.. _auto_curve_eng_get_necking_strain:

*COMPUTE THE NECKING STRAIN FROM AN ENG STRESS-STRAIN CURVE*
============================================================

Computes the necking (onset-of-instability) strain from an engineering stress-strain curve by converting to true stress-strain, then finding the intersection of the true-stress curve with its derivative. Use this worker during material characterization to extract the necking strain that separates uniform elongation from localised deformation.

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

Classification: **process**.

Tagged: ``engineering_stress_strain``, ``intersection``, ``material_characterization``, ``necking``, ``necking_strain``, ``offset_method``, ``true_stress_strain``, ``uniform_elongation``.

Inputs
------

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

   * - Label
     - ID
     - Type
     - Default
     - Required
     - Description
   * - Eng Stress Strain Curve
     - engstressstraincurve
     - vector
     - —
     - 
     - Engineering stress-strain curve (stress vs. strain) supplied as an XY vector; this is the primary input from which necking strain is derived.
   * - Elastic Modulus
     - elastic_modulus
     - scalar
     - 0.0
     - 
     - Young's modulus (same stress units as the input curve, e.g. MPa or GPa); used to construct the offset yield line — set to 0.0 to let the worker estimate it from the initial slope.
   * - Yield Type
     - yield_type
     - scalar
     - offset
     - 
     - Method used to locate the yield point: 'offset' (0.2 % proof stress line), 'strain' (fixed strain value), 'stress' (fixed stress value), or 'linearity' (end of linear region); default is 'offset'.
   * - Yield Offset Or Strain
     - yield_offsetor_strain
     - scalar
     - 0.002
     - 
     - Numeric value that accompanies yield_type — the offset strain (e.g. 0.002 for 0.2 %) or the absolute strain/stress threshold; not used when yield_type is 'linearity'; default is 0.002.
   * - Intersection Point Type
     - intersection_point_type
     - scalar
     - auto
     - 
     - Selects which intersection of the true-stress curve with its derivative to use as the necking point: 'auto' (first intersection), 'xfirst', 'xlast', 'xavg', or 'xmode'; default is 'auto'.
   * - Return Type
     - return_type
     - scalar
     - true
     - 
     - Value type to return

Outputs
-------

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

   * - Label
     - ID
     - Type
     - Description
   * - curve_eng_get_necking_strain_output_1
     - curve_eng_get_necking_strain_output_1
     - vector
     - Single-point XY vector representing the necking strain (x) and the corresponding true stress at the onset of necking (y), extracted from the input engineering stress-strain curve.

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

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

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

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

.. raw:: html

   <hr style="margin-top:2em">
   <p style="font-size:11px;color:#888">
   Auto-generated from <code>transformation</code> schema. Worker id: <code>curve_eng_get_necking_strain</code>. Schema hash: <code>5d0a43a2a812</code>. Hand-curated docs in <code>workerexamples/</code> override this page when present.
   </p>