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