Prof. Francisco Chinesta
ENSAM ParisTech| France
Plenary Lecture: Hybrid twins: adapting to multi-uncertain evolving environments
In the previous industrial revolution, virtual twins (emulating a physical system) were major protagonists. However, usually numerical models (virtual twins) are static, that is, they are used in the design of complex systems and their components, but they are not expected to accommodate or assimilate data. The reason is that the characteristic time of standard simulation strategies is not compatible with the real-time constraints mandatory for control purposes. Model Order Reduction techniques opened new possibilities for more efficient simulations.
The next generation of twins, the so-called digital twins, allowed for assimilating data collected from sensors with the main aim of identifying parameters involved in the model as well as their time evolution in real time, anticipating actions from their predictive capabilities. Thus, simulation-based control was envisaged and successfully accomplished in many applications. Despite an initial euphoric and jubilant period, unexpected difficulties appeared immediately. Namely, in practice significant deviations between the predicted and observed responses were noticed, limiting or abandoning their use in many applications.
In that framework of multi-uncertainty evolving environments, Hybrid Twins we proposed, consisting of three main ingredients: (i) a simulation core able to solve complex mathematical problems representing physical models under real-time constraints; (ii) advanced strategies able to proceed with data-assimilation, data-curation, data-driven modelling and finally data-fusion when using compatible descriptions for the physical and data-based models; and (iii) a mechanism to adapt the model online to evolving environments (control).
Institute for Mechanics of Materials and Structures, TU Wien | Austria
Plenary Lecture: Bridging the gap: a joint austro-chinese research project on multiscale modeling – structural analysis – experiments
Herbert A. Mang 1,2, Eva Binder 1,2, Hui Wang 1,2, Thomas Schlappal 2, Jiao-Long Zhang 1,2, Rodrigo Díaz 2, Johannes Kalliauer 2, Yong Yuan 1, Bernhard Pichler 2
1 Tongji University, 1239 Siping Road, Shanghai, China
2 TU Wien – Vienna University of Technology, Karlsplatz 13/202, 1040 Vienna, Austria
The lecture consists of a report about a joint research project of Tongji University, Shanghai, and Vienna University of Technology. Its title reads as “Bridging the Gap by Means of Multiscale Analysis”. The project was inspired by the tunnel, bridging the gap between the two parts of the Hongkong-Zhuhai-Macao Bridge (HZMB), connecting cities on opposite sides of the mouth of the Pearl River into the South Chinese Sea [1, 2]. The project stretches over the time period 2015-2019. It is financially supported by the Austrian Science Fund (FWF) and the China Scholarship Council (CSC). The project focuses on the use of modern multiscale material models for concrete in the context of structural analysis. It consists of four topics.
The first one deals with the increase of the high-dynamic strength of specimens made of concrete with increasing speed of loading. It is quantified by means of an engineering mechanics model. The structural nature of the dynamic strength increase factor (DIF) is verified with the help of a comparison of model predictions with results from laboratory tests [1, 2]. The analysis model takes the statistical scatter of the quasi-static strength and the uncertainty regarding the failure pattern into account . Furthermore, the evolution of the DIF as a function of hardening of concrete at material ages beyond 28 days is studied by combining the engineering mechanics model with a predictive multiscale material model for the quasi-static compressive strength of concrete .
The second topic is devoted to the thermal expansion of mature cement paste as a nonlinear function of the internal relative humidity . The microstructural origin of this behavior is identified by means of an inverse analysis based on a quantitative multiscale poromechnics model. It is found that a temperature increase (or decrease) results in a quasi-instantaneous release (or uptake) of water by nanoscopic cement hydrates . This yields a quasi-instantaneous increase (or decrease) of the internal relative humidity. Consequently, the effective pore underpressures, acting on the solid skeleton, decrease (or increase). This amplifies the temperature-induced swelling (or shrinkage) observed at macroscopic material scales . The validated multiscale model is used as input for linear thermo-mechanical Finite-Element simulations of structures subjected to sudden temperature changes [2, 4].
The third topic deals with reinforced concrete hinges subjected to eccentric compression. They exhibit a ductile failure behavior . This is analyzed by means of nonlinear three-dimensional Finite Element simulations. The required input parameters are identified based on experimental data from laboratory experiments. Material tests include creep and strength tests of plain concrete specimens subjected to uniaxial compression. Structural tests include centric creep tests and short-term eccentric compression tests of reinforced concrete hinges subjected to serviceability loads. Parameter identification is supported by a multiscale model for tensile failure of concrete and linear-elastic two-dimensional Finite Element simulations . After parameter identification, bearing capacity tests by Schlappal et al.  are simulated. The obtained results agree well with the experimental observations.
Multiscale structural analysis of segmental tunnel rings subjected to ground pressure is the last topic. The structural model combines analytical solutions of the linear theory of slender circular arches with interface models. The latter describe relative rotations as a function of the bending moment and the normal force transmitted across the interfaces between neighboring segments. Both unreinforced and bolted interfaces are analyzed. The interface models account for linear-elastic and ideally-plastic behavior of both concrete and steel. Elastic limits and bearing capacities of segmental tunnel rings are quantified as a function of the coefficient of lateral ground pressure. The simulations are validated by comparing numerical output with results from real-scale bearing capacity tests of segmented tunnel rings. The tests were carried out at Tongji University .
The presented examples underline the benefits resulting from the combination of modern multiscale and multiphysics material modeling, structural analysis, and innovative experiments both at material and structural scales.
 E. Binder, H. Wang, T. Schlappal, J.-L. Zhang, Y. Yuan, B. Pichler, and H.A. Mang. “Bridging the Gap Between Concrete Microstructures and Tunnel Linings”, Advances in Computational Plasticity, Computational Methods in Applied Science, E. Oñate (Editor); Springer International Publishing, 2018, pp. 23-44.
 H. Wang, E. Binder, H.A. Mang, Y. Yuan, and B. Pichler. “Multiscale structural analysis inspired by exceptional load cases concerning the immersed tunnel of the Hong Kong-Zhuhai-Macao Bridge”, Underground Space 3(4), 2018, pp. 252-267.
 H. Wang, Ch. Hellmich, Y. Yuan, H.A. Mang, and B. Pichler. “May reversible water uptake/release by hydrates explain the thermal expansion of cement paste? – Arguments from an inverse multiscale analysis”, Cement and Concrete Research 113, 2018, pp. 13-26.
 R. Díaz, H. Wang, H.A. Mang, Y. Yuan, and B. Pichler. “Numerical analysis of a moderate fire inside a segment of a subway station”, Applied Sciences 8(11), 2018, 2116.
 T. Schlappal, M. Schweigler, S. Gmainer, M. Peyerl, and B. Pichler. “Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments”, Materials and Structures 50, 2017, 244.
 J. Kalliauer, T. Schlappal, H.A. Mang, and B. Pichler. “Parameter identiﬁcation as the basis for Finite Element simulations of Ultimate Limit States of concrete hinges”, Proceedings of the Conference on Computational Modelling of Concrete Structures (EURO-C 2018), G. Meschke, B. Pichler, J. Rots (Editors); Taylor and Francis, 2018, pp. 689-696.
 J.-L. Zhang, T. Schlappal, Y. Yuan, H.A. Mang, and B. Pichler. “The influence of interfacial joints on the structural behavior of segmental tunnel rings subjected to ground pressure”, Tunnelling and Underground Space Technology 84, 2019, pp. 538-556.
Institute of Scientific Computing – Technische Universität Braunschweig | Germany
Plenary Lecture: Inverse bayesian problems as filtering maps
Bayesian updating was originally formulated in terms of probability measures, and is the basis of probabilistic conditioning. Later it was mathematically based on the notion of conditional expectation, which is more general and versatile. It is proposed here that it is also a good basis for numerical approaches, as it allows one to also deal computationally with the – in the Bayesian setting really generic – case that the posterior measure is singular and not absolutely continuous w.r.t. the prior measure, and hence has no density one could sample from by some kind of Markov chain Monte Carlo (MCMC) procedure.
It will be demonstrated that the conditional expectation is based on orthogonal projections, a procedure which translated into numerical computations in a stable way. As the conditional expectation works on random variables, one may use this to construct a new (posterior) random variable (RV), which is a function of the prior or forecast RV and the actual observation, in other words a filter, such that this new RV has the proper Bayesian posterior distribution.
When one attemps to perform all of this numerically, it becomes clear that a number of approximations are necessary so that this becomes a practical procedure. It will be shown that well-known filters as the family of Kálman-like filters, which are based on the Gauss-Markov theorem, as well as variational approaches such as 3D or 4D VAR are some of the simplest examples of such filtering approaches.
Institute of Mechanics, Civil Engineering –Duisberg – Essen University | Germany
Plenary Lecture: Characterization of magneto-electric composites: an algorithmic scale-bridging scheme
Materials which combine two or more ferroic characteristics are known as multiferroics and can exhibit an interaction between electric and magnetic fields.
This magneto-electric (ME) coupling can find applications in sensor technology or in electric field-controlled magnetic data storage devices.
Since most ME single-phase materials show an interaction between electric polarization and magnetization far below room temperature and therefore outside of a technical relevant temperature range, the manufacturing of two-phase composites, consisting of a ferroelectric matrix with magnetostrictive inclusions, becomes important.
They generate the ME coupling at room temperature because of the interaction of their constituents.
We distinguish between the direct and converse ME effect, whereas the direct effect characterizes magnetically induced polarization, where an applied magnetic field yields a deformation of the magneto-active phase which is transferred to the electric phase.
Furthermore, the converse effect characterizes electrically activated magnetization.
Hence, the ME coupling of composite materials significantly depends on the material behavior of both phases as well as on the morphology of the composite’s microstructure.
In this contribution we discuss the modeling of micro-heterogeneous composites with electrically and magnetically active phases, which exhibit as a product property an effective (macroscopic) magneto-electric coupling.
In order to determine the effective properties a homogenization approach, the so-called FE2 method, is performed, which combines via a scale bridging the macro- and microscopic level. In order to predict a realistic coupling behavior we implemented suitable material models on the microscopic level for the individual phases to depict the characteristic hysteresis loops.
J. Schröder. A numerical two-scale homogenization scheme: the FE2 method. In Plasticity and Beyond: Microstructures, Crystal-Plasticity and Phase Transitions, Editors: J. Schröder & K. Hackl, CISM courses and lectures, (2014) , Vol. 550, 1-64, Springer- Verlag.
J. Schröder, M. Labusch, M.-A. Keip. Algorithmic two-scale transition for magneto-electro-mechanically coupled problems. FE2-scheme: Localization and Homogenization. Computer Methods in Applied Mechanics and Engineering (2016), 253-280.
N.A. Spaldin, M. Fiebig. The renaissance of magnetoelectric multiferroics. Materials Science (2005), 391-392.
S.C. Hwang, C.S. Lynch, R.M. McMeeking. Ferroelectric/ferroelastic interactions and a polarization switching model. Acta Metallurgica et Materialia (1995), 2073-2084.
School of Engineering,University of Porto | Portugal
Plenary Lecture: Fracture of polymer composite materials: simulation across the scales
The need to decrease both time and cost of aircraft design and certification relies on the capability to replace physical tests by simulation. This presentation will address the models that have been developed at different length scales to predict inelastic deformation and final failure of polymer composite materials reinforced by unidirectional fibres. The micro-mechanical models proposed are based on the discrete representation of all constituents, fibre, matrix and fibre-matrix interface. Some pitfalls associated with the use of micro-mechanical models will be discussed. Continuum damage mechanics-based models combined with cohesive elements provide the basis for the representation of the failure mechanisms at the meso-scale. The capability of a unique modelling strategy to simulate failure of specimens with different levels of complexity will be addressed. Finally, macro-models, based on Finite Fracture Mechanics, will be described and applied to the uncertainty quantification required in aircraft structural design.
School of Aerospace Engineering, Tsinghua University, Beijing | China
Plenary Lecture: Computation-based design polymer composite for shock wave energy attenuation
To prevent biology body vulnerated from high frequency and overpressure blast wave, the polymer-based composite material is designed and manufactured as the layers of protective meta-material through developing multiscale theoretical models and computations, as well as related experiments. There are three key characteristics with attenuating energy in the material, which are viscoelasticity, microstructure resonance and stress wave scattering. In the analysis, the coarse-grained molecular dynamics model (CG-MD) is developed and chemical structure is optimized by changing the ratio of soft and hard chain segments at micron scale. The storage modulus and loss modulus are designed based on frequency function, in order to let material has frequency selection character and weaken harmful portion of shock wave. The extended finite element (XFEM) is used to evaluate the attenuation property during wave propagation in the material at mesoscale. The microstructure volume fraction and configuration are designed to induce geometrical and viscoelastic energy scatter and attenuation. The fluid-solid coupling FEM model is developed to simulate shock wave propagating into the biology body at macroscale. To validate the polymer composite material, there are a few kinds of multiscale experiments are conducted by AFM, DMA, Ultrasonic and SHPB, as well as the animal experiments in shock tube to optimize the material and verify the theoretical and numerical models. This is a closed-link research work, which starts from the mechanics target to drive the polymer composite material design, the data of material behavior experiments and animal protection experiments in shock tube are used to re-design material and re-checkout theory and computation works. This is also an intersect discipline researches include wave dynamics, high molecular material and biomedicine.
Keywords: Coarse-grained molecular dynamics; Polymer composite; Shock wave; Energy attenuation; XFEM
Zhanli Liu, J. Oswald, T. Belytschko, XFEM modeling of ultrasonic wave propagation in polymer matrix particulate/fibrous composites, Wave Motion, 2013, 50:389–401
Wang CY, Liu ZL, Gao LJ, Xu DD, Zhuang Z, Analytical and numerical modeling on resonant response of particles in polymer matrix under blast wave, Computational Materials Science, 2017, 140:70-81