mechanical performance, rendering prospects for purposive optimization.
In order to assess the predictive capabilities of the proposed multiscale model, the experimentally determined structural response of coil springs, consisting of glass-fiber-reinforced epoxy, is compared to numerical results obtained from the proposed multiscale approach. Effective braid properties are hereby applied to a suitable FE representation of the spring at component scale, accounting for the local geometric braid characteristics, such as e.g. curvature-induced variation of the braid angle.

Acknowledgement
This research was funded by the K-Regio project “Innovative Tube Design – Entwicklung und Optimierung von neuen High-Tech Faserverbundstrukturen für den industriellen Einsatz auf Basis modell- und simulationsbasierter Methoden” in cooperation with Thöni Industriebetriebe GmbH, superTEX composites GmbH, Intales GmbH. Financial support by the Tyrolean Government, the European Regional Development Fund (ERDF) and the University of Innsbruck is gratefully acknowledged.

 

12:05 - 12:25
Multiscale model for braid-reinforced polymers. II: Extension to viscoelastic properties
Ulrich Hofer (University of Innsbruck)

Multiscale modeling is standardly employed to obtain the effective (homogenized) physical properties of composites, whereas both analytical and numerical upscaling methods are commonly applied. As regards effective viscoelastic properties, analytical methods are often obtained by extending their elastic counterparts to viscoelasticity by exploiting the so-called correspondence principle. As regards numerical methods, FE-based unit cells are standardly employed to determine the viscoelastic behavior of composites.
Within the presented multiscale method, fractional viscoelastic models are used to describe the time-dependent behavior of the matrix, well-capturing the experimentally observed viscoelastic behavior with a comparatively low number of parameters. At three observation scales – defined similar as in [Luger et al. 2018] – upscaling methods are introduced to obtain effective viscoelastic properties at each scale, whereas the properties of the constituents, i.e. fiber and matrix, serve as input for multiscale modeling:
● At yarn scale, the Chamis-equations – standardly used for predicting the effective elastic properties of unidirectionally-reinforced composites – are extended towards viscoelasticity by employing the aforementioned correspondence principle. Hereby, the viscoelastic homogenization problem is transformed into the Laplace-Carson domain, where the corresponding elastic problem is solved. An inverse Laplace-Carson transformation gives closed-form expressions for the effective viscoelastic properties of the yarns [Hofer et al. 2018].
● At braid scale, the upscaling strategy described in [Luger et al. 2018] is extended towards viscoelastic behavior. By doing so, FE-based unit cells are employed to obtain the effective viscoelastic braid properties, applying the effective yarn properties as obtained by the extended Chamis-equations and considering the influence of geometric braid properties, such as the braid angle.
● At the component scale, the effective braid-properties are employed within structural simulations to obtain the viscoelastic response of braid-reinforced components.
In order to assess the quality of the multiscale model, compressional creep tests on braid-reinforced tubes are performed. The model results agree well with the experimentally obtained results. Moreover, the experimentally observed influence of the braid geometry onto the viscoelastic behavior is well reproduced by the proposed multiscale method.

Acknowledgement
This research was funded by the K-Regio project “Innovative Tube Design – Entwicklung und Optimierung von neuen High-Tech Faserverbundstrukturen für den industriellen Einsatz auf Basis modell- und simulationsbasierter Methoden” in cooperation with Thöni Industriebetriebe GmbH, superTEX composites GmbH, Intales GmbH. Financial support by the Tyrolean Government, the European Regional Development Fund (ERDF) and the University of Innsbruck is gratefully acknowledged.

References
[Luger et al. 2018] Luger, M., Traxl, R., Hofer, U., Hirzinger, B., Lackner, R. (2018). RUC-based multiscale model for braid-reinforced polymers: Application to coil springs. Composites Part B: Engineering. Under revision.
[Hofer et al. 2018] Hofer, U., Luger, M., Traxl, R., Lackner, R. (2018). Closed-form expressions for effective viscoelastic properties of fiber-reinforced composites considering fractional matrix behavior. Mechanics of Materials. In Print.

Location

Venue and Date

The workshop will be held in the Hotel dasMEI at Mutters on Thursday, October 18, 2018.

Arrival

By car: Highway A13, direction Brenner / Italy, exit Innsbruck-Süd, direction Mutters

By public transport: Train until Innsbruck main station, then change to the tram line "STB" (direction Fulpmes or Kreith)

You can find the exact location here

Hotel booking

Accommodations can be found here:

https://www.innsbruck.info/en/innsbruck-city.html