FEBio 4.7

New Features:

• Added ability to select reactive plastic damage material as base (elastic) material of reactive viscoelastic materail, enabling viscoplastic damage analyses
• Added C2-smooth option for loadcurves
• Added "volume change" log variable.
• A new body load "moving frame" was added to the solid module that simulates the effects of the model being embedded in a moving frame. A similar feature was added to the fluid module, where the load is called "fluid moving frame".
• Added Quemada viscous fluid formulation
• Added "body force" plot variable.
• Added plot variable for enclosed volume change
• Added plot variable for fluid body force. Improved formulation of stiffness matrix for body forces in fluid and fluid-FSI domains to include stiffness due to variation of fluid velocity. Minor tweaks to fluid-FSI solver.
• Added the mat_axis domain property, which is used to initialize the material point material axis parameter.
• Added option to export nodal reaction forces for explicit solver.
• Added "ideal gas pressure" which applies a pressure based on the ideal gas law.
• Added debug log output and a plot variable for outputting the current pressure of an ideal-gas-pressure load.
• Introduced ReactionRateRuberti to model strain-dependent fiber degradation
• Added FEVec3dValuator object to FEFiberExpPowSBM and FEFiberPowLinearSBM to make them behave consistently with other fiber models.
• An (internal) mechanism was added for auto-differentation of Stress and Tangent routines. This is available to plugin developers who wish to avoid calculating the explicit form of the Stress and/or Tangent.
• Added edge-to-surface sliding contact, which can be used to enforce contact between beams or trusses and a surface. Also renamed potential-based edge-to-surface contact.

Improvements:

• Added option to set element type to HEX8G6 in feb4 input file.
• added missing s in some instances of output_negative_jacobians
• Added default load curve to surface force load.
• Added units of time for bond relaxation constants
• Added descriptions for viscoelastic and reactive viscoelastic damage, and reactive viscoplasticity and reactive viscoplastic damage to User Manual
• Changed long names of pressure- and cv-virial coefficients in real vapor, changed long name of viscosity-virial coefficient in Newtonian real vapor, added plot variable for fluid relative thermal Peclet number
• Updated thermo-fluid module to use latest version of real vapor, added Newtonian real vapor and thermal conductivity real vapor material models. Added plot variables for tangents of fluid pressure with respect to volume and temperature. Used virtual functions to evaluate derivatives of functions of state with respect to volume and temperature
• Added documentation for enclosed volume change
• Updated Theory Manual to describe stiffness contribution from variations of fluid velocity to fluid body force calculation
• Contact potential now also calculates total contact force.
• Augmentations can now be done optionally for the sliding-elastic contact by attaching a load curve to the tolerance parameter.
• Documented the stress and tangent of the "HGO unconstrained" material in the theory manual.
• Improved consistency in PrepStep among fluid solvers, by calling UpdateModel instead of fem.Update in all the solvers.
• Comments are now parsed in XMLReader::GetChar (this was to avoid a problem when a tag's value contains a comment)
• Modified FiberExpPowSBM and FiberPowLinearSBM to use FEParamDouble properties.
• Updated remodeling interface materials to calculate solid mass density for elastic solids, solid mixtures, and multiphasic materials
• Implemented Init function for several contact material point classes.
• Error messages for reset_test are printed to cerr instead of the log file.
• Each contact interface now defines the laugon parameter so that the correct values can be specified.
• added mechanism for plotting strain energy and specific strain energy for components of solid mixtures
• Minor change to optimization output formatting.
• X column now prints time for data-fit objective for optimization problems.
• Implemented nodal integration rule for line elements. This is now default in edge-to-surface contact.
• Added support for body forces for elastic-truss domain.

Bug fixes:

• Removed update of rigid nodal velocities in FERigidSolver::PrepStep since it was incorrect.
• Initialized m_rt material point member when created.
• Made sure augmentations of prestrain constraint are not done when tolerance is zero.
• Allowed prestrain gradient to work with shell domains.
• Fixed issue with rigid solver to improve convergence
• Made sure shell bottom flag is set in initialization.
• Fixed bug in initialization of FEInitialVelocity and FEInitialShellVelocity.
• Fixed plugin paths in Windows scp-to-repo script [skip ci]
• Initialized m_ksi and m_ct parameters of FEFluidMovingFrameLoad to fix crash on Windows.
• Fixed errors in evaluation of stress and tangent of "HGO unconstrained".
• Fixed issue with reading xml tag values that are space-delimited.
• Fixed issue with new FEPlotIdealGasPressure plot variable.
• Fixed crash on Linux caused by buffer overflow in snprintf call
• Fixed typo in ParseSurfaceData when reading vec2d data.
• Fixed sprintf deprecation warnings by using snprintf
• Fixed issues with plotting specific strain energy
• Fixed plotting of specific strain energy when density is zero
• Fixed crash due to recent change in linear solver cleanup.
• Fixed issues with remodeling solids that belong to a solid mixture. Finalized implementation of strain energy density and specific strain energy for solid components of a mixture
• Linear solver is not deallocated in Deactivate since this may cause issues when resetting model.
• Made minor changes to multiphasic domains to properly initialize sbmrmin and sbmrmax
• Fixed issue with material point tree when using elastic mixtures.
• Added serialization for FESymmetryPlane.
• Now ignoring some white space characters when reading tag values.
• Fixed dynamic cast issues when writing discrete element force log data.
• Fixed issues with processing edges from feb4 input file.
• Removed mentioning of model title since that parameter no longer exists.

FEBio 4.6

New Features:

• Two new rigid constraints were added to prescribe the rotation of a rigid body: rigid_rotation_vector prescribes the rotation via a rotation vector. The rigid_euler_angles prescribes the rotation via Euler angles.
• Added "moving frame" body load, which can be used to emulate the effects of being embedded in an accelerating and rotating coordinate system.
• Added new weak bond recruitment functions for reactive viscoelastictiy, including Weibull, log-normal, quintic, and gamma. Added new damage CDF function gamma.
• Added filtering capabilities for RVE generations, RVE bonds, RVE recruitment and RVE strain, to plot these variables for specific solid mixture constituents
• Added some initial support for body forces for beams. (Will only work with constant body forces.)
• Added "field" plot variable, which can be used to output any field variable. Field variables are the internal solution variables that FEBio solves for. The available field variables depend on the physics module.
• Added "rotation" plot variable, which writes the nodal orientation of beam elements.
• Added Lagrange multiplier method to linear constraints in FEAugLagLinearConstraint

Improvements:

• Array variables (e.g. solute concentrations) are now exported as FIELD variables in VTK export.
• Added units to rigid force and mixture normal traction
• Added option to use solute/sbm name in concentration dofs.
• For dynamic analysis, the initial accelerations are now calculated based on the applied loads at time 0. This may improve the accuracy and convergence for dynamic problems.
• Added initial values for some of the discrete Hill material parameters.
• Modified mixture stress plot variable so that you can specify the material as well as the solid component.
• Added additional plot variables for discrete element length and direction.
• Added option to turn off deprecation warnings. These are now turned off for older file formats.
• Simplified implementation of (uncoupled) fiber-exp-linear a bit.
• Costly evaluations of the zero stiffness matrix contributions of constant body forces are now avoided, which may significantly speed up models that use constant body forces.
• Discrete domains are now processed after they have been read in, which is more efficient.
• Improved memory management of the dump stream used during serialization.
• Modified fiber-exp-linear models to optionally enforce continuity of the strain energy density and elasticity when the user sets c3=0.
• Changed default value of tolerance parameter to 0.1 in FEThermoFluidPressureLoad
• Added units to 'orthotropic elastic' and 'orthotropic CLE' materials
• Modified 'recruitment user' to use 'function' instead of 'cdf' for the recruitment function.
• Modified reactive viscoelastic and uncouple reactive viscoelastic materials to use 'bond recruitment' functions instead of 'damage CDF' functions. Modified the weak bond recruitment algorithm from published paper formula to accommodate strain reversal in cyclical loading.
• Added support for writing FMT_MULT mesh data to plot file.
• Added check to make sure that the value of int parameters is indeed a number. If not, an exception is thrown.
• Changed type for FEThermoFluidPressureLoad from 'fluid pressure' to 'fluid pressure constraint'
• Added additional scenarios for material test.
• Improved calculation of incomplete Gamma function needed for the evaluation of the Malkin reduced relaxation function. Limited the range of the Malkin exponent to be >= 1
• Plotfile is now created after model has been initialized. This allows some of values calculated during initialization to be stored in the plot file (e.g. initial discrete element force).
• Now using full Newton in tangent diagnostic, which seems to work a bit better.
• Updated FEThermoFluidPressureLoad to include penalty, augmented Lagrangian, Lagrange multipler methods.

Bug fixes:

• Fixed bug in contact potential initialization.
• Fixes some issues to the velocity calculations in the biphasic and multiphasic solvers.
• Fixed several issues with rigid body dynamics.
• Fixed issue with surface data map that caused crash with cold restart.
• Fixed problem with processing const surface data. Also provided more accurate error message when bc type is not recognized.
• Fixed additional issue with reading old 2.5 files.
• Fixed some issues with serialization of some material point data classes.
• Fixed issue with merging maps for vec3d mesh data.
• Fixed issue that was preventing old 2.5 files from running.
• Fixed the reactive viscoelastic material response when weak bond recruitment is included, so that the response remains physical and meaningful during strain reversal, such as cyclical strain or cyclical stress
• Fixed and updated several material parameter units.
• Fixed strain energy density calculation for fiber-exp-linear when a non-zero c3 is specified by the user, to enforce continuity of the strain energy density.
• Fixed bug that caused a crashed when plot file type was not initialized.
• Fixed problem with restart when using VTK plot files.
• Fixed some problems with serialization of model parameters.
• Fixed cause of crash when using body forces with the rigid shell domain.
• Fixed FEThermoFluidPressureLoad to make prescribed pressure spatially variable
• Fixed implementation of nonlinear constraints in the fluid solver, thermofluid solver, and polar fluid solver.
• Fixed issue with reading body loads that was always activating the loads, regardless of what step they are defined in.

Documentation:

• Added description of dump_stride command line option and made some minor formatting changes to the febio command line section.
• Updated user manual entry for uncoupled fiber-exp-linear and corrected formula for C6 in user manual .
• Modified User Manual to describe continuous strain energy density for fiber-exp-linear and uncoupled version.
• Updated User Manual to describe optional enforcement of strain energy density and elasticity continuity in fiber-exp-linear materials.
• Minor edits to nonlinear constraints section of Theory Manual, such as adding equations numbers.
• Updated Theory Manual to display representative continuous relaxation spectra and corresponding reduced relaxation functions
• Fixed typo in Holmes-Mow material.
• Updated theoretical description of nonlinear constraint enforcement.

FEBio 4.5

New Features:

• A simple beam formulation has been implemented in FEBio. The stress-strain relation is linear, but allows for large deformations. It can be used in both quasi-static and dynamic analysis.
• Added option to stiffness_test diagnostic to output the actual and approximate stiffness matrices.
• Added output_stride option to control data output frequency.
• Added support for body loads to linear trusses.
• Added support for exporting stresses for linear trusses.

Improvements:

• Made parameters of muscle and tendon materials mappable.
• Added unit specification to offset parameter in sliding-elastic contact interface
• Added check to see if XML writer failed to create the file.
• Modified "force" parameter definition of the surface "force" load so that it shows units and cannot be assigned a load controller.
• Added units and initial values for "isotropic elastic" material.
• Added check in reading Elements section of input file to make sure element IDs are increasing.
• Added support for writing element data with NODE format to VTK file (as point data).

Bug fixes:

• Fixed some bugs in node-element list and element-element list classes.
• Plot file now stores the FEFacetSets, not the FESurfaces because the latter can change in restarts, which could corrupt the plot file.
• Fixed typo when reading rigid bc from 2.5 format. Also added check when setting parameter value to avoid crash.
• Fixed bug in FindSSI function that assumed one-based node indexing.
• Fixed issue with beam's reference frame. Line searches can now be used with beams.
• Fixed minor issue in output of shell directors.

Documentation:

• The plot file format is now described in Appendix D of the FEBio user manual.

FEBio 4.4

New Features:

• FEBio can now output directly in the VTK file format. (Use to output febio results to a VTK file instead of the standard FEBio plot file.)
• Added Yeoh constitutive model for uncoupled solid materials
• Implemented dynamics for linear truss elements.
• Added reaction rate for solutes modeled as SBMs for consistency with constant reaction rate for SBMs.
• Added log variables "EulerX", "EulerY", and "EulerZ" for exporting rigid body Euler angles to the log file.

Improvements:

• Expanded description of building plugin on windows in developer's manual.
• Added check for valid rigid body ID in rigid initial conditions.
• Modified FEPrescribedActiveContractionFiber so that it works better with FEBio Studio.
• Added check for nodal IDs
• Updated theory for tied-fluid interface
• Made output of "damage" plot variable consistent with output of "D" log variable.
• Nodal IDs are now stored on the mesh when reading feb files and written to the plot file.
• Improved calculation of multiphasic tangent stiffness by accounting for tangents of referential solid volume fraction with respect to strain.
• Updated documentation to include description of Yeoh material
• Added units to material parameters of Holzapfel-Gasser-Ogden materials
• Added support for creating node sets from part lists when reading the febio input file.
• Added check to ensure that the parent material of "perm-Holmes-Mow" is biphasic or multiphasic.
• Added initialization of the "E" parameter of the linear spring material.

Bug Fixes:

• Fixed issue with restarts that use surface, domain, or model log data.
• Fixed restart issue for prescribed normal displacement.
• Fixed some serialization issuess with solutes and tied multiphasic interface.
• Fixed bug with calculation of stv parameter in FEActiveFiberStress and FEActiveFiberStressUC
• Fixed issue with "cylindrical" fiber generator.
• Fixed bug with selection of solute id for Nims reaction rate.
• Fixed bug where exact_eigen now returns correct eigenvalues for a diagonal matrix
• Fixed typo in user's manual for coupled MR.
• Added dllexport to some fecore debug functions.
• Fixed issue with old solid solver for dynamic problems.
• Fixed bug with initialization of elastic fiber materials.
• Fixed issue with output of contact gap log variable for node-on-facet contact interface.
• Fixed couple bugs in "tied-multiphasic" contact interface.
• Fixed issue with log output of contact pressure (issue #71).
• Fixed issue with serialization of item lists and domain maps.
• Fixed issue with serialization of mesh nodes.

FEBio 4.3

New Features:

• The "CG-solver" now supports preconditioners (#67)
• Added fluid supply function to biphasic-FSI materials.
• Added Starling fluid supply constitutive model for biphasic-FSI fluid supplies.
• Implemented nrrd image reader.
• Added support for storing global data in plot file. By default, PID controller values are now stored to the plot file.
• Added "mesh_data" plot variable, which allows storing mesh data in the plot file.

Improvements:

• Added support for reading part lists from feb4 file.
• Improved error detection in fluid dilatation calculation of the "real vapor" material.
• Added check for node ID numbers in linear constraints.
• Updated default analysis type for biphasic analyses to be TRANSIENT.
• The "m" parameters of Ogden materials now support maps.
• Added support for reading vector of strings as xml tag.
• Modified default settings for biphasic-solute and multiphasic analyses to be TRANSIENT (instead of STEADY-STATE).
• Added units for coefficients c1 and c2 of Mooney-Rivlin materials that were missing them.
• Added units to velocity in fluid normal velocity.
• Added documentation on CG-solid solver.
• Added error message when a fixed constraints has no dofs fixed.
• Now, storing initial line coordinates of line object.
• Updated some plot variables that were not thread-safe.
• Added support for domain data stored as FMT_NODE.
• The Surface-to-surface map is now evaluated at the nodes so that it can be replicated more accurately in a plot variable.
• Updated error message when the fiber property of a material cannot be found when parsing ElementData section.
• Added support for .fiber variable in ElementData. (which allows the "old" way of assigning user fiber data to mixture components.)

Bug Fixes:

• Fixed bug in assembling stiffness of linear constraints.
• Fixed bug with assigning maps to array parameters.
• Fixed issue with model reset.
• Fixed issue with attributes getting processed twice.
• Fixed issue with default name for line objects.
• Fixed issue with initialization of rigid body COM so the correct values are available for PID controllers that reference these parameters.
• Fixed bug in "fluid surface force" plot variable to update surface area and surface normal at each time point, producing correct results for fluid-FSI problems. Fluid problems not affected.

FEBio 4.2

New Features:

• A fluid-solutes module has been introduced, for fluid analyses with solute transport and reactive processes.

Improvements:

• Updated description of porous neo-Hookean material to indicate that solid volume fraction is inherited from parent material if biphasic or multiphasic
• Exporting additional symbols from febiorve (to make them available to plugins on Windows).
• Added out-of-bounds check to ImageMap::gradient.
• Modified multiphasic framework so that solutes that represent solid-bound-molecules do contribute to the referential solid volume fraction of the multiphasic mixture, by modifying FEMultiphasic::SolidReferentialVolumeFraction. Also updated order of initialization of material points in FEMultiphasicSolidDomain::InitMaterialPoints and FEMultiphasicShellDomain::InitMaterialPoints.
• Updated User Manual to improve description of elastic fluid materials and to explain that solutes that represent solid-bound-molecules can now contribute to the referential solid volume fraction
• Deleted deprecated FEPoroTraction files
• Deprecated FEMultipihasicFluidPressureLoad for versions > 4.0. Changed FEMulatiphasicFluidPressureBC description to "actual fluid pressure" to avoid conflict with "fluid pressure" BCs in fluid, fluid-FSI and fluid-solutes analyses. Minor fix to FEBioFluidSolutes.cpp.
• Added FEMultiphasicFluidPressureBC as a BC that supersedes deprecated FEMultiphasicFluidPressureLoad.
• Added plot variables for various strain measures derived from the growth tensor of a kinematic growth material. Updated the kinematic growth material so that it correctly stores the elastic and growth deformation gradients. Cleaned up the method for creating material point data for the kinematic growth material. Fixed the UpdateSpecializedMaterialPoints function of FEKinematicGrowth to properly replace the deformation gradient calculated from the deformation with the elastic deformation gradient evaluated from the multiplicative decomposition. This provides the correct deformation gradient for calculation of strain-dependent stress, permeability, etc., and associated tangents.
• Added description of the "contact potential" formulation ot user manual.
• Fixed bug in FEKinematicGrowth that prevented proper integration with solid mixtures.
• Updated FEPoroTraction to FEMixtureNormalTraction. Modified FECarterHayes to accept sbm specification as name instead of number. Added units to FEInitialConcentration. Added long names to parameters of FESolidBoundMolecule. Minor tweaks to serialization of FETiedMultiphasicInterface.
• Added default calculation of divergence of body force from trace of stiffness (its spatial gradient).
• Updated body force class to include a function for the calculation of the divergence of the body force. Updated derived classes to perform that calculation. Fixed the calculation of the body force stiffness matrix in the fluid-solutes domain, using divergence of body force.
• Added NodeNormal and UpdateNormals functions to FESurface.
• Created version of fluid RCR boundary condition for fluid-solutes solver. Added units to parameters in FEFluidRCBC, FEFluidRCRBC, FEFluidRCRLoad, FEFluidResistanceBC, FEFluidResistanceLoad, FEFluidSolutesResistanceBC. Updated new formulation for fluid-solutes module. Modified sequential solver in fluid-solutes module to ignore concentration residual when ctol=0. Updated solutes back flow stabilization for new formulation of fluid-solutes solver.
• Added units of length for gap tolerance and search radius fields for several contact interfaces.
• Added dynamic analysis capability to EAS and ANS shell domains using generalized-alpha method. Added units to initial velocity condition. Modified secant stress and secant tangent routines to return material stress and elasticity tensors when requested.
• Added FEBIOMECH_API to FEFiberMaterialPoint (for plugins on Windows).
• Renamed FEInitialFluidPressure to FEInitialMixtureFluidPressure to avoid naming conflict with FEBioFluid library.
• Added initial fluid pressure in FEBioFluid and separate version in FEBioFluidSolutes. Added FEFluidSolutesResistanceBC class. Changed call to Dilatation virtual function in FEElasticFluid to exclude solute concentration. Added units to various initial conditions.
• Added default load curve flags on nodal force and nodal load parameters.
• Added plot variables for fluid relative Reynolds number and solute relative Peclet number.
• Added new fiber models FEFiberCDF and FEFiberCDFUncoupled. Added plot variable for 'deviatoric elasticity' which saves the DevTangent of uncoupled materials.
• Simplified evaluation of FEPorousNeoHookean::ReferentialSolidVolumeFraction.
• Changed serialization from FEPorousNeoHookean.
• Update FEPorousNeoHookean to be more robust to inclusion in an elastic mixture which is the solid part of a biphasic/biphasic-solute or multiphasic material.
• Added FEStiffnessDiagnostic.
• Added set command to febio prompt.
• Added support for feb4 step section in restart input file.
• Now storing covariant and contravariant vectors in shell element instead of recomputing each time.
• Minor changes to omp logic in FEExplicitSolver::DoSolve.
• Improved serialization for fluid-related solvers, materials, boundary conditions and domains.
• Initialized L0 in bool FEElasticTrussDomain::Init().
• Removed serialization of m_dof in FESurfaceLoad since it's already serialized in FEModelLoad.

Bug Fixes:

• Fixed issue with name attribute of ElementData tag.
• Fixed crash if no analysis steps are defined.
• Modified how attributes are processed in FEBioMeshDataSection4::ParseElementData so that invalid attributes can be identified.
• Modified how the fibers are defined for the HGO-coronary material so that they show up correctly in febio studio.
• Fixed some issues with setting the preconditioner for the cg, fgmres, and bicgstab iterative solvers
• Fixed issue with incomplete Cholesky and CG iterative solver.
• Fixed error in description of CG iterative solver.
• Fixed incorrect values for output_level.
• Fixed issue with serialization of data maps.
• Fixed bug in plotting solid mixture nested variables, when plotting component that doesn't exist.
• Fixed serialization of FENodalLoad.
• Fixed problem with copying valuators.
• Fixed issue with initialization of load controllers added in restart input file.
• Fixed bug in serialization of rigid nodeset.
• Fixed issue with rigid shell initialization.
• Fixed bug with setting dump file name.
• Fixed several serialization issues.
• Fixed serialization of FEMathValuator.

FEBio 4.1

• Fixed issue with exporting log data "contact pressure" and "contact gap".
• Added element ID in Holmes-Mow permeability error message.
• Fixed problem with initialization of FERigidBC in multi-step analysis.
• Added all node, element, and facet sets defined in the input file to the plot file.
• Fixed issue with linear constraints for multi-step problems.
• Added config option (show_warnings_and_errors) to suppress warnings and error messages.
• Added parameter to param_run task to generate standard febio output files.
• Hide "clamp_shells" parameter in FERigidNodeSet since it has no effect currently.
• Now printing const scaled value for prescribed FEParamDouble values.
• Some changes that address minor inconsistencies between the BCs that replace their deprecated "load" versions.
• Fixed error in description of Hill discrete material.
• Added enums to solve_strategy parameter of FEFluidSolutesSolver.
• Minor change to console update.
• Corrected unit of P1 muscle material parameter in user manual.
• Fixed issue caused when febio prompt recieves EOF on Linux.
• Log data is now also evaluated and output at time 0.
• Fixed issue with missing material point data in multigeneration material.
• Fixed issue with initialization of FERealGas and FEOsmCoefManning.
• Fixed issue with initialization of FEMappedValueVec3 class and FEElasticFiberMaterial_T.
• Added check for invalid tags when reading rigid body force.
• Replaced NANDetected with NANInSolutionDetected and NANInResidualDetected.
• Minor formatting change when printing vec3d mapped parameters.
• Changed range for FEDamageFiberExponential k2 parameter.
• Fixed bug in allow-mixed-bcs logic in multistep analysis.
• Added support for target rigid moments.
• Added support for referencing domain parameters. This can now be used in the param_run task.
• Fixed bug in periodic boundary related to projection search radius.
• Updated reaction rates (const, expSED, Huiskes and Nims) to use FEParamDouble instead of double for material properties.
• Fixed initiation of referential solid volume fraction in multiphasic solid and shell domains.
• Added support for reading linear constraint offset and fixed issue related to offset.
• Added plot variable for specific strain energy in multiphasic materials (to account for solid remodeling).
• Added rigid body names to echo input.
• Updated User Manual to described fixed pressure, prescribed pressure, fixed concentration, prescribed concentration, fluid pressure (for multiphasic analyses), and add description of update flag to solute natural flux surface load
• Added FEMultiphasicFluidPressureLoad to allow prescribing the actual fluid pressure in a multiphasic analysis. Modified FESoluteNaturalFlux to provide better numerical convergence for this surface load.
• Moved up initialization of rigid system so PID load controllers can reference rigid body parameters.
• Fixed couple issues with explicit solver: initialized FETimeInfo and fixed bug in using prescribed rigid displacements.
• Fixed issue with shell dofs in explicit solver. Made some minor performance improvements.
• Renamed FEPrescribedFluidPressure to FEPrescribedNodalFluidPressure to avoid naming conflict.
• Fixed bug in parsing vector from input file.
• Fixed bug in parsing input file comments that contain '-' characters.

FEBio 4.0

FEBio4 is a major upgrade from FEBio3. Although it will continue to read most older files (version 3, 2.5, 2), a new format (version 4) is the preferred format. Files can be converted with FEBio Studio 2. Most of the important changes in this update are under the hood and improved the consistency between the internal representation of the febio model, the input file format, and the model representation in febio studio 2. The changes facilitated the direct integration of febio into febio studio. See the release notes of febio studio 2 for additional information regarding this integration.

• Fixed sign issue with evaluating body loads on rigid bodies. (Only affects the output of the rigid body reaction forces.)
• Added mat_axis property to solid mixtures, mostly to better support older file formats.
• Fixed a crash when an error was detected in the update of the contact potential.
• Added some error checking for -import command line option.
• Fixed bug in evaluation of FENodalFluidFlux
• Increased precicion when writing floating point values.
• Fixed some issues with parsing comments from the xml file.
• Rigid wall adds surface to mesh in feb3 import.
• Rigid node sets can now be applied in multi-step analyses.
• Fixed crash in parabolic map.
• Fixed several issues with mesh data generators.
• Added support for redefining load contollers in restart file format 3.
• Fixed issue with BSpline initialization.
• Added property validation for properties defined via empty tags.

FEBio 3.8

• Several issues with the cold restart capability were addressed.
• An issue was caused that could cause a crash when rigid rotational dofs are coupled to a biphasic element.
• Added dump stride parameter, which allows users to specify how often the dump file is written.
• Added "contact_traction" log variable.
• Added names of parent when printing model parameter values.
• Support for the MKL-DSS solver was added, which seems to work better for certain types of models than the default pardiso solver.
• Added gap offset option to facet-2-facet sliding.
• Fixed issue with plot output logic when first step does not request output.
• Fixed bug in "element center of mass" plot variable.
• Parameters of "orthotropic elastic" material can now be mapped.
• Added "discrete element signed force" plot variable.
• Added log variables for discrete element force components.
• Fixed bug in compressible Gent material.
• Added "facet area" log variable.
• Added "deformation gradient" plot variable.
• Fixed issue with initialization of FEParamMat3d parameters.
• Added FEMathExpression that refactored some of the logic previously in FEMathValue. FEMathValueVec3 now also uses FEMathExpression so that it can support maps.
• Added prescribed fiber active contraction models. (Similar to uniaxial, but fiber direction can be defined by user.)
• Added support for mixture stress log variable.
• The "mixture stress" plot variable now also works for uncoupled mixtures.
• Fixed calculation of fixed charge density in multiphasic and triphasic materials (in FEBio3)
• Added error exception in Holmes-Mow permeability to catch pathological case.
• Added "contact area" log variable.
• Updated Theory Manual to fix calculation of fixed charge density in reactive multiphasic materials that use charged solid-bound molecules
• Added description of fluid RCR surface load in User Manual
• Fixed the fluid RCR surface load and made it ready for release. Simplified the fluid resistance to be consistent with fluid RCR.
• Allow the initial referential mass density of solid-bound molecules, m_rho0, to be a FEParamDouble.
• Updated FEMembraneMassActionForward and FEMembraneMassActionReversible to use areal concentration of solid-bound molecules. Updated FEMembraneReactionRateIonChannel to accommodate solid-bound molecules in the calculation of the reaction rate.
• Added exponential damage CDF (useful for reactive viscoelastic materials with exponentially increasing weak bond fractions with increasing strain)
• Added aggressive interpolation type as user-specifiable option in BoomerAMG solver.
• Modified FEFiberPowLinear and FEFiberPowLinearUncoupled to use FEParamDouble material coefficients.
• Updated FEIdealGasIsentropic and FEIdealGasIsothermal to run properly in current version of FEBio.
• Point Source Updates
• Fixed bug in FEContinuousFiberDistribution::Stress
• Fixed issue with exporting plot parameter for mapped parameters of nodal loads.
• Added support for X, Y, Z in generic hyperelastic material.
• Restricted nodal reaction forces plot variable to non-rigid materials.

FEBio 3.7

• Added support for setting solver parameters via restart input file.
• Clarified error message when a property fails to initialize.
• Improved speed of initialization of FSI problems.
• Added lung material and documentation.
• Added warning that nonzero value for dtmax will be ignored when must points were defined.
• Fixed some issues related to reset of contact problems. This bug could have affected outcome of parameter optimization for certain contact problems.
• Modified the reset test to print out some useful stats.
• Allowed export to specific domains for domain plot variables. Previously this was only supported for some surface plot variables.
• Made a change to HGOCoronary so that fiber vector plot variable works for this material.
• Contact potential now outputs nonzero values for contact pressure and contact area.
• Implemented parameter scaling option for constrained levmar. To enable parameter scaling, set the control parameter "scale_parameter" to 1.
• Box constraints are now enforced explicitly in constrained levmar.
• Added model log data classes. Added log variable for printing solution vector norm.
• For prestrain materials, the density now takes the prestrain into account.
• Added Shenoy material and documented it in user manual.
• Local coordinate system is now taken into account in FEHGOCoronary.
• Updated reactive viscoelastic materials to properly account for damage when the elastic bond material is modeled with either a reactive damage or a reactive fatigue material.
• Added integral of solute concentration log data.
• Added log output option for printing integral of sbm concentration.
• Fixed serialization of contact material point data.
• Fixed issue with reallocation of linear system during restart.
• Implemented missing Serialize functions for FELinearElasticFluid and FENonlinearElasticFluid.
• Added serialization of FEBiphasicFSIDomain3D::m_btrans.
• Added missing serialization of generic hyperelastic materials.
• Fixed serialization of FEBearingLoad.
• Fixed restart and serialization issues with linear constraints.
• Fixed serialization issues for model parameters. Added missing serialization of FEInSituStretchGradient.
• Added missing Serialize to FEReactivePlasticity.
• Minor change to FEUT4Domain::Create to avoid problem with restart.
• Added serialization for FEMathFunction.
• Added missing serialization of FEBiphasicSolidDomain::m_nodePressure.
• Added "test" solver, which doesn't solve anything, just returns zeroes. (Added to facilitate debugging of large problems.)
• Fixed issue with allocation of default "elastic" property of FEFluid.
• Implemented HGO-coronary material.
• Added "facet area" plot variable.
• Added small clarification about elasticity of some fiber models at strain origin.
• Updated User Manual to include description of solute natural flux, CDF power, and plot variable RVE strain
• Added new 'solute natural flux' surface load for biphasic-solute and multiphasic domains which prescribes a solute molar flux equal to (solute concentration)*(solvent volumetric flux) on a boundary, where concentration and fluid flux are averaged from the element underneath the selected boundary face. This allows a solute to naturally flow out of a boundary without the user having to prescribe a solute concentration or specific value of solute flux on that boundary. Current implementation has a barebones stiffness matrix, may need to be fully populated in future implementation.
• Minor cleaning up of reactive viscoelastic code.
• Added a scaling parameter to FEDamageCDFPower.
• E parameter of FEFiberPowLinearUncoupled a FEParamDouble.
• Added description of auto time step algorithm for reducing the time step size in user manual.
• Expanded user manual entry for fiber-exp-pow-linear
• Fixed user manual entry for definition of formulas related to fiber-exp-pow-linear
• Fixed bug in newly introduced fiber-exp-pow-linear, to enforce continuity of the elasticity at the exp-pow-linear transition.
• Added FEGlobalVariable to prevent memory leak when adding global variables. Global variables are now also copied in FEModel::CopyFrom.
• Added feature for developers, to plot scalar value of prescribed surface load. Modified FEBearingLoad and FEFluidNormalVelocity to test it out.
• Updated User Manual to describe new bearing load
• Added functionality to prescribed a radial bearing load on a cylindrical surface (FEBearingLoad). Copied and adapted Quadric and QuadricFit functions from FEBioStudio to fit bearing surface and detect its axial and radial directions. Updated vec3d and matrix to reproduce missing functionalities that are available in their FEBioStudio equivalents. Updated surface element traits to include/return parametric coordinates of the surface centroid (in parametric space).
• Added serialization of surface pairs.
• Added operators for mat3d+/-/* mat3da and for mat3d+/-mat3ds operation
• Added description of surface force load in User Manual
• Added functionality for prescribing a force on a surface which is converted to a uniform traction.
• Added description of fixed normal displacement constraint
• Added functionality for prescribing a fixed normal displacement constraint.
• Cleaned up FEForceVelocityMaterialPoint and provided missing default values for some of the material parameters.
• Updated User Manual to describe the force-velocity-Estrada active fiber contraction model
• Modified FERVEDamageMaterial to a working version
• Fixed one more item to make FEDamageMaterialUC more consistent with FEDamageMaterial.
• Added description of fiber-exp-pow-linear material
• Added symbolic derivative for H (Heavyside function).
• Modified FEDamageMaterialUC to be consistent with FEDamageMaterial. Replaced FEFiberPowerLinear (which was duplicate of FEFiberPowLinear) with FEFiberExpPowLinear, which uses exponential-power law in the toe region.
• Deleted old (invalid) FEFatigueMaterial
• Derived FEPolynomialHyperElastic from FEElasticMaterial instead of FEUncoupledMaterial, since this material won't work with the three-field formulation.
• Fixed base class call in FEActiveFiberContraction::Init.
• Added pre-stretch functions to FEElasticFiberMaterial to replicate capabilities previously implemented in FEElasticFiberMaterialUC
• Added another example of parameter optimization specification in user manual.
• Fixed trans iso materials that use active fiber contraction to not crash when active fiber contraction is not included.
• Updated FETransIsoMooney-Rivlin and FETransIsoVerandaWestmann to use FEActiveContractionMaterial class to accommodate multiple active fiber contraction materials.
• Derived FEActiveFiberContraction from FEActiveContractionMaterial.
• Added Ana Estrada's model for force-velocity contraction of the cardiac muscle, superposed on a trans iso Mooney-Rivlin material.
• Added new materials "reactive fatigue" and "uncoupled reactive fatigue".
• Added check for repeated time coordinates in load curves.
• Added "infinitesimal strain" plot variable.
• Modified plot parameter so that it maps directly for FMT_MULT data maps without projecting to nodes.
• Fixed bug in closest-point-projection and FESurfaceElement::facet_edge.
• Added getter for FEDataMap to FEMappedValue.
• Fixed some issues with the MDerive operator.
• Fixed issue with evaluating math expression's derivatives.
• Implemented (uncoupled) polynomial hyperelastic material.
• Created missing UpdateSpecializedMaterialPoints function for FEBiphasic, FEBiphasicSolute, FETriphasic and FEMultiphasic materials. Also updated Init() function for these materials.
• Fixed output issue when reporting boolean load parameter values.
• Modified plot logic so that for multi-step analysis, first state is written after first step activation.
• Now checking if the contact interface is active when writing contact plot variables.
• Added support for shells in "density" plot variable.
• Fixed bug in FELogElemSolidStress.
• Implemented support for shells in "Lagrange Strain".
• The "relative volume" plot variable now also supports shells.
• Fixed bad cast issue in FEMassDamping::force.
• Added method to store and plot correct value of uncoupled pressure (for uncoupled materials), including when using 3-field formulation.
• Added trace-free neo-Hookean material, which can be used in ground matrix of solid component of biphasic materials, for equivalence with Mooney-Rivlin material when comparing short-term biphasic and uncoupled elastic responses.
• Fixed bug when passing material point array data in uncoupled elastic mixtures.
• Added FEBondRelaxationMalkinDist continuous spectrum relaxation function with distortional strain-dependent time constants. Added FEDamageCDFPower power-law (pseudo-)damage CDF, which can be useful for specifying weak bond recruitment in reactive viscoelastic materials.
• Fixed issues with CopyFrom for discrete domains.
• Fixed bug reading dump level from cmd + dump at must-points (#37)
• Added log variables for solid stress.
• Added log output for permeability.
• Renamed the "general spring" to "nonlinear spring"
• Implemented new general spring material.
• Added example for reactive plasticity with PFC math flow curve
• Added regression coefficient (R2) as output of parameter optimization analyses (linear regression between y=fitted and x=data). Added ability to fit the y-value of points on point functions representing material parameters.
• Added recruitment module to reactive viscoelastic and uncoupled reactive viscoelastic materials to further accommodate nonlinear viscoelastic response with increasing strain. Added plot variable RVE strain to report the strain measure used for recruitment. Extended Weibull CDF to incorporate location parameter.
• Fixed bug with assignment operator of model parameters.
• Fixed issue with allocation and serialization of discrete element sets.
• Fixed bug in Pa...