Summary of "Plasticity - FEA using ANSYS - Lesson 8"

Main ideas / lessons conveyed

• The video demonstrates nonlinear static structural analysis with an emphasis on plasticity in ANSYS.
• It compares/introduces two plasticity hardening model types:
  • Bilinear isotropic hardening
  • Multi-linear isotropic hardening

• The modeling workflow shown is:

  1. Define the plasticity material model (elastic + hardening table).
  2. Build simplified geometry using symmetry.
  3. Mesh the model.
  4. Apply displacement-based loading with symmetry constraints.
  5. Enable nonlinear solution controls (e.g., large deflection, auto time stepping).
  6. Post-process plastic strain/stress to observe effects such as necking.

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Plasticity model concepts explained

Bilinear isotropic hardening

• Uses a bilinear stress–strain relationship:
  • Elastic branch: defined by the elastic modulus (E).
  • Plastic behavior after yield: defined by:
    • Yield strength
    • Tangent modulus (slope of the plastic branch)

Multi-linear isotropic hardening

• Uses the same elastic branch definition (elastic modulus).
• After yielding, the plastic response follows multiple piecewise lines (multiple hardening points).
• Important input detail: the hardening table is defined in terms of plastic strain, not total strain.
  • The first row must correspond to first yield at:
    • Plastic strain = 0
  • Subsequent rows add additional yield/hardening points using increasing plastic strain values.
• For each table entry, the user specifies:
  • Plastic strain value
  • Corresponding yield/stress value

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Step-by-step methodology shown (ANSYS setup)

1) Create the material with plasticity

• Create a new elastic-plastic material (named “steel” in the example).
• Add Isotropic Elasticity for the elastic branch:
  • Units converted to English units (psi).
  • Example Young’s modulus: 29,000 ksi (entered in psi).
  • Example Poisson’s ratio: 0.3.
• Add Multi-linear isotropic hardening for plastic behavior:
  • Define a table where:
    • First point: plastic strain = 0 (first yield)
      • Example yield stress: 36,000 psi (36 ksi)
    • Additional hardening points (piecewise):
      • Plastic strain = 5 → slightly increased stress
      • Plastic strain = 20 → stress increased to 50 ksi
  • After reaching the last hardening point, the model behaves like perfect plasticity at the capped stress level in this simplified representation.

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2) Build geometry (symmetric quarter-model)

• Coupon dimensions are in inches, representing a tensile test specimen in the example.
• Simplify using symmetry:
  • Instead of modeling the full specimen, model only one quarter.
  • Use center lines as symmetry planes/constraints.
• Thickness:
  • Example thickness: 0.25 in.
• Add a fillet/radius:
  • Example radius: 0.25.
• Partition faces to create grip regions:
  • Assume grips extend to about half the length.
  • Split faces at 50% along relevant directions.
  • Also split front/back faces so boundary conditions align with existing split boundaries.

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3) Apply symmetry constraints (ANSYS Mechanical)

• Add Symmetry regions so the quarter model represents the full coupon.
• Create two symmetry regions:
  • One symmetry plane along an edge:
    • symmetry normal set to X-axis (default)
  • One symmetry plane for the lower edge:
    • symmetry normal changed to Y-axis
• These enforce mirrored displacement/strain behavior across the omitted portions.

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4) Assign material to the geometry

• Change the solid object material from default structural steel (elastic) to the newly defined plastic steel material.

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5) Mesh

• Create a mesh using:
  • Multi-zone method
• Use a rectangular/structured-style meshing preference due to regular shapes.
• Example default element size: 0.1 in.
• Generate the mesh and proceed.

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6) Define loading as displacement-controlled test

• Use displacement boundary conditions rather than forces.
• Assume grips on two faces:
  • One grip face:
    • Apply zero displacement in X and Y
  • Opposite grip face:
    • Apply zero displacement in X and Y
    • Pull in Y via a +0.5 inch displacement (described as the Y component pulled up by half an inch)
• This represents a tensile-test style pull apart using displacement control.

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7) Configure nonlinear analysis settings

• Enable large deflection:
  • Rationale: 0.5 in displacement over a 3 in coupon implies large strains.
• Enable auto time stepping:
  • Example settings: start with ~100 time steps, min 100, max 1000.
• Solve and monitor convergence:
  • Use Solution Information / convergence output to observe iteration behavior.

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Results interpretation (what the video emphasizes)

• Plasticity develops early; convergence may struggle when transitioning between plasticity branches in the multi-linear model.
• The analysis runs successfully from time 0 to 1.
• Post-processing outputs include:
  • Total deformation
  • Equivalent plastic strain
  • Equivalent (von Mises) stress
• Observed behavior:
  • Plasticity localizes into a concentrated deformation region.
  • Equivalent stress rises to about ~50 ksi, then follows perfect plasticity behavior beyond that point in the multi-linear model.
  • Necking is observed:
    • Stress and plastic strain localize to a thinner region.
    • Necking location can depend on mesh/element shape functions, so the exact position may vary.
  • The video reports:
    • Equivalent plastic strain at the necking region reaches nearly ~77 (very high).
  • Total deformation matches the imposed displacement (about 0.5 in).

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Speakers / sources featured

• No named speaker is provided in the subtitles.
• Source featured: ANSYS Mechanical / ANSYS plasticity (FEA) workflow, demonstrated by an unnamed instructor/tutorial narrator.

Category

Educational

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