High-performance hierarchically parallel multiscale framework for modeling heterogeneous materials

Heterogeneous multiscale materials are present in our everyday lives, embodied in engineered systems such as filled and layered composites, and in nature as soils and layered rock formations. The overall behavior of these materials is heavily influenced by the widely ranging size, shape, distribution, and material property contrasts of their microscale constituents. Understanding how changes in these microstructure parameters affects the overall behavior of the material is important to optimal design and safety assessment of novel materials. Because of the wide range of spatial scales, Direct Numerical Modeling (DNM) of such composite systems is often too computationally expensive, even for today’s super computers. Therefore, we have developed a hierarchically parallel numerical framework based on the Generalized Theory of Computational Homogenization (GTCH). The GTCH assumes a separation of the macro- and microscales and links the overall macroscopic response to the microscale response of a Representative Unit Cell through the variational energy equivalence (Hill’s Lemma). No assumption is made on the form the macroscopic response, and the response is governed purely by the interaction of the microscale constituents which are generally well understood. In this way, the GTCH numerical framework provides a pathway towards predictive simulation and design of novel material systems. Wepresent a verification study of the multiscale solver against DNM simulation and show excellent agreement with a reduction in the total number of degrees of freedom required by the multiscale method to achieve an equivalent accuracy. In addition, we present results from highly resolved multiscale simulations of failure of engineering-scale structures consisting of particle reinforced composites or reinforced adhesive layers. Finally, we demonstrate the high-performance aspects of the hierarchically parallel numerical framework by a computational scaling study up to tens of thousands of computing cores

Fully coupled multiscale modeling of cohesive failure in heterogeneous interfaces using high performance computing

Multiscale interfaces are prevalent throughout engineering design and application, often in the form of layered composites and adhesive joints. Most modern adhesives are highly heterogeneous, containing a wide range of sizes, shapes, and material properties of reinforcing constituents. Predicting how the size, shape, orientation, and distribution of the reinforcing particles change the failure response of the bonded structure is important for design and safety assessment. Using Direct Numerical Modeling to predict the failure of engineering-scale bonded structures is often too computationally expensive, even for today’s supercomputers. Therefore, we have developed a hierarchically parallel numerical framework using Computational Homogenization (CH) to compute the multiscale failure response of heterogeneous interfaces in the 3D finite strain setting. The CH framework assumes a separation scales, and locally attaches a Representative Unit Cell (RUC) of the microstructure to each macroscopic point on the interface. The response of the different scales is linked through the variational energy equivalence (Hill’s Lemma) for interfaces. The macroscopic cohesive law is thereby computationally derived with no assumption of its functional form. We present three-dimensional microscale simulations that resolve the large range of spatial scales, from the failure-zone thickness up to the size of the RUC, in damage mechanics problems of particle reinforced adhesives. We show that resolving this wide range of scales in complex three-dimensional heterogeneous morphologies is essential to apprehend fracture characteristics. Moreover, we show that computations that resolve the essential physical length-scales of the problem capture the particle size-effect in fracture toughness, for example. These simulations are computationally expensive and highlight the need for high-performance computing. To overcome the large computational burden of modeling the failure of bonded systems, we have developed a verified, highly scalable, hierarchically parallel client-server CH framework that uses our high-performance finite element solver to simultaneously compute both the macro- and microscales. We present fully coupled multiscale simulations resolving from O(10) nm to O(10) mm (O(106) length scales) requiring over 1 billion elements computed using fewer than 2000 processing cores. Fully coupled multiscale simulations of interfacial failure including matrix tearing and particle-matrix debonding are also presented

Effects of biofilm heterogeneity on the apparent mechanical properties obtained by shear rheometry

Rheometry is an experimental technique widely used to determine the mechanical properties of biofilms. However, it characterizes the bulk mechanical behavior of the whole biofilm. The effects of biofilm mechanical heterogeneity on rheometry measurements are not known. We used laboratory experiments and computer modeling to explore the effects of biofilm mechanical heterogeneity on the results obtained by rheometry. A synthetic biofilm with layered mechanical properties was studied, and a viscoelastic biofilm theory was employed using the Kelvin-Voigt model. Agar gels with different concentrations were used to prepare the layered, heterogenous biofilm, which was characterized for mechanical properties in shear mode with a rheometer. Both experiments and simulations indicated that the biofilm properties from rheometry were strongly biased by the weakest portion of the biofilm. The simulation results using linearly stratified mechanical properties from a previous study also showed that the weaker portions of the biofilm dominated the mechanical properties in creep tests. We note that the model can be used as a predictive tool to explore the mechanical behavior of complex biofilm structures beyond those accessible to experiments. Since most biofilms display some degree of mechanical heterogeneity, our results suggest caution should be used in the interpretation of rheometry data. It does not necessarily provide the “average” of the mechanical properties of the entire biofilm if the sample is vertically stratified

Multimodální kontrastní látky umožňující snímání pH na podkladě organickými molekulami funkcionalizovaných zlatých nanoslupek s manganato-zinečnato feritovým jádrem

Highly complex nanoparticles combining multimodal imaging with the sensing of physical properties in biological systems can considerably enhance biomedical research, but reports demonstrating the performance of a single nanosized probe in several imaging modalities and its sensing potential at the same time are rather scarce. Gold nanoshells with magnetic cores and complex organic functionalization may offer an efficient multimodal platform for magnetic resonance imaging (MRI), photoacoustic imaging (PAI), and fluorescence techniques combined with pH sensing by means of surface-enhanced Raman spectroscopy (SERS). In the present study, the synthesis of gold nanoshells with Mn-Zn ferrite cores is described, and their structure, composition, and fundamental properties are analyzed by powder X-ray diffraction, X-ray fluorescence spectroscopy, transmission electron microscopy, magnetic measurements, and UV-Vis spectroscopy. The gold surface is functionalized with four different model molecules, namely thioglycerol, meso-2,3-dimercaptosuccinate, 11-mercaptoundecanoate, and (11-mercaptoundecyl)-N,N,N-trimethylammonium bromide, to analyze the effect of varying charge and surface chemistry on cells in vitro. After characterization by dynamic and electrophoretic light scattering measurements, it is found that the particles do not exhibit significant cytotoxic effects, irrespective of the surface functionalization. Finally, the gold nanoshells are functionalized with a combination of 4-mercaptobenzoic acid and 7-mercapto-4-methylcoumarin, which introduces a SERS active pH sensor and a covalently attached fluorescent tag at the same time. H-1 NMR relaxometry, fluorescence spectroscopy, and PAI demonstrate the multimodal potential of the suggested probe, including extraordinarily high transverse relaxivity, while the SERS study evidences a pH-dependent spectral response.Vysoce komplexní nanočástice kombinující multimodální zobrazování se snímáním fyzikálních vlastností v biologických systémech mohou výrazně zlepšit biomedicínský výzkum. Zlaté nanoslupky s magnetickými jádry a komplexní organickou funkcionalizací mohou nabídnout účinnou multimodální platformu pro zobrazování magnetickou rezonancí (MRI), fotoakustické zobrazování (PAI) a fluorescenční techniky kombinované se snímáním pH pomocí povrchově zesílené Ramanovy spektroskopie (SERS). V této studii je popsána syntéza zlatých nanoslupek s Mn-Zn feritovými jádry, a také jejich struktura, složení a základní vlastnosti. Zlatý povrch byl funkcionalizován čtyřmi různými modelovými molekulami, jmenovitě thioglycerolem, meso-2,3-dimerkaptosukcinátem, 11-merkaptoundekanoátem a (11-merkaptoundecyl)-N,N,N-trimethylamoniumbromidem. Bylo zjištěno, že částice nevykazují významné cytotoxické účinky, bez ohledu na funkcionalizaci povrchu. Nakonec byly zlaté nanoslupky funkcionalizovány kombinací kyseliny 4-merkaptobenzoové a 7-merkapto-4-methylkumarinu. NMR relaxometrie, fluorescenční spektroskopie a PAI demonstrují multimodální potenciál navrhované sondy, včetně mimořádně vysoké příčné relaxivity, zatímco studie SERS potvrzuje spektrální odezvu závislou na pH