ARAI BASIC PRINCIPLES
ARAI TECH PUSHING THE BOUNDERIES OF HELMET TECHNOLOGY Arai is leading in innovative helmet technology. If you’re looking for a new helmet, you might be asking yourself; can there really be that much difference these days between one brand and another? And if so, are these differences that do exist, pretty slim? The simple truth is, while there are indeed a lot of helmets out there, there is still only one Arai. Our technology is what makes us truly different. Here you can find out the background of not only this technology, but also the philosophy and the passion that drives us in making the best helmet possible.
It is the shell that really works.
The following three topics are key in this respect:
Impact absorption capacity is measured by dropping a helmet with a headform inside it onto a rigid anvil. The impact energy transmitted to the headform should stay below specified level. When the helmet meets this requirement, consumers and the industry as well may assume that the helmet is therefore capable of protecting the wearer’s head at real life impacts.
1 Shell Configuration
But there is a significant difference between test speeds and real life speed. The velocity of a helmet at the time of impact during tests is less than 28 km/h! This is true for even the most stringent motorcycle helmet standard in the world. Kinetic energy goes up in proportion to square of velocity. Therefore the head of a rider at 100 km/h is carrying more than 10 times(!) the amount of energy than the headform during a standard impact test. This kind of energy is far more than the impact absorption capacity of any helmet. Yet, in the real world there are helmets that have proven to protect riders’ heads in actual accidents at even higher speeds. This fact alone tells that there is quite a difference in the nature of impacts under real world and test lab conditions. In the real world, it is seldom that an impact is aligned straight towards the center of the head, as is the case during impact tests. Instead, the impact can originate from any location, from any direction, at any speed, any angle and by any object. Therefore only if the outer shell is constructed and functions properly, there may be the possibility that a decent portion of the impact energy is diverted by sliding over, or by glancing off, the object hitting it. This explains how some helmets do a good job even in accidents at racing speeds where huge energies are involved.
V
About the Arai Standard
About the ‘’Basic Principles’’
Impact velocity
7.75m/s
When a helmet is caught by an obstacle, this may cause rotational and acceleration forces. When the helmet slides, energy is diverted. Round, smooth surfaces of outer shells offer the best chance to slide during or after impacts from any direction.
1
sliding in horizontal direction keep traveling in horizontal direction
max. speed
28 km/h
sliding in horizontal direction
Kinetic = 1 energy 2
mass
(Velocity)
2
shock absorbing test
at 100km/h speed
velocity at 28 km/h speed = 7.75
velocity at 100 km/h speed = 27.78
1 2
mass
1 2
(7.75) 2
= 30.03 mass The difference
mass
(27.78) 2
= 385.80 mass
12.85 times
2 Shell Laminate
B
2
To divert the energy of an impact, a shell needs to function as a “sled” to slide over uneven surfaces or to glance off obstacles hitting it. The strong laminate material of the outer shell needs to be able to sustain the impact load, as well as to resist deformation that could cause rotational forces, in order to perform this role.
A
sliding in horizontal direction
3
A=B
generate rotational energy at the point of damage
headform
headform shock absorbing liner
A
in the real world
A>B
shock absorbing liner
Shell
B
shock absorbing test
generate rotational energy from horizontal traveling
There are ways to make a helmet shell that performs excellently under test lab conditions. Yet, when it comes to real world performance, what needed are solid basic properties that are less likely to fail you. And that is exactly what Arai has been doing throughout its long history. The role of the outer shell in real world conditions is far more important than in a test lab.
Impact management test
Shell penetration test
Test anvils simulate impact objects in real accident scenarios, and there are different anvil configurations. A fllat anvil may simulate impact against flat road surface. A kerbstone anvil may be used to simulate impact against curbstone or a guardrail. When an anvil shape is more round, the contact surface of the impact becomes less and that will cause more stringent impact energy to the helmets. The Arai Standard specifies impact management test to be conducted with a hemispherical anvil that has a much smaller contact impact surface (causing higher breaking energy) than flat or kerbstone anvils.
kg mass In the event of fall, the rider’s 3penetration head may hit against the road test striker surface or slide in unexpected directions. The possibility that the helmets hit against for instance a guardrail, motorcycle foot pegs or any other object in the road shoulder may not be quite low. Performance evaluation against hard, sharp objects might therefore be important for motorcycle helmets. Outer shells should offer certain toughness, that is why the Arai Standard defines shell penetration test with a 3 kilo sharp tip metal striker, falling from 3 meter height anywhere on the helmet above its test line.
ECE R22-05
Impact velocity
RX-7 RC
RX-7 GP
* 7.75m/s
Quantum-ST
XXS, XS, S size
3m
Peak acceleration
Impact velocity
not exceed
275 G
M, L size
7.5m/s
Peak acceleration not exceed
275 G
XL size
Peak acceleration not exceed
Peak acceleration not exceed
275 G
264 G
XXL size
Peak acceleration not exceed
243 G
*7.75 m/s for first impact second impact velocity depends of test headform size
The Arai Standard does not specify fixed impact points and requires any point above its test line needs to comply to the requirements.
ECE R22-05 Test area
SNELL 2010
SNELL standard requires 2 time impact at the same spot while ECE R22-05 requires a single impact test line
RIGID OR SOFT OUTER SHELL? shock absorption by liner squash
Satisfying both ECE R22-05 and Snell M2010 performance requirements
SNELL 2010
ECE R22-05
SNELL 2010
ECE R22-05 requires maximum peak acceleration should not exceeds 275G while SNELL standard requires lower maximum peak acceleration depending on size ranges.
Shell
3 Shock Absorption The true role of impact absorption in real world conditions is to act as a suspension at the time the energy is diverted. Good suspension eases the transmission of the impact to the rider’s head.
The “Basic Principles” are a summary of what we have been observing decade after decade. In fact, we have never made helmets that contradict with these principles throughout the history of Arai. Thanks to this fact, we can present these “Basic Principles” without hesitation. Yet, it may not be the same for manufacturers with a different historical background. The number of helmets on the market today that conflict with these principles is in fact overwhelming. Why? Because these principles may not only be annoying to some manufactures. Even to such an extent that they completely dismiss the principles. By the plain facts do us justice. The principles should therefore be acknowledged. Not only for ourselves, but especially for the sake of our fellow riders and the helmet industry in general.
The self established Arai in-house standard is a series of tests performed in addition to mandatory national standards. That is the so called “Arai Standard” and it is applied to most Arai products to provide superior helmet performance for motorcyclists.
The difference between industrial and motorcycle helmets
1. No helmet is used: the head hits the wall and stops almost instantly. The brain however keeps on moving due to inertia and smashes against the inside of the skull resulting in considerable injury. .
shock absorption by shell destruction
No one knows where it hits! crown region
frontal region occipital region
Let’s look at two types of helmets to make a comparison for a shock absorbing test. In this test the helmet is dropped from a certain height with a metal alloy headform to determine peak acceleration. The test will be done with two completely different helmets: Typ A: R igid outer shell with soft density inner shell (as Arai) Typ B: S oft outer shell with hard density inner shell (as the helmets with injection molded shells)
Either Type A or B may pass the same standard. But the reason why B may pass is that a non-rigid shell breaks itself and absorbs impact energy in doing so. The remaining energy, which the shell cannot absorb is then absorbed by the hard density inner shell, which can also work as part of shell function. Note that the absorption of the non-rigid shell may not be enough to absorb large impact energy and/or multiple impacts which hit the same impact sights because the harder density inner shell may not sufficient to absorb the total energy that received throughout. The Type A helmet spreads the force of the impact evenly across
wider surface, the soft density inner shell then easily absorbs the retaining energy that is transferred through the outer shell, even when multiple impacts are applied. Helmets designed as Type B may save much weight in the shell. However, when we talk about higher performance helmet shells, there should be another requirement in addition to “light weight”, and that will be “strong enough”.
2. With helmet against a flat wall: the impact energy is absorbed by the inner shell. The velocity of the brain is reduced during a much longer period of time resulting in less injury for the brain.
Type A helmet under impact: the impact force is diverted across the wider surface of the outer shell. The soft inner shell absorbs impact energy by compressing the inner shell material.
Type B helmet under impact: the impact force is not diverted across the wider surface of the outer shell but absorbs the energy with limited surface resulting direct transmission to the inner shell. The hard inner shell receives direct impact transmission and transfers the impact force to the skull and brain.
Everybody is familiar with the sight of construction workers wearing their white or yellow safety helmets. Why don’t motorcycle riders use the same, cheap, helmets? The reason is that they are made for a completely different purpose. Construction helmets are designed to protect against impacts from outside such as a falling brick or a bolt lost by a colleague working high above him. Motorcycle helmets are designed, strange as it may sound, against impacts from the inside. The impact energy that causes injury comes from opposite directions and that is why these helmets must be so different. Also read the caption about the Arai ‘’Basic Principles’’ for a better understanding of this matter.
It is the general thought that a helmet must protect the head from an impact from an object from the outside. But motorcycle helmets must handle much more than just that simple task. During a motorcycle accident, the mass of the head increases the impact energy significantly: the helmet itself stops quickly at the impact, but inertia makes the head inside it carry on. When a motorcycle helmet hits the road surface for instance, the head may impact right through the inner shell and hit the inside of the outer shell.
To explain this phenomena, take a look at the following examples of possible impact against a wall:
3. With helmet (or cushioning device) hitting a protruding object: the rigid outer shell distributes the impact force over the complete surface of the outer shell. The inner shell absorbs the remaining impact energy. The brain will suffer less harm.
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Helmet manufacturing process
OUTER SHELL CONSTRUCTION
UP TO FIVE DIFFERENT OUTER SHELLS
CRUCIAL: CENTRE OF GRAVITY
B Both helmets straight
RC construction
2 Super-Fiber strings are chopped and then sprayed on a metal mesh mold in a chamber, and shaped into what looks like a straw hat.
A
E
D
C
The RC construction was first developed for the Formula 1 GP car racing helmet. RC stands for ‘Racing Carbon’ referring to the carbon fibre outer shell. Arai uses only the highest grade carbon fibre material as used in aerospace technology. The supply of this carbon fibre is however very limited and restricted to a select number of end-users. Arai is one of them and it is the use of this special carbon fibre that makes the Arai outer shell stands out. The construction of the RC outer shell consists of an extremely stiff and light carbon fibre outer shell, reinforced with the ’Peripherally Belted’ construction. This system consists of a strengthening belt across the helmet, just above the visor opening, giving the outer shell even more strength and stiffness. Every RC outer shell is handmade and it takes a skilled Arai craftsman a full working day just to make one outer shell.
4 The hot shell is taken from the molding device. It does not have the aperture or visor opening yet during this stage. The different layers of fiberglass and other materials are clearly visible in the transparent shell.
3 This ‘’straw hat’’ together with additional Super-Fiber and other fiber materials are put in a molding device, and then resin is poured into the mold. The molding device is then closed tightly with a lid that has a balloon underneath it. The balloon is inflated and the molding device is heated to form an outer shell..
6 Every shell is then carefully inspected for thickness, weight and structural correctness. Then it is sent to another inspection department for final inspection. Each outer shell is therefore inspected twice.
PB-SNC ‘Structural Net Composite’ is Arai’s unique advanced shell construction. ‘PB’ is short for ‘Peripherally Belted’. This system was originally developed for the special Formula 1 helmets and consists of a strengthening belt across the helmet, just above the visor opening, giving the outer shell even more strength and stiffness. ‘SNC’ incorporates a structural net reinforcing material embedded between Arai’s exclusive Super Complex Laminate Construction layers. The specially developed strands bond the layers more rigidly to further improve shell integrity and impact-force management. PB-SNC also allows for more weight to be removed from the top of the shell, reducing overall helmet weight, while it lowers the centre of gravity, resulting in better balance and reduced fatigue for more comfort.
absorbing inner shell is installed into the outer shell.
8 Decals are applied onto the shells for models that come with graphics.
9 Holes for visor, chinstrap and ventilation ducts are drilled, and then the shells are trimmed with edge rubbers.
13 The helmets are then shipped to customers world wide.
11 Visor, ventilation ducts and other parts are mounted, making sure each part fit and functions properly.
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12 After polishing and labeling each helmet is inspected carefully, and then proceeds to packaging.
appropriate thickness for every size. This may cost extra as each individual homologation is granted per shell size, but Arai helmets provide the same level of protection performance. Arai does not like to see a very small person with a rather big, ‘oversized’ looking helmet. All Arai full face helmets feature the ‘Hyper Ridge’ construction at the bottom of the outer shell. This ridge greatly enhances stiffness and strength of the shell.
A Centre of gravity of helmet (far from C) B Centre of gravity of helmet (close to C) C Centre of gravity of the human head. It is not logical to simply state that lightweight helmets are ‘better’ than heavier ones. Instead we should define ‘better helmets’ by the stress transferred to the neck, and helmet weight is just one of the many factors that may cause stress to the neck. In general, the mass of a human head differs between ± 5 kilos. Even if the helmet weight is measured on a scale, you still cannot tell whether the helmet will give much stress on the neck or
7 Passed shells are then undercoated and sanded. This process is repeated twice to get a fine, even surface for a smooth finishing coat.
10 The shock
Unlike many other manufacturers Arai provides one shell for one or two helmet sizes. The total number of outer shells can be as high as five for some models. Most manufactures use only one or two outer shells for their complete size range. The advantage of using different shell sizes (instead of just one or two inner shells and the use of additional or less foam padding to stretch the size range) is that on all helmets the inner shell and comfort material can always maintain the
Patented PB-SNCR Construction
A) Molding device and helmet molding B) Layers of fiberglass C) Pouring resin in D) C losed molding device lid, with balloon underneath E) Inflating the balloon
5 The visor opening, chin vent and other vent holes are cut out by a laser cutting robot.
Normal helmet centre of Gravity
ScLc (Super Complex Laminate Construction) Two layers of Super Fibre, one middle layer of special fibre. The middle layer consists of a very special material, a chemical fibre exclusive to Arai, which is stronger and lighter.
cLc (Complex Laminate Construction) Two layers of Super Fibre, one middle layer of composite fibre. This middle fibre is lighter and stronger and better suited for production in larger numbers.
sFL - Standard Super Fibre (Super Fibre Laminate) One layer of Super Fibre, this is the basic Arai outer shell and is therefore called ‘Standard Super Fibre Laminate’
not. Why? Because we hardly feel the weight of the helmet if it’s positioned straight above the head in a totally upright seating position, as both the human head centre of gravity and the helmets centre of gravity are close together when wearing a helmet. But we will experience stress on the neck by helmet weight in a crouching position. When the helmet is straight (vertically) on the head, the centres of gravity of A, B and C are in line and we do not feel much difference. In a
crouching position, as shown in this sketch, a difference in load or pressure between A and B will be noticed. When the centre of gravity is positioned at point A, the down force on the head will be much higher compared with the force caused by the centre of gravity at point C. Arai helmets offer a centre of gravity much very close to the important center of gravity of the human head.
FACIAL CONTOUR SYSTEM (FCS)
ADVANCED MULTIPLE DENSITY INNER SHELL
FCS (FACIAL CONTOUR SYSTEM) PEEL-AWAY PADS
The polystyrene Arai inner shell, which fits exactly in the outer shell, absorbs impact energy. It smoothly reduces the impact energy. If the density of the expanded polystyrene inner shell is too high, it will be too hard and will therefore absorb the impact force less evenly. In order to provide the best possible protection, the inner shell should not be too loose, causing the helmet to ‘dance’ around your head, nor too
Another Arai breakthrough in advanced helmet technology is FCS, short for ‘’Facial Contour System’’. The FCS cheek pads offer an integrated ‘’spring’’ action. This makes putting the helmet on easier with less effort needed. With FCS the wraps under the jaw bone and on the cheek bones
instead of mostly on the soft cheek area. Although the fit feels more loose, FCS actually offers secure support over a larger area providing superior stability and comfort with minimal pressure. The new ‘’Peel Away’’ pads offer thin surface pads that can be removed from the head inner shell as well as the top surface of booth cheek pads to achieve the best possible, personal fit and minimize the need to purchase additional padding.
THE DOUBLE D-RING CHIN STRAP FASTENER tight so that it constricts and causes pain. Arai’s inner shell is like no other, comprised of several different densities seamlessly molded into a single piece. The unique benefit is the direct contact area that each inner shell cell shares with its neighboring cells creating a mutual support area. As one cell is crushed under impact, the surrounding cells assist with the energy absorption.
The ‘Double-D’ ring is well known and generally accepted as the best and most efficient chin strap fastening device among the helmet industries for a long time. Arai’s double “D” ring buckle is designed to give less pressure to wearer’s jaw. The chin strap is provided with a small red push button to secure the strap end, which can only be fastened if the chin strap has been tightened in proper way. Another advantage of the D-ring fastener is the fact that everybody understands how its functions, and can therefore easily be released in case the chin strap has to be unfastened.
BooQi products are produced under license and are subject to design registrations and trademarks. © Booqi Media Solutions BV www.booqi.com NO call +31 (0)20 7163151 NO14933/31 16210/31
1 The construction of the outer shell is the start of the helmet manufacturing process. Super-Fiber strings form the base of the shell. Besides Super-Fiber, other materials such as Kevlar®, Nylon and carbon fiber are used on selected shells.
Arai helmet centre of Gravity
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