---
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]]"
source_refs:
  - source: "[[Midas-NFX-Analysis-Manual|Midas NFX Analysis Manual]]"
    raw_path: ".raw/MidasNFXAnalysisManual/"
    raw_files:
      - "MidasNFXAnalysisManual_002.md"
      - "MidasNFXAnalysisManual_015.md"
    md_indices:
      - 2
      - 15
    match: "heuristic-heading-keyword"
    confidence: low
---

# 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.