Characterizing and Verifying Parameters for Two New 

Mechanical Systems Through the Multiaxial Deformation 

of Automotive Sheet Metal

Daevin Bhathal Hugh

Mentors: Thomas Gnäupel-Herold

Justin Milner

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Motivation

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(Courtesy of WorldAutoSteel)

Rising fuel economy standards

Classes and Properties of Automotive Sheet Metals

→ Need for lighter vehicles → Need for mechanical properties of new metals → Methods for determining formability outcomes
Neutron Diffraction Experiments

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Distance Lattice Moves

+

Lattice Geometric 

Parameters +

Modulus of 

Elasticity

Stress

Neutron Diffraction

Strain

Formability Outcomes
The Mechanical Systems

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Octo-Strain In-Plane Shearing Device

▪ Capable of stressing a sample along eight directions 

in a single plane.

▪ Each arm can move independently of the other 

seven arms.

▪ Load cells on each arm used to measure force.

▪ Sample can be rotated 360oin-plane . 

Arm

Load Cell

▪ Capable of shearing samples in-plane.

▪ Top clamp can hold the top of the sample 

stationary, in tension, or in compression.

▪ Bottom clamp can move in-plane horizontally.

▪ Sample can be rotated 90oin-plane. 

Top Clamp

Bottom Clamp
Preparation of Samples

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1. 2. 3.

Clean Sample

Apply White Coat

Spray Speckle Pattern
Digital Image Correlation Setup

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Digital Image Correlation Setup

▪ Sample placed in mechanical system.

▪ Cameras positioned to provide an appropriate field 

of view of the sample.

▪ Lights rotated and positioned to provide even 

lighting.

Sample

Lights

Cameras
Basics of Digital Image Correlation

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Typical Number of Subsets in One Image

Movement of a Subset 

During Tracking

(correlatedsolutions.com)

ε =

lf − lo

lo

1 2 3
Octo-Strain:

Parameters Researched

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Octo-Strain

Parameters:

▪ Strain Control

• Allows more complex strain paths.

• No user input required during testing.

• More accurate than current control 

methods.

▪ Testing Strain Paths
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Two Current Control Methods:

▪ Force Control:

• Load cells read forces exerted on each arm.

• Computer code changes speed of motors to approach the arm forces that the user 

has defined.

▪ Displacement Control:

• Computer code sets speed of motors based on user defined strain targets and rates.

Octo-Strain:

Control Methods

New Control Method:

▪ Strain Control:

• Digital Acquisition (DAQ) setup reads strain from Digital Image Correlation (DIC) system.

• Code changes speed of motors based on comparing a user defined strain path to the DAQ strain 

readings.
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Strain Control:

Results

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.00 0.02 0.04 0.06 0.08 0.10 0.12

εyy

εxx

Equi-biaxial tests

Displacement Control

Force Control

Strain Control

All tests were run to be equi-biaxial.

Equi-biaxial means that at each point:

εyy = εxx

%error = 

εxx−εyy

εyy

* 100%

Strain control has lowest %error.
0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

-0.2 -0.1 0 0.1 0.2 0.3

Major Strain

Minor Strain

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Octo-Strain:

Plane Strain Test Results

Failed

Plane Strain
0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

-0.2 -0.1 0 0.1 0.2 0.3

Major Strain

Minor Strain

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Octo-Strain:

Equi-Biaxial Test Results

x-direction 

strain

y-direction 

strain
0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

-0.2 -0.1 0 0.1 0.2 0.3

Major Strain

Minor Strain

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Octo-Strain:

Path Change Test Results

Equi Pre Draw -Biaxial
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Octo-Strain:

Pure-Shear Test Results

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

-0.2 -0.1 0 0.1 0.2 0.3

Major Strain

Minor Strain

Pure-Shear
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In-Plane Shearing Device

Parameters:

▪ Planar sample geometry with the most 

homogeneity in strain.

In-Plane Shearing Device:

Parameters Researched
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In-Plane Shearing Device:

Homogeneity in Strain Results

5mm high sample 9mm high sample

More Pullout Less Pullout

More Homogeneity Less Homogeneity
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In-Plane Shearing Device:

Homogeneity in Strain Results

5mm high sample 5mm notched high sample

Less Homogeneity More Homogeneity
Summary of Results

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▪ A new control method, strain control, has been developed.

• Advantages:

o Complex strain paths can be defined easily in Excel.

o No user input required during testing.

o More accurate strain tests.

▪ Geometric parameters to achieve the highest homogeneity in strain for planar samples have been determined.

• Smaller Height = Greater Homogeneity

• Notches = Greater Homogeneity
Acknowledgements

Special Thanks To:

▪ Dr. Thomas Gnäupel-Herold

▪ Dr. Justin Milner

▪ Dr. Julie Borchers

▪ Dr. Joseph Dura

▪ NCNR Director Dr. Robert Dimeo

▪ NIST Center for Neutron Research

▪ Center for High Resolution Neutron Scattering (CHRNS)

▪ SURF Program

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Questions?

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