user manual - biocore, llc · 2018-05-07 · 2016 schutt air xp pro v1.0 3 3. helmet model...

Copyright 2018 Biomechanics Consulting and Research (Biocore) LLC. All Rights Reserved

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NFL Engineering

Roadmap: Numerical

Model Crowdsourcing

User Manual

Finite Element Model of 2016 Schutt Air XP Pro Helmet

(Safety Equipment Institute model 789102)

Version 1.0 for LS-DYNA

Authors:

Will Decker, Xin Ye, Alex Baker, Joel Stitzel, Scott Gayzik

Date: May 9th, 2018, Document Version (v) 1.0


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Biomechanics Consulting and Research, LLC (Biocore) and Football Research Inc. (FRI) with support from

the National Football League (NFL) have collaborated with Centers of Expertise (COEs) at their university

partners to develop open-source finite element (FE) models of four modern football helmets and

associated test equipment and methods. These publicly available FE models were created as a platform

and baseline resource for injury prevention research and to stimulate the development of novel and highly

effective helmet designs. These FE models are licensed and distributed by Biocore subject to the terms of

the Licensing Agreement and Citation Policy.

The COE for this helmet model is the Wake Forest University Center for Injury Biomechanics.

Helmet COE contact information

Wake Forest University Center for Injury Biomechanics

575 N. Patterson Ave. Suite 120

Winston-Salem, NC 27106

POCs:

Scott Gayzik, Ph.D.

[email protected],

Joel D. Stitzel, Ph.D.

[email protected]

COE Web:

www.wakehealth.edu/cib/

Biocore contact information

1621 Quail Run

Charlottesville, VA 22911

www.biocorellc.com

[email protected]

http://biocorellc.com/fe-model-license/

http://biocorellc.com/citation-policy/

mailto:[email protected]


http://www.wakehealth.edu/cib/

http://www.biocorellc.com/



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Contents 1. About this Document ............................................................................................................................ 1

2. About the Project .................................................................................................................................. 1

2.1. The Model Package ....................................................................................................................... 2

3. Helmet Model Development Summary ................................................................................................ 3

3.1. Helmet Geometry Development ................................................................................................... 3

3.2. Material Characterization ............................................................................................................. 3

3.3. Validation and Verification Simulations ........................................................................................ 4

4. Schutt Air XP Pro Model Information ................................................................................................... 5

4.1. Running the Model ....................................................................................................................... 6

4.2. Organization of the Helmet Keyword Cards ................................................................................. 8

4.3. Toggles Programmed into the Model ......................................................................................... 10

4.4. Model Output Information ......................................................................................................... 10

4.5. Model Number Conventions ....................................................................................................... 11

5. Review of Model Components ............................................................................................................ 12

5.1. Interior View ............................................................................................................................... 12

5.2. Deep Layer View ......................................................................................................................... 13

6. Model Validation ................................................................................................................................. 13

6.1. Material Validation ..................................................................................................................... 13

6.2. Sub-Assembly Validation ............................................................................................................ 14

6.3. Helmet Validation ....................................................................................................................... 15

6.4. Objective Evaluation ................................................................................................................... 19

7. Technical Notes ................................................................................................................................... 19

8. Troubleshooting .................................................................................................................................. 20

9. Model Updates .................................................................................................................................... 21

10. Acknowledgements ......................................................................................................................... 22

11. References ...................................................................................................................................... 23

12. Appendix A ...................................................................................................................................... 24


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Figures

Figure 1. Helmet front view (Left) and side view (Right) with global coordinate system sign convention. . 5

Figure 2. DYNA file include hierarchy. .......................................................................................................... 8

Figure 3. Schutt XP Pro numbering convention diagram. ........................................................................... 11

Figure 4. Full helmet model with labels of components from outermost view. Colors are used for

visualization and may not reflect product colors. ...................................................................................... 12

Figure 5. Helmet model with labels of components from interior view. Colors are used for visualization

and may not reflect product colors. ........................................................................................................... 12

Figure 6. Helmet model with labels of components from deep layer view. Colors are used for

visualization and may not reflect product colors. ...................................................................................... 13

Tables

Table 1. Baseline geometrical data of the model. ........................................................................................ 3

Table 2. Summary of impact conditions used for helmet validation. ........................................................... 4

Table 3. Schutt Air XP Pro helmet model summary. ..................................................................................... 5

Table 4. Mesh quality details. ....................................................................................................................... 5

Table 5. Helmet model unit system. ............................................................................................................. 5

Table 6. LS-DYNA build used in model development and debugging. .......................................................... 6

Table 7. Required keyword cards included in each main impact condition keyword file. ........................... 8

Table 8. Included ‘Toggles’ in the model. ................................................................................................... 10

Table 9. Model outputs found in helmet model. ........................................................................................ 10

Table 10. Material level validation cases. ................................................................................................... 13

Table 11. Sub assembly validation cases. ................................................................................................... 14

Table 12. Pendulum impact (PI) validation tests. ....................................................................................... 15

Table 13. Linear impactor (LI) validation tests. ........................................................................................... 16

Table 14. Drop impact (DI) validation tests with NOCSAE headform. ........................................................ 17

Table 15. Drop impact (DI) validation tests with HIII headform. ................................................................ 18

Table 16. Overall CORA evaluation. ............................................................................................................ 19

Table 17. Pendulum impact CORA scores ................................................................................................... 24

Table 18. Linear impact CORA scores. ........................................................................................................ 25

Table 19. NOCSAE drop impact CORA scores (NOCSAE_v1.1.k was used) ................................................. 26

Table 20. HIII drop impact CORA scores ..................................................................................................... 26

2016 Schutt Air XP Pro v1.0

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1. About this Document This manual applies to the 2016 Schutt Air XP Pro (Safety Equipment Institute model 789102) finite

element (FE) model developed by the Wake Forest University Center for Injury Biomechanics under the

contract ID GTS#: 44891, “Crowdsourced Helmet Model Development” (v1.0 at the time of release of this

manual), sponsored by Biomechanics Consulting and Research, LLC (Biocore) and Football Research Inc.

(FRI) with support from the National Football League (NFL). It is intended to serve as a manual and quick

start guide for users. This document is intended to serve as a manual and quick start guide for users, and

provides general information on the FE model, including best practices for running the model. This manual

applies only to the use of the model with LS-DYNA solver (LSTC, Livermore, CA).

2. About the Project The NFL has convened academics with entrepreneurs to stimulate innovation of player-ready safety

equipment. It’s part of what the NFL calls the Engineering Roadmap. The Engineering Roadmap is a

comprehensive and dedicated plan to try and bring knowledge, research and tools together to develop

and improve protective equipment for the head. As part of this Roadmap, Biocore and FRI with support

from the National Football League have collaborated with university partners to develop open-source

finite element (FE) models of four modern football helmets and associated test equipment and methods.

These publicly available FE models are available as a platform and baseline resource for injury prevention

research and to stimulate the development of novel and highly effective helmet designs. The models were

developed by Centers of Expertise (COEs) at the University of Virginia, Wake Forest University, KTH Royal

Institute of Technology, and the University of Waterloo. Technical specifications and experimental

validation data for the models were developed by Biocore and provided to these COEs, who created the

computational models using physical helmets. The COEs are listed below.

University of Waterloo

Xenith Model COE

Principal Investigator: Duane Cronin, Ph.D.

University of Virginia

Vicis Model COE and Helmet Assessment Models COE

Principal Investigator: Matthew B. Panzer, Ph.D.

Wake Forest University

Schutt Model COE

Principal Investigators: Joel Stitzel, Ph.D. and Scott Gayzik, Ph.D.

KTH Royal Institute of Technology

Riddell Model COE

Principal Investigator: Madelen Fahlstedt, Ph.D. and Peter Halldin, Ph.D.

https://www.playsmartplaysafe.com/newsroom/videos/nfls-engineering-roadmap-driving-progress-toward-better-protective-equipment/


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2.1. The Model Package The following items are included in the model package:

• A compressed file containing the model –

2016_Schutt_Air_XP_Pro_Helmet_Model_v1.0.zip

Extracting this file will create three folders

o 01_Manual

o 02_Helmet

o 03_BoundaryConditions

Details on the contents are found below in Section 4.


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3. Helmet Model Development Summary This helmet model was developed in three general steps: geometry development, material

characterization, and model validation.

3.1. Helmet Geometry Development Geometry development was performed using various scanning, segmentation, and geometry processing

techniques. Scanning of the helmets was done using Computed Tomography (CT). The helmets were

scanned as fully assembled, fully disassembled, and fully assembled fit with a 3D printed NOCSAE head

form. Most metal components such as screws were replaced with plastic counterparts to minimize

scanner artifact. Scanning was performed at 0.6 mm cubic voxel resolution.

Scan data was then segmented part by part using commercially available image segmentation software,

using the fully assembled scans, and saved as stereolithography files (.stl). The disassembled and fully

assembled fit with a 3D head form scan data was utilized throughout the process as supplemental

resources. The stl files were processed through commercially available reverse engineering software.

Depending on the part of the helmet, the stl files were meshed as 2D quad or 3D hexahedral elements.

Two-dimensional mesh structures include the helmet shell, vinyl pad covering, and conical absorbers,

whereas three-dimensional mesh structures include the five different types of foam. The facemask was

recreated by fitting one-dimensional lines through midpoint measurements along the scan data and

creating 1D beam elements of a prescribed edge length of 10 mm. Helmet details are listed in Table 1.

Table 1. Baseline geometrical data of the model.

Baseline Helmet Model Data

Make Model Size SEI Model Number

Schutt Air XP Pro Large 789102

3.2. Material Characterization Material characterization was performed using coupon testing across various strain rates. Experimental

strain rates varied from 0.001/s (quasi-static) to upwards of 550/s. Slow rate (under 100/s) tests were

performed on universal testing machine that allowed for displacement-controlled conditions. Due to large

strain variations in plastic materials within the gage length, strains were measured using digital image

correlation. Dynamic tests (over 100/s) were performed with a custom test type device that allows for

much higher strain rates with no displacement control. Strains in the dynamic tests were also measured

using digital image correlation.

Tensile characterization tests were performed on every material using ASTM D368 Type V dogbone

specimens. Compressive tests were performed on foams and the outer shell. The foam materials also

underwent double-lap shear testing. The Blue TPU cone material was too thin to adequately measure

compressive stresses and material properties were back-calculated using single cone finite element

simulations matched to experiments. A total of 9 material characterization tests were completed and are

summarized in Section 6.1.


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3.3. Validation and Verification Simulations Several subassembly or component tests were run prior to impact simulations to verify the helmet’s

response on a component level basis. This included a compressive test of a single functional unit of the

conical absorbers at both quasi-static and dynamic rates. Furthermore, a pad unit (vinyl and foam

together) were tested in compression quasi-static and dynamic rates. An MTS Landmark Servohydraulic

Test System was used for quasi-static testing of the helmet shell and facemask at a speed of 0.1 mm/s.

The helmet shell was compressed in the anterior-posterior, lateral, and superior-inferior directions, while

the facemask was compressed in the anterior-posterior and lateral directions, for a total of 5 tests.

The helmet model was also validated in dynamic loading for the following three impact conditions:

Pendulum Impact (PI), Linear Impact (LI), and Drop Impact (DI). A total of 67 simulations were performed

with the full helmet, using either a Hybrid III (HIII) or NOCSAE headform (Table 2). The Hybrid III head-

neck (HIII H-N) was used in a series of pendulum (Cobb et al., 2016) and linear impact (Viano et al., 2012)

tests. A drop impact test condition was also used with the HIII and NOCSAE headforms with rigid necks.

The final test matrix consisted of 12 VT pendulum tests, 24 linear impactor tests, 19 drop impact tests

with the NOCSAE headform, and 12 drop tower tests with the HIII headform. Please refer to the impactor

user’s manual (Impactor_Users_Manual_v1.0.docx) for additional details on the development and use of

the headforms and impactor models. Further description of the impact conditions used for helmet

validation and results are provided in Section 6.3.

Table 2. Summary of impact conditions used for helmet validation.

Impact Condition Dummy Impact Location Impact Velocity

(m/s) Number of Tests

PI HIII H-N Back, Front,

Front Boss, Side 3.0; 4.6; 6.1 12

LI HIII H-N A, AP, B, C, D, F, R, UT

5.5; 7.4; 9.3 24

DI NOCSAE

Back, Front, Mask*, Side, Top

2.9; 3.7; 4.9; 6.0 19

HIII Back, Front,

Side, Top 2.9; 4.9; 6.0 12

*NOCSAE Mask impact at 6.0 m/s was not evaluated.

The helmet model was fit onto an FE model of a NOCSAE and Hybrid III headform which was then used

for the respective test matrix in Table 2. Fitting was performed by moving the helmet model to the correct

position, scaling down the headform, and using *BOUNDARY_PRESCRIBED_FINAL_GEOMETRY to expand

the headform to its original state. The mid-plane nodes of the helmet model were constrained laterally

and vertically to keep the helmet in place during fitting and allow natural deformation. Helmet-to-

headform positioning was based on available measurements and photographic documentation of the

physical test (Section 6.3). Initial stress of the foams was implemented into the model post-fitting with

initial foam reference geometry. This uses the pre-fit nodal locations of the foam to calculate the stress

of the foams at the initial state of simulation.


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4. Schutt Air XP Pro Model Information Table 3 below provides general information about the model.

Table 3. Schutt Air XP Pro helmet model summary.

Main file name (02_Helmet): SchuttAXP_v1.0_0main_Nofit.dyn

Elements: 276,157

Nodes: 272,301

Number of Parts: 15

Mass (kg): 1.71

Moments of Inertia (principal axes, kg-mm²) Ixx = 22400, Iyy = 20278, Izz = 15762

The file naming is based on the helmet make, model, and version. Details on the mesh quality are

summarized in Table 4. The unit system used in the model is shown in Table 5. Deviations from this unit

system will require the use of a unit transform in LS-DYNA (see *INCLUDE_TRANSFORM).

Table 4. Mesh quality details.

Jacobian Warpage Aspect ratio Skew

(elements < 0.7): 3% Minimum: 0.35

(elements > 5°): 5% Maximum: 81°

(elements > 5): 0% Maximum: 4.17

(elements > 60°): 0% Maximum: 58°

Table 5. Helmet model unit system.

Time Length Mass Force Stress

ms mm kg kN GPa

The model is in a global coordinate system defined by SAE J211/1 sign convention. A diagram of the

coordinate system and model orientation can be seen below in Figure 1.

Figure 1. Helmet front view (Left) and side view (Right) with global coordinate system sign convention.


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4.1. Running the Model The specific COE, as well as others in this project have exclusively used LS-DYNA in the model development

for this version of the model. While not standards, the Center for Injury Biomechanics at Wake Forest

University currently performs all the jobs on the Wake Forest DEAC cluster, a centrally managed resource

with support provided in part by the university. All the jobs are performed with 12 cores (6GB per core).

Table 66 summarizes the current LS-DYNA build used for model development and debugging.

Table 6. LS-DYNA build used in model development and debugging.

Version Precision Revision SVN Ver. Platform OS

MPP R7.1.2 Single 95028 95028 Linux RHEL 5.4 Platform-MPI 8.1.1 Xeon64 ul

Executable

${DynaPath}/64-Bit/ls-dyna_mpp_s_r7_1_2_95028_x64_redhat54_ifort131_sse2_platformmpi

Use the following steps to open and run the model. While file structure is meant to be consistent across different helmet models; material formulations, control cards, parts, elements, etc. were developed based on the COE’s discretion and will vary between helmet models.

1. Unzip the file (2016_Schutt_Air_XP_Pro_Helmet_Model_v1.0.zip) to a location on your system.

This creates three folders (01_Manual, 02_Helmet, 03_BoundaryConditions).

2. Within 01_Manual are two files

a. Manual_2016_Schutt_Air_XP_Pro_Helmet_Model_v1.0.docx

b. Impactor_Users_Manual_v1.0.docx

c. helmet_colormap

d. READ_ME.txt

3. Within 02_Helmet (unfitted helmet model files)

a. SchuttAXP_v1.0_0main_Nofit.dyn

b. SchuttAXP_v1.0_chinstrap_Nofit.k

c. SchuttAXP_v1.0_control.k

d. SchuttAXP_v1.0_helmet.k

e. SchuttAXP_v1.0_nodes_Nofit.k

4. Within 03_BoundaryConditions (includes fitted helmet model)

• 0Includes (listed alphabetically)

a. 0Main_DI_HIII_SchuttAXP_v1.0.k

b. 0Main_DI_NOCSAE_SchuttAXP_v1.0.k

c. 0Main_LI_HIII_SchuttAXP_v1.0.k

d. 0Main_PI_HIII_SchuttAXP_v1.0.k

e. DropImpactor_0main_HIII.k

f. DropImpactor_0main_NOCSAE.k

g. DropImpactor_Arm_HIII.k

h. DropImpactor_Arm_NOCSAE.k

i. DropImpactor_Carriage.k

j. DropImpactor_LC.k

k. HIII_head.k


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l. HIII_head_0main.k

m. HIII_headneck.k

n. HIII_neckmount_LI.k

o. HIII_neckmount_PI.k

p. LinearImpactor.k

q. NOCSAE_v1.0.k

r. NOCSAE_v1.1.k

s. PendulumImpactor.k

t. SchuttAXP_v1.0_0main_HIIIfit.dyn

u. SchuttAXP_v1.0_0main_NOCSAEfit.dyn

v. SchuttAXP_v1.0_chinstrap_HIIIfit.k

w. SchuttAXP_v1.0_chinstrap_NOCSAEfit.k

x. SchuttAXP_v1.0_control.k

y. SchuttAXP_v1.0_helmet.k

z. SchuttAXP_v1.0_nodes_HIIIfit.k

aa. SchuttAXP_v1.0_nodes_NOCSAEfit.k

• Drop_Impact

• Linear_Impact

• Pendulum_Impact

5. Within the desired impact condition folder (Drop_Impact, Linear_Impact, or Pendulum Impact),

there are nested folders containing preset main files (0Main.k) for each impact condition, dummy,

location, and speed condition that was targeted for model validation (Section 6.3):

a. 03_BoundaryConditions\“impact condition”\XX_“dummy”_”location”_“speed”\0Main.k

where XX indicates the impact condition (PI, LI, or DI).

6. Load the desired 0Main.k file into LS-DYNA and execute the simulation.

A main file can be used directly for simulation or modified by the user for an arbitrary impact condition.

To modify the file for an arbitrary condition:

1. Open a 0Main.k file.

2. Change the desired parameters under the *PARAMETER keyword.

3. Save the file to another directory. If the main file is moved to a different directory, ensure that

the 0Includes path in 0Main.k is referenced accordingly under *INCLUDE_PATH_RELATIVE.

4. Load the modified 0Main.k file into LS-DYNA and execute the simulation.

Details on parameter naming and referencing within keyword files is included in the impact user’s manual.

Although main files have been preset to the validation conditions (Section 6.3), the user should confirm

these parameters prior to simulation (see notes within each 0Main.k file banner for important details). In

additional to the main three folders, a helmet color map (01_Manual) that was used to render the helmet

in the color scheme shown in this manual when using LS-PrePost, and a README.txt file have been

included in the model package. Information on technical support and other resources to assist model

users is available at our FAQ page.

http://biocorellc.com/faqs/


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4.2. Organization of the Helmet Keyword Cards Main simulation input files (0Main.k) rely on a series of other keyword files that are incorporated through

several *INCLUDE or *INCLUDE_TRANSFORM cards. Each main input file includes a main impact condition-

helmet file (0Main_XX_“dummy”_SchuttAXP_v1.0.k), where XX indicates the impact condition (PI, LI, or

DI) which includes additional simulation files. An include hierarchy is shown in Figure 2 and notable

included files are listed for each impact condition file (Table 7). Outputs defined in the included keyword

files are also noted. Refer to Section 4.3 for a detailed description of the model outputs.

Figure 2. DYNA file include hierarchy.

Table 7. Required keyword cards included in each main impact condition keyword file.

Pendulum Impact: 0Main_PI_HIII_SchuttAXP_v1.0.k Included File Include Card Description Outputs

HIII_headneck.k *INCLUDE_TRANSFORM HIII H-N model positioned

according to impact location

Head accelerometer, Head rotation,

Lower neck load cell, Upper neck

load cell

HIII_neckmount_PI.k *INCLUDE_TRANSFORM HIII neck mount

positioned according to impact location

N/A

PendulumImpactor.k *INCLUDE_TRANSFORM Pendulum impactor

model with ID’s offset through transformation

Pendulum accelerometer

SchuttAXP_0main_HIIIfit.dyn *INCLUDE_TRANSFORM Helmet model positioned on the head according to

COE specification N/A

**SchuttAXP_v1.0_control.k *INCLUDE Standardized card that includes all control and

database cards N/A


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Linear Impact: 0Main_LI_HIII_SchuttAXP_v1.0.k Included File Include Card Description Outputs

HIII_headneck.k *INCLUDE_TRANSFORM HIII H-N model positioned

according to impact location

Head accelerometer, Head rotation,

Lower neck load cell, Upper neck

load cell

HIII_neckmount_LI.k *INCLUDE_TRANSFORM HIII neck mount

positioned according to impact location

N/A

Linear_Impactor.k *INCLUDE_TRANSFORM Linear impactor model positioned according to

impact location

Impactor accelerometer Impactor load

cell

SchuttAXP_0main_HIIIfit.dyn *INCLUDE_TRANSFORM Helmet model positioned on the head according to



database cards N/A

Drop Impact: 0Main_DI_HIII_SchuttAXP_v1.0.k 0Main_DI_NOCSAE_SchuttAXP_v1.0.k

Included File Include Card Description Outputs

HIII_head_0main.k *NOCSAEv1.1.k

*INCLUDE_TRANSFORM Dummy headform model positioned according to

impact location

Head accelerometer

DropImpactor_0main_HIII.k DropImpactor_0main_NOCSAE.k

*INCLUDE_TRANSFORM Impactor transformation and sub-part definitions

N/A

**DropImpactor_Arm_HIII.k **DropImpactor_Arm_NOCSAE.k

*INCLUDE_TRANSFORM

Drop carriage arm positioned according to

impact location with ID’s offset through transformation

N/A

**DropImpactor_Carriage.k *INCLUDE_TRANSFORM

Drop carriage positioned to impact location with

ID’s offset through transformation

Carriage accelerometer

**DropImpactor_LC.k *INCLUDE_TRANSFORM

Drop load cell positioned to impact location with

ID’s offset through transformation

Load cell

SchuttAXP_0main_HIIIfit.dyn SchuttAXP_0main_NOCSAEfit.dyn

*INCLUDE_TRANSFORM Helmet model positioned on the head according to



database cards N/A

*File version 1.1 was used for model validation (Section 6.3); file version 1.0 has not been verified through simulation. **Files are included indirectly.


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4.3. Toggles Programmed into the Model The following parameters (Table 88) are coded into the model as options.

Table 8. Included ‘Toggles’ in the model.

Foam Pad Airbags (see SchuttAXP_v1.0_helmet.k)

Cross-sectional vent area of “Open” vinyl (see Rairopen under *PARAMETER)

Default: 0.420 *Tuned to replicate isolated pad response testing

Cross-sectional vent area of “Closed” vinyl (see Rairclose under *PARAMETER)

Default: 0.820 *Tuned to replicate isolated pad response testing

4.4. Model Output Information Table 99 below provides a summary of available preprogrammed model output information for the

helmet model. These are useful for tracking kinematics and quantifying deformations. Current outputs

preprogrammed into the model are located within keyword file banners.

Table 9. Model outputs found in helmet model.

Value LS-DYNA Output Notes

Drop Test: Outer Shell, Facemask

Contact force ELOUT: (EID: 100016033) Force output for drop tests

Carriage acceleration NODOUT: (NID: 10002458) Acceleration for drop carriage

Linear Impactor Test: Outer Shell, Facemask

Contact force ELOUT: (EID: 61000) Force output for linear impactor

Impactor acceleration NODOUT: (NID: 70075) Acceleration for ram

HIII Headform in BC

HIII head CG accelerometer NODOUT: (NID: 17905) Head CG acceleration

HIII head OC rotation NODOUT: (NID: 17906) Head rotation about OC pin

Lower Neck Load Cell (T1) ELOUT: (EID: 56421) Load cell for T1

Upper Neck Load Cell (OC) ELOUT: (EID: 56422) Load Cell for OC

NOCSAE Headform in BC

NOCSAE head CG accelermometer

NODOUT: (NID: 61099) Head CG acceleration


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4.5. Model Number Conventions The numbering convention is used throughout model and is summarized in Figure 3.3.

Region Part Name Part Number Range of Element Number

Conical Absorbers

Conical_absorbers Connecting_Ribs

90004 (2D) 90005 (2D)

103162-108158 316092-321489

Foams

Low_density_grey_foam High_density_grey_foam

Black_foam Yellow_foam_1 Yellow_foam_2

90006 (3D) 90007 (3D) 90008 (3D) 90009 (3D) 90010 (3D)

355841-360840 350635-354562 362279-363918 355383-355840 354563-355382

Vinyl Covering Thin_Grey_Vinyl Thick_Grey_Vinyl

90011 (2D) 90012 (2D)

413000-417999 421959-425765

Chin Strap Chincup_2D

Chinstrap_1D Chinstrap_2D

90013 (2D) 90014 (1D) 90015 (2D)

367521-368300 433962-434060 380004-380877

Helmet Shell Helmet_shell 100008 (2D) 325745-330743

Facemask Facemask_small Facemask_large

100009 (1D) 100010 (1D)

90000-90112 90013-90201

Figure 3. Schutt XP Pro numbering convention diagram.


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5. Review of Model Components The helmet model included a total of 15 parts. Below is the visualization of the virtual helmet model, with

labels denoted each part (Figure 44).

Figure 4. Full helmet model with labels of components from outermost view. Colors are used for visualization and may not reflect product colors.

5.1. Interior View The interior view of the helmet model is shown below in Figure 5.5. The components were highlighted

with labels for visualization.

Figure 5. Helmet model with labels of components from interior view. Colors are used for visualization and may not reflect product colors.


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5.2. Deep Layer View The deep layer structure is shown in Figure 6.6.

Figure 6. Helmet model with labels of components from deep layer view. Colors are used for visualization and may not reflect product colors.

6. Model Validation A hierarchical approach was used for model validation. Validation consisted of material subassembly and

full helmet tests. The following sections detail the validation performed in these three steps.

6.1. Material Validation Material models were created using MCalibrate (Veryst Engineering, Needham Heights, MA) by matching

single-element LS-DYNA simulations to experimental results. Resulting material models minimized the

normalized mean absolute difference between the simulation and the experimental evaluation criteria.

The list of materials and associated evaluation criteria can be found in Table 1010. Refer to Figure 4 4 – 6

Figure 6.for corresponding components on the helmet model.

Table 10. Material level validation cases.

Test Mode Rate(s) Evaluation

Criteria Experiment

Shell Tension, Compression

QS, Dyn 𝜎 vs. 𝜀

Blue TPU Tension,

Compression A

QS, Dyn 𝜎 vs. 𝜀, F vs. D


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Criteria Experiment

Thin Grey Vinyl

Tension QS, Dyn 𝜎 vs. 𝜀

Black Foam Tension,

Compression, Shear


High-Density Grey Foam

Tension, Compression, Shear


Low-Density Grey Foam



Yellow Foam 1



Yellow Foam 2



Chinstrap Tension QS F vs. D

A Compression was tested using a single cone and resulting F vs. D was measured. Refer to figures above for precise location. QS – Quasi-static, Dyn – Dynamic, 𝜎 – Stress, 𝜀 – strain, F – Force, D – Displacement

6.2. Sub-Assembly Validation A series of validation tests and simulation were also performed at the sub assembly level (Table 1111).

Table 11. Sub assembly validation cases.


Criteria Simulation Experiment

Conical Absorber

Axial compression

QS, Dyn F vs. D


15

Meso-scale foam

Compression QS, Dyn F vs. D

Helmet Thermoplastic Shell

Anterior, lateral and crown compression

QS F vs. D

Facemask Anterior-

posterior, lateral compression

QS

F vs. D

QS – Quasi-static, Dyn – Dynamic, F – Force, D – Displacement

6.3. Helmet Validation A total of 67 simulations were run with the full helmet, using either a HIII or NOCSAE headform. The HIII

H-N were impacted via linear impactor and the NOCSAE headform was used in a drop tower. The HIII

headform was used for a third set of tests run per the current Star rating system developed at Virginia

Tech (Davis et al., 2016 and Rowson et al., 2015). The final test matrix consisted of 24 linear impactor

tests, 19 drop tower tests used with the NOCSAEv1.1.k headform, 12 drop tower tests with the HIII

headform, and 12 VT pendulum tests (Tables 12 – 15). The helmet model normal terminated in all 67

simulations (Table 6). Within the NOCSAE headform drop impact test matrix, the back and facemask

impacts were used to test robustness and were not used for CORA evaluation, due to excessive rotation

in the nominally rigid connection and this could not be captured in the model. More details on the

impactors and headform models can be found in the impactor user’s manual.

Table 12. Pendulum impact (PI) validation tests.

Impact Configuration

Evaluation Criteria

Simulation

Impact Velocity

[m/s]

Force versus Time

Linear Acceleration versus Time

Angular Velocity

Front 3.0 4.6 6.1

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG (XYZ)


16

Front Boss

3.0 4.6 6.1

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG (XYZ)

Side 3.0 4.6 6.1

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG (XYZ)

Back 3.0 4.6 6.1

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG (XYZ)

Table 13. Linear impactor (LI) validation tests.


Evaluation Criteria

Simulation Experiment

Impact Velocity

[m/s]

Force versus Time


Angular Velocity

A 5.5 7.4 9.3

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG

(XYZ)

AP 5.5 7.4 9.3

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG

(XYZ)

B 5.5 7.4 9.3

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG

(XYZ)

C 5.5 7.4 9.3

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG

(XYZ)


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D 5.5 7.4 9.3

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG

(XYZ)

F 5.5 7.4 9.3

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG

(XYZ)

R 5.5 7.4 9.3

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG

(XYZ)

UT 5.5

7.4* 9.3

Contact Force

(Impact direction)

Head CG

(XYZ)

Impactor (Impact

direction)

Head CG

(XYZ)

Table 14. Drop impact (DI) validation tests with NOCSAE headform.


Evaluation Criteria


Impact Velocity

[m/s]

Force versus Time


Back*

2.9 3.7 4.9 6.0

Contact Force (XZ)

Head CG (X)

Carriage Acc. Z

Front

2.9 3.7 4.9 6.0

Contact Force (XZ)

Head CG (XZ)

Carriage Acc. Z

Mask* 2.9 3.7 4.9

Contact Force (XZ)

Head CG (X)

Carriage Acc. Z


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Side

2.9 3.7 4.9 6.0

Contact Force (XZ)

Head CG (YZ)

Carriage Acc. Z

Top

2.9 3.7 4.9 6.0

Contact Force (XZ)

Head CG (XZ)

Carriage Acc. Z

*Cases not included in overall CORA rating, used for robustness only.

Table 15. Drop impact (DI) validation tests with HIII headform.


Evaluation Criteria


Impact Velocity

[m/s]

Force versus Time


Back 2.9 4.9 6.0

Contact Force (XZ)

Head CG (XYZ)

Carriage Acc. Z

Front 2.9 4.9 6.0

Contact Force (XZ)

Head CG (XYZ)

Carriage Acc. Z

Side 2.9 4.9

6.0*

Contact Force (XZ)

Head CG (XYZ)

Carriage Acc. Z

Top 2.9 4.9 6.0

Contact Force (XZ)

Head CG (XYZ)

Carriage Acc. Z


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6.4. Objective Evaluation CORA is a software program that quantitatively compares two signals: a reference signal (experimental

test data in current study) and a simulation signal (model measurements in current study). The current

study utilized the cross-correlation score to compare the experimental and model responses, and

generated three output ratings based on shape, size and phase agreement. The corridor rating was not

used, but a cross correlation score was calculated for all experimental tests, even repeated tests, and

scores were averaged.

CORA ratings range between 0 and 1, where 0 means the two signals compared are completely different,

and 1 indicates the signals are identical, thus it is like a grading system. A detailed explanation for the

mathematical calculation of the shape, size, and phase rating can be referenced in the CORA user manual

(Thunert, 2012 – Partnership for Dummy Technology and Biomechanics). Additionally, weighting factors

based on experimental peak magnitude values were applied to determine the overall average objective

evaluation rating for a signal with orthogonal components. This factor is referred to as the Test Magnitude

Factor, or TMF (Rowson et al., 2011). Weighting was applied only to the orthogonal component signals

from the same sensor. Weight factors were derived by normalizing the peak value for each orthogonal

signal of a single sensor, e.g., X, Y, and Z, by the sum of peaks for each orthogonal signal (Equation 1).

𝑇𝑀𝐹 =𝑅𝑖

𝑅𝑥 + 𝑅𝑦 + 𝑅𝑧 (1)

Where Ri is the peak value of the test trace for a given signal. The magnitude factor is then applied to the

CORA score for each respective orthogonal signal. The final CORA score for a sensor is then considered to

be the sum of the magnitude weighted orthogonal components. The overall score for a given test is the

mean of all sensors in the test. The overall score is the mean of all tests in the series. CORA scores were

evaluated over the first 30ms of impact. The overall CORA score is presented in Table 16. Individual CORA

scores are presented in Appendix A.

Table 16. Overall CORA evaluation.

Overall Weighted CORA Score

Drop Tower NOCSAE

Drop Tower HIII

Linear Impactor

Pendulum

0.766 0.723 0.772 0.766

Legend 0.00 0.25 0.50 0.75 1.00

7. Technical Notes Some assumptions were made in the development of the model and are detailed below:

• In the physical helmet, the foam is free floating within the grey vinyl. To minimize contacts and

maximize stability, this interface was modeled as node-to-node.

• The physical helmet has pads with air vents and pads that are “closed” and may be inflated for

fitting purposes. Component level testing was performed on both types of pads and numerical


20

“airbags” were implemented into the model to represent the air component of the pads. These

airbags provide a control volume approach to modeling relating pressure and volume. Venting

was defined in the model and the cross-sectional area of the vents was optimized to match the

component level pad response. These values are described in Table 88 and may be changed if the

user chooses.

• The FE model defined the plastic connections of the facemask to the helmet shell as rigid body

connections. Similarly, button connections of the conical absorbers to the helmet shell were

modeled as rigid body connections. Velcro connections of the pads to the conical absorbers were

modeled as tied contacts with at thickness of 1 mm.

• The chinstrap is modeled as a 2D chincup with rigid connections to the 2D chinstrap, which is

connected to the helmet shell with a 1D beam. The 1D beam is defined as an elastic spring discrete

beam and has a default initial force of 40 N which tightens the chinstrap to the head form prior

to impact. This value may be changed by the user.

• In the physical linear impactor test the puck of the VN600 and the endcap separated from the

impactor in the front impact condition (F). In the FE simulations the impactor and VN/endcap puck

were fixed together. This may influence the results since the impactor may be restricting the

helmet/head motion in the FE simulations.

• Note that environmental factors such as temperature and humidity were not considered during

model development. There are built in venting parameters to vary the vent area of the grey vinyl

that covers the padding. The current parameters are default and were chosen to optimize pad

compression response to physical test data.

8. Troubleshooting Technical support and other resources to assist model users is available at our FAQ page.

Time Step: The model was developed and tested with specific time step targets for the explicit time

integration. Without mass scaling, the time step of the model is 0.18 μs. The user can specify a time-step

through mass-scaling (DT2MS on the *CONTROL_TIMESTEP). Less than 1% mass should be gained if scaling

to a time step of 0.3 μs. This is the default mass scaling. The model has also been tested for mass scaling

to 0.5 μs. For this scaling, the total mass gained should be less than 5%. The model has not been tested at

mass-scaling above 0.6 μs. Caution should be exercised when mass scaling, the user should investigate

the total mass gained and the location of the additional mass. Added mass can artificially lead to higher

forces and spurious energy gain observed in the simulation.

Control Cards: The model was developed and tested with specific control cards parameters. These

parameters were selected based on model performance as well as inclusion with other boundary

conditions. Default values were selected for most control parameters to reduce model incompatibilities.

However, some specific changes to the default control card parameters were required for model

development and should be noted prior to running with another model. For example, the contact

thickness is set as the actual shell thickness for the CONTACT_AUTOMATIC_SINGLE_SURFACE definition



21

used in this model. This deviates from the default method in which a contact thickness is provided by the

user. Details regarding these control cards can be found in the SchuttAXP_v1.0_control.k file.

Material Properties: The current model uses material properties based on reverse engineering. Altering

the material properties within the cards of the model will alter the performance of the models.

Hourglass Control: It has been shown that hourglass control has a large influence on stability and

compliance of soft materials, specifically foams in LS-DYNA. The COE has developed and refined the

hourglass control in the model to tradeoff model stability and response. The model response may be

affected using different hourglass formulations. Users can refer to our FAQ page for a list of technical

resources available to model users.

Contact Definitions: Modifications to contact parameters in a region where instability is occurring may be

investigated if contact stability is an issue. This refers to parameters such as soft, contact thickness (sst,

mst, sfst, sfmt) or scale factor (sfs, sfm). To reduce negative volume errors in LS-DYNA, the use of

*CONTACT_INTERIOR is recommended to help prevent elements from inverting. The current model has a

part set that is included in *CONTACT_INTERIOR card (psid: 1990001). A part that is experiencing negative

volumes may be added to this set if instability occurs. Users can refer to our FAQ page for a list of technical

resources available to model users.

9. Model Updates This model may be updated over time. Users should refer to the models download page for the latest

model version. If users identify features of the model that may be improved or enhanced, they should

contact Biocore at [email protected].




http://biocorellc.com/finite-element-models/



22

10. Acknowledgements The Schutt Air XP Pro COE at Wake Forest University’s Center for Injury Biomechanics gratefully

acknowledges the following organizations and individuals for their generous support and hard work.

Sponsors: National Football League Football Research, Inc. Biocore, LLC Richard Kent, PhD Principal Engineering Consultant and co-Founder Ann Bailey Good, PhD Senior Engineer Gwansik Park, PhD Senior Engineer Lee Gabler, PhD Senior Engineer Roberto Quesada, MS Engineer Brian McEwen, BS Engineer Schutt Air XP Pro COE Wake Forest University School of Medicine Co-PIs: F. Scott Gayzik, Joel D. Stitzel Lead Engineer: William B. Decker Engineering Team: Alex M. Baker, Xin Ye, Philip J. Brown

University Collaborators Xenith X2E COE

University of Waterloo PI: Duane Cronin Engineering Team: Jeffery Barker, Donata Gierczycka, Michael Bustamante, David Bruneau, Miguel Corrales

Riddell Revolution Speed Classic COE KTH Royal Institute of Technology Co-PIs: Peter Halldin, Madelen Fahlstedt Engineering Team: Marcus Arnesen, Erik Jungstedt

Vicis Zero 1 and Impactor COE

University of Virginia, Center for Applied Biomechanics PI: Matthew Panzer Lead Engineer: J. Sebastian Giudice Engineering Team: Adrian Caudillo, Sayak Mukherjee, Kevin Kong, Wei Zeng


23

11. References Cobb BR, Zadnik AM, Rowson S. Comparative analysis of helmeted impact response of Hybrid III and

National Operating Committee on Standards for Athletic Equipment headforms. Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology. 2016;230(1):50-60.

Davis ML, Koya B, Schap JM, Gayzik FS. Development and full body validation of a 5th percentile female

finite element model. Stapp Car Crash Journal. 2016;60:509-544. Rowson B, Rowson S, Duma SM. Hockey STAR: a methodology for assessing the biomechanical

performance of hockey helmets. Annals of biomedical engineering. 2015;43(10):2429-2443. Rowson S, Duma SM. Development of the STAR evaluation system for football helmets: integrating

player head impact exposure and risk of concussion. Annals of biomedical engineering. 2011;39(8):2130-2140.

Viano DC, Withnall C, Halstead D. Impact performance of modern football helmets. Annals of biomedical engineering. 2012;40(1):160-174.


24

12. Appendix A Individual CORA scores are presented in Error! Reference source not found.7 – 20. All results were

obtained from simulations using LS-DYNA mpp R7.1.2 single precision. CORA analyses were performed

over a 30ms time window from the start of impact. Simulations for a subset of cases were also run in

R7.0.0 and R9.1.0 (mpp) to test model stability. These additional simulations terminated normally;

however, their results were not validated against the experimental data.

Table 17. Pendulum impact CORA scores

Test Condition Pendulum Lin. Acc.

Head Lin. Acc.

Head Ang. Vel.

Overall

Front (3.0 m/s) 0.805 0.766 0.653 0.741

Front (4.6 m/s) 0.590 0.774 0.666 0.676

Front (6.1 m/s) 0.418 0.613 0.671 0.567

Front Boss (3.0 m/s) 0.779 0.571 0.653 0.668

Front Boss (4.6 m/s) 0.773 0.690 0.740 0.734

Front Boss (6.1 m/s) 0.659 0.712 0.643 0.671

Back (3.0 m/s) 0.798 0.805 0.798 0.800

Back (4.6 m/s) 0.900 0.923 0.894 0.906

Back (6.1 m/s) 0.871 0.744 0.807 0.808

Side (3.0 m/s) 0.849 0.778 0.878 0.835

Side (4.6 m/s) 0.934 0.865 0.919 0.906

Side (6.1 m/s) 0.922 0.832 0.904 0.886 0.766


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Table 18. Linear impact CORA scores.

Test Condition Impactor Lin. Acc.

Head Lin. Acc.

Head Ang. Vel.

Impact Force

Overall

AP (5.5m/s) 0.634 0.758 0.670 0.708 0.693

AP (7.4m/s) 0.796 0.749 0.741 0.780 0.767

AP (9.3m/s) 0.771 0.806 0.832 0.853 0.815

A (5.5m/s) 0.912 0.804 0.702 0.785 0.801

A (7.4m/s) 0.757 0.757 0.774 0.814 0.775

A (9.3m/s) 0.570 0.760 0.698 0.781 0.702

B (5.5m/s) 0.914 0.866 0.834 0.708 0.831

B (7.4m/s) 0.816 0.851 0.822 0.748 0.809

B (9.3m/s) 0.842 0.830 0.839 0.795 0.827

C (5.5m/s) 0.878 0.823 0.730 0.868 0.825

C (7.4m/s) 0.842 0.818 0.703 0.829 0.798

C (9.3m/s) 0.769 0.813 0.688 0.823 0.773

D (5.5m/s) 0.840 0.774 0.913 0.671 0.799

D (7.4m/s) 0.721 0.792 0.901 0.658 0.768

D (9.3m/s) 0.696 0.807 0.873 0.686 0.765

F (5.5m/s) 0.804 0.677 0.596 0.773 0.712

F (7.4m/s) 0.804 0.703 0.568 0.775 0.713

F (9.3m/s) 0.639 0.800 0.646 0.690 0.694

R (5.5m/s) 0.834 0.786 0.700 0.768 0.772

R (7.4m/s) 0.793 0.803 0.826 0.781 0.801

R (9.3m/s) 0.766 0.824 0.813 0.827 0.807

UT (5.5m/s) 0.876 0.780 0.862 0.682 0.800

UT (7.4m/s) 0.799 0.756 0.804 0.692 0.763

UT (9.3m/s) 0.616 0.764 0.802 0.711 0.723 0.772


26

Table 19. NOCSAE drop impact CORA scores (NOCSAE_v1.1.k was used)

Impact Condition Carriage Lin. Acc.

Head Lin. Acc.

Impact Force

Overall

Front (2.9m/s) 0.941 0.827 0.821 0.863

Front (3.7m/s) 0.857 0.827 0.751 0.812

Front (4.9m/s) 0.810 0.812 0.740 0.787

Front (6.0m/s) 0.840 0.790 0.782 0.804

Back (2.9m/s)* 0.803 0.364 0.612 0.593

Back (3.7m/s)* 0.844 0.314 0.698 0.618

Back (4.9m/s)* 0.852 0.212 0.687 0.584

Back (6.0m/s)* 0.696 0.267 0.423 0.462

Top (2.9m/s) 0.687 0.493 0.649 0.610

Top (3.7m/s) 0.676 0.485 0.536 0.566

Top (4.9m/s) 0.816 0.590 0.690 0.699

Top (6.0m/s) 0.896 0.714 0.816 0.809

Side (2.9m/s) 0.865 0.594 0.769 0.743

Side (3.7m/s) 0.953 0.729 0.836 0.839

Side (4.9m/s) 0.975 0.685 0.860 0.840

Side (6.0m/s) 0.982 0.639 0.833 0.818

Face Mask (3.7m/s)* 0.788 0.500 0.789 0.692

Face Mask (3.7m/s)* 0.669 0.391 0.746 0.602

Face Mask (3.7m/s)* 0.643 0.311 0.780 0.578 0.766

*Cases not included in overall CORA rating, used for robustness only.

Table 2021. HIII drop impact CORA scores

Impact Condition Carriage Lin. Acc.

Head Lin. Acc.

Impact Force

Overall

Front (2.9m/s) 0.898 0.847 0.833 0.859

Front (4.9m/s) 0.872 0.834 0.896 0.867

Front (6.0m/s) 0.911 0.736 0.887 0.844

Back (2.9m/s) 0.810 0.704 0.689 0.735

Back (4.9m/s) 0.758 0.687 0.693 0.713

Back (6.0m/s) 0.723 0.697 0.715 0.711

Top (2.9m/s) 0.704 0.602 0.561 0.622

Top (4.9m/s) 0.783 0.593 0.625 0.667

Top (6.0m/s) 0.695 0.578 0.666 0.646

Side (2.9m/s) 0.719 0.614 0.624 0.652

Side (4.9m/s) 0.772 0.644 0.711 0.709

Side (6.0m/s) 0.707 0.563 0.686 0.652 0.723

user manual - biocore, llc · 2018-05-07 · 2016 schutt air xp pro v1.0 3 3. helmet model...

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