FEBio & SOFA Soft-Tissue Biomechanics (.feb, .scn)

@modelscript/febio (languages/febio) provides native WebAssembly parsing, hyperelastic and biphasic poroelastic material stability verification, element Jacobian volume positivity checking, non-linear strain-energy and Cauchy stress evaluation, DAEBuilder lowering, and CalculiX .inp / Modelica projections for FEBio (febio_spec 3.0 / 4.0) soft-tissue biomechanics and SOFA Framework (.scn) real-time surgical simulation scenes.

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Supported Extensions & Standards

Extension	Format	Description
.feb	FEBio Specification	XML specification of Material, Mesh / Geometry, Boundary, Loads, Contact, and Step blocks
.scn	SOFA Scene Graph	Simulation Open Framework Architecture (Node, MechanicalObject, TetrahedronFEMForceField, CollisionPipeline)

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Key Capabilities

1. Hyperelastic, Viscoelastic & Biphasic Constitutive Models

• Parses and evaluates soft-tissue strain energy density functions $W(\mathbf{C})$ across biological constitutive laws:
  • Neo-Hookean & Mooney-Rivlin: $W=C_1(I_1-3)+C_2(I_2-3)+\frac{1}{2}K(\ln J{)}^2$
  • Ogden Hyperelastic: $W=\sum _{p=1}^N\frac{{\mu }_p}{{\alpha }_p}({\lambda }_1^{{\alpha }_p}+{\lambda }_2^{{\alpha }_p}+{\lambda }_3^{{\alpha }_p}-3)$
  • Holmes-Mow & Biphasic Poroelastic: Articular cartilage fluid-solid mixture hydraulic permeability $k$ and interstitial fluid pressure.
• Enforces Drucker stability (${\mu }_p{\alpha }_p>0$), positive bulk/shear moduli, and positive element Jacobians ($det\mathbf{J}>0$).

2. CalculiX FEA, Modelica & DAE Lowering

• Solves Principal stretches, Cauchy stresses, and strain energy densities (solveHyperelasticMechanics), exports to CalculiX / Abaqus .inp (febioToCalculixInp) and Modelica (febioToModelica), and lowers lumped compliance dynamics into DAEBuilder.

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Pre-Flight Diagnostics

10 rules9 error1 warning

Code	Rule	Severity	Message
M9401	febio-invalid-material-constant	error	Non-physical material constant <paramDesc> in material '<materialName>'.
M9402	febio-inverted-element-jacobian	error	Element '<elemId>' (<elemType>) has non-positive Jacobian determinant det(J) = '<detJ>'.
M9403	febio-unresolved-node-or-set	error	Unresolved <refKind> reference '<refId>' in '<contextName>'.
M9404	febio-unconstrained-rigid-body	warning	Model '<modelTitle>' has no fixed or prescribed displacement boundary conditions to prevent rigid-body motion.
M9405	febio-invalid-biphasic-permeability	error	Invalid biphasic/poroelastic parameter (<reason>) in material '<materialName>'.
M9406	febio-invalid-time-stepper	error	Invalid <Control> time-stepper configuration: time_steps='<timeSteps>', step_size='<stepSize>' (both must be > 0).
M9407	febio-unresolved-material-id	error	Unresolved material ID '<matId>' referenced in '<contextName>'.
M9408	febio-contact-penalty-invalid	error	Contact interface '<contactName>' has invalid configuration: <detail>.
M9409	febio-sofa-missing-mechanical-object	error	SOFA <Node> '<nodeName>' contains '<<forceFieldType>>' without a '<MechanicalObject>' state container.
M9410	febio-duplicate-entity-id	error	Duplicate <entityKind> identifier '<id>'.

Generated from languages/febio/src/lints/rules.ts. All languages →

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CLI Usage

# Inspect FEBio materials, mesh nodes/elements, and boundary conditions
msx febio inspect LiverHyperelastic.feb

# Validate Drucker hyperelastic stability and element Jacobian determinants
msx febio validate LiverHyperelastic.feb

# Solve hyperelastic strain energy and Cauchy stress response
msx febio solve LiverHyperelastic.feb

# Project FEBio mesh and materials to CalculiX/Abaqus .inp or Modelica
msx febio to-inp LiverHyperelastic.feb > LiverHyperelastic.inp
msx febio to-modelica LiverHyperelastic.feb > LiverHyperelastic.mo