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FEPro 3D Extension (v3.63.1)

Integrated 3D Solid, Shell & Contact Mechanics Engine for LittleDef (fem1)

Overview

FEPro is the 3D finite element extension integrated into LittleDef (fem1). It extends 2D beam frame models into full 3D solid and shell continuum meshes, enabling high-resolution stress distributions, multi-body penalty contact, non-linear material laws, and parametric connection design.

FEPro 3D GUI displaying General FEA Mode with OpenGL 3D rendering and post-processing tools.

Key Architecture & Highlights

Dual Operating Modes:
- Parametric Section Mode: Automatically extrudes 2D LittleDef beam cross-sections into 3D Hex8 solid elements with prestressing, rebars, and shear studs.
- General 3D FEA Mode: Full 3D pre/post-processor supporting general Hex8 solids, Quad4 DKT shells, 3D Timoshenko beams, and 2-node spring elements.
ANSI89 C Accelerator Core: Optional compiled C library (fepro_solver.so / fepro_solver.dll) providing Pthreads multi-threaded sparse matrix assembly, Preconditioned Conjugate Gradient (PCG) solver, and fast contact pair detection. Runs in pure Tcl fallback mode if C compiler is unavailable.
Advanced Non-Linear Constitutive Models:
- J2 Plasticity (von Mises with isotropic & kinematic hardening)
- Concrete Damage Plasticity (CDP) & 3D Non-linear Concrete
- Drucker-Prager Soil & Geotechnical Plasticity
- Lemaitre Continuum Damage Mechanics & Johnson-Cook High-Strain Metal Plasticity
- Tsai-Wu Orthotropic Anisotropic Composites & RC Bond-Slip Contact Interface
Multi-Body Contact Mechanics: Non-linear penalty contact formulation for 3D surfaces and clinch joints (master-slave node-to-surface and surface-to-surface).
Parametric Connection Wizards:
- Single & Double Clinch Joint Wizard (v2 conforming mesh)
- Bolted End-Plate Connection Wizard (EN 1993-1-8 compliant)
- Prestressed Concrete Beam & RC Slab Mesh Generator
CLI & Micro-Commands: Full uFEM-compatible CLI command engine (engen, nsel, d, f, solv) supporting headless scripting and batch verification execution.

3D Renderings & Stress Post-Processing

Parametric Beam Render

Parametric 3D solid beam mesh (450 Hex8 elements, 744 nodes) generated from 2D section.

J2 Plasticity Strain Contour

Von Mises equivalent plastic strain distribution in structural steel section.

Constitutive Material Models

Multilinear Steel Hardening

True stress vs plastic strain multilinear hardening curve.

Concrete Damage Plasticity (CDP)

Compressive & tensile damage evolution laws for concrete.

CLI & Scripting Commands

FEPro supports direct uFEM macro execution and interactive command-line mode:

# uFEM Compatible Command Script Example
csys, cartesian
n, 1, 0.0, 0.0, 0.0
n, 2, 12.0, 0.0, 0.0
e, 1, 1, 2
d, 1, all, 0.0
f, 2, fy, -50000.0
engen, cant_beam, 12.0, 0.30, 0.60
solv, nonlin

Hardware Benchmarks & Accuracy Verification

FEPro includes an automated 4-problem benchmark suite verifying solver throughput (DOFs/s) and numerical accuracy against analytical solutions:

3D Solid Cantilever (120 Hex8, 1320 DOFs): Verified vs Timoshenko Beam Elasticity Theory.
3D DKT Thin Plate (100 Quad4, 726 DOFs): Verified vs Navier Series Analytical Bending Solution.
10-Storey 3D Frame (400 Beams, 1056 DOFs): High-throughput sparse matrix PCG solver verification.
3D Clinch Joint Contact (392 Hex8, 5016 DOFs): Non-linear multi-body penalty contact convergence.

Platform Compatibility

Like LittleDef, FEPro is written in strict Tcl/Tk 8.0+ (and Tk 9.0 compatible) with an ANSI89 C acceleration library. It runs seamlessly on SGI IRIX 6.5, Linux, FreeBSD, and Microsoft Windows.