02.43 · Short fibers: alignment carried into laminate stiffness

This exercise examines how reinforcement geometry and orientation affect the effective elastic response of a short-fibre material. The aim is to connect the model inputs to the resulting directional properties, while keeping elastic load transfer separate from a prediction of fibre breakage or composite strength.

Open this exercise in Workbench

Prepare the baseline

Before running, note fibre length, diameter, fractions and orientation settings. Change the quantity requested in the task while retaining the other settings, then record all directional moduli rather than only the largest one. Where two geometries have the same aspect ratio, compare their results explicitly; this helps identify which geometric information the selected idealization actually uses.

Worked procedure

1. Follow the linked short-fiber Micro recipe into the laminate. The initial 16-ply [0/+45/−45/90]2s stack uses 0.125 mm plies, for a total thickness of 2 mm. Every ply references the same Micro material so within-ply alignment can be changed without changing the layup.

2. Create a companion copy with sixteen 0° plies at the same thickness. For both stacks, sweep Fa = 0, 0.25, 0.50, 0.75 and 1.00 with Fp = 1. Keep the constituent properties, fiber length and volume fractions identical to the first exercise.

3. Read the laminate engineering constants Ex, Ey and Gxy after each change. Under membrane tension, use free transverse contraction rather than prescribed zero transverse strain. Compare the all-0° stack with the single-lamina results and confirm negligible extension–bending coupling in the symmetric stacks.

4. Explain why the all-0° laminate gains directional stiffness while the equal-angle quasi-isotropic laminate remains near 24.11 GPa in both in-plane directions under this particular averaging model. Capture the layup and computed property plots together. This is a stiffness comparison, not a laminate strength study.

Review checkpoints

The all-0° laminate reproduces the lamina in-plane elastic constants.

The symmetric quasi-isotropic stack has Ex = Ey and negligible B coupling.

For this prescribed orientation mixture, quasi-isotropic Ex remains near 24.11 GPa across the sweep; do not infer that all layups improve with alignment.

Model limits

Illustrative elastic screening, not measured material data or strength prediction. Prescribed axial/planar orientation mixture with stiffness-domain averaging, perfect interface and monodisperse fibers. Transverse and shear closure is approximate. Zero strength inputs mean failure is not assessed.

Interpret the comparison

Use the model’s reported transfer and efficiency outputs to explain the stiffness comparison. Treat any displayed fibre geometry as an illustration unless its dimensions are explicitly part of the calculation. If you save the result as a material, inspect which fields were predicted and which remain blank; an elastic snapshot is not a complete set of qualified material properties.

How information passes between models

Micro → Laminates: Predicted ply stiffness, strength, density and expansion properties.

Materials → Micro: Constituent stiffness, strength, density and thermal / moisture properties.

Mechanical → Simulation: SIMULATION selects this case and its analysis model; the case owns its applicable cycle and input references.

Laminates → Mechanical: Ply angles and thicknesses, stiffness, mass and ply properties.

Geometry → Mechanical: Part shape and dimensions, thickness or section definition, and model-specific geometric inputs. Each selected case consumes only the dimensions its model supports.

Models → Micro: Applied model assignment: Cox shear-lag elastic. Model parameters and formulation are used by Micro.

Models → Mechanical: Applied model assignment: CLT · Linear static with failure indices. Model parameters and formulation are used by Mechanical.; Maximum stress

Further reading and evidence

Review the recorded validation scope. Retain the original inputs and solver notices with the results. Representative teaching data are not design allowables.