Development of Safety Specifications for Martial Arts Sparring Equipment

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Development of Safety Specifications for Martial
Arts Sparring Equipment

• Prof. Dennis K. Lieu
• Department of Mechanical Engineering
• University of California Berkeley

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What is this?
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Taekwondo

• Full contact
• Rules important
• Safety equipment required

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Safety Equipment

• Organizers concerned about safety
• Chest protectors
• Headgear
• No standards for safety exist

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Goals

• Establish safety standards
• Establish equipment test standards
• Eliminate unsafe designs
• Aid with development of new, safer designs

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What is an Injury?

• Many nuisance injuries (bruises)
• Moderate injury causes temporary cessation of
  the activity
• Consider AIS 3 for serious injuries
• A serious injury will result in long term
  disability or death unless medical treatment is
  received

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The Kick

• High speed video

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The Kick

• Swing kicks
• 12-16 m/s terminal velocity
• 2 kg effective mass (equivalent energy)
• Thrust kicks
• 7-10 m/s terminal velocity
• 3 kg effective mass (equivalent energy)
• Both around 200 J kinetic energy

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Head Injury Mechanism
Brain
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Head Injury Mechanism
Brain
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Head Injury Mechanism
Brain
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Head Injury Mechanism
Brain
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Head Injury Mechanism

• Skull moves, brain stays still
• Skull smacks brain
• Skull pushes brain
• Skull stops, brain keeps moving
• Brain smacks other side of skull
• Head acceleration is important
• Duration of acceleration is important

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Headgear Function

• Energy absorption
• Main function
• Reduction of acceleration
• Force dispersion
• A secondary effect

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Early Testing at UC Berkeley

• Head Injury Criteria

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Early Testing at UC Berkeley
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Early Testing at UC Berkeley

• Hybrid III head/neck

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Modeling of the Kick

• The projectile, 2 kg., rubber tipped

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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Early Testing at UC Berkeley
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Where is this Leading?

• American Society for Testing and Materials
• The largest industrial standards group in US
• Draft ASTM spec for martial arts headgear
• Draft ASTM spec for torso protectors
• Proposed standard supported by two largest
  martial arts equipment makers in US
• Also supported by largest tournament and school
  insurance company in US
• Anticipated release this year

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Setting Performance Limits

• Based on known human tolerance in Gs
• Based on what is currently achievable with
  equipment today
• Testing is done at room temperature and normal
  humidty
• Testing also done at elevated temperature and
  humidity
• Tester design must be simple and inexpensive

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ASTM Headgear Specification

• Striking test
• Falling test
• Retention
• Ear pressure relief
• Temperature and humidity
• Vision
• Interior and exterior construction

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Getting Kicked

• People most worried about it

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The ASTM Strike Tester
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Test Headform
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The ASTM Strike Tester
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Instrumentation

• PCB 356B21 tri-axial piezo-electric accelerometer

10 mm
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Hybrid III Head/Neck
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ASTM Limit

• 5 m/s strike produces less than 50 G head
  acceleration
• 8 m/s strike produces less than 150 G head
  acceleration

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Falling

• Falling creates the most serious injuries

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ASTM Fall Tester

• Same test and limit as for bicycle and many other
  helmets
• 3 m/s fall produces less than 100 G head
  acceleration
• 4 m/s fall produces less than 300 G head
  acceleration

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Ear Pressure Relief

• Must have airway path in case hearing holes are
  sealed by strike

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Vision

• Must have minimum clearance for vision

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Retention Test

• Headgear comes off, a lot
• Due to elastic strap, which is very popular but
  dangerous

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ASTM Roll-off Tester
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Inside/Outside Construction

• Outside must be cushioned to Shore A 40 durometer
• All hard material must be cushioned
• No protrusions

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ASTM Torso Guard Specification

• Striking test (high and low energy)
• Retention test
• Coverage
• Temperature and humidity
• Interior and exterior construction

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ASTM Torso Guard Specification

• Getting kicked is the major mechanism of injury

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Modeling of the Chest

• Chest compression

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Torso Injury Mechanism
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Torso Injury Mechanism
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Torso Injury Mechanism
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Torso Injury Mechanism
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Torso Injury Mechanism

• Compression
• Static crushing of tissues (bone)
• 20 limit for chest compression
• Wave propagation
• Dynamic displacement of (soft) tissues

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Chest Protector Function

• Force dispersion (over a larger area)
• Primary function
• Prevents localized trauma
• Energy absorption
• A secondary effect

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Chest Protectors
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What is this used for?
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GE RTV 6166 Silicone Gel
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Modeling the Torso

• At this time, model only the soft tissue
• Hard tissue injury at a later date

GE 6166 Silicone Gel
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Torso Instrumentation
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Modeling the Torso

• Gel block instrumented with micro pressure gage.
  PCB 138M103 peizo-electric pressure sensor,
  modified with additional electric shielding

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Simulated Torso
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Torso Strike Test
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Torso Strike Test

• 8 m/s strike produces less than 0.25 MPa pressure
• 12 m/s strike produces less than 1.0 Mpa pressure

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Torso Strike Test
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Coverage
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Retention

• Pull with a force perpendicular to the body
• Spec 50 N force creates a gap of less than 50 mm

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Thank You

• Questions?