Impact engineering: Why all head protection is in need of a redesign

The humble helmet dates back nearly 3000 years and though it has been used prolifically in warfare, it is now most commonly used to provide head protection outside the combat arena. 

However, although applications might have diversified, it is still fundamentally designed and used to provide the same thing.

So when this most traditional of objects is combined with modern sensor technologies, greater test data resolution and analysis, there is bound to be fresh insight.

And this is the case for many conventional designs where sensors, test and measurement technologies are changing conventional thinking into how something has been designed, to how it should be designed.

It sets the scene and means helmet design is on a collision course for further impact protection, specifically in preventing serious brain injury by giving helmet designers greater clarity in to the mechanical forces at play in any particular scenario.

It was this, along with a lifetime of comprehensive knowledge, which enabled biomechanist Dr John Lloyd, research director of BRAINS, to start up a company dedicated to improving current helmet technology and ultimately improve protection for wearers. He aims to shed new light on helmet design, and improve protection against the fundamental causes of concussion and brain injury.

“There are two key forces at play during a head impact,” said Dr Lloyd, speaking at this year’s National Instruments Week in Austin, Texas. “Firstly there are linear forces, these are the ones that cause visible injuries such as bruising and skull fractures. However, the second is the rotational forces. These are the ones that cause invisible injuries such as concussion and brain injury.

“Current helmet testing technologies measure the linear forces. However, at this time, they do not measure the rotational forces, so consequently we have helmets for many sports that do not test against their ability to provide protection against concussions and brain injury.”

Whether it is for riding a bike, horse riding, skiing or indeed for the soldier in the field, the effect of rotational movement is the same. Yet, it is rarely tested for, and even less frequently measured, to see how effective any helmet is in rotation force protection.

Dr Lloyd modified the standard apparatus used for testing helmets (see the rig on page 28), where a head section is raised 2m on a rig and dropped under gravity before it hits a striking plate with an impact force in the region of 4500N. However, instead of using a standard head form, Dr Lloyd replaced it with a standard automotive crash test dummy head and neck section. This way, when the head impacts the striking plate at the bottom of the test rig it will rotate, and the movement measured.

“We had multiple sensors embedded in the centre of mass of this head form,” explained Lloyd. “So, during the impact we were able to measure the linear acceleration as well as the angular motion of the head.

“My measuring apparatus includes sensors from several manufacturers.. The angular rate sensor, for example, that is used to measure the rotational forces is a highly specialised sensor. And, as a result, has its own data acquisition hardware and software.”

Simplifying synchronisation
Trying to integrate all this data from different sensors was a challenge at best. And to make matters more complicated, the peak linear acceleration and peak angular acceleration actually happen at different points in time.

“So while you can just line up the data,” he said, “there is a lag between them. So we need to measure that lag, which is a critical measurement in the research.”

To resolve the problem, Dr Lloyd uses both the National Instruments LabView graphical software and a CompactDAQ to interface with the sensors and provide the necessary synchronisation between the various sensors.

Dr Lloyd modified his apparatus for testing helmets used by American footballers in the National Football League (NFL), to develop understanding of the how spinal and head injuries are caused and improve the design of the standard helmet.

“The results are pretty alarming in terms of how little protection they provide against concussions and traumatic brain injuries,” he said.

“Based on lessons learned from that study, I have developed a new ‘football’ helmet prototype. This uses a patent pending matrix of non-Newtonian materials and when we tested the prototype helmet, on the same apparatus, the result blew me away. Not only did these materials reduce the linear forces but compared to the standard football helmet they actually reduced the rotational forces that cause concussion and brain injury by an amazing 50%.”

The non-Newtonian materials Lloyd has in mind are inexpensive and produce a helmet that is considerably lighter and even said to be more comfortable for those wearing them.

Dr Lloyd is now expanding the concept of reducing rotation forces in helmets in every application and said it can be applied to almost any helmet design to help reduce concussion and brain injuries from sports to leisure and even back to warfare.

Building a rig and conducting the test
A modification to the US National Operating Committee on Standards for Athletic Equipment (NOCSAE) standard test apparatus was used by Dr John Lloyd, research director of US helmet research start-up, BRAINS.

He developed and validated a new helmet test rig to measure the impact of protective headwear to include measurements of both linear and angular kinematics. This apparatus consists of a twin wire fall test system equipped with a drop arm that incorporates a 50th percentile Hybrid III head and neck assembly from HumaneticsATD crash test dummy, as used in the automotive industry.

The aluminium fly arm runs on Teflon sleeves through parallel braided stainless steel wires, which are attached to mounting points in the building structure and anchored into the concrete foundation. The anvil, onto which the head drop systems impacts, consists of a 350mm x 350mm steel based plate.

Both the standard Riddell Revolution Speed US university football helmet, and the prototype BRAINS helmet that incorporates a non-Newtonian matrix, were dropped from a height of 2m onto a flat steel anvil, in accordance with American Society for Testing and Materials (ASTM) standards. This generated an impact velocity of 6.2 m/s (13.9 mph).

Instrumentation: 
A triaxial accelerometer from PCB Piezotronics and three DTS-ARS Pro 18k angular rate sensors (Diversified Technical Systems) were affixed to a tri-axial block installed at the centre of mass in the Hybrid III head form. Data from the accelerometer and angular rate sensors were acquired using National Instruments compactDAQ hardware.

Analysis: 
Data from the analogue sensors were acquired at 10,000Hz, per channel, using LabView and then filtered in Matlab using a phaseless 4th order Butterworth filter with a cut off frequency of 1650Hz. Angular acceleration values were derived from the angular velocity data based on a 5-point least squares quartic equation.

Result:
The result of the new helmet design shows significant improvement in rotational acceleration exerted on the head and neck, cutting the overall force by nearly 50%.

Author
Justin Cunningham

– See more at: http://www.eurekamagazine.co.uk/design-engineering-features/technology/why-all-head-protection-is-in-need-of-a-redesign/66493/#sthash.6Tv5duXE.dpuf

Motorcycle Accident Expert in Biomechanics and Human Factors

Motorcycle accident analysis is a highly specialized discipline in which Dr. Lloyd is eminently qualified. In addition to holding a PhD in Ergonomics (Human Factors), with a specialization in Biomechanics, John has more that 20 years and 200,000 miles of experience riding motorcycles. John-Lloyd-expert-witness-motorcycleDr. Lloyd has completed numerous advanced programs, including Motorcycle Safety Foundation (MSF), Experienced Rider Course and Total Rider Tech Advanced training.

Motorcycle Helmets and Brain Injury

To consider whether a motorcycle helmet might reduce the risk of brain trauma in a motorcycle accident it is first important to understand the two primary mechanisms associated with traumatic brain injury – impact loading and impulse loading.

Impact loading involves a direct blow transmitted primarily through the center of mass of the head, resulting in extracranial focal injuries, such as contusions, lacerations and external hematomas, as well as skull fractures. Shock waves from blunt force trauma may also cause underlying focal brain injuries, such as cerebral contusions, subarachnoid hematomas and intracerebral hemorrhages. Whereas, impulse or inertial loading caused by sudden movement of the brain relative to the skull, produces cerebral concussion. Inertial loading at the surface of the brain can cause subdural hemorrhage due to bridging vein rupture, whereas if affecting the neural structures deeper within the brain can produce diffuse axonal injury (DAI).

Holbourn was the first to cite angular / rotational acceleration as an important mechanism in brain injury. Gennarelli, Thibault, and colleagues, in a series of studies using live primates and physical models investigated the role of rotational acceleration in brain injury. They concluded that angular acceleration contributes more than linear acceleration to brain injuries, including concussion, axonal injury, and subdural hematoma.

Motorcycle Helmet Testing

Traditional testing of motorcycle helmets focuses on reducing the effect of linear impact forces by dropping them from a given height onto an anvil and measuring the resultant peak linear acceleration. According to the Federal Motor Vehicle Safety Standard (FMVSS) 218, commonly known as the DOT helmet standard, the test involves dropping a motorcycle helmet onto a flat steel and hemispherical anvil at an impact velocity of 6.0 m/s (13.4mph).   In general, if peak linear acceleration is less than 400g, the helmet is considered acceptable. Current motorcycle helmet testing standards do not incorporate measures of angular acceleration and therefore do not address whether any helmets can provide adequate protection against catastrophic brain injuries, such as concussion, axonal injury and subdural hematoma.

In 1995, the European Commission Directorate General for Energy and Transport initiated a Cooperative Scientific and Technical Research (COST) program to investigate Motorcycle Safety Helmets. Several agencies from Finland, the United Kingdom, France and Germany participated in this study, which compiled and analyzed data from 4,700 motorcycle fatalities in Europe, each year. The COST report [i] documents that 75% of all fatal motorcycle accidents involve head injury. Linear forces were present in only 31% of fatal head injuries, while rotational forces were found to be the primary cause in over 60% of cases. Within the scope of this study experiments were performed using drop tests with accelerometers to measure linear and rotational accelerations of the brain and skull mass associated with different types of impacts. These tests confirmed rotational acceleration to be a primary cause of brain injury in helmeted motorcycle accidents.

John-Lloyd-expert-witness-motorcycle-helmet

  • Rotational forces acting on the brain are the underlying cause of traumatic brain injuries.
  • Motorcycle helmets, including those certified under DOT and SNELL standards are designed to mitigate forces associated with linear acceleration.
  • Motorcycle helmets are not currently certified under either DOT or SNELL standard against their ability to protect against the angular / rotational forces.
  •  Epidemiologic evidence from the COST-327 report  indicates that motorcycle helmets do not provide adequate protection against closed head and brain injuries

Human Factors of Motorcycle Accidents

Human factors in vehicle collisions include all factors related to drivers and other road users that may contribute to a collision. Examples include driver behavior, visual and auditory acuity, decision-making ability, and reaction speed. A 1985 report based on British and American crash data found driver error, intoxication and other human factors contribute wholly or partly to about 93% of crashes.

Motorcycle Teardown and Safety Inspection

Motorcycle accident analysis often requires involves a teardown and careful inspection of the machine to investigate for possible contributing factors. Our engineers have a combined 70 years experience with motorcycle mechanics.

John Lloyd motorcycle teardown safety inspection

A thorough evaluation includes inspection of tires, brakes, suspension setup, electrical components as well as any aftermarket parts.

Do Helmets Prevent Brain Injury?

In a word. No.

A better question might be “Can Helmets Prevent Brain Injury?” Same answer – No.

It is not currently possible to develop a helmet that can protect all persons under all foreseen and unforeseen circumstances. But, given current medical understanding of head and brain injuries as well as 21st Century advanced materials, it is certainly possible to protect most people from life-threattening brain injuries under foreseen circumstances.

Helmets are actually intended to protect against blunt trauma injuries to the head. They are not specifically designed to prevent brain injuries.

The mechanisms which cause head and brain injuries are quite different. Forces associated with linear accelerations are responsible for visible injuries, such as lacerations, contusions and skull fracture. Whereas, brain injuries, including concussions, axonal injury and subdural hematoma are caused by forces associated with angular / rotational accelerations. When the head impacts a surface, the skull may come to an abrupt stop, but inertia acting on the brain will cause it to continue to move This inertia strains the nerves and blood vessels of the brain, causing injuries. The type of injury is dependent on the magnitude of this strain and the time duration over which it acts on the brain.

Helmets may indeed reduce the rotational forces acting on the brain. But since helmets are not currently certified according to their ability to protect against brain injury the level of protection is not standardized. Hence, it is possible to sustain catastrophic brain injuries, even while wearing a helmet.

I have performed extensive biomechanical testing of helmets for various applications, including military, motorcycle, football, skiing / snowboarding and cycling. My testing involves measurement of both linear and angular accelerations, thereby characterizing helmets in terms of their ability to protect against head and brain injuries. Results vary substantially between manufacturers that offer helmets for particular applications and between applications. Based on my testing to date, I can report that certain football helmets seem to outperform helmets in other categories in terms of their ability to protect against head and brain injuries.

There are companies within each category, whom I believe are going beyond required standards for their particular application to develop  helmets that afford superior protection against both head and brain injuries. These companies include Xenith football helmetsAtomic ski helmets and 6D motorcycle helmets, which I report without the bias of any affiliation.

Much research has been conducted to understand and quantify biomechanical thresholds for various head and brain injuries, including skull fractures, concussions, axonal injury (damage to nerve fibers in the brain) and subdural hematomas (bleeding in the brain). Why then don’t all helmet manufacturers strive to provide necessary protection?

There are certain intrinsic or personal factors that might increase one’s risk of head and brain injury, but for the rest of us, why do helmets provide inadequate protection against life-threatening head and brain injuries during reasonable or foreseen use?

One example of this is the life-threatening brain injury which former Formula One superstar, Michael Schumaker sustained when he fell while skiing and impacted a rock. It has been reported that Mr. Schumaker was only skiing at about 13mph when he fell and the likelihood of impacting a fixed object while skiing, such as a tree or rock is certainly not unforeseen. So why did his helmet fail to provide necessary protection?

Advanced materials certainly exist to provide required protection for normal persons, including Mr. Schumaker and many other unfortunate victims, under normal or foreseen circumstances. As end-users, we must demand that regulatory organizations require helmet manufacturers meet standards that protect persons who are not otherwise at heightened risk from head and brain injuries due to foreseen circumstances.

NI Week features John Lloyd football helmet expert

I had the privilege to present my research on football helmets as part of the Keynote address at the National Instrument conference in Austin, TX this week. The audience of 5,000+ attendees learned about my research into biomechanics of the brain.

 

It has been said that helmets cannot prevent concussions. I disagree.

As a biomechanist I have dedicated my career to studying the biomechanics of brain injuries. There are two key mechanical forces that give rise to head and brain injuries (1) linear forces, which are responsible for visible injuries, including bruising and skull fractures, and (2) rotational forces, which cause invisible injuries, such as concussion and brain injury.

Since helmets are currently designed to pass testing standards that focus on linear forces only, it is no surprise that helmets have limited benefit in preventing concussions. Through advances in medicine we have learned that concussions can potentially have life-long neurological consequences, including memory impairement and personality changes / behavioral effects.

Over the past years I have developed and validated a testing method to evaluate helmets in terms of their ability to protect against both linear and rotational forces. Using this apparatus I characterized football helmets, results of which have been submitted to Science for publication.

Based on lessons learned from my biomechanical evaluation of various sports helmets, I have devised a matrix of shear-thickening non-Newtonian materials. A prototype helmet was constructed using this matrix liner, results of which show that rotational forces that cause concussion and other brain injuries are reduced by up to 50% compared to a leading football helmet, while also reducing linear forces.

helmet prototype reduces concussion risk

helmet prototype reduces concussion risk

It is my goal and my passion to work with leading helmet companies to make this technology available to players and sports participants of all aged to enhance their protection against brain trauma. I am looking to collaborate with one manufacturer in each sport to offer an exclusive license patent-pending technology.

New Football Helmet Reduces Concussion Risk

John Lloyd of Lloyd Industries, Inc. announced today that football head injuries and concussions can be reduced up to 50 percent with their new helmet safety breakthrough. 

football helmet prototype

football helmet prototype

San Antonio, FL – Dr.John Lloyd PhD of Lloyd Industries, Inc. announced their latest breakthrough in football helmet safety today. The unique new helmet technology promises to provide up to 50 percent more protection against football head injuries and concussions. The technology has wide application and can be used in every kind of helmet from baby helmets to military helmets, and for all athletes at risk of concussion and head injuries such as football players, cyclists, skiers, snowboarders, skateboarders, hockey players, baseball players, lacrosse players, boxers, soccer players, equestrian / horse-riding sports, such as polo and horse racing, as well as motorcycle and race car drivers.

Recent medical research documents found that concussions and cumulative head impacts can lead to lifelong neurological consequences such as chronic traumatic encephalopathy, a degenerative brain disease known as CTE and early Alzheimer’s.

The U.S. Centers for Disease Control and Prevention, estimates 1.6 – 3.8 million sport-related brain injuries annually in the United States. Of these 300,000 are attributed to youth football players, some of whom die from their injuries every year – a tragedy difficult for their mothers and families to recover from.

The severity of the issue touching both the nation’s youth and professional athletes has led to thousands of lawsuits and Congressional Hearings. Growing concern has spread to the White House where President Obama recently spoke at the Healthy Kids and Safe Sports Concussion Summit.

The Lloyd Industries research team, led by renowned brain injury expert, Dr. John Lloyd, has worked for years on their project to help make sports safer. A controversial subject, some opponents have stated that concussion prevention is impossible. Dedicated to saving lives and preserving brain health, Dr. Lloyd and team persevered with their work leading to this new innovation. “Our results show that forces associated with concussion and brain injury are reduced up to 50% compared to similar testing with a leading football helmet,” said Dr. John Lloyd, Research Director.

helmet prototype reduces concussion risk

helmet prototype reduces concussion risk

“The patent-pending matrix of non-Newtonian materials will not only benefit football, but can be utilized in all sports helmets as well as military, motorcycle and even baby helmets to improve protection and dramatically reduce the risk of brain injuries,” reported Dr. Lloyd.

The materials are inexpensive, and produce a helmet that is considerably lighter and more comfortable than a traditional helmet.   Two additional applications of this new safety technology include medical flooring especially in hospitals and nursing homes or child play areas , as well as vehicle interiors.

 

About Lloyd Industries, Inc.

Lloyd Industries, Inc., located in San Antonio, Florida, is a research and development company focused on the biomechanics of brain injuries. The company was founded in 2004 by John D. Lloyd Bio, Ph.D., CPE, CBIS, Board Certified Ergonomist and Certified Brain Injury Specialist. He has also provided expert witness services nationwide for over 20 years in the fields of biomechanics, ergonomics and human factors, specializing in the biomechanics of brain injury, including sport and motorcycle helmet cases, slips and falls, motor vehicle accidents and pediatric head trauma. Lloyd Industries is open to licensing with manufacturers to bring this much-needed technology to market for the protection of sports participants and athletes of all ages. For additional information visit : http://drbiomechanics.com/sports-helmet-football-helmets/new-helmet-technology/  or call 813-624-8986.

The Latest Concussion Research

Dr. Frank Conidi and I presented our research, titled “How Well Do Football Helmets Protect Against Concussion and Brain Injury” at the American Academy of Neurology annual meeting in Philadelphia on April 30th, 2014.

Tom Collins, a writer for Neurology Now wrote a summary of our presentation, which can be viewed by following this link

 

Infant Short Falls

Head Kinematics Associated with Short Falls in Children

John D. Lloyd, Ph.D., M.Erg.S., CPE, CBIS
Board Certified Ergonomist | Certified Brain Injury Specialist
32824 Michigan Avenue, San Antonio, FL 33576
Tel: (813) 624-8986
Email: John@DrBiomechanics.com

This study involved systematic assessments of falls from heights ranging from 2 to 6 ft onto varying flooring surfaces including concrete, linoleum, apartment grade carpeting with underlay, berber carpet with underlay, commercial carpeting without pad, and wood laminate.

A CRABI-12 biofidelic mannequin (29.5 in / 22lb), calibrated and certified by Denton ATD, Inc. and a Hybrid III-3 year old (37.2in / 35.65lb) biofidelic mannequin, calibrated and certified by Key Safety Systems, Inc. were used during this systematic evaluation of short falls.

A tri-axial piezo-electric accelerometer, was installed at the center of mass of the headforms, in accordance with convention described in SAE J211. Still photography and high-speed video (240Hz) was used to record the fall sequences.

A height adjustable platform was used to represent the fall surface. The platform has trap-doors which are held in place by electromagnets. Interruption of power to the electromagnets causes the sprung trapdoors to open instantaneously, thereby initiating the fall sequence.  One-hundred-and-seventy-five trials were completed to investigate biomechanical mechanisms of injury associated with short falls in children.

Data from the tri-axial piezo-electric accelerometer, mounted in the head of the biofidelic mannequin were acquired at a rate of 10,000 samples per second using LabView software. Data were analyzed using MatLab, including Fast Fourier Transform analysis to visualize the frequency spectrum of the data, followed by phase-less filtering using a 4th order low-pass Butterworth filter with a cut off frequency of 1650Hz (per SAE J211).

The peak magnitude value of head linear acceleration components was calculated and presented in G’s. This value was then used to compute Head Injury Criterion values.

As anticipated, the larger Hybrid III 3-year old biofidelic mannequin generated higher linear accelerations, HIC values and forces upon impact associated with short falls. Interestingly, both the CRABI12 infant-representative and Hybrid III toddler representative exceeded injury threshold values from a fall height of only 2 feet (61 cm), based on peak magnitude linear acceleration and Head Injury Criterion, which indicates that such short falls can cause substantial head / brain injuries in young children.

Shaken Baby Syndrome

Biomechanical Evaluation of Head Kinematics During Infant Shaking Versus Pediatric Activities of Daily Living

John D. Lloyd, Ph.D., CPE, CBIS
Board Certified Ergonomist | Certified Brain Injury Specialist
32824 Michigan Avenue, San Antonio, FL 33576
Tel: (813) 624-8986
Email: John@DrBiomechanics.com

Abusive shaking of infants has been asserted as a primary cause of subdural bleeding, cerebral edema, and retinal hemorrhages. Manual shaking of various biofidelic mannequins, however, has failed to generate the head kinematics believed necessary to cause these intracranial symptoms in the human infant. This study seeks to compare linear and angular accelerations between infant shaking and pediatric activities of daily living.

Using sensors attached to the heads and torsos of two infant surrogates, the investigators collected linear and angular motion data during resuscitative, aggressive and gravity-assisted shaking as well as during various non-abusive activities normally experienced by infants, such as burping, rough play, etc. The researchers also collected data from a 7-month old infant child spontaneously at play in a commercial jumping toy. Results were compared between the experimental conditions, against other biomechanical studies of shaking and in contrast to accepted biomechanical thresholds of injury.

In these experiments, the peak rotational acceleration generated, averaged across nine adult subjects, during aggressive shaking of the CRABI-12 biofidelic mannequin (1068.3rad/s2) were both consistent with the reports of prior biomechanical studies and, most interestingly, statistically undifferentiated from angular accelerations spontaneously generated and well tolerated by a normal 7-month-old infant at play in a commercially available jumping toy (954.4rad/s2).

Non-contact shaking appears to result in head kinematics that are well tolerated by normal infants, even if these rotational accelerations are repetitive, as experienced by the infant at play. Our data would indicate that intracranial injury in an infant is unlikely to be the direct result of the linear and/or angular accelerations generated during non-contact shaking.

Dr. Lloyd Talks with Ben Utecht about Concussions in Football

I recently attended and presented at the 66th annual meeting of the American Academy of Neurology, hosted by the City of Philadelphia. During my meeting I had the opportunity to spend a few minutes talking to retired football player, Ben Utecht.

Ben-Utecht

Ben Utecht  is perhaps best known playing for the Indianapolis Colts (2004-2008), His best season was the 2006 season, with 37 receptions for 377 yards. In the 2006 postseason, Utecht had 5 receptions for 41 yards. He would then go on to help the Colts win Super Bowl XLI

Ben-Utecht-superbowl

Utecht, suffered five known concussions during his football career. By late 2011, at only 30 years old, he was experiencing memory loss, attributable to his football-related brain injuries.  

Ben and I spoke about the effects of his football-related brain injuries. He described several events, which concerned him, including loss of any memories of a good friend’s wedding. Though memories of past events continue to evade him, now retired from football, he is thankful that he is able to enjoy family life with his wife and daughters without further consequences, though he is concerned about the possibility of effects later in life.

Utecht has said that he might have quit football earlier had he known of the potential risks of multiple concussions. Utecht describes himself as an advocate for awareness about traumatic brain injury. 

I described my research regarding biomechanical evaluation of football helmets, which Ben found very interesting. He was especially excited about the prospect of developing a new generation of football helmets that promise improved protection against concussion and the long-term consequences of football-related brain injuries for football players of all ages.

Ben is also

Ski Helmets Not The Best Protection Against Brain Injury

Helmets are designed with one purpose, that is to prevent skull fractures. But, what’s about the brain?

There is no doubt that ski helmets can and do prevent death. Take the recent accident of Formula One superstar, Michael Schumacher, who fell headfirst while skiing off-piste in the French Alps on December 29, 2013. Had he not been wearing a helmet when his head struck a rock, the result would be far more grave.

Michael-Schumacher-Skiing

Another tragic example is that all Sally Franklyn, an avid skier and writer, who tumbled 800 feet two years ago. Fortunately, Sally was also wearing a helmet which likely saved her life. However both Sally and Michael will have a lifelong scars of traumatic brain injury.

Sally-Francklyn-skiing

Dr. John Lloyd, a biomechanists from Tampa who has dedicated his career to the study of traumatic brain injury, has conducted a study on the protective properties ski helmets. While results show that wearing a ski helmet will dramatically improve protection against potentially fatal injury, findings also show that ski helmets may not provide sufficient protection for the brain against traumatic brain injury. The mechanism which causes a skull fracture is quite different from that which causes the traumatic brain injury.

ski-helmet-tests-2  ski-helmet-tests-1

We have a great physicist, Prof. Holbourn from Cambridge University in England, to thank for his 1943 paper on the mechanisms of head injuries. Dr. Holbourn showed, using a bowl full of Jell-O, that forces associated with linear acceleration all likely to give rise to focal head injuries, such as skull fractures. Whereas rotational forces are those more likely to give rise to brain injuries including concussion and brain bleeding.  This is because as you can see when trying to rotate a bowl full of Jell-O, the Jell-O moves greatest toward the center of the bowl

As to whether or not a better helmet can be designed to protect both the skull from fracture and the brain from traumatic injury, Dr. Lloyd says absolutely. In fact, within the scope of his research into helmet protection, Dr. Lloyd’s findings show that football helmets provide far greater protection of the head and brain from traumatic injury then do ski helmets.

Upon impact their are linear and rotational forces acting on the head. Rotational forces being tangential to the linear forces. If a tangential for snacks on a material such as EPS foam we would expect little, if any, deformation of the material since such materials, as shock absorbing materials, are designed to mitigate linea forces acting directly on them.