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Publication Number: FHWA-HRT-04-094
Date: November 2004

Evaluation of LS-DYNA Soil Material Model 147

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Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296


Foreword

This report documents the evaluation of a soil material model that has been implemented into the dynamic finite element code, LS-DYNA, beginning with version 970. This material model was developed specifically to predict the dynamic performance of the foundation soil in which roadside safety structures are mounted when undergoing a collision by a motor vehicle. This model is applicable for all soil types when one surface is exposed if appropriate material coefficients are inserted. Default material coefficients for National Cooperative Highway Research Program (NCHRP) Report 350, Strong Soil, are stored in the model and can be accessed for use.

This report is one of two that completely documents this material model. The first report, Manual for LS-DYNA Soil Material Model 147 (FHWA-HRT-04-095), completely documents this material model for the user. The second report, Evaluation of LS-DYNA Soil Material Model 147 (FHWA-HRT-04-094), completely documents the model's performance and the accuracy of the results. This performance evaluation was a collaboration between the model developer and the model evaluator. Regarding the model performance evaluation, the developer and evaluator were unable to come to a final agreement regarding the model's performance and accuracy. (The material coefficients for the default soil result in a soil foundation that may be stiffer than desired.) These disagreements are listed and thoroughly discussed in chapter 9 of the second report.

This report will be of interest to research engineers associated with the evaluation and crashworthy performance of roadside safety structures, particularly those engineers responsible for the prediction of the crash response of such structures when using the finite element code LS-DYNA.

Michael F. Trentacoste
Director, Office of Safety
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.



Technical Report Documentation Page

1. Report No.
FHWA-HRT-04-094

2. Government Accession No.

3. Recipient's Catalog No.

4. Title and Subtitle
EVALUATION OF LS-DYNA SOIL MATERIAL MODEL 147

5. Report Date
November 2004

6. Performing Organization Code

7. Author(s)
J.D. Reid and B.A. Coon, Midwest Roadside Safety Facility (MwRSF) B.A. Lewis, S.H. Sutherland, and Y.D. Murray, APTEK, Inc.

8. Performing Organization Report No.
TRP-03-124-02

9. Performing Organization Name and Address
MwRSF, University of Nebraska at Lincoln
1901 Y Street, Building C
Lincoln, NE 68588-0601

10. Work Unit No. (TRAIS)

APTEK, Inc.
1257 Lake Plaza Drive
Colorado Springs, CO 80906-3558

11. Contract or Grant No.
DTFH61-98-C-00071

12. Sponsoring Agency's Name and Address
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

13. Type of Report and Period Covered
Final Report
09-28-1998 through 12-23-2003

14. Sponsoring Agency's Code

15. Supplementary Notes

Contracting Officer's Technical Representative (COTR): Martin Hargrave, Federal Highway Administration, Turner-Fairbank Highway Research Center, 6300 Georgetown Pike, McLean, VA 22101-2296.

16. Abstract

This report documents the evaluation of a new soil material model intended for roadside safety simulation applications using the nonlinear finite element code LS-DYNA.

This report concentrates on the 18 parameters required for the soil material. The focus is on obtaining the appropriate parameter values (through testing or by analytical means), providing an engineering understanding of the parameters, and providing bounds for the effects of varying the parameters.

Although extensive progress has been made on the soil material model, there is considerably more to be accomplished before the model would be effective in most roadside safety applications.

The companion manual to this report is:

Manual for LS-DYNA Soil Material Model 147 (FHWA-HRT-04-095)

17. Key Words
Soil material model, roadside safety simulation, LS-DYNA

18. Distribution Statement
No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161.

19. Security Classif. (of this report)
Unclassified

20. Security Classif. (of this page)
Unclassified

21. No. of Pages
85

22. Price

Form DOT F 1700.7 (8-72)                                                                          Reproduction of completed page authorized


Preface

The goal of the work performed under this program, Development of DYNA3D Analysis Tools for Roadside Safety Applications, is to develop soil and wood material models, implement the models into the LS-DYNA finite element code,(1) and evaluate the performance of each model through correlations with available test data.

This work was performed under Federal Highway Administration (FHWA) Contract No. DTFH61-98-C-00071. The FHWA technical monitor was Martin Hargrave.

Two reports are available for each material model. One report is a user's manual, the second report is a performance evaluation. The user's manual, Manual for LS-DYNA Soil Material Model 147,(2) thoroughly documents the soil model theory, reviews the model input, and provides example problems for use as a learning tool. This report, Evaluation of LS-DYNA Soil Material Model 147, comprises the performance evaluation for the soil model. It documents LS-DYNA parametric studies and correlations with test data performed by a potential end user of the soil model, along with commentary from the developer. The reader is urged to review the user's manual before reading this evaluation report. A user's manual(3) and evaluation report(4) are also available for the wood model.

Development of the soil model was conducted by the prime contractor. The associated soil model evaluation effort to determine the model's performance and the accuracy of the results was a collaboration between the developer and evaluator. The developer created and partially evaluated the soil model. The evaluator performed a second, independent evaluation of the soil model, provided finite element meshes for the evaluation calculations, and provided shear test data for correlations with the model. Finally, the soil model was implemented into the LS-DYNA finite element code.

Regarding the second, independent evaluation of the soil model-the developer and evaluator were unable to come to a final agreement regarding several issues associated with the model's performance and accuracy. These issues are listed and thoroughly discussed in chapter 9 of this evaluation report. Throughout this report, the developer of the soil material model, is referred to as the developer. The evaluator, a potential end user of the soil material model, is referred to as the user. The user's calculations and final evaluation of the soil model are documented in chapters 1 through 8 of this evaluation report.



Table of Contents

CHAPTER 1. INTRODUCTION

CHAPTER 2. DIRECT SHEAR TESTING

CHAPTER 3. BASELINE MODEL: DIRECT SHEAR TEST SIMULATION

BASELINE PARAMETERS

CHAPTER 4. MATERIAL INPUT PARAMETER STUDY

SOIL DENSITY, RHO

Mass Verification

PLOTTING OPTIONS, NPLOT

SPECIFIC GRAVITY, SPGRAV

DENSITY OF WATER, RHOWAT

VISCOSITY PARAMETERS, Vn AND GAMMAR

BULK MODULUS, K

SHEAR MODULUS, G

Poisson's Ratio

Appropriate Values for Bulk and Shear Moduli

ANGLE OF INTERNAL FRICTION, PHIMAX, AND COHESION, COH

Cohesion

Angle of Internal Friction

DRUCKER-PRAGER COEFFICIENT, AHYP

PLASTICITY ITERATIONS, ITERMAX

ECCENTRICITY PARAMETER, ECCEN

STRAIN HARDENING PARAMETERS, An AND Et

MOISTURE CONTENT, MCONT

PORE-WATER EFFECTS ON THE BULK MODULUS, PWD1

PORE-WATER EFFECTS ON PORE-WATER PRESSURE, PWD2

SKELETON BULK MODULUS, PWKSK

RESIDUAL SHEAR STRENGTH, PHIRES

VOID FORMATION ENERGY, VDFM, AND VOLUMETRIC STRAIN, DINT

DELETION DAMAGE, DAMLEV, AND PRINCIPAL FAILURE STRAIN

CHAPTER 5. DEVELOPER'S RECOMMENDED PARAMETERS

CAUSE OF INSTABILITY

CHAPTER 6. ELEMENT FORMULATION: HOURGLASSING

CHAPTER 7. LARGE DEFORMATION TECHNIQUES

CHAPTER 8. USER'S CONCLUSIONS AND RECOMMENDATIONS

CHAPTER 9. DEVELOPER'S COMMENTS

TABLE OF SOIL MODELING TOPICS

ITEMIZED SOIL MODEL TOPICS

Issue 1: Model Will Not Run to Completion

Issue 2: Hourglass, ALE, and Element Choice

ADDITIONAL EVALUATION TOPICS

Material Input Parameter Study

Angle of Internal Friction: Damage and Dilation

Modified Yield Surface

Iterations Parameter

DS-4 Simulation Instabilities

Determining Input Parameter Values

DIRECT SHEAR TEST SIMULATION

MATERIAL MODEL PARAMETERS, HOURGLASSING, AND ELEMENT CHOICE

USER'S MANUAL QUESTIONS AND ANSWERS

APPENDIX A. INITIAL SOIL EXPERIENCE OF USER

APPENDIX B. VERIFICATION OF RESULTS ON DIFFERENT COMPUTER PLATFORMS

SINGLE ELEMENT MODELS

Model hydten1: Hydrostatic Tension

Model txc3-4pr0c.k: Triaxial Compression

MULTI-ELEMENT CYLINDER: TRIAXIAL COMPRESSION TEST

REFERENCES

 

List of Figures

  1. General direct shear testing performance
  2. Results of two direct shear testing results (performed at the user's facility)
  3. Finite element model of large-scale direct shear test
  4. Soil displacement: Baseline model
  5. Cohesion parameter (Coh) variations
  6. Ahyp influence on yield surface
  7. Itermax parameter variations
  8. DS-4 simulation results from the developer
  9. Hourglass control type 1, qm = 0.1
  10. Hourglass control type 4, qm = 0.005
  11. Lagrangian approach: Stable large deformations, modified honeycomb material
  12. Taylor problem
  13. Direct shear test
  14. Soil modulus failure
  15. Soil shear failure
  16. Triaxial compression results: Effective stress
  17. Internal energy
  18. Cross section force through cylinder
  19. Deformed geometry

List of Tables

  1. Developer's and baseline material parameters

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