Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session B53: Disordered Networks: From Mechanical Properties to FailureInvited
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Sponsoring Units: GSNP GSOFT Chair: J. M. Schwarz Room: BCEC 253C |
Monday, March 4, 2019 11:15AM - 11:51AM |
B53.00001: Experimental study of failure in a granular material Invited Speaker: Axelle Amon Solid amorphous materials, when submitted to large enough stresses, display localization of the deformation. This localization can take several forms from local plastic events to shear-bands formation. I will present recent experimental results showing how those processes occur in a granular material submitted to a biaxial test. |
Monday, March 4, 2019 11:51AM - 12:27PM |
B53.00002: Mechanics of cells in disordered environments Invited Speaker: Chase Broedersz Living cells typically grow and move in a 3D fibrous matrix such as collagen. Macroscopically, these biopolymer matrices exhibit striking nonlinear mechanical responses. At the scale of the cell, the network is highly disordered. The implications of the extreme mechanical response and structural disorder of the matrix for cells embedded in the meshwork remain largely elusive. In fact, it is unknown what the network mechanics looks like from the perspective of such a cell, and it is unclear how the cell interacts with this network at the microscopic scale to sense stfiness and regulate the mechanics of its surrounding matrix. In this talk, I will present our recent theoretical and experimental progress to understand how cells mechanically interface with their environment. Finally, I will discuss how such structured confining environments, which we mimick by using micropatterns, affect cell migration. |
Monday, March 4, 2019 12:27PM - 1:03PM |
B53.00003: Towards a virtual bone lab: multiscale interplay between architecture, complexity, and dynamics Invited Speaker: Jean Carlson Trabecular bone is a flexible, lightweight tissue that exhibits hierarchical mechanisms of fracture resistance across scales. At the mesoscale, it resembles a web of interconnected struts (trabeculae) that erode with age and diseases such as osteoporosis, resulting in increased fracture propensity. Recent ex vivo experiments have indicated that the traditional macroscale diagnostic marker of osteoporosis, bone mineral density (BMD), correlates poorly with bone strength when used as a sole predictor, but that it can explain much of the variation in bone strength when considered in conjunction with architectural features. We introduce a novel approach to modeling trabecular bone that combines network analysis with simulations of mechanical loading and failure, enabling a unique characterization of how bone architecture contributes to robustness and resilience. We generate network models from tomographic images of real human vertebral bone. Weighted edges represent trabeculae and nodes represent branch points where trabeculae meet. We simulate loading and deformation on finite element models in which edges are replaced by beams, resulting in a considerable reduction in computation time in comparison with fine- grained models used for in silico validation. The beam-element analysis facilitates direct comparison of mechanics and topology at multiple scales ranging from that of individual edges (beams) to the network as a whole. In addition, we discuss implications of our work in the context of clinical application, facilitated by advances in data acquisition methods for assessing fine tissue structure, and we highlight future directions for integrating our results into a comprehensive characterization of bone that links its molecular constituents at the nanoscale to its architecture at large. |
Monday, March 4, 2019 1:03PM - 1:39PM |
B53.00004: A quasi-cotinuum appoach for modeling fracture in disordered networked materials: Can small world architectures save the day? Invited Speaker: Ahmed Elbanna The skeleton of many natural and artificial structures may be abstracted as networks of nonlinearly interacting elements. Examples include rubber, gels, soft tissues, and lattice materials. Understanding the multiscale nature of deformation and failure of networked structures hold key for uncovering origins of fragility in many complex systems including biological tissues and enables designing novel materials. However, these processes are intrinsically multiscale and for large scale structures it is computationally prohibitive to adopt a full discrete approach. |
Monday, March 4, 2019 1:39PM - 2:15PM |
B53.00005: Mechanical failure of disordered networks derived from frictional packings Invited Speaker: Estelle Berthier Disordered networks are used widely to study heterogeneous material failure. These structures are inherent to many systems, such as rigid foams or granular materials. In particular, the latter exhibit highly heterogeneous force chain networks that appear to control the response of such media to external perturbations. To characterize these networks, we focus on their mechanical stability. We study the uniaxial response of networks with geometry derived from the force chains observed in granular experiments. We perform experiments on samples created by laser-cutting these networks from acrylic sheets. We find that the mean degree of the network is a control parameter of the failure behavior, which ranges from ductile to brittle. We explain this ductile-brittle transition with rigidity analysis using a frictional (3,3)-pebble game algorithm. We find that the brittle behavior corresponds to the emergence of a percolating rigid cluster occurring at a mean degree close to the isostatic value of a high friction coefficient packing. Moreover, we find that for networks close to the transition point, failure events predominantly occur within the floppy regions between the rigid clusters. To perform an analysis that is not restricted to the networks close to the transition point, we develop a test to study the failure locations. We use a measure taken from network-science tools and capable of identifying likely failure locations in the samples. It consists in comparing the relative importance of the beams of the lattice by studying their geodesic edge betweenness centrality. |
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