A CDS study is a dependency graph, not an isolated equation. Material records, constitutive models, ply definitions, geometry and boundary conditions determine which equations can be solved. Results belong to the input state used for that run; changing a linked record does not update an earlier stored solution.
Choose the physical idealization before choosing numerical resolution. A through-thickness transport model assumes in-plane uniformity. A laminate membrane model does not resolve local contact or a three-dimensional edge field. More nodes or smaller steps improve the numerical approximation within an idealization; they do not remove that idealization's limits.
Constituent and ply properties use material axes, while loading and geometry use structural axes. State the transformation convention, engineering shear convention, thickness direction and stress signs. Convert units at interfaces rather than mixing unit systems inside a stiffness or transport operator.
Resolve linked records and model compatibility, assemble material and laminate properties, apply initial and boundary conditions, advance the selected fields, recover stresses and evaluate failure measures. An unsupported coupling must remain explicitly excluded. A successful run is a numerical outcome, not evidence of design qualification.
1.1 1. Framework and Scope
1. Framework and Scope
CDS release r15 is a unified constituent-to-process-to-structure framework. Every physical ply may independently use automatic property resolution, embedded micromechanics, or direct measured properties; supply its own polymer process data; and enter the common damaged laminate and selectable plate, cylinder, or beam solution. Classical Lamination Theory supplies the membrane-bending foundation while mapped temperature, moisture, cure shrinkage, crystallization shrinkage, cohesive interfaces, and per-ply failure routing remain integrated without treating the stochastic short-fiber branch as the whole formulation.
Fiber, matrix, filler, void, architecture, and measured overrides resolve into the complete 3D elastic, strength, expansion, density, and transport definition for each ply.
Each ply can use a linked micromechanics recipe or measured material properties. Different plies may use different sources.
Thin-laminate CLT, transformed orthotropic ply stiffness, full A–B–D coupling, and three-node-per-ply recovery remain the section-analysis foundation.
Each ply selects a compatible failure theory. New failures degrade only the activated fiber, matrix, or shear family before equilibrium is solved again at the same load.
Temperature and moisture fields generate damaged force and moment resultants. They are recomputed after every stiffness change.
A heterogeneous 1D heat/moisture model uses independent top and bottom schedules, cure or crystallization kinetics, and per-ply transport properties before structural loading.
A mixed-mode cohesive law can represent delamination only when local interface separation history is supplied externally.
Prescribed σz, τxz, and τyz are recovered in global and local axes, contribute to failure, and add independent E3, G13, and G23 damage families.
Every active ply can use a different material, orientation, environmental state, strength set, and eligible failure criterion during the same progressive analysis.
Compatible equal-thickness master-ply stacks can be mapped to a stiffness-matched Tsai Double-Double family. The user chooses whether downstream analysis retains the supplied angles or uses the recommendation.
Tsai Double-Double stiffness matching
For a compatible stack, CDS searches the staggered family [+Φ/−Ψ/−Φ/+Ψ]rT on a 0.5° grid. The objective minimizes the normalized mismatch between the supplied laminate extensional stiffness and the candidate Double-Double stiffness while also reporting coupling and homogenization measures.
Meaning, notation and theory source
Definitions and derivation: Tsai Double-Double stiffness matching
Laminate flag 17 equals 0 to retain the supplied angles or 1 to use the compatible recommendation before all downstream laminate and progressive-failure calculations. Every ply row, material, thickness, property, and interface is preserved; only eligible ply angles are replaced. The Double-Double recommendation summarizes compatibility, recommended angles, coupling, homogenization, and stiffness error, while the ply-angle table reports original, recommended, and selected angles.
Connected analysis sequence
- 1. Read one schemaResolve eight scalar groups, constituent and ply tables, optional matrix shear laws, two surface histories, kinetics, loads, geometry, interfaces, and outputs.
- 2. Generate or accept each plyUse the established resolver, embedded micromechanics, or direct measured properties independently. Preserve measured overrides.
- 3. Solve discontinuous RVEs when selectedRebuild interaction segments, insert ordered Weibull breaks, couple RVE curves in series, and screen critical clusters.
- 4. Recommend or retain the layupWhen compatible, calculate the stiffness-matched Double-Double candidate and use laminate flag 17 to retain or substitute its angles.
- 5. Solve and map process historyInterpolate schedules, solve heat/diffusion/polymer state, and form per-ply process resultants.
- 6. Assemble equilibriumIntegrate damaged A, B, and D and superimpose mechanical, thermal, moisture, process, and σz-Poisson actions.
- 7. Solve the structureSelect plate, shell/Hyer cylinder, or beam and recover stiffness, response, buckling, and frequency results.
- 8. Evaluate and redistributeCheck each ply independently, reduce newly failed families, and repeat equilibrium at the same load until stable.
- 9. ExportReturn named engineering results with material lineage, process fields, structural results, detailed discontinuous events, properties, and matrices.
1.2 14. Assumptions and Limitations
14. Assumptions and Limitations
- The in-plane foundation is thin-laminate CLT with small strains and rotations. The r11 transverse extension prescribes uniform tractions and performs layerwise constitutive recovery; it is not a general 3D equilibrium solution.
- Hashin is the retained 2D plane-stress form; the model does not resolve 3D fiber kinking, fracture-plane rotation, or nonlinear matrix plasticity.
- Transport is one-dimensional through thickness. Lateral heat flow, edge drying, tool-contact geometry, damage-assisted diffusion, and spatial hot spots require a higher-fidelity model.
- Cure, crystallization, diffusion, saturation, reaction heat, and process shrinkage require material-grade and process-specific calibration; default kinetics rows are inert.
- Moduli, strengths, and fracture energies are not currently functions of temperature or moisture concentration.
- The cohesive branch requires externally supplied local kinematics and does not predict crack-front shape, migration, multiple finite-area delaminations, or contact.
- Conductivity and heat capacity are reported as pristine homogenized properties and are not degraded by cracks.
- Residual stiffness factors and stochastic short-fiber parameters require calibration and convergence studies.
- ROM/Reuss, Halpin–Tsai, approximate Mori–Tanaka, approximate self-consistent, fabric, filler, and directional-void branches are reduced-order engineering property generators; critical architecture-specific use requires calibration or a higher-fidelity RVE.
- Micromechanics generates pristine properties. Progressive damage is applied only in the laminate solver.
- Loss of numerical stiffness under load control is a collapse indicator, not a physical post-failure strain trajectory.
Chapter review
Resolve linked records and model compatibility, assemble material and laminate properties, apply initial and boundary conditions, advance the selected fields, recover stresses and evaluate failure measures. An unsupported coupling must remain explicitly excluded. A successful run is a numerical outcome, not evidence of design qualification.
References and source sections
References are retained with the formulations they support. Software instructions describe implementation scope; a cited source does not establish independent validation of a CDS calculation.