Category Archives: biomechanics expert

Biomechanics expert Dr. John Lloyd has served attorneys nationwide for 25+ years in biomechanics, human factors, helmet testing and motorcycle accident expert

Concussion and Brain Injury Associated with Headrest Impacts in Rear End Car Crashes

The following is a case study in which biomechanics expert, Dr. John Lloyd, evaluated the risk of concussion and brain injury associated with headrest impact in rear end crashes.

Headrest Impact Test Apparatus:

In accordance with prior published test methods [1],[2],[3], a test apparatus was constructed to evaluate the biomechanical protection afforded by an exemplar automobile headrest against head and brain injuries during occipital head impacts in a simulated rear-end motor vehicle collision.

The apparatus involves a pendulum arm, attached by bearing housings to a weighted base. The upper body, including neck and head of a 50th percentile Hybrid III crash test dummy was mounted to the pendulum arm. Data acquisition was initiated by triggering an electromechanical release mechanism, allowing the mannequin to fall, under acceleration due to gravity, until the crash test dummy impacted the headrest and backrest (Figure 1). 

Figure 1: Test apparatus

Test apparatus for studying concussion and brain injury associated with headrest impacts in rear-end car crashes, designed to simulate the forces on the head and neck during a collision and measure resulting injuries.

The fundamental elements and principles of this testing have been utilized in other laboratories. By utilizing a Hybrid III neck, the head impact tests are more realistic, causing head rotation at the axis between the head and neck, which produces measures of head and brain angular kinematics. The methods presented herein are based upon standardized test methodologies and published research.

Instrumentation

Four PCB Piezotronics tri-axial accelerometers (model # 356A01) were mounted in an X,Y,Z array at the center of mass of the Hybrid III headform, along with a tri-axial angular rate sensor produced by Diversified Technical Systems (composite Figure 2). 

Figure 2: Sensor installation in Hybrid III headform

Sensor installation in a Hybrid III headform involves placing sensors within the headform to measure impact forces, acceleration, and rotational motion during crash tests, helping to assess head injury risks.

Sensor Calibration:

All sensors were calibrated by the manufacturer. Verification of calibration of the linear accelerometers was performed prior to testing using a calibration shaker. Results indicate that the sensors were operating in the specified frequency range and output (Figure 3).

Figure 3: Pre-test verification of linear accelerometer sensors 

Pre-test verification of linear accelerometer sensors ensures the accuracy and functionality of sensors used to measure linear acceleration during impact tests, confirming proper calibration before conducting experiments.

For the angular rate sensor, a simple validation method was devised in which the sensor was affixed to a digital goniometer that was rotated through a 90-degree angle. Using LabVIEW software, the integral of angular rate was computed, reflecting concurrence with the digital goniometer for all three planes of motion (Figure 4).

Figure 4: Pre-test validation of angular rate sensor calibration

Pre-test validation of angular rate sensor calibration ensures the accuracy of sensors measuring rotational motion, confirming their proper calibration before conducting tests to assess impact and injury risks.

Headrest Impact Testing:

The mannequin head was raised from the headrest in 2-inch increments from 2 inches to 30 inches, generating head impact speeds from 1 to 25 miles per hour. Two headrest positions were evaluated, along with two different Hybrid III necks representative of a stiff and relaxed neck (Figure 5), for a total of sixty tests.

Figure 5: Test apparatus with Hybrid III loose neck and headrest in lower position

Test apparatus featuring a Hybrid III dummy with a loose neck and headrest positioned in the lower setting, used to simulate and analyze head and neck movement during crash tests.

Data Acquisition and Analysis:

Data from the analog sensors were acquired in accordance with SAE J211 [4], using a National Instruments compact DAQ data acquisition system and LabVIEW software (National Instruments, Austin, TX). The raw data was then filtered in MATLAB (The MathWorks, Natick, MA) using a phaseless eighth-order Butterworth filter with cutoff frequencies of 1650 Hz and 300Hz for the linear accelerometers and angular rate sensors, respectively.

Angular acceleration values for sagittal, coronal and axial planes were computed from the angular velocity data using the 5-point central difference by least squares method (Equation 1):

Equation 1: Five-point central difference by least squares method

headrest impact test - Five-point central difference by least squares method

Angular acceleration vales were also derived from the array of linear accelerometers, by the mathematical method documented by Padgaonkar et al [5].

Linear velocity was calculated by integrating linear acceleration. Mathematical methods were performed using Matlab to compute characteristic values from variables of interest. Figure 6, below illustrates peak linear acceleration and angular velocity associated with a 6.8 mph occipital head impact against a headrest.

Figure 6: Linear acceleration and angular velocity associated with headrest impact

Linear acceleration and angular velocity associated with headrest impact measure the forces and rotational motion experienced by the head during rear-end car crashes, helping to assess the severity of potential concussions or brain injuries.

It is noted that the major component of linear acceleration was in the X-axis (anterior-posterior), while the major component of angular velocity was in the sagittal plane, as expected. 

Linear acceleration values were used to calculate Maximum Pressure (Equation 2), Gadd Severity Index (GSI) (Equation 3), and Head Injury Criterion (HIC15) (Equation 4).

Equation 2: Maximum Pressure

Maximum pressure refers to the highest amount of force applied per unit area during an impact or collision, often used to assess the potential for injury in crash testing or material deformation.

Equation 3: Gadd Severity Index

The Gadd Severity Index is a measure used to evaluate the potential for head injury based on the acceleration forces experienced during an impact, combining both the magnitude and duration of the force to assess the severity of the trauma.

The Head Injury Criterion (HIC) is an empirical measure of impact severity describing the relationship between the linear acceleration magnitude, duration of impact and the risk of head trauma (Equation 4).

Equation 4: Head Injury Criterion

Head Injury Criterion (HIC) is a measure used to assess the likelihood of head injury in crash tests, based on the acceleration experienced by the head during an impact. A higher HIC value indicates a greater risk of injury.

where a is resultant head acceleration, t2-t1 < 15 msec

With reference to the Figure 7,  below, the HIC value is used to predict the risk of head trauma:
Minor –skull trauma without loss of consciousness; nose fracture; superficial injuries
Moderate – skull trauma with or without dislocated skull fracture and brief loss of consciousness. Fracture of facial bones without dislocation; deep wound(s)
Critical – Cerebral contusion, loss of consciousness for more than 12 hours with intracranial hemorrhaging and other neurological signs; recovery uncertain.

Figure 7: Probability of specific head trauma level based on HIC value

Peak angular velocity was determined as the maximum angular velocity related to peak linear acceleration impact time. Angular velocity values were used to derive Maximum Principal Strain (MPS) (Equation 5), Cumulative Strain Damage Measure (CSDM) (Equation 6), and Brain Rotational Injury Criterion (BrIC) (Equation 7). 

The probability of specific head trauma levels based on the HIC (Head Injury Criterion) value estimates the likelihood of various head injuries, such as concussions or skull fractures, depending on the severity of the acceleration forces experienced during an impact.

Equation 5: Maximum Principal Strain

Maximum Principal Strain refers to the highest amount of deformation experienced by a material or tissue during an impact, used to predict the potential for injury, particularly in brain tissue during crash testing or simulations

Equation 6: Cumulative Strain Damage Measure

Cumulative Strain Damage Measure quantifies the total strain experienced by a material or tissue over time or multiple impacts, helping to assess the risk of injury, particularly in repetitive or prolonged traumatic events like car crashes.

An analysis method validated by Takhounts [6] establishes physical injury criteria for various types of traumatic brain injury and uses Anthropomorphic Test Device (ATD) data to establish a kinematically based brain injury criterion (BrIC) for use with ATD impact testing. This method was utilized to express risk of diffuse brain injury according to the revised AIS scale [7] in terms of peak angular head kinematics, where:

Equation 7: Brain Rotational Injury Criterion

Brain Rotational Injury Criterion (BRIC) is a measure used to assess the risk of brain injury caused by rotational forces during an impact, focusing on how rotational acceleration affects brain tissue and increases the likelihood of injuries like concussions or axonal damage.

Headrest Impact Results:

A summary of key results is presented in Table a-d, below. The driver was aware of the pending impact, as he depressed the accelerator in an attempt to avoid the collision in the moments prior to the crash. In rear end collision tests involving human subjects, volunteers instinctively tensed their neck muscles as a protective response.  Given that the driver anticipated the crash his neck muscles were likewise expectedly tense as an instinctive protective response. Therefore, the results most consistent with the subject case are presented in Tables a and b. Rows highlighted in green are consistent with change in velocity experienced by the driver during the subject crash.

Table a: Summary of test results – Neck – Stiff; Headrest – lower position

Test results with a stiff neck and lower headrest position show increased risk of head and neck injuries due to reduced flexibility and altered impact dynamics.

Table b: Summary of test results – Neck – Stiff; Headrest – upper positio

Test results with a stiff neck and headrest in the upper position show that these conditions may reduce the effectiveness of impact absorption, potentially increasing the risk of head and neck injuries.

Table c: Summary of test results – Neck – Loose; Headrest – lower position

Test results with a stiff neck and headrest in the upper position show that these conditions may reduce the effectiveness of impact absorption, potentially increasing the risk of head and neck injuries.

Table d: Summary of test results – Neck – Loose; Headrest – upper position

Test results with a stiff neck and headrest in the upper position show that these conditions may reduce the effectiveness of impact absorption, potentially increasing the risk of head and neck injuries.

Skull Fracture

With reference to Ono 8, none of the impact tests approached the occipital skull fracture threshold of 140 g for impacts lasting longer than 7 milliseconds. Therefore, vehicle headrests provide excellent protection against acute skull fractures at impact speeds below 25 mph.

Traumatic Head Injury

With reference to Figure 7 and Tables a-d, maximum recorded HIC values were consistent with a 5 percent or less risk of moderate traumatic head injury. Whereas, the HIC value computed at impact speeds similar to the crash was only 3.4, at which the risk of minor or moderate traumatic head injury is negligible.

Mild Concussion

With reference to Figure 8 below, the risk of an occupant sustaining a mild concussion in a rear-end collision producing a change in velocity of 6.25 mph (range 5.4 to 7.2 mph) can be determined based on the following calculation: Risk AIS-1 = 31.744*ln(x) + 6.1748 (R2=0.67). The risk of and AIS-1 mild concussion, without post-concussion syndrome, in such an impact is 64.3% (range 59.7 to 68.8%).

Figure 8: Risk of mild concussion (AIS-1) associated with headrest impact

Risk of mild concussion (AIS-1) associated with headrest impact examines how forces from the headrest during a collision can lead to minor brain injuries, such as concussions, based on the severity of the impact.

Severe Concussion

With reference to Figure 9, below, the risk of an occupant sustaining a severe concussion in a rear-end collision producing a change in velocity of 6.25 mph (range 5.4 to 7.2 mph) can be determined based on the following calculation: Risk AIS-2 =  0.198e0.234x (R2=0.85). The risk of severe concussion in such an impact is 0.85% (range 0.70 to 1.07%).

Figure 9: Risk of severe concussion (AIS-2) associated with headrest impact

Risk of severe concussion (AIS-2) associated with headrest impact evaluates the likelihood of more serious brain injuries, such as moderate concussions, caused by higher impact forces from the headrest during a collision.

Traumatic Axonal Injury: 

Figure 10, below, is adapted from Margulies et al. 20 in which thresholds for axonal injury were developed and published based on mathematical modeling, animal testing and physical experiments. Results from occipital head impact against an exemplar headrest at a speed of 6.2 miles per hour are represented, indicating that rotational head and brain kinematics associated with such impact are well below scientifically-accepted thresholds for traumatic axonal injury.

Figure 10: Scientific Thresholds for Axonal Injury 

Scientific thresholds for axonal injury refer to the levels of force or acceleration that can cause damage to the brain's axons, often leading to conditions like diffuse axonal injury, which can occur during high-impact collisions or trauma.

Figure 11, below was generated from data presented in Tables a through d, to present the risk of traumatic axonal injury associated with head impact against an headrest.

Figure 11: Risk of traumatic axonal injury (AIS-4) associated with headrest impact

headrest impact test - Risk of traumatic axonal injury associated with headrest impact

Results show that the risk of an occupant sustaining traumatic axonal injury in a rear-end collision producing a change in velocity of 6.25 mph (range 5.4 to 7.2 mph) can be determined based on the following calculation: Risk AIS-4 = 0.0271e0.2391x (R2=0.85). The risk of traumatic axonal injury in an impact of the magnitude experienced by the driver is 0.12% (range 0.10 to 0.15%).

Conclusions

Biomechanical testing of head and brain injury risk associated with occipital head impact against a headrest, in accordance with published methods, shows a significant risk (59.7 to 68.8%) of AIS-1 mild concussion, without post-concussion syndrome, in a 6.2 mph rear-end collision. However, the risk of an AIS-2 severe concussion in such an impact decreases to 0.70 to 1.07%, and the risk of traumatic axonal injury is only 0.10 to 0.15%. Moreover, the mechanical traumatic axonal injury is not consistent with a sagittal plane impact.

References

[1]     Caccese V, Lloyd J, Ferguson J (2014) An Impact Test Apparatus for Protective Head Wear Testing Using a Hybrid III Head-Neck Assembly. Experimental Techniques.

[2]     Lloyd J & Conidi F. (2015). Brain Injury in Sports. Journal of Neurosurgery. October.

[3]     Lloyd J. (2017). Biomechanical Evaluation of Motorcycle Helmets: Protection Against Head and Brain Injuries.Journal of Forensic Biomechanics. 

[4]     SAE (2014) J211/1. Instrumentation for Impact Test – Part 1 – Electronic Instrumentation. Society of Automotive Engineers International, Surface Vehicle Recommended Practice, Warrendale, PA.

[5]     Padgaonkar AJ, Krieger KW and King AI. Measurement of Angular Acceleration of a Rigid Body using Linear Accelerometers. J Applied Mechanics. Sept 1975.

[6]     Takhounts EG, Craig MJ, Moorhouse K, McFadden J (2013) Development of Brain Injury Criteria (BrIC). Stapp Car Crash Journal 57: 243-266. 

[7]     Abbreviated Injury Scale (2008) Association for the Advancement of Automotive Medicine, Des Plaines, IL.

Researchers Discover Objective Indicator of Concussion

Opportunity to Protect Professional and Youth Sports Players from Traumatic Brain Injuries

sport concussion and sport accident reconstruction expert Dr. John Lloyd
Sport concussion researchers teamed up with football players at a Florida high school. Ten players were equipped with Riddell Revolution Speed helmets, with the embedded Simbex HITS encoders, which were worn throughout the 2011/2 football season. The HITS system recorded the severity and location of all head impacts during both football practice sessions and games.

To measure the physiological effects of acute and cumulative head impacts, players agreed to wear a wireless EEG system, which was housed on the back of the shoulder pads. In addition, heart rate variability, respiration rate as well as linear and angular motion was recorded using a Tricorder developed by ReThink Medical.

During the 2011/2- football season, several concussive level impacts were recorded. Two players were removed from the field due to suspected sport concussion / mTBI, one of whom was wearing the complete data acquisition system, including HITS encoders, Nicolet EEG and ReThink Tricorder at the time of impact and for approximately 30 minutes post-impact. For the first time we have the opportunity to investigate physiological responses and brain activity changes in response to a concussive level head impact.

sport concussion and sport accident reconstruction expert John Lloyd PhDAnalysis of one player’s self-reported concussive impact clearly shows decreased Gamma band activity and increased Theta band activity in the frontal cortex of the brain immediately following significant head impact. This suggests that the player had reduced cognitive performance and was perhaps in a ‘drowsy’ state for about 10 minutes following impact. During this time, the player may have been dazed and confused and certainly less effective on the field. But more importantly, his ability to protect himself from a second, potentially harmful impact was greatly compromised.

The findings of our study clearly indicate compromised brain activity as a result of head impact, which appears to be correlated with the magnitude of the impact.EEG graph showing sport concussion by expert witness Dr. John Lloyd

Normalized Power Trend Analysis. Normalized Theta (Left) and Gamma (Right) Power (log of % power within band) of a football player, who experienced a concussion following a moderately forceful head impact (Red line), show phasic modulations in power throughout the practice. Fluctuations in power rarely exceed 25% of the total average power for the recording session in Theta and Gamma frequencies. Yet, immediately following a violent hit (Red line), gamma power begins to decline rapidly and exceeds an arbitrary criterion of ±50% change from average power (peaking at 90 min.). Indeed gamma power remained within 20% of the mean for most of the duration of practice, exceeding this degree of change for over 10 minutes after the impact and two other brief episodes (around 20 min. and 50 min. for less than five minutes; Note, the first and last five minutes were ignored due to the temporal filtering artifact at both edges). Whereas, a peak in theta power coincided with the greatest change in gamma power, the degree of change from the mean normalized power never exceeded 10%. This preliminary data suggests that our algorithms provide (1) the sensitivity to detect significant change in brain activity following a concussive event, and (2) specificity in detecting which frequency band (i.e., gamma) provides the most meaningful brain signal for detecting concussion / brain trauma

Our future goals for the upcoming football season include a new micro-EEG recorder, which is in development, that will allow unobtrusive measurement of several players simultaneously during both football practice and games.

Ultimately, it is our hope that this technology will be widely available to both professional and youth teams so that medical staff can monitor the brain health of players in real-time so that injured participants can be objectively identified, effectively protected and successfully treated.

Scientific Articles

Biomechanics

Admissibility of Biomechanics Testimony on the Causation of Injury

Forensic Biomechanics – The Science of Injury Causation

Motorcycle Accidents

Biomechanics of Solo Motorcycle Accidents

Conspicuity of Motorcycles and Riders

Left Turn Across Motorcycle Path

Solo Motorcycle Crashes

Motorcycle Helmets

Biomechanical Evaluation of Motorcycle Helmets: Protection Against Head & Brain Injuries

What Every Rider Needs to Know About Motorcycle Helmets

Crash-Related Motorcycle Helmet Retention System Failures

Helmets – The Ultimate Protection?

Helmets Do Not Prevent Brain Injury

Motorcycle Helmets Provide Inadequate Protection Against Traumatic Brain Injury

Sport and Football Helmets

Brain Injury in Sports

How Well Do Football Helmets Protect Against Concussion and Brain Injury?

Researchers Discover Objective Indicator of Concussion

New Helmet Technology Reduces Brain Injuries

Forensic Biomechanics – The Science of Injury Causation

Human injury is complicated. If we lived our lives inside a protective bubble then, one day experienced an incident, it may be relatively simple to ascribe any injuries to the traumatic event. But that is typically not the case. As an aging nation, our bodies experience mechanical trauma every day – from work, sports, recreation and potential incidents. The question is whether forces and accelerations acting on the body as a result of a traumatic incident, such as an automobile collision, slip and fall, or recreational accident, were the direct and ultimate cause of injuries. Answering those questions is the unique role of forensic biomechanics and is typically beyond the expertise of most medical doctors.

Forensic biomechanics is the study of injury causation by measuring forces acting on and within the human body using methods of mechanics, to determine whether such forces exceed known thresholds of injury. As such, a biomechanist possesses expertise in the fields of both mechanics and human anatomy. Biomechanists and medical doctors serve complementary roles in the medico-legal system. Medical Doctors have specific knowledge to diagnose and treat a patient, however forensic biomechanics is not taught in medical school. Therefore, a biomechanist is required, based on their specialized education, training and experience, to serve as the necessary ‘bridge’ between medicine and engineering by calculating the forces acting on the body as a result of a claimed incident and thereby explaining the diagnosed injuries in terms of mechanical causation.

In a motor vehicle accident case, a biomechanist will assist the trier of fact by relating the impact forces and motions of the vehicles (automobiles, trucks, motorcycles, bicycles or pedestrians) to the resultant motion of occupants or other persons involved (kinematics). and forces they experience (kinetics) due to often multiple impacts within the vehicle interior or ground, then relate those forces to explain the mechanical causation of their medically diagnosed injuries.

Motorcycle, bicycle and pedestrian involved accidents can be substantially more complex, since the vehicles and operators tend to become separated and travel independently to their final rest positions. In Florida and many other states, motorcyclists have the right to choose whether or not to wear a helmet. Dr. Lloyd has conducted and published extensive research on the biomechanics of helmet protection, which shows that while helmets are effective at reducing the risk of penetrating head injury due to skull fracture, helmets do not offer adequate protection against traumatic brain injury, which can occur whether the rider is helmeted or not.

In a recent jury trial, Dr. Lloyd provided expert testimony in the fields of accident reconstruction, biomechanics and human factors on behalf of a plaintiff who suffered traumatic brain injury and a broken neck in a high-speed truck collision when a distracted driver drove through a stop sign. The jury awarded the plaintiff more than $14.5 million in damages.

Forensic biomechanics is also key to the analysis of cases involving slips, trips and falls, which are frequently claimed in all manners of environments, including workspaces, shopping arenas, restaurants, etcetera. Slips may occur whenever the coefficient of friction (CoF) between one’s footwear and flooring surface is too low, often due to the presence of a foreseeable foreign substance, such as a fluid. Whereas a trip may occur whenever the CoF between the footwear and flooring is too great, or unexpected, such as a transition between different surfaces. Unprotected falls can and do generate inordinate forces on the human body caused by acceleration due to gravity. For example, a simple fall from approximately 3 feet can generate an impact velocity of 10 miles per hour! But, more important is how quickly the human body comes to rest upon impact. It has been shown that a simple fall from only 12 inches onto a hard surface, such as concrete, can generate more than 1000 pounds of force on the human head, which is sufficient to cause fatal injury.

One recent slip and fall case in which Dr. Lloyd testified, involved a vascular surgeon, who went to sit down on a ‘budget’ stool to write his post-surgical notes. In that case, it was determined that the choice of casters on the wheeled stool were inappropriate for the environment, causing the stool to slip out from beneath the surgeon, who fell backwards, striking his head on the hard floor, resulting in traumatic brain injury and ongoing epileptic episodes. The surgeon, who suffered severe neurological deficits as a result of the incident was unable to return to work and also suffered many other lifelong effects. At trial the jury awarded the surgeon $10 million for injuries caused by the slip and fall.

In conclusion, a forensic biomechanical analysis may be pertinent to the success of a variety of cases, including: motor vehicle accidents (involving automobiles, trucks, motorcycles, bicycles and pedestrians), recreational accidents (including boating, jet skiing, ATVs, etc.), sports injuries / helmet protection as well as slips, trips and falls. The opinions formulated by Dr. Lloyd and other forensic biomechanists regarding the quantitative accelerations and forces necessary to result in injury are uniquely biomechanical opinions, and no other area of science or medicine is as appropriate to offer such opinions. Neither mechanical engineering nor physics include the prerequisite background concerning human body tissue properties and human anatomy. Similarly, medical training does not provide the necessary understanding of biomechanical principles to identify qualitative relationships between physical trauma and human tissue injury. Thus, a forensic biomechanist serves the legal system by quantifying the forces associated with an incident and comparing those forces against scientifically accepted thresholds of injury thereby explaining the medical diagnosis.

Judge Healey of the State of Florida First District Court of Appeals (Case No. 1D11-4210) recently upheld the importance of forensic biomechanics testimony in his ruling, which stated that “a biomechanics expert is qualified to offer an opinion as to causation if the mechanism of injury falls within the field of biomechanics” and as such is “relevant to establishing a reasonable hypothesis … that the victim’s injuries were consistent with … trauma”.

Ultimately, the success of any expert lies in their ability to convey often complex matters to a jury. Based on over 20 years of experience as an expert, during which time Dr. Lloyd has provided testimony at trial or in deposition more than 80 occasions, he has become highly proficient in using methods that express complex matters in simplistic terms for the purpose of educating the jury as to the facts of a case.

Research

Biomechanical Analysis Athletic Protectors

Concussion and Brain Injury Associated with Headrest Impacts in Rear End Car Crashes

Helmeted Motorcyclist Fatality

Motorcycle Pothole Crash

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