Abaqus Composite Material Analysis: Laminate Modeling, Damage, and Progressive Failure

Abaqus Composite Material Analysis: Laminate Modeling, Damage, and Progressive Failure

I started working with composites about eight years ago, and honestly, the learning curve was steeper than I expected. The orthotropic material properties, the ply angles, the layup sequence — get any of those wrong and your analysis is meaningless. But once it clicks, Abaqus handles composites really well. Let me walk you through how I set up laminate definitions, run progressive failure with Hashin damage, and model delamination.

Composite Laminate Definition

Material Properties

1. Module: Property > Create Material
2. Type: Elastic > Engineering Constants (orthotropic)
3. Set ply properties (e.g., carbon fiber/epoxy):

| Property | Value | |----------|-------| | E1 (fiber direction) | 135 GPa | | E2 (transverse) | 9.5 GPa | | E3 (thickness) | 9.5 GPa | | ν12 | 0.30 | | ν13 | 0.30 | | ν23 | 0.45 | | G12 | 5.0 GPa | | G13 | 5.0 GPa | | G23 | 3.0 GPa | | Density | 1580 kg/m³ |

4. Strength properties (for damage):
   • Xt: Tensile strength in fiber direction (1500 MPa)
   • Xc: Compressive strength in fiber direction (1200 MPa)
   • Yt: Transverse tensile strength (50 MPa)
   • Yc: Transverse compressive strength (250 MPa)
   • SL: Shear strength (80 MPa)
   • St: Transverse shear strength (80 MPa)

Composite Layup

1. Module: Property > Composite Layup
2. Define:
   • Layup name: e.g., "Skin_Layup"
   • Element type: Shell or Continuum Shell
   • Layup orientation:
     • Reference direction: 0° fiber direction
     • Additional rotation: Per ply angle
3. Plies:

| Ply # | Material | Thickness (mm) | Angle (°) | |-------|----------|---------------|----------| | 1 | CFRP_UD | 0.125 | 0 | | 2 | CFRP_UD | 0.125 | 45 | | 3 | CFRP_UD | 0.125 | -45 | | 4 | CFRP_UD | 0.125 | 90 | | 5 | CFRP_UD | 0.125 | 90 | | 6 | CFRP_UD | 0.125 | -45 | | 7 | CFRP_UD | 0.125 | 45 | | 8 | CFRP_UD | 0.125 | 0 |

4. Total thickness: 8 × 0.125 = 1.0mm
5. Layup: [0/45/-45/90]s (symmetric)

Element Selection

Shell Elements

| Element | Type | Use | |---------|------|-----| | S4R | 4-node, reduced | General composite shells (default) | | S8R | 8-node, reduced | Higher accuracy (curved geometry) | | S4 | 4-node, full | When hourglass is problematic |

• Advantages: Fast, efficient, good for thin laminates
• Limitations: Constant shear through thickness, no edge effects
• Output: Per-ply stresses and strains

Continuum Shell Elements

| Element | Type | Use | |---------|------|-----| | SC8R | 8-node, reduced | 3D composite shells (default) | | SC6R | 6-node (wedge) | Transition geometry |

• Advantages: 3D stress state, better edge effects, through-thickness stress
• Limitations: Slower than shell, more elements
• Use when: Through-thickness stress is important, thick laminates

Solid Elements (3D)

| Element | Type | Use | |---------|------|-----| | C3D8R | Hex, reduced | Each ply as a solid layer | | C3D20R | Hex, quadratic | High accuracy (expensive) |

• Advantages: Full 3D stress, delamination between plies
• Limitations: Very expensive (many elements for many plies)
• Use when: Detailed delamination, thick composites, impact

Damage Initiation (Hashin)

Hashin Damage Criteria

1. Property > Material > Damage > Hashin Damage
2. Four failure modes:

Fiber Tension (σ11 > 0)

• (σ11/Xt)² + α × (τ12/SL)² + α × (τ13/ST)² ≥ 1
• α: Shear contribution factor (typically 1.0)

Fiber Compression (σ11 < 0)

• (σ11/Xc)² ≥ 1

Matrix Tension (σ22 > 0)

• (σ22/Yt)² + (τ12/SL)² + (τ13/ST)² ≥ 1

Matrix Compression (σ22 < 0)

• (σ22/Yc)² + (τ12/SL)² + (τ13/ST)² ≥ 1

3. Set parameters:
   • Xt, Xc: Fiber tensile/compressive strength
   • Yt, Yc: Matrix tensile/compressive strength
   • SL, ST: Shear strengths
   • α: Shear contribution factor (1.0 default)

Damage Evolution

1. After initiation, damage evolves:

   • Type: Energy (fracture energy per unit area)
   • Gft, Gfc: Fiber tensile/compressive fracture energy
   • Gmt, Gmc: Matrix tensile/compressive fracture energy
   • Softening: Linear or exponential

2. Typical fracture energies (CFRP):

| Mode | G (mJ/mm²) | |------|-----------| | Fiber tension (Gft) | 90 | | Fiber compression (Gfc) | 80 | | Matrix tension (Gmt) | 0.5 | | Matrix compression (Gmc) | 1.5 |

3. Damage variable (0 to 1):
   • 0: No damage (intact)
   • 1: Fully damaged (no load capacity)
   • Stiffness degrades: Cdamaged = C × (1 - d)

Progressive Failure Analysis

Setup

1. Step > Static, General (NLGEOM ON)
2. Apply load incrementally
3. Abaqus:
   • Monitors each ply at each integration point
   • When Hashin criterion is met: damage initiates
   • Stiffness degrades per damage evolution law
   • Load redistributes to undamaged material
   • Damage may propagate to adjacent elements
4. Element deletion:
   • When damage variable = 1: element loses all stiffness
   • Element can be deleted from analysis (visualize as removed)

Results

1. Damage variables:
   • HSNFTCRT: Fiber tension damage initiation criterion
   • HSNFCCRT: Fiber compression criterion
   • HSNMTCRT: Matrix tension criterion
   • HSNMCCRT: Matrix compression criterion
   • DV: Damage variable (0 to 1)
2. Failed elements: Where DV > 0.99
3. Stress redistribution: Load path changes as damage progresses
4. Load-displacement curve: Shows stiffness loss and peak load

Typical Progressive Failure Sequence

1. First-ply failure: Matrix cracking in 90° plies (transverse tension)
2. Damage propagation: Matrix cracking spreads to adjacent 90° plies
3. Fiber failure: When stress redistributes to 0° plies, fiber tension may exceed Xt
4. Final failure: Fiber fracture in 0° plies → laminate fails

Delamination Modeling

Cohesive Zone for Delamination

1. Insert cohesive elements between plies:
   • COH3D8: 3D cohesive element
   • Thickness: 0.001-0.01mm (or zero-thickness)
2. Or use surface-based cohesive:
   • Interaction > Cohesive Behavior
   • Between ply interfaces
3. Interface properties:
   • Normal strength (tN): 50-100 MPa (composite interface)
   • Shear strength (tS, tT): 30-80 MPa
   • Mode I fracture energy (GIC): 0.3-1.0 mJ/mm²
   • Mode II fracture energy (GIIC): 1.0-3.0 mJ/mm²
4. Mixed-mode:
   • Power law: (GI/GIC)^α + (GII/GIIC)^α = 1
   • BK (Benzeggagh-Kenane): For Mode I/II mixity

Virtual Crack Closure Technique (VCCT)

1. Alternative to cohesive zone:
   • Interaction > VCCT
   • Calculate energy release rate at crack tip
   • Compare to critical: G ≥ GC → crack advances
2. Advantages:
   • No need for cohesive elements
   • Based on LEFM (linear elastic fracture mechanics)
   • Good for brittle delamination
3. Parameters:
   • GIC, GIIC: Mode I and II critical energy release rates
   • Mixed mode: Power law or BK

Impact Analysis (Abaqus/Explicit)

Low-Velocity Impact Setup

1. Step > Dynamic, Explicit
2. Impactor:
   • Rigid sphere (e.g., 16mm diameter, 2kg)
   • Initial velocity: e.g., 5 m/s (low-velocity impact)
3. Composite plate:
   • S4R or SC8R elements
   • Hashin damage enabled
   • Cohesive zone between plies (for delamination)
4. Contact:
   • General Contact (Explicit)
   • Impactor-to-plate contact
5. Duration: 2-5 ms (typical impact event)

Impact Results

1. Damage patterns:
   • Fiber damage: On impact face (compression) and back face (tension)
   • Matrix damage: Spreading from impact point
   • Delamination: Between plies at different angles (mode II dominant)
2. Energy absorption:
   • By fiber fracture, matrix cracking, delamination
   • Check energy balance: KE → IE + damage + friction
3. Barely visible impact damage (BVID):
   • Surface: Minimal visible damage
   • Internal: Significant delamination
   • Critical for aircraft inspection

Post-Processing

Per-Ply Results

1. Results > Field Output > Section Points:
   • Select ply number (1 through N)
   • View stress, strain, damage per ply
2. Through-thickness:
   • Plot stress through all plies
   • Identify which ply fails first

Failure Envelope

1. Plot failure index vs. load:
   • Hashin criterion at each ply
   • First-ply failure load
   • Ultimate failure load
2. Compare to test data:
   • Tensile test: [0/90]s laminate
   • Compression test: [0/45/-45/90]s laminate
   • Shear test: [±45]s laminate

Verification Checklist

• [ ] Material properties are orthotropic (E1, E2, E3, G12, G13, G23, ν12, ν13, ν23)
• [ ] Ply angles are correctly defined in composite layup
• [ ] Layup sequence matches design (symmetric, balanced, etc.)
• [ ] Element type is appropriate (shell for thin, continuum for thick)
• [ ] Hashin damage parameters match material test data
• [ ] Fracture energies (Gft, Gfc, Gmt, Gmc) are in correct units
• [ ] Damage evolution is stable (no sudden energy release)
• [ ] Delamination interface properties are correct (if modeled)
• [ ] First-ply failure load matches analytical prediction
• [ ] Ultimate failure load matches test data (if available)

Wrapping Up

Composites analysis in Abaqus comes down to two things: getting your material properties right and choosing the right damage model. I always start with a simple [0/90]s laminate and compare first-ply failure to a hand calculation before running anything complex. If the simple case doesn't match, your properties or layup definition is wrong — no point running a full progressive failure analysis on a bad foundation. And don't forget delamination — I've seen too many composite analyses that only model in-plane damage and completely miss the out-of-plane failure that actually drives the design.