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+---
+type: concept
+title: "Midas NFX Material and Composite Models"
+created: 2026-06-02
+updated: 2026-06-02
+address: c-000176
+aliases:
+  - NFX material models
+  - NFX composite models
+tags:
+  - concept
+  - finite-element-method
+  - midas-nfx
+  - materials
+  - composites
+status: current
+related:
+  - "[[Midas-NFX-Analysis-Manual|Midas NFX Analysis Manual]]"
+  - "[[midas NFX]]"
+  - "[[Finite Element Plasticity]]"
+  - "[[Abaqus Material Library and Data Definition]]"
+  - "[[Abaqus Progressive Damage and Failure]]"
+  - "[[Midas NFX Element Library]]"
+sources:
+  - "[[Midas-NFX-Analysis-Manual|Midas NFX Analysis Manual]]"
+---
+
+# Midas NFX Material and Composite Models
+
+## Definition
+
+The NFX material-model thread covers the elastic, nonlinear, plastic, hyperelastic, thermal, viscoelastic, laminated-composite, and composite-failure behavior described in the [[Midas-NFX-Analysis-Manual|Midas NFX Analysis Manual]].
+
+## Material Families
+
+The manual includes isotropic, orthotropic, anisotropic, and rigid elastic materials; nonlinear elastic material behavior; plastic material properties; hyperelastic behavior; thermal conductivity properties; age-independent and age-dependent viscoelasticity; and temperature-dependent material properties.
+
+## Composite Laminate Theory
+
+For laminated composites, the source gives the classic membrane-bending relation
+
+```text
+{N, M} = [[A, B], [B, D]] {epsilon_0, kappa}
+```
+
+where `A`, `B`, and `D` represent in-plane, coupling, and bending stiffness. The manual also includes transverse shear stiffness and thermal expansion terms for average temperature change and through-thickness temperature gradient.
+
+## Composite Failure
+
+The composite failure section covers maximum stress, maximum strain, Tsai-Hill, Hoffman, Tsai-Wu, and NASA LaRC02 criteria. The output concepts include finite-element failure index, failure index, and strength ratio.
+
+## Solver Development Use
+
+For a custom solver, this page points to two implementation layers: constitutive integration at integration points and laminate section integration through thickness. Composite failure should be treated as a postprocessing or damage-initiation contract unless the solver explicitly implements degradation, because a failure index alone does not define stiffness loss.
+
+## Connections
+
+- [[Finite Element Plasticity]] and [[Abaqus Constitutive Integration]] cover path-dependent material updates.
+- [[Abaqus Material Library and Data Definition]] and [[Abaqus Progressive Damage and Failure]] provide sibling commercial material/failure references.
+- [[Midas FEA Concrete Cracking and Material Models]] is a MIDAS sibling focused on civil concrete and interface material behavior.