286 research outputs found
Subdivision Shell Elements with Anisotropic Growth
A thin shell finite element approach based on Loop's subdivision surfaces is
proposed, capable of dealing with large deformations and anisotropic growth. To
this end, the Kirchhoff-Love theory of thin shells is derived and extended to
allow for arbitrary in-plane growth. The simplicity and computational
efficiency of the subdivision thin shell elements is outstanding, which is
demonstrated on a few standard loading benchmarks. With this powerful tool at
hand, we demonstrate the broad range of possible applications by numerical
solution of several growth scenarios, ranging from the uniform growth of a
sphere, to boundary instabilities induced by large anisotropic growth. Finally,
it is shown that the problem of a slowly and uniformly growing sheet confined
in a fixed hollow sphere is equivalent to the inverse process where a sheet of
fixed size is slowly crumpled in a shrinking hollow sphere in the frictionless,
quasi-static, elastic limit.Comment: 20 pages, 12 figures, 1 tabl
Compaction of Quasi One-Dimensional Elastoplastic Materials
Insight in the crumpling or compaction of one-dimensional objects is of great
importance for understanding biopolymer packaging and designing innovative
technological devices. By compacting various types of wires in rigid
confinements and characterizing the morphology of the resulting crumpled
structures, here we report how friction, plasticity, and torsion enhance
disorder, leading to a transition from coiled to folded morphologies. In the
latter case, where folding dominates the crumpling process, we find that
reducing the relative wire thickness counter-intuitively causes the maximum
packing density to decrease. The segment-size distribution gradually becomes
more asymmetric during compaction, reflecting an increase of spatial
correlations. We introduce a self-avoiding random walk model and verify that
the cumulative injected wire length follows a universal dependence on segment
size, allowing for the prediction of the efficiency of compaction as a function
of material properties, container size, and injection force.Comment: 7 pages, 6 figure
Scaling of the buckling transition of ridges in thin sheets
When a thin elastic sheet crumples, the elastic energy condenses into a
network of folding lines and point vertices. These folds and vertices have
elastic energy densities much greater than the surrounding areas, and most of
the work required to crumple the sheet is consumed in breaking the folding
lines or ``ridges''. To understand crumpling it is then necessary to understand
the strength of ridges. In this work, we consider the buckling of a single
ridge under the action of inward forcing applied at its ends. We demonstrate a
simple scaling relation for the response of the ridge to the force prior to
buckling. We also show that the buckling instability depends only on the ratio
of strain along the ridge to curvature across it. Numerically, we find for a
wide range of boundary conditions that ridges buckle when our forcing has
increased their elastic energy by 20% over their resting state value. We also
observe a correlation between neighbor interactions and the location of initial
buckling. Analytic arguments and numerical simulations are employed to prove
these results. Implications for the strength of ridges as structural elements
are discussed.Comment: 42 pages, latex, doctoral dissertation, to be submitted to Phys Rev
A model for the fragmentation kinetics of crumpled thin sheets
As a confined thin sheet crumples, it spontaneously segments into flat facets
delimited by a network of ridges. Despite the apparent disorder of this
process, statistical properties of crumpled sheets exhibit striking
reproducibility. Experiments have shown that the total crease length accrues
logarithmically when repeatedly compacting and unfolding a sheet of paper.
Here, we offer insight to this unexpected result by exploring the
correspondence between crumpling and fragmentation processes. We identify a
physical model for the evolution of facet area and ridge length distributions
of crumpled sheets, and propose a mechanism for re-fragmentation driven by
geometric frustration. This mechanism establishes a feedback loop in which the
facet size distribution informs the subsequent rate of fragmentation under
repeated confinement, thereby producing a new size distribution. We then
demonstrate the capacity of this model to reproduce the characteristic
logarithmic scaling of total crease length, thereby supplying a missing
physical basis for the observed phenomenon.Comment: 11 pages, 7 figures (+ Supplemental Materials: 15 pages, 9 figures);
introduced a simpler approximation to model, key results unchanged; added
references, expanded supplementary information, corrected Fig. 2 and revised
Figs. 4 and 7 for clearer presentation of result
Atomistic continuum simulations for nano-indentation and compression of multi-layer graphene
Graphene has attracted a great share of research interest due to its extraordinary electrical, thermal, mechanical, and physical properties. Such spectacular properties of graphene open a wide range potential of applications in electronics, energy storage, composites, and biomedical fields. The mechanical properties of graphene can have a huge impact on its performance in graphene-based devices and thus it is important to study them. But the difficulties in experimental characterization and computational limitations to simulate large graphene sample consisting of billions of atoms makes it a challenging task. Thus, accurate and efficient simulation tools to predict the complex deformation of large graphene samples are needed but are still elusive.
The objective of this thesis is to utilize the atomistic-continuum foliation (AC) model developed by Ghosh and Arroyo (2013) and modified by Upendra Yadav, to reproduce the Nano-indentation experiments accurately. This atomistic - continuum foliation (AC) model enables one to directly reproduce the experimental results, something that was not possible before. Using this model we can study the effects of different variables like adhesion, frictional force, indenter radius and stress concentration which is not possible to obtain from the experiments.
This thesis also includes the simulation results for different surface morphology like wrinkles and ripples generated on the multi-layer graphene samples under uniaxial and biaxial compression for different van der Waals potential, which paves a way to study the multifunctionality and control of crumpling and unfolding of graphene to enhance its performance in graphene-based devices
Rim curvature anomaly in thin conical sheets revisited
This paper revisits one of the puzzling behaviors in a developable cone
(d-cone), the shape obtained by pushing a thin sheet into a circular container
of radius by a distance [E. Cerda, S. Chaieb, F. Melo, and L.
Mahadevan, {\sl Nature} {\bf 401}, 46 (1999)]. The mean curvature was reported
to vanish at the rim where the d-cone is supported [T. Liang and T. A. Witten,
{\sl Phys. Rev. E} {\bf 73}, 046604 (2006)]. We investigate the ratio of the
two principal curvatures versus sheet thickness over a wider dynamic range
than was used previously, holding and fixed. Instead of tending
towards 1 as suggested by previous work, the ratio scales as .
Thus the mean curvature does not vanish for very thin sheets as previously
claimed. Moreover, we find that the normalized rim profile of radial curvature
in a d-cone is identical to that in a "c-cone" which is made by pushing a
regular cone into a circular container. In both c-cones and d-cones, the ratio
of the principal curvatures at the rim scales as ,
where is the pushing force and is the Young's modulus. Scaling
arguments and analytical solutions confirm the numerical results.Comment: 25 pages, 12 figures. Added references. Corrected typos. Results
unchange
Discrete Differential Geometry of Thin Materials for Computational Mechanics
Instead of applying numerical methods directly to governing equations, another approach to computation is to discretize the geometric structure specific to the problem first, and then compute with the discrete geometry. This structure-respecting discrete-differential-geometric (DDG) approach often leads to new algorithms that more accurately track the physically behavior of the system with less computational effort. Thin objects, such as pieces of cloth, paper, sheet metal, freeform masonry, and steel-glass structures are particularly rich in geometric structure and so are well-suited for DDG. I show how understanding the geometry of time integration and contact leads to new algorithms, with strong correctness guarantees, for simulating thin elastic objects in contact; how the performance of these algorithms can be dramatically improved without harming the geometric structure, and thus the guarantees, of the original formulation; how the geometry of static equilibrium can be used to efficiently solve design problems related to masonry or glass buildings; and how discrete developable surfaces can be used to model thin sheets undergoing isometric deformation
Non-smooth developable geometry for interactively animating paper crumpling
International audienceWe present the first method to animate sheets of paper at interactive rates, while automatically generating a plausible set of sharp features when the sheet is crumpled. The key idea is to interleave standard physically-based simulation steps with procedural generation of a piecewise continuous developable surface. The resulting hybrid surface model captures new singular points dynamically appearing during the crumpling process, mimicking the effect of paper fiber fracture. Although the model evolves over time to take these irreversible damages into account, the mesh used for simulation is kept coarse throughout the animation, leading to efficient computations. Meanwhile, the geometric layer ensures that the surface stays almost isometric to its original 2D pattern. We validate our model through measurements and visual comparison with real paper manipulation, and show results on a variety of crumpled paper configurations
Modelling the forming mechanics of engineering fabrics using a mutually constrained pantographic beam and membrane mesh
A method of combining 1-d and 2-d structural finite elements to capture the fundamental mechanical properties of engineering fabrics subject to finite strains is introduced. A mutually constrained pantographic beam and membrane mesh is presented and simple homogenisation theory is developed to relate the macro-scale properties of the mesh to the properties of the elements within the mesh. The theory shows that each of the macro-scale properties of the mesh can be independently controlled. An investigation into the performance of the technique is conducted using tensile, cantilever bending and uniaxial bias extension shear simulations. The simulations are first used to verify the accuracy of the homogenisation theory and then used to demonstrate the ability of the modelling approach in accurately predicting the shear force, shear kinematics and out-of-plane wrinkling behaviour of engineering fabrics
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