Transcript Accuracy of Fully Elastic vs Elastic Plastic.ppt

Accuracy of Fully Elastic vs. Elastic-Plastic Finite Element Analysis
Masters of Engineering
Rensselear Polytechnic Institute
By
Nicholas Szwaja
May 17, 2012
Introduction
• Purpose: Analyze the accuracy of Finite
Element Analysis (FEA) when it is used to
compare fully elastic and elastic-plastic
deformation in high strength steel
• Method: Use FEA to model a tensile test
using a standard specimen.
– Apply tensile load using fully elastic and
elastic-plastic material properties
Fully Elastic
• Linear relationship governed by Hookes
Law: σ = Eε
– where:
• σ = Stress
• E = Modulus of
Elasticity
• ε = Strain
Provided by memry.com
Elastic Plastic
• Plastic deformation is defined as
permanent change in shape or size of a
solid body without fracture
– Occurs after yield point
– Non-linear
– FEA requires manual input of yield stress and
strains from existing tests/calculated data
Expected Outcome
• Fully Elastic
– Accurate stress/strain curve up to the yield point in FEA.
Stress/Strain will continue to act linearly through plastic region
– Hand calculation will validate linear relationship for uniaxial
stress
• Elastic-Plastic
– Accurate stress/strain curve up to the fracture point in FEA.
Stress/strain will be linear up to the yield point then non-linear
from the yield point to fracture.
– Hand calculations will provide significant challenge and some
percentage of error could exist. Hand calculations will have to
consider arbitrary assumptions. i.e no stress/strain in y or z
direction (only axial)
Work Accomplished
•
Fully Elastic FEA Model
successfully built and
analyzed
Work Still Required
• Analyze model with elastic-plastic input
– Develop stress/strain curve for elastic-plastic
model
• Develop hand calculations for fully elastic
and elastic plastic to validate FEA models
• Verify FEA is accurate
• Initial draft of the report