03.42 · Creep & stress relaxation

Time-dependent response depends on what is held fixed during the experiment. This exercise distinguishes a held-strain relaxation calculation from a held-stress creep calculation, using the supplied material model to make that difference visible in the response curves.

Illustrative calibration only. Start with a 16-ply cross-ply reference laminate; this is a separate, reference-state study.

Open this exercise in Workbench

Prepare the baseline

Inspect the laminate reference modulus, branch parameters, time units and calibration temperature. Identify the loading control before running the baseline. Change one supported time-dependent parameter, rerun, and retain the same loading and time range so that you can attribute the difference to that parameter rather than a different experiment.

Worked procedure

1. Follow the study’s laminate link and inspect the stack and resolved properties that it will use. Then read the model scope and identify the additional specimen, loading or calibration inputs belonging to this separate study. Record which values are supplied independently rather than assuming that every required quantity is inherited from the laminate.

2. Run the supplied study as a baseline and inspect the complete response curves, including their axes, units and parameter settings. Retain the numerical values or a clearly labelled capture before changing an input. Use the interpretation guidance below and the linked formulation to identify what each curve represents and which conclusions remain outside its scope.

3. Choose one editable parameter that belongs to this model and record its original and revised values. Keep the other inputs fixed, rerun the study, and compare the same output quantities over the same range. Explain the observed change using the linked formulation, including a discussion of whether the comparison stays within the model’s calibration and assumptions.

Review checkpoints

Do not interpret example calibration values as material allowables.

Record the assumptions and distinguish analytical verification from experimental validation.

Model limits

Linear uniaxial response at the calibration temperature. Reference Ex is the instantaneous modulus. Three Maxwell branches; creep is solved from stress equilibrium, not the reciprocal relaxation modulus. No thermal shifting or nonlinear creep.

Interpret the comparison

Describe the curve in terms of the imposed condition and the evolving response. Do not obtain creep behaviour by simply taking the reciprocal of a relaxation curve. Retain the formulation’s small-strain, uniaxial and calibration-temperature scope, and review its refinement checks before discussing long-time behaviour.

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.

Models → Micro: Applied model assignment: Halpin–Tsai. Model parameters and formulation are used by Micro.

Models → Mechanical: Applied model assignment: Generalized Maxwell · axial Prony. Model parameters and formulation are used by Mechanical.

Further reading and evidence

• Advanced analytical models: equations, calibration and limits
• Edit laminate materials, angles and thicknesses
• Run and review a model
• Connected inputs and result freshness

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