[IN REVIEW] Refactor EAS to handle NonLinearElastic

CHANGELOG.md

@@ -84,6 +84,12 @@ SPDX-License-Identifier: LGPL-3.0-or-later
   ([#337](https://github.com/ikarus-project/ikarus/pull/337))
 - `Observers` and `Observables` are replaced with `Broadcasters` and `Listeners`. Existing loggers work almost the same.
  A noteworthy difference is that, the Broadcaster (e.g. a nonlinear solver) has to be registered to a Listener (e.g. a logger) with `logger.subscribeTo(solver)` ([#349](https://github.com/ikarus-project/ikarus/pull/349))
+- Refactor EAS to handle NonLinearElastic ([#325](https://github.com/ikarus-project/ikarus/pull/325))
+    - This also includes a new interface method in the `Mixin` called `updateState` with the respective `impl()` function.
+    - For EAS, `updateStateImpl()` is used to update the internal variable `alpha_` in a nonlinear analysis.
+    - Missing functions like `getStress` and `materialTangentFunction` are added to `LinearElastic` and `NonLinearElastic`, respectively.
+    - `EnhancedAssumedStrains` class now takes a struct denoting the enhanced strain type as a template argument, which implements the
+      enhanced strain value, its first and second derivatives w.r.t the displacements and the internal variable `alpha_`.
 
 ## Release v0.4 (Ganymede)
 

docs/literature.bib

@@ -107,6 +107,17 @@ @incollection{wunderlich_strategies_1981
 	pages = {63--89},
 }
 
+@article{bischoffShearDeformableShell1997b,
+  title = {{Shear deformable shell elements for large strains and rotations}},
+  author = {Bischoff, M. and Ramm, E.},
+  year = {1997},
+  journal = {International Journal for Numerical Methods in Engineering},
+  volume = {40},
+  number = {23},
+  pages = {4427-4449},
+  doi = {10.1002/(SICI)1097-0207(19971215)40:23<4427::AID-NME268>3.0.CO;2-9},
+}
+
 @article{riks_application_1972,
 	title = {The {Application} of {Newton}’s {Method} to the {Problem} of {Elastic} {Stability}},
 	volume = {39},
@@ -210,6 +221,14 @@ @book{bonet2008nonlinear
 	doi  = {https://doi.org/10.1017/CBO9780511755446}
 }
 
+@phdthesis{bieberLockingHourglassingNonlinear2024,
+  title = {Locking and Hourglassing in Nonlinear Finite Element Technology},
+  author = {Bieber, Simon},
+  year = {2024},
+  address = {Stuttgart},
+  langid = {english},
+  school = {Institut f{\"u}r Baustatik und Baudynamik, Universit{\"a}t Stuttgart}
+}
 
 @book{trustregion,
 	author = {Conn, Andrew R. and Gould, Nicholas I. M. and Toint, Philippe L.},

ikarus/finiteelements/ferequirements.hh

@@ -204,7 +204,7 @@ auto scalarAffordance(VectorAffordance affordanceV) {
 namespace AffordanceCollections {
   inline constexpr AffordanceCollection elastoStatics(ScalarAffordance::mechanicalPotentialEnergy,
                                                       VectorAffordance::forces, MatrixAffordance::stiffness);
-}
+} // namespace AffordanceCollections
 
 /**
  * \class FERequirements

ikarus/finiteelements/mechanics/CMakeLists.txt

@@ -1,6 +1,6 @@
 # SPDX-FileCopyrightText: 2021-2025 The Ikarus Developers [email protected]
 # SPDX-License-Identifier: LGPL-3.0-or-later
-add_subdirectory(eas)
+add_subdirectory(strainenhancements)
 add_subdirectory(loads)
 add_subdirectory(materials)
 # install headers
@@ -12,7 +12,6 @@ install(
         kirchhoffloveshell.hh
         membranestrains.hh
         loads.hh
-        easvariants.hh
         truss.hh
   DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/ikarus/finiteelements/mechanics
 )