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• Characterization of magneto-electric composites: product properties and multiscaling

  J. Schröder, M. Labusch, M. Keip

  Videos of Plenary Lectures presented at the XIII International Conference on Computational Plasticity (COMPLAS 2015).

  
  

  Abstract

  Coupling between electric and magnetic fields enables smart new devices and may find application in sensor technology and data storage. Materials showing magneto-electric (ME) coupling properties combine two or more ferroic characteristics and are known as multiferroics. Since singlephase materials show an interaction between polarization and magnetization at very low temperatures and at the best a too small ME coefficient at room temperature, composite materials become important. These ME composites consist of magnetically and electrically active phases and generate the ME coupling as a strain-induced product property. It has to be emphasized that for each of the two phases the ME coupling modulus is zero and the overall ME modulus is generated by the interaction between both phases. Here we distinguish between the direct and converse ME effect. 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 electro-active phase. As a result, a strain-induced polarization in the electric phase is observed. On the other hand, the converse effect characterizes electrically activated magnetization. Several experiments on composite multiferroics showed remarkable ME coefficients that are orders of magnitudes higher than those of single-phase materials. Due to the significant influence of the microstructure on the ME effect, we derived a two-scale finite element (FE2) homogenization framework, which allows for the consideration of microscopic morphologies. A further major influence on the overall ME properties is the polarization state of the ferroelectric phase. With this in mind, a material model is implemented that considers the switching behavior of the spontaneous polarization and enables a more exact comparison to experimental measurements.

  Abstract
  Coupling between electric and magnetic fields enables smart new devices and may find application in sensor technology and data storage. Materials showing magneto-electric [...]

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• Computational design of engineering materials: an integrated approach for multiscale topological structure optimization

  J. Oliver, J. Cante, A. Ferrer

  Videos of Plenary Lectures presented at the XIII International Conference on Computational Plasticity (COMPLAS 2015).

  
  

  Abstract

  Multiscale topological material design, aiming at obtaining optimal distribution of the material at several scales in structural materials is still a challenge. In this case, the cost function to be minimized is placed at the macro-scale (compliance function), but the design variables (material distribution) lie at both the macro-scale and the micro-scale. The large number of involved design variables and the multi-scale character of the analysis, resulting into a multiplicative cost of the optimization process, often make such approaches prohibitive, even if in 2D cases. In this work, an integrated approach for multi-scale topological design of structural linear materials is proposed. The approach features the following properties: The “topological derivative” is considered the basic mathematical tool to be used for the purposes of determining the sensitivity of the cost function to material removal. In conjunction with a level-set-based “algorithm” it provides a robust and well-founded setting for material distribution optimization. The computational cost associated to the multiscale optimization problem is dramatically reduced by resorting to the concept of the online/offline decomposition of the computations. A “Computational Vademecum” containing the micro-scale solution for the topological optimization problem in a RVE for a large number of discrete macroscopic stress-states, is used for solving that problem by simple consultation. Coupling of the optimization problem at both scales is solved by a simple iterative “fixedpoint” scheme, which is found to be robust and convergent. The proposed technique is enriched by the concept of “manufacturability”, i.e.: obtaining sub-optimal solutions of the original problems displaying homogeneous material over finite sizes domains at the macrostructure: the “structural components”. The approach is tested by application to some engineering examples, involving minimum compliance design of material and structure topologies, which show the capabilities of the proposed framework.

  Abstract
  Multiscale topological material design, aiming at obtaining optimal distribution of the material at several scales in structural materials is still a challenge. In this case, [...]

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• Computational inelasticity at different scales - FE technology and beyond

  A. Radermacher, S. Reese, J. Kochmann, S. Wulfinghoff

  Videos of Plenary Lectures presented at the XIII International Conference on Computational Plasticity (COMPLAS 2015).

  
  

  Abstract

  The necessity to provide physically reasonable and mathematically sound descriptions of mechanical behaviour at different scales is without discussion. Nevertheless, for engineering design quick estimations of important quantities such as stresses and strain are needed. This is not even enough. At a larger scale, information about the overall behaviour of complex systems has to be supplied. For this reason, we need to develop computational methods which on the one hand enable a detailed material description, on the other hand allow the bridging to coarser scales without losing too much information. In the present contribution, methods such as the phase field method are combined with FE technology, and, FE technology is combined with model reduction in order to reach this goal.

  Abstract
  The necessity to provide physically reasonable and mathematically sound descriptions of mechanical behaviour at different scales is without discussion. Nevertheless, for engineering [...]

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• Isogeometric Phase-field Modeling of Brittle and Ductile Fracture

  M. Borden, T. Hughes, C. Landis

  Videos of Plenary Lectures presented at the XIII International Conference on Computational Plasticity (COMPLAS 2015).

  
  

  Abstract

  The phase-field approach to predicting crack initiation and propagation relies on a damage accumulation function to describe the phase, or state, of fracturing material. The material is in some phase between either completely undamaged or completely cracked. A continuous transition between the two extremes of undamaged and completely fractured material allows cracks to be modeled without explicit tracking of discontinuities in the geometry or displacement fields. A significant feature of these models is that the behavior of the crack is completely determined by a coupled system of partial differential equations. There are no additional calculations needed to determine crack nucleation, bifurcation, and merging. In this presentation, we will review our current work on applying second-order and fourth-order phase-field models to quasi-static and dynamic fracture of brittle and ductile materials, within the framework of isogeometric analysis. We will present results for several two- and three-dimensional problems to demonstrate the ability of the phase-field models to capture complex crack propagation patterns. 

  Abstract
  The phase-field approach to predicting crack initiation and propagation relies on a damage accumulation function to describe the phase, or state, of fracturing material. The [...]

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• Plasticity for crushable granular materials via DEM

  A. Gens, M. Ciantia, M. Arroyo

  Videos of Plenary Lectures presented at the XIII International Conference on Computational Plasticity (COMPLAS 2015).

  
  

  Abstract

  The mechanical behavior of granular materials is characterized by strong non-linearity and irreversibility. These properties have been described by a variety of constitutive models, a large proportion of them are developed within an elasto-plastic framework. On top of the usual grain rearrangement mechanism, the presence of crushable grains adds one extra source of irreversibility to granular materials, a source that is frequently associated with instabilities. In his context, it is very instructive to obtain incremental responses of crushable granular materials but the experimental difficulties are formidable. This contribution describes a procedure to obtain incremental responses of this type of materials using the discrete element method. The DEM model is calibrated to represent Fontaineblau sand. The resulting granular assembly is incrementally tested starting from an initial oedometric (no lateral deformation) condition. The incremental behavior of the numerical models is studied by performing axisymmetric stress probes of equal magnitude but varying direction. Recent advances to enhance the efficiency of the numerical procedure are adopted. The cascading nature of crushing events complicates stress probe control but damping is effectively used to overcome this problem. The contribution of grain crushing to the incremental irreversible strain is identified and separately measured. Three components of the incremental strains are distinguished: elastic, plastic-unbreakable and plastic-crushing. Particular focus is placed on the effects of crushing on the direction of plastic flow.

  Abstract
  The mechanical behavior of granular materials is characterized by strong non-linearity and irreversibility. These properties have been described by a variety of constitutive [...]

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• Linking Process, Structure, and Property in Additive Manufacturing Applications through advanced materials modeling.

  W. Liu, O. Kafka, W. Xiong, Z. Liu, W. Yan, J. Smith, P. Cheng

  Videos of Plenary Lectures presented at the XIII International Conference on Computational Plasticity (COMPLAS 2015).

  
  

  Abstract

  Additive manufacturing (AM) processes have the ability to build complex geometries from a wide variety of materials. A popular approach for metal-based AM processes involves the deposition of material particles on a substrate followed by fusion of those particles together using a high intensity heat source, e.g. a laser or an electron beam, in order to fabricate a solid part. These methods are of high priority in engineering research, especially in applications for the energy, health, and defense sectors. The primary reasons behind the rapid growth in interest for AM include: (1) the ability to create complex geometries which are otherwise cost-prohibitive or difficult to manufacture, (2) increased freedom of material composition design through the adjustment of the ratios of the composing powders, (3) a reduction in wasted materials, and (4) the fast, low-volume, production of prototype and functional parts without the additional tooling and die requirements of conventional manufacturing methods. However, the highly localized and intense nature of these processes elicits many experimental and computational challenges. These challenges motivate a strong need for computational investigation, as does the need to more accurately characterize the response of parts built using AM. The present work will discuss these challenges and methods for creating multiscale material models that account for the complex phenomena observed in the AM production environment. The linkage between process, structure, and property of AM components, e.g., anisotropic plastic behavior combined anisotropic microstructural descriptors afforded through enhanced data compression techniques, will also be discussed. 

  Abstract
  Additive manufacturing (AM) processes have the ability to build complex geometries from a wide variety of materials. A popular approach for metal-based AM processes involves [...]

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