StructuralFEA

What this skill does

# StructuralFEA

Open source finite element analysis skill for structural validation of damper components and mechanical parts. Uses CalculiX, FreeCAD FEM, Gmsh, and ParaView.

## Workflow Routing

| Workflow | Trigger | Description |
|----------|---------|-------------|
| **QuickStress** | "quick stress check", "hand calc" | Analytical stress calculations before FEA |
| **ComponentFEA** | "analyze rod", "tube stress", "piston FEA" | Full FEA of specific component |
| **BucklingAnalysis** | "buckling", "column", "stability" | Euler and nonlinear buckling |
| **ModalAnalysis** | "natural frequency", "modal", "vibration" | Eigenvalue extraction |
| **FatigueCheck** | "fatigue", "endurance", "life" | Stress-life fatigue assessment |

## Toolchain Overview

```
┌─────────────────────────────────────────────────────────────────────┐
│                    OPEN SOURCE FEA STACK                            │
├─────────────────────────────────────────────────────────────────────┤
│                                                                     │
│   ┌─────────────┐     ┌─────────────┐     ┌─────────────┐          │
│   │  FreeCAD    │────▶│    Gmsh     │────▶│  CalculiX   │          │
│   │  (CAD/GUI)  │     │  (Meshing)  │     │  (Solver)   │          │
│   └─────────────┘     └─────────────┘     └──────┬──────┘          │
│         │                                         │                 │
│         │              ┌─────────────┐           │                 │
│         └─────────────▶│  ParaView   │◀──────────┘                 │
│                        │  (Post-proc)│                              │
│                        └─────────────┘                              │
│                                                                     │
│   Alternative paths:                                                │
│   - FreeCAD FEM Workbench (integrated GUI workflow)                │
│   - Salome-Meca (Code_Aster) for advanced nonlinear               │
│   - OpenFOAM for CFD (valve flow analysis)                         │
│                                                                     │
└─────────────────────────────────────────────────────────────────────┘
```

## Installation

### macOS (Homebrew)

```bash
# FreeCAD with FEM workbench
brew install --cask freecad

# Gmsh mesher
brew install gmsh

# CalculiX solver (requires tap)
brew tap costerwi/calculix
brew install calculix-ccx     # Solver
brew install calculix-cgx     # Pre/post (optional, requires XQuartz on macOS)

# ParaView post-processor
brew install --cask paraview

# Optional: OpenFOAM for CFD
brew install openfoam
```

### macOS Alternative (Conda)

```bash
# If you prefer conda
conda install conda-forge::calculix
conda install conda-forge::gmsh
```

### Linux (Ubuntu/Debian)

```bash
# FreeCAD
sudo apt install freecad

# Gmsh
sudo apt install gmsh

# CalculiX
sudo apt install calculix-ccx calculix-cgx

# ParaView
sudo apt install paraview

# Salome-Meca (alternative, more powerful)
# Download from https://www.code-aster.org/
```

### Windows

```powershell
# FreeCAD - via winget or download from freecad.org
winget install FreeCAD.FreeCAD

# Gmsh - via winget or download from gmsh.info
winget install -e --id Gmsh.Gmsh

# CalculiX - multiple options:

# Option 1: bConverged installer (recommended, includes GUI)
# Download from http://www.bconverged.com/calculix.php
# Provides ccx.exe and optional cgx.exe

# Option 2: Chocolatey (if installed)
choco install calculix

# Option 3: WSL (most reliable, identical to Linux)
# Install WSL, then: sudo apt install calculix-ccx calculix-cgx

# ParaView - via winget or download from paraview.org
winget install Kitware.ParaView
```

**Note:** CalculiX is Unix-native software. The bConverged installer is the easiest Windows option. For maximum compatibility, consider running CalculiX in WSL (Windows Subsystem for Linux) which provides identical behaviour to native Linux.

### Verify Installation

```bash
# Check versions
freecad --version
gmsh --version
ccx -v
paraview --version
```

## Material Database

### Aluminium Alloys (for CalculiX .inp files)

```
*MATERIAL, NAME=AL6061T6
*ELASTIC
68900, 0.33
*DENSITY
2700E-12
*EXPANSION
23.6E-6

*MATERIAL, NAME=AL7075T6
*ELASTIC
71700, 0.33
*DENSITY
2810E-12
*EXPANSION
23.4E-6

*MATERIAL, NAME=AL2024T351
*ELASTIC
72400, 0.33
*DENSITY
2780E-12
*EXPANSION
23.2E-6
```

### Steels (for CalculiX .inp files)

```
*MATERIAL, NAME=STEEL4140
*ELASTIC
205000, 0.29
*DENSITY
7850E-12
*EXPANSION
12.3E-6
*PLASTIC
655, 0.0
860, 0.10

*MATERIAL, NAME=STEEL4340
*ELASTIC
205000, 0.29
*DENSITY
7850E-12
*EXPANSION
11.7E-6
*PLASTIC
860, 0.0
1100, 0.08

*MATERIAL, NAME=STEEL174PH
*ELASTIC
196000, 0.27
*DENSITY
7780E-12
*EXPANSION
10.8E-6
*PLASTIC
1170, 0.0
1310, 0.06
```

### Material Properties Summary

| Material | E (MPa) | ν | ρ (kg/m³) | Sy (MPa) | Su (MPa) |
|----------|---------|---|-----------|----------|----------|
| 6061-T6 | 68,900 | 0.33 | 2,700 | 276 | 310 |
| 7075-T6 | 71,700 | 0.33 | 2,810 | 503 | 572 |
| 4140 QT | 205,000 | 0.29 | 7,850 | 655-860 | 810-970 |
| 4340 QT | 205,000 | 0.29 | 7,850 | 860-1100 | 950-1200 |
| 17-4 PH H900 | 196,000 | 0.27 | 7,780 | 1,170 | 1,310 |

## Component Templates

### Piston Rod - Axial + Bending Load

```
** ================================================
** PISTON ROD FEA - COMBINED LOADING
** ================================================
**
*HEADING
Damper Piston Rod - Axial Load with Side Force
**
*NODE, NSET=ALLNODES
** Node data imported from mesh file
*INCLUDE, INPUT=rod_mesh.inp
**
** ------------------------------------------------
** MATERIAL DEFINITION
** ------------------------------------------------
*MATERIAL, NAME=STEEL4140
*ELASTIC
205000, 0.29
*DENSITY
7850E-12
**
*SOLID SECTION, ELSET=EALL, MATERIAL=STEEL4140
**
** ------------------------------------------------
** BOUNDARY CONDITIONS
** ------------------------------------------------
** Fixed end (piston attachment)
*BOUNDARY
FIXED_END, 1, 3, 0.0
**
** ------------------------------------------------
** LOADING
** ------------------------------------------------
** Axial load (compression)
*CLOAD
LOAD_NODE, 3, -5000.0
**
** Side load (bending from misalignment)
*CLOAD
LOAD_NODE, 1, 500.0
**
** ------------------------------------------------
** ANALYSIS
** ------------------------------------------------
*STEP
*STATIC
**
*NODE FILE
U
*EL FILE
S, E
**
*END STEP
```

### Tube - Internal Pressure

```
** ================================================
** DAMPER TUBE - INTERNAL PRESSURE
** ================================================
**
*HEADING
Damper Tube Hoop Stress Analysis
**
*INCLUDE, INPUT=tube_mesh.inp
**
*MATERIAL, NAME=AL6061T6
*ELASTIC
68900, 0.33
**
*SOLID SECTION, ELSET=EALL, MATERIAL=AL6061T6
**
** Fixed end cap
*BOUNDARY
END_FIXED, 1, 3, 0.0
**
** Internal pressure (20 MPa = 200 bar)
*DLOAD
INNER_SURFACE, P, 20.0
**
*STEP
*STATIC
*NODE FILE
U
*EL FILE
S, E
*END STEP
```

### Buckling Analysis Template

```
** ================================================
** ROD BUCKLING ANALYSIS
** ================================================
**
*HEADING
Piston Rod Linear Buckling
**
*INCLUDE, INPUT=rod_mesh.inp
**
*MATERIAL, NAME=STEEL4340
*ELASTIC
205000, 0.29
**
*SOLID SECTION, ELSET=EALL, MATERIAL=STEEL4340
**
** Pinned bottom
*BOUNDARY
BOTTOM, 1, 2, 0.0
BOTTOM, 3, 3, 0.0
**
** Guided top (can move axially)
*BOUNDARY
TOP, 1, 2, 0.0
**
** Unit load for eigenvalue extraction
*CLOAD
TOP, 3, -1.0
**
** ------------------------------------------------
** LINEAR BUCKLING (EIGENVALUE)
** ------------------------------------------------
*STEP
*BUCKLE
5
**
*NODE FILE
U
*EL FILE
S
**
*END STEP
```

### Modal Analysis Template

```
** ================================================
** COMPONENT MODAL ANALYSIS
** ================================================
**
*HEADING
Natural Frequency Extraction
**
*INCLUDE, INPUT=component_mesh.inp
**
*MATERIAL, NAME=STEEL4140
*ELASTIC
205000, 0.29
*DENSITY
785