.. _auto_curve_yield_stress_instability:

*GENERATE AN INSTABILITY CURVE BASED ON YIELD CURVE BASED ON SWIFT. THANKS TO PAUL DU BOIS FOR HIS GUIDANCE.*
=============================================================================================================

Generates a forming-limit instability curve from an effective stress vs. effective strain (Swift hardening) yield curve using one of four Swift-based instability criteria. Use this worker to derive triaxiality-vs.-failure-strain loci for GISSMO or FLD calibration workflows.

When to use
-----------

Classification: **process**.

Tagged: ``FLD``, ``GISSMO``, ``forming_limit``, ``instability``, ``mat_failure``, ``paul_du_bois``, ``swift``, ``triaxiality``.

Inputs
------

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 20 20 20

   * - Label
     - ID
     - Type
     - Default
     - Required
     - Description
   * - Effective Stress Vs Effective Strain Curve
     - effective_stressvs_effective_strain_curve
     - vector
     - —
     - 
     - Effective stress vs. effective strain yield curve (dimensionless strain, stress in model units, e.g. MPa) used as the Swift hardening input; leave unconnected only if the curve is supplied via another upstream worker.
   * - Instability Type
     - type
     - scalar
     - swift_at
     - 
     - Swift instability criterion to apply: 'swift_at' (Considère / diffuse necking at), 'swift_beps' (biaxial equivalent plastic strain), 'swift_beps1' (alternate biaxial EPS formulation), or 'swift_eps2_eps1' (minor vs. major strain locus); default is 'swift_at'.
   * - Start Search
     - start_search
     - scalar
     - -1
     - 
     - Minimum triaxiality value for the sweep search domain (dimensionless); default –1.0 covers full compression-to-shear range.
   * - End Search
     - end_search
     - scalar
     - 1
     - 
     - Maximum triaxiality value for the sweep search domain (dimensionless); default 1.0 covers up to equi-biaxial tension.
   * - Search Increment
     - search_increment
     - scalar
     - 0.001
     - 
     - Triaxiality step size used during the sweep (dimensionless); default 0.001 gives high-resolution output — increase (e.g. 0.01) to reduce compute time for quick estimates.
   * - Reverse Points
     - reversepoints
     - scalar
     - yes
     - 
     - Whether to reverse the point order of the output curve ('yes' / 'no'); default 'yes' orients the curve from high to low triaxiality as expected by most downstream LS-DYNA GISSMO inputs.

Outputs
-------

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 20

   * - Label
     - ID
     - Type
     - Description
   * - curve_yield_stress_instability_output_1
     - curve_yield_stress_instability_output_1
     - vector
     - Computed Swift instability curve — triaxiality (x-axis, dimensionless) vs. equivalent plastic strain at instability (y-axis, dimensionless) — ready for direct use as a failure/instability locus in GISSMO or FLD definitions.

Disciplines
-----------

- data.curve.transform
- engineering.material.calibration
- engineering.material.characterization
- engineering.material.failure

Runnable example
----------------

A runnable example is registered for this worker. Open the example workflow on the d3VIEW canvas: `/api/workflow/example?id=curve_yield_stress_instability <https://www.d3view.com/api/workflow/example?id=curve_yield_stress_instability>`_

.. raw:: html

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   Auto-generated from <code>transformation</code> schema. Worker id: <code>curve_yield_stress_instability</code>. Schema hash: <code>c4b6e374a5b3</code>. Hand-curated docs in <code>workerexamples/</code> override this page when present.
   </p>