The 2014 Sandia Fracture Challenge (SFC2)

Challenge Information Packet

issued May 30, 2014

Brad L. Boyce blboyce@sandia.govSharlotte L.B. Kramer slkrame@sandia.gov

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Introduction

Thank you for participating in the 2nd Sandia Fracture Challenge. The purpose of this exercise is to: (a) compare methodologies for predicting fracture behavior of metallic alloys, and (b) identify methodologies that appear to be most predictive. This exercise is used to evaluate the state-of-health in computational mechanics prediction, identify areas of weakness for further development, and foster the building of relationships in the mechanics community.

In this exercise, participants are asked to predict the forces and displacements required to initiate and propagate a crack from a relatively simple geometry, and predict the path of crack propagation. Participants are allowed to bound their predictions as they see fit.

Details are provided regarding the challenge geometry and material (see subsequent slides).

Experiments will be performed by two independent test labs to confirm the experimentally observed behavior.

The following deadlines are in effect:(1) Any concerns regarding the challenge or sufficiency of the supplied data should be communicated to Brad Boyce blboyce@sandia.gov and copied to Sharlotte Kramer, slkrame@sandia.gov by June 15th. (2) Predictions must be e-mailed to blboyce@sandia.gov and copied to slkrame@sandia.gov by midnight, September 1st, 2014 (3 months after challenge was issued).(3)Experimental results will be e-mailed to all participants by November 1st, 2014.

Ethics: Detailed material property data has been included in the challenge, including chemistry certifications, hardness measurements, and tensile behavior (shear behavior will be forthcoming). By participating in the Sandia Fracture Challenge, all participants agree to not perform any mechanical experiments for the purpose of calibrating or validating their models. The intent of this exercise is to be a computational exercise based solely on data provided.

The 2014 Sandia Fracture Challenge (SFC2)

Geometry: An S-shaped sheet specimen with two slots and 3 holes tested in axial tension. Two larger holes are used for loading pins. Detailed engineering drawings provided on subsequent slides.

Material: commercial stock sheet of mill-annealed Ti-6Al-4V, thickness = 3.1500.025 mm (0.1240.001 inches ). Detailed certifications and material property measurements are provided on subsequent slides.

Loading Rate: the tests will be performed at two actuation rates spanning 3 orders of magnitude: 25.4 mm/sec and 0.0254 mm/sec. Please report predictions for both loading rates if possible.

Challenge Questions (a reporting table for the questions is provided on the following slide)For each of the two loading rates, please predict the following outcomes:Question 1: Report the force at following COD displacements: COD1= 1-mm, 2-mm, and 3-mm. (COD1 and COD2 are defined on slide 7) Note: COD1 and COD2 = 0 at the start of the test; the COD values refer to the change in length from the beginning of the test. Question 2: Report the peak force of the test.Question 3: Report the COD1 and COD2 values when the force has dropped by 10% (to 90% of the peak value). Question 4: Report the COD1 and COD2 values when the force has dropped by 70% (to 30% of the peak value). Question 5: Report the crack path (see slide 9 for examples on how to report crack path)Question 6: Report the expected force-COD1 and force-COD2 curves as two separate ASCII data files with column 1 as force (in N) and column 2 as COD (in mm).

Force (N) at COD1=1mm

Force (N) at COD1=2mm

Force (N) at COD1=3mm

Peak Force of Test(N)

COD1@90% of peak force (mm)

COD2@90% of peak force (mm)

COD1@30% of peak force (mm)

COD2@30% of peak force (mm)

Crack Path (e.g. A-D-C-E)

Upper Bound (optional)

Expected Value

Lower Bound (optional)

Actuation Rate = 25.4 mm/sec

Actuation Rate = 0.0254 mm/secForce (N) at COD1=1mm

Force (N) at COD1=2mm

Force (N) at COD1=3mm

Peak Force of Test(N)

COD1@90% of peak force (mm)

COD2@90% of peak force (mm)

COD1@30% of peak force (mm)

COD2@30% of peak force (mm)

Crack Path (e.g. A-D-C-E)

Upper Bound (optional)

Expected Value

Lower Bound (optional)

Full name, e-mail address, and institution of all team members contributing to this prediction

Example: John Z. Doe, jdoe@place.edu, University of Place; Jane A. Doe, jadoe@otherplace.org, Federal Institute of Otherplace

Reporting Table

Also, please attach ASCII force-COD1 and force-COD2 curves for both 25.4 mm/sec and 0.0254mm/sec. Filename should be “teamname_COD#_[fast or slow].txt”

E-mail predictions to Brad Boyce, blboyce@sandia.gov and Sharlotte Kramer, slkrame@sandia.gov by September 1st.

Detailed Engineering Drawing of Challenge GeometryDimensions in millimeters

3.150.025

millimeters0.051 unless noted otherwise

Detailed Engineering Drawing of Challenge GeometryDimensions in inches

.124.001

COD1 (no hole ahead of the notch)

COD2 (hole ahead of the notch)

About Plate Orientation, Actuation Direction, and Crack Opening Displacement (COD) Gauges

Upper (fixed) end of test specimen

Lower(actuated) end of test specimen

The COD gage measures the change in displacement between two ‘knife edge’ features on the sample (indicated by green arrow).

Orie

ntati

on o

f pla

te ro

lling

dire

ction

rela

tive

to s

ampl

e ge

omet

ry

About the test clevis grips…

Clevis grips are 17-4PH stainless steel manufactured in accordance with standard ASTM E 399. The grips were purchased from Materials Testing Technology (www.mttusa.net), model number ASTM.E0399.08.

About Crack Path Identification

B

D

E

C

A

F

G

Example crack path “B-G” Example crack path “A-E-D-F”Legend

Material Certification: Mill Annealed Ti-6Al-4V

Hardness Values

The average of 6 measurements from the Ti-6AL-4V plate for SFC2, was 36.1 HRC (Rockwell C), consistent with mill annealed Ti-6Al-4V.

Tensile Bar Geometry

A 25.4 mm (1-inch) extensometer was used to measure strain for the tensile tests.

3.150.025

Dimensions in millimeters

ID orientation Thickness Width Area Location Broke Nominal Ratemm mm mm^2

RD8 rolling direction 3.175 6.35 20.16 with in extensometer 0.0254 mm/sRD2 rolling direction 3.1623 6.35 20.08 with in extensometer 0.0254 mm/sRD9 rolling direction 3.175 6.35 20.16 with in extensometer 25.4 mm/sRD7 rolling direction 3.1496 6.35 20.00 with in extensometer 0.0254 mm/sRD6 rolling direction 3.175 6.35 20.16 with in extensometer 0.0254 mm/sRD5 rolling direction 3.1623 6.35 20.08 with in extensometer 0.0254 mm/sRD4 rolling direction 3.1623 6.35 20.08 with in extensometer 25.4 mm/s

RD10 rolling direction 3.1623 6.35 20.08 with in extensometer 25.4 mm/s

TD1 transverse direction 3.1496 6.35 20.00 within exten 25.4 mm/sTD2 transverse direction 3.1496 6.35 20.00 within exten 0.0254 mm/sTD3 transverse direction 3.1496 6.35 20.00 within exten 0.0254 mm/sTD4 transverse direction 3.1242 6.35 19.84 within exten 0.0254 mm/sTD5 transverse direction 3.1496 6.35 20.00 within exten 25.4 mm/sTD6 transverse direction 3.1242 6.35 19.84 within exten 0.0254 mm/sTD7 transverse direction 3.1242 6.35 19.84 within exten 0.0254 mm/sTD8 transverse direction 3.1242 6.35 19.84 within exten 25.4 mm/s

TD11 transverse direction 3.1369 6.35 19.92 within exten 25.4 mm/sTD12 transverse direction 3.1496 6.35 20.00 within exten 25.4 mm/s

Actual Measured Dimensions of Tensile Tests

0

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2

25.4 mm/sec, Transverse Direction

TD1TD5TD8TD11TD12

En

gin

ee

rin

g S

tre

ss (

MP

a)

Extensometer Strain [25.4 mm gage length] (mm/mm)

0

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2

25.4 mm/sec, Rolling Direction

RD4

RD9

RD10

En

gin

ee

rin

g S

tre

ss (

MP

a)

Extensometer Strain [25.4 mm gage length] (mm/mm)

0

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2

0.0254 mm/sec, Rolling Direction

RD2RD5RD6RD7RD8

En

gin

ee

rin

g S

tre

ss (

MP

a)

Extensometer Strain [25.4 mm gage length] (mm/mm)

0

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2

0.0254 mm/sec, Transverse Direction

TD2TD3TD4TD6TD7

En

gin

ee

rin

g S

tre

ss (

MP

a)

Extensometer Strain [25.4 mm gage length] (mm/mm)

Tensile Data Summary

RD2.txt

RD4.txt

RD5.txt

RD6.txt

RD7.txt

RD8.txt

RD9.txt

RD10.txt

TD1.txt

TD2.txt

TD3.txt

TD4.txt

TD5.txt

TD6.txt

TD7.txt

TD8.txt

TD11.txt

TD12.txt

Raw ASCII text data files embedded

Deformed Tensile Shape

Note: each of these images are at slightly different magnifications. In each image, the actual height of the grip region on the left side is 12.6 mm And the width of the grip region is 26.1 mm.These dimensions can be used to scale the rest of the image.

12.6

mm

26.1 mm

Tran

sver

se.0

254

mm

/sec

Tran

sver

se25

.4 m

m/s

ecRo

lling

25.4

mm

/sec

Rolli

ng0.

0254

mm

/sec

Deformed Tensile ShapeRD4 TD12

RD7 TD4

Note: absolute scale could be off by 5%, but these images capture the shape of the failure cross-section

RD80.0254 mm/sec

RD925.4 mm/sec

Tensile Fractography: Comparing Typical Low Rate and High-Rate Morphology

• Images of the high-speed pull tests were captured using a high-speed Phantom 611 camera.

• Images were analyzed in a computer vision software package (VIC 2D) to determine the relative change in distance between a pair of fiducials placed on the grips (see image)

• The software output data as a total change in distance between the fiducials in terms of pixels

• A pixels-per-inch ratio was determined by knowing the size of the fiducial, allowing for a determination of change of location per image.

• The velocity was determined by knowing the time-step between images. Because of the relatively small change in displacement per image, this data was quite noisy. Therefore, a 30-point (central difference) rolling average of the velocity data is presented.

• This data was compared to data collected by the MTS testing software, where the difference between displacement values was divided by the difference in the timestamp on the data for each line of data. (forward difference)

• Good agreement was seen (attached ASCII data files provide a detailed comparison).

Fast-Rate Velocity Confirmation

Velocity-as-determined-by-actuator-LVDT.txt

Velocity-as-determined-by-high-speed-camera.txt

Example of extensometer and optical fiducials for high-speed confirmation

Shear Failure Calibration Specimen

An ASTM standard does not appear to exist for calibration of shear failure in ductile metals. There are numerous methods in the literature, each with advantages and disadvantages. For this challenge, we will provide test data on a specimen geometry based on ASTM D 7078, the V-notched rail shear geometry. LVDT data of grip displacement will be provided, rather than strain gages described in the standard. The geometry has also been modified (deeper notch than the standard) to induce failure at lower forces, minimize grip rotation, and eliminate the potential for grip slippage.

This test data is not yet complete, but will be provided (expected completion: June 21, 2014)

Shear Failure Calibration Data

Data will be forthcoming (expected June 21st, 2014)

Check back on http://imechanica.org/node/16609

Or e-mail blboyce@sandia.gov and slkrame@sandia.gov if you have not received this information.

A note about fixturing for this rare test. The grips used are a hybrid of the two grips shown on the left, with a total of six bolts (3 tall, 2 wide) to minimize rotation during high-load testing. The grips are rigidly attached to the loadframe, but lateral compliance of the loadframe might be non-negligible, so we will provide data that describes both the axial and lateral motion of the grips.