mechanical traction testing of 3g surfaces -...

Mechanical Traction Testingof 3G Surfaces

James ClarkeMatt Carré

Kathryn SevernPaul Fleming

Sports EngineeringResearch Group

University of Sheffield

Civil and BuildingEngineering

Contents

• Introduction

• Engineering Methods

• Traction Rig

• Key Findings

• Summary

Player Performance - Traction

Performance - Players require sufficient traction to perform.

Traction – Horizontal Resistive force during the shoe-surface interaction.



•Sprints.


‘High traction characteristics are a necessary feature of shoe outsolesbecause they enhance the athletes ability to successfully run fast.’

Valiant 1990



•Sprints.

•Changes in Direction.


‘Friction is necesarry for rapid starting, stopping, cutting and pivoting’

Inklaar 1994



•Sprints.

•Changes in Direction.

•Prevent Slipping.


‘The forefoot pushoff movement is related to performance, where theplayer seeks sufficient traction to avoid slipping.'

Kirk 2007

Traction - Engineering Methods

FIFA Handbook:

•Pendulum test modified from a skid resistancetester.

•Peak deceleration, termed Stud DecelerationValue, is recorded.

•To meet the FIFA two star rating, its mean StudDeceleration Value over 5 tests must lie withinlimits of 3.0 g – 5.5 g

•The relevance of such a test is debatable.

Does it measure the traction a soccer player willexperience?

Traction - Engineering Methods

• Simulate game relevant loadingconditions.

• Portable design to measure on differentplaying surfaces and under variousweather conditions.

• Repeatability.• Adjustability of different load situations.

Mechanical test devices are required to understand the forces likely tobe experienced by stud-surface combinations

Grund et al, Technical UniversityMunich

Apply relevant forces

Apply relevant movements

Force-controlled Traction Rig

Pneumatic ram– forcecontrolleddisplacement

Hydraulic ram– normal force

Studdedplate

LDVT(displacement)

Horizontalandverticalload cells

•SERG Developed a device to measure traction.•Designed to simulate a push off movement.

Parameters –Vertical LoadingPlayers performed a push off into a sprintingmovement – when a player requires high traction.

-500

0

500

1000

1500

2000

2500

0.05 0.1 0.15 0.2 0.25 0.3 0.35

Time (s)

Fo

rce

(N)

Fx

Fy

Fz

Push Off

0

0.05

0.1

0.15

0.2

0.25

0.3

0.222 0.242 0.262 0.282 0.302 0.322

Fy/Fx

Fy/Fz

•Peak Fy/Fz = Player is most at risk of slipping duringpush off – after 0.3 seconds.

•After 0.3 seconds Fz = 350 N. This is an appropriatevertical force for mechanical tests simulating a pushoff movement.

FX

FZ

FY

Fy - High

Fz - Low

Direction of

stud motion

Direction of

player

Parameters - Movement

High Speed Video Analysis:

Small horizontal movement (~ 10 mm) between shoe and surfaceafter initial contact.

0

50

100

150

200

250

300

350

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Horizontal Displacement (mm)

Ho

rizo

nta

lF

orc

e(N

)

Surface B

Surface C

The Horizontal force after 10 mm displacement is measured.

Aim

Understand how stud design and surface properties affect

traction on 3G surfaces.

Surface A B C D

Fibre Material Polypropylene Polyethylene Polyethylene Polyethylene

Fibre Type Monofilament Monotape MonofilamentFibrilated fibre and a curly

fibre (to help hold infill)

Pile Height (mm) 35 40 5065 (fibrillated fibre)

(Also curly stabilising fibre)

No. of Tufts per m2 10600 25200 33600 33600

No. of Fibres per Tuft 12 18 8 2 (which then fibrillate)

Fibre Width (mm) 1.5 1.5 1.3 1 – 3

Fibre Thickness(mm)

0.025 0.025 0.026 0.026

Total Number of Fibres perm2 127200 453600 268800 67200*

Silica Sand0.2 – 0.7 mm

10 kg/m2 10 kg/m2 10 kg/m2 10 kg/m2

SBR Rubber Crumb0.5 – 1.5 mm

4 kg/m2 7 kg/m2 12 kg/m2 20 kg/m2

Aim

Understand how stud design and surface properties affect

traction on 3G surfaces.

The surfaces were tested with 13different bespoke stud designs -resulting in a total of 52 stud-surface combinations.

The 13 stud designs varied inlength, width, and conicity.

The studs were configured in a 5stud formation.

40 mm

30 mm

37 mm

29 mm

30 mm

92 mm

75 mm

Direction of Movement

Translational Traction - Performance

Friction due to the interaction between the outsole and the turf

Ploughing Traction due to the stud and plate clearing a path through the turf

Skin Friction due to the interaction of the stud material with the turf

Ploughing Traction (Fp)

Friction (μp)

Skin Friction (μs)

Normal Reaction Force(N)

The coefficients are dependant on the particular stud andsurface types.

Direction of stud motion

Key FindingsComparing the surfaces – significant differences:

D<A,B,Cp = .012, .005, .032

Traction D<A,B,Cp = 0, 0, .041

VerticalDisplacement

Key Findings

Surface DSurface C

Higher Traction Force Lower Traction ForceResults

Comparing the surfaces – significant differences:

D<A,B,Cp = .012, .005, .032



Key Findings

Surface D

Lower Infill

DensityHigher Fibre

Density

Surface Lower Fibre

Density

Higher Infill

DensityStabilisingfibres’

Higher PileHeight

Surface C

High Traction Force Low Traction ForceResults


D<A,B,Cp = .012, .005, .032



Key Findings

Surface D

Lower Infill

Density

Stud and Outsole Penetrates

Surface

Higher Fibre

Density

High Ploughing

Traction Friction

Surface

Hypothesis

Lower Fibre

Density

Higher Infill


Higher PileHeight

Surface C



D<A,B,Cp = .012, .005, .032



Key Findings

Surface D

Lower Infill

Density


Surface

Higher Fibre

Density

High Ploughing

Traction Friction

Surface

Hypothesis Stud Compresses

Infill and curlyfibres

Lower Fibre

Density

Lower Ploughing

Traction Friction

Higher Infill


LowPenetration

Higher PileHeight

Surface C



D<A,B,Cp = .012, .005, .032



Key Findings

Surface D

Lower Infill

Density


Surface

Higher Fibre

Density

High Ploughing

Traction Friction

Higher Traction

Surface

Hypothesis Stud Compresses

Infill and curlyfibres

Lower Fibre

Density

Lower Ploughing

Traction Friction

Lower Traction

Higher Infill

Density

Result

Stabilisingfibres’

LowPenetration

Higher PileHeight

Surface C



D<A,B,Cp = .012, .005, .032



SummaryConclusions:

•Despite differences in make up (fibres, infill, etc) no significant differences intraction were found between surfaces A, B, and C.

•Significantly lower traction and vertical displacement was found with surfaceD.

•The stabilising fibres in surface D prevents stud penetration – this results inhigh skin friction forces but low ploughing traction.

Current / Future work:

•Benchmark Traction – what is considered acceptable traction.

•Effects of stud geometry – investigating the effects of individual stud-surfacecombinations.

Thank you

QUESTIONS??

Acknowledgments:

Bob Kirk

Conclusions

Linear relationships were found between stud penetration with stud length,width, and conicity.

The trend between stud width and traction force differed on different surfacemake ups.

It is possible for the traction performance of a stud to significantly differ fromsurface to surface.

More appropriate test methods and recommendations when assessing thesuitability of third generation artificial surfaces for use in soccer.

The stabilising fibres in surface D prevents stud penetration, resulting in lowertranslational traction.

RECOMMENDATIONS FOR FUTURE WORKtional area of the studs, and the friction between the surface and the stud edges and the general interaction between stud, fibre and infill. A controlled set of experiments could quantify these parameters for different surface and stud combinations.

Key Findings

0

2

4

6

8

10

12

14

16

18

20

L1 L2 L3 L4 L5

Stud Reference

Vert

ticalD

isp

lacem

en

t(m

m)

Outsole

Stud

Figure 5. Mean vertical displacement (± 95 %confidence limit) of studs and outsole plate at timeof initial movement for surface A with 350 N verticalforce applied.

Linear relationships were found between stud penetration with studlength, width, and conicity. The depth of penetration of a stud intoa third generation artificial surface is dependent on the make up ofthe surface, particularly the density of fibres and infill.

0

2

4

6

8

10

12

14

16

18

W1 W2 W3 W4 W5

Stud Reference

Vert

ticalD

isp

lacem

en

t(m

m)

Outsole

Stud

Figure 5. Mean vertical displacement (± 95 %confidence limit) of studs and outsole plate at timeof initial movement for surface A with 350 N verticalforce applied.

Parameters – Horizontalal Loading

• Force-control perhaps more relevant to manyfootball movements

• Ideal movement: Vhor = 0

– foot pushes against surface

• Surface failure

– performance lost (immediately)

mechanical traction testing of 3g surfaces -...

Documents