Composite Laminates & Progressive Damage

Layered materials: carbon fibre, glass fibre, sandwich — strong along the fibre, weak across it.

1. What is it?

Composites are stacked layers (plies) with fibres running in chosen directions. Strength depends on direction, so one scalar "von Mises" can't judge them. Laminate analysis tracks each ply:

Tsai-Wu failure index per ply: a combined-stress envelope for orthotropic layers. Index < 1 = that ply survives; ≥ 1 = predicted failure of that ply.
Progressive damage: as plies fail, stiffness degrades and load redistributes — the analysis continues to first-ply-failure and beyond, ramping damage monotonically.

"This carbon drive shaft: which ply fails first, at what torque?"

2. When do I use it?

Use when	Don't use for
Fibre-reinforced laminates, bonded layups, anisotropic panels	Isotropic metals (use [Static Structural](static-structural.md))
Layered materials: carbon fibre, glass fibre, sandwich	3D solid composites (shell/surface only)
Need ply-by-ply failure analysis	Simple isotropic stress check

Use cases

Problem Type	Industry	Example
First-ply failure	Aerospace	Wing skin laminate sizing
Impact damage	Automotive	CFRP bumper beam
Delamination growth	Aerospace	Panel edge debonding
Bolted composite joints	Aerospace	Bearing-bypass analysis
Wind energy blade	Energy	Glass fibre blade layup
Marine hull	Marine	Sandwich panel buckling

3. The flow

Design — geometry (shell/surface). The Laminate Coupon preset is

the plane-stress strip the FE link can smear.

Boundary — supports and loads. A coupon is pulled in-plane: clamp

one end, load the other axially.

Mesh — generate.
Simulate → Composites. Three routes, one ply book:
CLT check — classical lamination theory on the ply book alone, no

mesh. Gives the ABD matrix, the smeared engineering constants, the first-ply failure index, and the damage ramp.

FE link — Apply laminate to mesh, solve, then *Run per-ply FE

margins*. Margins come from the SOLVED strain field, per element and per ply.

Redistributing ramp — degrade the failed elements and re-solve at

every load step, so the load path moves. This is the post-first-ply capacity estimate; the frozen ramp only gives the onset factor.

Results — ply-by-ply failure indices, ABD, damage progression.

4. Reading your results

Failure Index

Value	Meaning
< 1	Ply survives
≥ 1	Ply fails

Damage Progression

Shows which plies fail first and how load redistributes.

Criterion

One selection for the whole domain — Tsai-Wu (quadratic interaction) or Hashin (fibre/matrix modes, plane stress). Under Hashin a ply is degraded only in the mode that failed: fibre failure kills E₁, matrix failure kills E₂/G₁₂. Tsai-Wu degrades all three moduli on any initiation.

5. Boundaries of truth

What's validated

Case	Reference	Error
Composite laminate	Published	< 5%

What's NOT covered

3D solid composites — shell/surface only
Delamination — in-plane failure only; the DCB cohesive check lives in

the Fracture workbench

Impact damage — static loading only
Bending coupling in the FE link — the smear installs the A-matrix

only, so B is dropped by construction