Cracks in complex materials: varifold-based variational description
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Cracks in complex materials: varifold-based variational description. Paolo Maria Mariano. University of Florence - Italy. Some prominent cases. Y. Wei, J. W. Hutchinson, JMPS , 45, 1253-1273, 1997 (materials with strain-gradient plastic effects)

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Cracks in complex materials: varifold-based variational description

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Cracks in complex materials varifold based variational description

Cracks in complex materials: varifold-based variational description

Paolo Maria Mariano

University of Florence - Italy


Some prominent cases

Some prominent cases

  • Y. Wei, J. W. Hutchinson, JMPS, 45, 1253-1273, 1997 (materials with strain-gradient plastic effects)

  • R. Mikulla, J. Stadler, F. Krul, K.-H. Trebin, P. Gumbsch, PRL, 81, 3163-3166, 1998 (quasicrystals)

  • C. C. Fulton, H. Gao, Acta Mater., 49, 2039-2054, 2001 (ferroelectrics)

  • C. M. Landis, JMPS, 51, 1347-1369, 2003 (ferroelectrics)

  • F. L. Stazi, ECCOMAS prize lecture, 2003 (microcracked bodies)

Tentatives for a non-completely variational unified description

  • PMM, Proc. Royal Soc. London A, 461, 371-395, 2005

  • PMM, JNLS, 18, 99-141, 2008


Point of view

Point of view

  • I follow here a variational view on fracture mechanics

  • As in G. Francfort and J.-J. Marigo’s proposal, deformation and crack are distinct but connected entities

  • In contrast to that proposal, fractures are represented by special measures: curvature varifolds with boundary

  • Griffith’s energetic description of fracture is evolved up to a form including effects due to the curvature of the crack lateral margins, the tip, and possible corners

  • Material complexity is described in terms of the general model-building framework of the mechanics of complex materials

  • Even possible non-local interactions among microstructures could appear in the energy considered

  • Miminizers of that energy are lists of deformation, descriptors of the material morphology, families of varifolds: pertinent existence theorems are shown

  • The jump set of the minimizing deformation is contained in the support of the minimizing varifold


Cracks in complex materials varifold based variational description

Minimality of the energy is required over a class of bodies parameterized by families of varifolds and classes of fields


Consequences

Consequences

  • Crack nucleation can be described without additional failure criterion: it is intrinsic to the variational treatment

  • Partially open cracks can be described

  • The list of balance equations coming from the first variation is enriched: such equations include curvature-dependent terms

  • Nucleation of macroscopic line defects in front of the crack tip is naturally described

  • Interaction with the crack pattern of microstructure line defects, and microstructure domain patterns can be accounted for by appropriate choices of functional spaces

  • Energy can be attributed to the tip and corners

Remark

The choice of a function space as ambient for minimizers is a constitutive prescription which can be considered analogous to the explicit assignment of the energy


Ingredients 1

Ingredients - 1

  • A reference macroscopic place

  • Standard deformations

  • Descriptor map of the inner material morphology

    belonging to a function space equipped with a functional

  • which is l.s.c. in L1

  • is compact for the L1 convergence for every k

  • s. t. if

  • and in L1

  • Example:


Cracks in complex materials varifold based variational description

Examples of descriptors of the inner material morphology

Polymer chain

n

n

n  n

First moment of the distribution of n

Porous body

Slip systems generating plastic flows


Ingredients 2

Ingredients - 2

  • A fiber bundle with typical fiber the Grassmanian of k-planes over the reference place, k=1,…, n-1,

  • Non-negative Radon measures V over such a bundle: varifolds

  • A subclass defined over

  • Densities s.t.

    defining rectifiable varifolds

  • Special case. Densities with integer values: integer rectifiable varifolds

  • MassM(V) of a varifold: over the set where V is defined


Ingredients 2 sequel

Ingredients – 2 sequel

Stratified families

k = 2, … , n-1


Why stratified varifolds

Why stratified varifolds?

Approximate tangent spaces describe locally the crack patterns.The star of directions in a point collects all possibilities for the possible nucleation of a crack.

Stratified families of varifolds:V2-support is C,V2-support is the whole C,V1-support is the tip alone.


The energy

The energy

  • Cases

  • the latter being the n-vector containing 1 and all minors of the spatial derivative of n


Some reasons for the curvature

Some reasons for the curvature

  • Rupture due to bending of material bonds induces related configurational effects measured by the curvature

  • Surface microstructural effects – a coarse account of them

  • Analytical regularization


Functional choices for the deformation 1

Functional choices for the deformation - 1


A closure theorem

A closure theorem


Ingredients 3

Ingredients - 3

: a. e. approximately differentiable map

Assume

Graph

  • n-current orientation over the graph

  • Mass

Boundary current


Functional choices for the deformation 2

Functional choices for the deformation - 2


Another closure theorem

Another closure theorem


Existence for extended weak diffeomorphisms

Existence for extended weak diffeomorphisms

  • Assumptions on the energy density


Sequel

Sequel

: the space hosting minimizers


An existence theorem

An existence theorem


Existence for sbv diffeomorphisms

Existence for SBV-diffeomorphisms

Assumptions about the energy: H1-1 remains the same,

H2-1 changes in


Cracks in complex materials varifold based variational description

: the space hosting minimizers

The relevant existence theorem follows


Another case

Another case

The interaction between deformation and microstructure depends on the whole set of minors of Du and Dn


Assumptions about the energy

Assumptions about the energy


Cracks in complex materials varifold based variational description

: the space hosting minimizers

  • The microstructure may create domains

  • The closure theorem for SBV-diff implies that the energy two slides ago is L1-lower semicontinuous on

The relevant existence theorem follows


Remarks

Remarks

  • The comparison varifold can be even null – there is then possible nucleation

  • Stratified families of varifolds allow us to distribute energy over submanifolds with different dimensions (the tip, its corners, etc)

  • No external failure criterion has to be assigned a priori: energy and boundary conditions determine the minimizing varifold, then the crack pattern


Cracks in complex materials varifold based variational description

Details in

  • M. Giaquinta, P.M.M., G. Modica, DCDS-A, 28, 519-537, 2010 “Nirenberg’s issue”

  • See also (for the varifold-based description of fractures in simple bodies)

  • M. Giaquinta, P.M.M., G. Modica, D. Mucci, Physica D, 239, 1485-1502, 2010

  • P.M.M., Rend. Lincei, 21, 215-233, 2010

  • M. Giaquinta, P.M.M., G. Modica, D. Mucci, Tansl. AMS, 229, 97-117, 2010


Cracks in complex materials varifold based variational description

A model is a ‘speech’ about the nature, a linguistic structure over empirical data. It is conditioned by them but, at the same time, it transcends them.


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