Plasticity and Fracture Prediction of Metal Sheets

Under Nonlinear Loading

Yuanli Bai (bai@ucf.edu)

Assistant Professor, Dept. of Mech., and Aero. Engr.,

Lab of Solid and Structure Mechanics

University of Central Florida, Orlando, FL, 32816

October 28, 2016

1

Proposed project for SMF roadmap conference at UNH

mailto:bai@ucf.edu

Outline

• Background on nonlinear loading in sheet metal forming

• Proposed testing and modeling research

• Timeline and proposed deliverables

Background: Examples of nonlinear loading conditions in sheet metal forming

• (a) Strain reversal in a punching process

• (b) An example of two step forming

• (c) Edge crack of AHSS metal sheets

• (d) Forming to crash simulation in car bodies

(a)

(b)

(c) (d)

Proposed testing efforts under monotonic and multiaxial loadings

Uniaxial

Tension

Speckle painting is used for DIC measurement.

Notch

Tension

Punch Test Pure

Shear

Uniaxial / Biaxial / Plane Strain Compression

Through-Thickness Compression

4

All tests can be

done in one

universal testing

machine.

Proposed testing efforts under nonlinear loading

Reduced Size Dogbone Specimen with Anti-buckling Device

Opened Window

for DIC

5

Rolling Direction

for Second Step

Two-stage Uniaxial Tension

with Orientation Change

An example of test matrix for Mg AZ31B-H24 conducted at UCF

Loading Type Orientations Repeated Total Tests

Uniaxial Tension 5 3 15

Uniaxial Tension (1mm) 3 3 9

Notch Tension 5 3 15

Uniaxial Compression 5 3 15

Biaxial Compression 5 3 15

Plane Strain Compression 5 3 15

Through-Thickness Compression 1 3 3

Pure Shear 5 3 15

Punch 1 3 3

Reverse Loading 3 3 9

Two-Stage Uniaxial Tension 56

170

6 *Jia, Y., Bai, Y, “Experimental Study of the Mechanical Properties in AZ31B-H24 Magnesium Alloy Sheets under Various Loading Conditions”, International Journal of Fracture, January 2016, 197(1): 25-48.

Proposed modeling efforts under nonlinear loading

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Isotropic

Hardening

Kinematic

Hardening

Cross

Hardening

Loading Condition

Dependency

Anisotropic

Yield Criterion

A Fully Modularized Framework

Combined Different Types of Hardening

General Framework for Multiple Materials

User-friendly Application

Non-aftereffect on Model Calibration

Easy to be Implemented into FEA

Anisotropic eMMC fracture model for metal sheets

* Jia, Y., Bai, Y., “Ductile fracture prediction for metal sheets using all-strain-based modified Mohr-Coulomb model”, International Journal of Mechanical

Sciences, 2016, 115: 516–531.

Comparison between tested and simulated strain histories for magnesium

AZ31B-H24 sheets (a), and TRIP780 steel sheets (b), in the space of

anisotropic equivalent plastic strain versus strain angle Φ.

(a) (b)

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Timeline, cost and proposed deliverables

• (a) It should be a long term project (3-5 years)

• (b) Experimental, analytical and numerical studies are involved.

• (c) The object is come up with one accurate and reliable modeling and prediction methodology for industrial application.