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manual-cohesive_elements_insertion.tex
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manual-cohesive_elements_insertion.tex
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For cohesive material, \akantu has a pre-defined material selector to
assign the first cohesive material by default to the cohesive elements
which is called
\code{DefaultMaterialCohesiveSelector} and it inherits its properties from
\code{DefaultMaterialSelector}. Multiple cohesive materials can be assigned
using mesh data information (for more details,
see \ref{intrinsic_insertion}).
\subsection{Insertion of Cohesive Elements}
Cohesive elements are currently compatible only with static simulation
and dynamic simulation with an explicit time integration scheme (see
section~\ref{ssect:smm:expl-time-integr}). They do not have to be
inserted when the mesh is generated (intrinsic) but can be added
during the simulation (extrinsic). At any time during the simulation,
it is possible to access the following energies with the relative
function:
\begin{cpp}
Real Ed = model.getEnergy("dissipated");
Real Er = model.getEnergy("reversible");
Real Ec = model.getEnergy("contact");
\end{cpp}
A new model have to be call in a very similar way that the solid
mechanics model:
\begin{cpp}
SolidMechanicsModelCohesive model(mesh);
model.initFull(SolidMechanicsModelCohesiveOptions(_explicit_lumped_mass, true));
\end{cpp}
\subsubsection{Extrinsic approach \label{extrinsic_insertion}}
The dynamic insertion of extrinsic cohesive elements should be initialized
in the following way:
\begin{cpp}
model.updateAutomaticInsertion();
\end{cpp}
During the simulation, stress has to be checked along each facet in
order to insert cohesive elements where the stress criterion is
reached. This check is performed by calling the
method \code{checkCohesiveStress}, as example before each step
resolution:
\begin{cpp}
model.checkCohesiveStress();
model.solveStep();
\end{cpp}
In case the extrinsic cohesive method is used in the implicit solution
scheme, the cohesive elements are inserted one by one, starting from
the highest locally stressed element (more precisely, the most
stressed element per material type is inserted). When a cohesive
element is inserted, the new equilibrated solution of the last
incremental step is sought. Then, the
method \code{checkCohesiveStress} is called again to check if new
cohesive elements have to be inserted. When the insertion is
terminated, the solution of the incremental loading step is stored,
and the simulation can advance to the next incremental loading step.
This procedure is managed by the function \code{solveStepCohesive}
(for more details see \ref{sect:smm:static})
The area where stresses are checked and cohesive elements inserted can
be limited using the method \code{limitInsertion} during
initialization. As example, to limit insertion in the range $[-1.5,
1.5]$ in the $x$ direction:
\begin{cpp}
model.limitInsertion(_x, -1.5, 1.5);
model.updateAutomaticInsertion();
\end{cpp}
Additional restrictions with respect to $y$ and $z$ directions can be added as well.
\subsubsection{Intrinsic approach \label{intrinsic_insertion}}
Intrinsic cohesive elements are inserted in the mesh with the method
\code{insertIntrinsicElements}. Similarly, the range of insertion can me limited
with \code{limitInsertion}. As example with a static simulation,
\begin{cpp}
model.limitInsertion(_x, -1.5, 1.5);
model.insertIntrinsicElements();
\end{cpp}
Mesh data information becomes vital to the insertion of cohesive
elements along surface with more sophisticated geometry or when
multiple cohesive materials are wanted. To do so, cohesive elements
can be inserted along a specific group of surface elements identified
in a GMSH geometry file. This can be achieved with the material
selector (see section~\ref{sect:smm:materialselector}), in the input
file specify the name of these physical groups in the corresponding
cohesive materials, and call these material in the \textit{mesh
parameters} section. As example, with two physical surfaces named
\textit{weak\_interface} and \textit{strong\_interface} defined in the GMSH
geometry file:
\begin{cpp}
...
material %\emph{cohesive\_constitutive\_law}% [
name = weak_interface
sigma_c = $value$
...
]
material %\emph{cohesive\_constitutive\_law}% [
name = strong_interface
sigma_c = $value$
...
]
mesh parameters [
cohesive_surfaces = weak_interface,strong_interface
]
\end{cpp}
In this case, there is no need to call \code{insertIntrinsicElements} anymore
since the insertion of cohesive elements along physical surfaces is performed
automatically during \code{initFull} call.

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