SE530225C2 - Protective helmet testing device, comprises head secured to base by mounting part comprising flexible section for simulating neck and instrument section with sensor - Google Patents

Abstract

The helmet is placed on top of a model head which in turn is secured to a base part via a mounting part provided with instruments. The mounting part includes a flexible section secured to the base part, which has a rigidity and damping chosen so that it simulates the human neck. The flexible section comprises a soft part made from e.g. rubber. The section of the mounting part secured to the head is used to support the instrumentation comprising a six component sensor for recording force and momentum vectors transmitted to the head.

Description

530 225 å.) This deficiency in the standard can also lead to further incorrect results when assessing helmet tests ..

An important source of error is thus that, especially in tests with a free-falling head without control, part of the total fall energy at the moment of impact is transformed into rotational energy due to the fact that in the general case eccentric shock occurs. Up to 50 percent of the original fall energy can in this way be converted into rotation, which is thus not registered under the current standard (10). The measured acceleration will then be less than if the impact had been purely central. Since the rotation effect is completely disregarded, by making a helmet elongated or with protruding parts, it would be possible to make it more prone to rotation and therefore with the current test standard falsely show better protective properties.

Admittedly, this can lead to a distortion of helmet development by allowing manufacturers to make helmets with a more rotational shape to make them pass the certification tests more easily. Although such intentions cannot be said to have been decisive for currently in use types of elongated helmets, such as bicycle helmets, certain types of helmets have been able to develop uncritically without having to take into account the greater risk of harmful rotational force such as the elongated geometry may cause. A more stylistic design with a streamlined shape and thus greater torque uptake has thus been prioritized for marketing reasons, without the thereby increasing tendency to rotate having to be taken into account. A helmet approved according to the current standard therefore does not guarantee full head protection against external violence, especially as the violence in practice is usually combined with rotation.

In addition, it can also be emphasized that large differences in results have been found between CEN and ISO standard methods for testing head protection [l0]. These methods differ mainly by varying degrees of control of the sample head at the moment of impact, leading to a corresponding difference in energy lost by rotation, which is not recorded in the sample. It has been found that the ISO method of controlling the case, and thus less possibility of rotation, gives a larger number of failed helmets than the CEN tests, which have a free-falling head without control. Tests according to the ISO standard are therefore stricter than CEN because with ISO a comparatively larger part of the total energy affects the helmet as registered linear acceleration.

This further highlights the importance of taking into account the rotation effect in certification tests on safety helmets in order to be able to achieve compatibility between results from different test rigs and laboratories and thus get to the point where the desire for a single globally accepted test standard can be met and become realistically possible. 530 225 Description.

Proposal for a new methodology and test rig.

The proposal for a rig for helmet testing outlined in lgur l differs from the current standard mainly in that it enables simulation of the general and most common case of both linear force and rotation that occurs during a blow to the head.

The method is based on a well-defined shock hitting the helmet, stationary mounted on a model head, which in turn is attached to an fi indament via an instrument crate bracket. This bracket has closest to the foundation an fl exible part with stiffness and cushioning that simulates the human neck in that this part consists of a suitably chosen softer element of, for example, rubber.

The second part of the bracket, closest to the module head, carries instrumentation which consists of a six-component sensor for recording results obtained to the module head of a collar and a torque vector with three components each from the applied shock.

The impact is conveniently achieved by allowing a drop weight, elongated for good vertical guidance, to hit the test object, the helmet, from a laterally (x- and y-direction) slidable blank. The vertical guide consists of three or fl your surrounding posts of, for example, steel pipes evenly divided. The cylindrical part of the drop weight can be provided near the ends with sliding surfaces of, for example, te fl on to reduce the friction during the fall. The tower is installed on a coordinate table with a heavy stable base plate, which has adjusting screws and scales for adjusting given desired x - y displacements and locking in this position to the foundation. The tower can in this way be accurately positioned for wood on a stop body according to fi gur l - 2, with minimal mass, and with the stop body held against the helmet at the predetermined point of impact via a harness with three or four thin radial rubber bands in the horizontal plane according to fi gur 2. suggested to be made the same as that of the model head including helmet to get the same energy content in the shock as in the current standard. For increased vertical stability of the weight, the mass can be concentrated towards the ends of the weight with an intermediate rigid part, however, the main part of the mass can lie at the end closest to the point of impact to obtain the best lateral stability through the inertial forces at oblique strokes. On the foundation there is the possibility of installing the module head with its axis within a 90-degree sector in a plane perpendicular to the x-direction of the empty space and with the angle of the axis variable from horizontal to vertical outer position. For each set position, the center of gravity common to the helmet model head is maintained at the same coordinate point. The possibility of angular variation within said sector can be continuous or in discrete increments through, for example, sun-spring-arranged holes within this sector. The latter for the best opportunity for stable installation. By the fact that the module head is also rotatably mounted on a sleeve with a ball joint, the possibilities for orienting the vertical impact from the drop weight towards all the desired areas on the helmet are increased.

Instead of a fall tower which is displaceable in the x and y directions, one can alternatively have the fall inch stationary and the model head with its bracket horizontal: displaceable in the said directions. However, as this seems to be more difficult to solve in terms of construction, the alternative with variable empty space has been chosen here.

In this way, it is possible to aim for a central or eccentric impact in the desired impact area on the helmet with the impact energy determined by the mass of the fall weight and the set fall height. In addition, the rate of fall of the weight is measured immediately before the grant. For the intended eccentric shock, the desired torque arm in relation to the known center of gravity position of the head can be adjusted with the help of the adjusting screws and the dimensional scales in the x- and y-directions on the coordinate table. Alternatively, the torque signal from the kra fi torque sensor in the neck of the nozzle head can also be used in the set-up in order to be able to calculate the corresponding torque from it. A pure central shock on a safety helmet can, as in the current standard method, only be achieved with blows straight from above (erown), but the possibilities for a more pure central shock in other areas are better with the new method because the setting here has an increased number of controlled degrees of freedom. 530 225 'i Instead of a drop test, a calibrated directional pneumatic gun according to Figure 3 may also be used with a piston and an associated axially movable push rod (corresponding to the drop weight) to provide the impact load against the desired area of the stationary mounted helmet test head. Because the cannon is universally directed and can be moved in parallel in x- and y-directions relative to the test head and helmet, which are centrally mounted and rotatably attached to the ball joint, the desired eccentric or almost straight central shock can be obtained as predetermined in the drop weight method. hit area.

The mass and speed of the push rod are adapted to the desired impact energy. The pneumatics provide a relatively simple possibility of automatic return of the push rod for faster production, which is also conceivable, albeit somewhat more complicated, even with the alternative with a movable drop tower. The method with drop weight should, however, be preferred by its ability to better precision the prediction of the impact energy for each desired hit area. The anvil in the current CEN and ISO test standard corresponds in the present proposal to the above-mentioned stationary loose impact body (according to fi gur 1 and 2) with the least possible mass and with instrumentation for measuring the requirements, torques and accelerations included in the helmet. During the test, the stop body is first placed on the surface of the helmet in the desired test area and held in place in relation to the center line of the empty or push rod with the aforementioned rubber strap in a plane perpendicular to the center line so as not to dampen the movement of the drop weight (or push rod). When the drop weight is released, the impact body is hit by the flat end surface of the weight, whereby the impact is transmitted to the helmet shell.

By, according to the abutment body, being provided with spherically convex contact surfaces of a radially large curling radius, intervention in the helmet shell of the edges of the abutment body can be avoided in the event of eccentric shock.

The contact surface of the impact body against the helmet shell may have a certain defined roughness in order to include controlled simulation of rotational force by eccentric shock and frictional forces during movable contact with, for example, a road surface. The contact surface against the helmet can therefore be provided with, for example, a dense pattern of engraved concentric circles with sharp ridges in between as a suitable spherical friction surface.

In this way and with the various setting options, you can also get a specified eccentric shock in this rig with a given impact angle against the helmet surface and minimal energy loss due to lateral movement of the weight and impact body, which is also under control through the possibilities of registering forces generated during the impact. and torque. In the case of very oblique abutments against the helmet surface, the separate abutment body can alternatively be omitted and instead the end of the drop weight (push rod) is designed with a friction surface for direct contact with the helmet, where the disadvantage can be problems with movable wires. The abutment surface may be designed as an oblique disc, which could also be defensible if measurements are made of corresponding lateral force acting on the helmet. In this case, for disc reasons, the disc should need to be integrated with drop weight or push rod to be controlled against both tilting and axial rotation .

The stop body can be made in i your editions, designed as a judgment or part of a puck to enable the same equipment to be used for both penetration tests on helmets and in tests with simulated puck shots against face protection.

The test rig with drop weight described above can also be used to subject the helmet to a more pure torque, via a device for example according to Figure 4, for simulation of rotational force transmitted from the helmet to the head. With the helmet installed on the model head, a (unobstructed) steel band is attached to the helmet and wound around it one or two turns in the desired torque plane. The steel strip is supported by break pulleys according to Figure 4 and joined at the ends with a stop plate. At impact, the helmet is affected by an almost pure torque. Registration takes place both on the impulse moment generated on the helmet through the input collar in the belt and measured reaction moment in the neck bracket on the model head.

In a simpler variant of this test, it is conceivable to use a lever attached to one end of the helmet, which is supported by the drop weight at its free end. With a moderate length of the lever, a dominant torque moment can always be obtained with the type of test rig in question. is mixed with straight central shock. 530 225 ö 'Reasonable values for the elasticity and cushioning of the neck bracket shall be determined for the best possible simulation of the fl flexibility of the human neck under real conditions. This can be achieved by combining the neck sensor with a rubber damper closest to the attachment in the foundation as above, the rubber damper being adapted for normal rigidity and damping properties of the human neck.

Compared with the current standard, the influence of the naturally low flexural stiffness of the proposed neck bracket is calculated to give an extended acceleration characteristic of the model head with more realistic pulse times.

This should be desirable, but requires a closer examination to assess the choice between linking to the conditions in the current standard or to a more deviating but naturally simulated pulse characteristic.

A computer simulation of the test rig and its function will be used to optimize the overall flexibility of the bracket and the mass of the drop weight for selecting reasonable values of the drop height for adaptation and practical ironability with real circumstances regarding speed and energy content in the impact of a helmet and head in a motorcycle accident. alternative testing principles.

Here are summarized some different types of testing principles that are conceivable for certification of helmets, taking into account the protective effect against both linear force and rotational force. The possibility of performing these tests could for the most part be included among the properties of the proposed test rig.

Performance data can be recalculated to link to the current standard. 1) An interesting alternative to the current assessment basis for safety helmets has been the registration of requirements and torque instead of acceleration measurement, which would mean a better opportunity to take care of simulation of rotational force via load with torque. The registration for the fall test can include forces and moments with calculation of, for example, max, average value, effective value, damage index and transmissibility, measured before and after the model head with a helmet. Here it is also possible to recalculate forces and torques to the corresponding acceleration values to be linked to the current standard. 2) If one instead starts directly from acceleration measurement, which is related to the current standard, one calculates correspondingly max, mean value, effective value, damage index and transmissibility with respect to obtained values for simulated linear and more or less pure rotational force. 3) The assessment of helmet quality can be based on. absorbed energy registered partly as total input energy obtained from the velocity and mass of the drop weight (push rod), partly in the helmet locally dissipated deformation energy measured via an impedance head and partly the remnant of linear and rotational energy calculated from the model head's measured forces, torques and accelerations the helmet during a fall test. The function of the impedance head is to locally register accelerations and forces, from which the corresponding energy can be calculated after integration of the acceleration. 4) Another alternative for helmet testing is the use of vibration telemics by measuring hearths for acceleration, forces and moments and from them obtain values of phase angle rotation, resonance, transmissibility and dissipated energy to comfortably obtain the damping in the helmet and thereby assess its protective ability. . This method would require a special adapter with the ability to apply and measure both draft and pressure at given points and in given directions on the surface of the helmet. The adapter could be designed as a ring-shaped holder that attacks and measures simultaneously at two diametrically opposite points on the helmet centrally or eccentrically. Instead of attaching a model head with a helmet to a special neck bracket, the vibration excitation can easily be applied to a freely laid or suspended model head with a helmet. The forced exertion could include impact stress by making the connection to the adapter with a given clearance for nonlinear shock excitation. The method has limitations in that it can hardly be applied in all points and directions on the helmet, but it should be able to be used as a complement to other types of tests, and in tests where demands for quick answers are prioritized. 530 225 i »The above-mentioned variants are examples of test methods with the possibility of simulating and measuring both direct central force and rotational force against the head and are compatible with the principle of stationary model head on a simulated human flexible neck for vectorial measurement data. It would be of interest to gain practical experience of testing different helmets in order to be able to select one of these testing principles to replace the current standard or to initially be included as a complement to other methods.

The practical possibility of using this proposed vibration method for helmet testing is first intended to be investigated with the aid of a specific computer modulation model. In this way, one can evaluate the possibility of simplifying or supplementing helmet testing that this proposal would entail. Through studies on the simulation model, it is possible to optimize in advance the required data on the corresponding type of rig for tests on safety helmets with regard to suitable values for eg power, frequency range, resonance, phase shift and amplitude of corresponding mass elastic systems for helmet tests in reality. The above-mentioned possibility of applying the vibration excitation to the helmet here on a freely suspended or laid model head can mean a simplified test procedure. There is also the possibility that this principle can be used to separately test different cushioning materials for helmets.

Measuring equipment.

Incoming local impact force fi on the helmet must be measured with sensors in the previously mentioned impact body.

The intention is to measure input forces and torques to size and direction with a six-component sensor for vector registration of three kra fi and three torque components. After initial testing with this six-component sensor, it can be assessed whether the equipment can be simplified by switching to a sensor with fewer components.

The measuring equipment in the impact body alternatively also includes an impedance head with accelerometer and power sensor for one or preferably fl your components for measuring locally absorbed energy in each set impact area on the helmet. In addition, the corresponding direction and resultant of these locally applied input data for the helmet can also be obtained from the impedance head's signals for accelerations and forces as a basis for calculating the applied rotational force. However, it would prove appropriate to divide certain samples into different custom separate sensors so as not to overload a single impactor with your sensor functions. Instead of being mounted in the loose abutment body, sensors can be built into the outer end of the drop weight (shock bar) to thereby enable more oblique shocks. However, this can cause some conduction problems during the shock process, which is similar to the current standard method with a falling head. Optionally, the alternative with the tangential force device listed below may be suitable in this case.

Reaction forces and torques on the model head are measured with a six-component sensor in the nearest rigid part of the neck bracket. Measured data is referred here to a coordinate system originating in the center of gravity of the model head. This coordinate system must be linked to the sensor calibration.

For vectorial measurement on the model head of both linear and rotational acceleration, six, possibly nine simple accelerometers placed orthogonally on are suitably used. the surface of the model head with the maximum distance from the center of gravity of the head to obtain the best possible precision. The signals from these sensors can also be used to obtain corresponding integrated values of the head speed and displacement in order to, together with registered force and torque data, also make it possible to calculate the energy transmitted to the model head.

A tangential impact on the helmet can be simulated with the device according to fi Figure 4 for pure torque, where specified instrumentation in the impact body, model head and neck bracket can be used to record the corresponding data. This type of simulation can be used to assess the helmet's protective effect against rotational force. relative movements in the layer between the head and the helmet shell.

Speed measurement on drop weight and shock bar is included in standard testing and is performed using a sensor mounted as close to the shock point as possible. 530 225 "lr The aforementioned proposed method of vibration excitation requires a corresponding dynamometer with the ability to generate the required performance for the test with respect to, among other things, frequency, power kra and amplitude. In principle, the above types of sensors for forces, torques and accelerations are also applicable for this alternative, Discussion Testing of safety helmets is linked to their ability to prevent damage to the human brain in the event of violence against the helmet wearer's head.Available injury criteria for the human brain are based on medical research results with acceleration measurements.It has therefore come close to standardized helmet tests use measured acceleration values to assess the protective capacity of helmets, if another type of helmet sample is to be used as an alternative, it should therefore be possible to refer to the corresponding acceptable acceleration value in the center of gravity of the model head.

So far, however, as has been pointed out, only the linear part of the acceleration has been taken into account in the certification of helmets; one thus completely ignores the helmet's protective ability against rotational force in the current standard, much due to the difficulty of measuring and evaluating the rotational force and the absence of suitable equipment.

An attractive alternative would therefore be to use recorded values of input and output forces and torques in the model head instead of acceleration measurement, as it would be easier to register a power fi and a morphine vector in pairs via a corresponding conventional six-component sensor (wind tunnel wave) in each desired measuring point. each three components to thereby evaluate the helmet's protective capacity with respect to both rotational force and straight central force, To study vectorial linear and rotational accelerations in the model head center of gravity from measured force and torque values in the current method with standard rig and falling head without steering to carry out initial tests, which in addition to the linear force also contain some limited possibility for measurements of rotational force on the anvil prescribed in the current standard.

This would then be designed as an integrated six-component sensor with the possibility of vectorically registering the shock pulses for requirements and torques included in the model head via the helmet. This sensor must have great rigidity and small tethered mass. The impact surface of the anvil should then also have a certain roughness to simulate lateral friction at the impact of the head against, for example, a road surface. You may then also consider tilting the anvil and providing it with a larger impact surface with low mass. In this case, a six-component sensor is particularly advantageous because it thereby provides measurement results in size and direction for both linear and rotational force.

What then happens during the blow is that the helmet's shell and padding are compressed, whereby the corresponding defonation resistance arises and increases as the deformation progresses. The resistance consists of forces and moments which, for their type, can be, for example, elastic, viscous or friction and, as a result of the mass-elastic system, have the character of damped oscillation in order to reach a maximum with a certain fixed displacement and then return to repeat cyclically. and form a high frequency pulse. When the return is not complete, this means an energy loss, which means that the amplitude of the oscillation within the duration of the pulse rapidly decreases through the resistance of viscose and friction character, which also manifests as hysteresis, residual deformation and heat generation until all kinetic energy from the fall weight is exhausted. A visible effect of the deformation force, the reaction, may also be that the helmet model head unit will be accelerated in the direction of the reaction force in the form of a bounce with rotation.

The question now is whether one can use measured forces and moments in the contact surface between the anvil and the helmet with the aid of the six-component sensor integrated in the anvil for calculating the corresponding linear and rotational accelerations attributed to the center of gravity common to the model head and helmet. 530 225 At first you can then study the case with pure central shock. If no other force acts on the system, the resulting reaction force measured on the anvil will act via the helmet on the total mass of model head and helmet, which thereby has a negative acceleration (deceleration). Due to the proportionality between force and acceleration, this acceleration can therefore be calculated as attributable to the common center of gravity with knowledge of the total mass of the model head and helmet. From this, the desired damage criteria can then be obtained.

The difference between on the one hand acceleration measurement in the center of gravity of the head and on the other hand measurement of the kra k-torque components in the contact surface would in the latter case be expected to measure a somewhat more unampled characteristic for the kra fi-torque components than for accelerations measured in the model head's center of gravity. lost. A preliminary study confirms this and otherwise shows a largely uniform characteristic for both methods, which supports the idea of the possibility of using measured forces and elements for assessing the protective effect against central shock for different helmets.

In the general case of eccentric shock, the problem is more complicated, in that the shock process, in addition to the force vector, also contains a torque vector. Taking into account the rotation requires knowledge of the coordinates of the point of attack on the model head helmet in a movable system originating in said common center of gravity. This must be measured in relation to the sensor. Consideration must also be given to the change of the torque arm during the impact process, for example through the rotational movement of the head. For the principle of free-falling head without control, the method of acceleration measurement bound to the coordinate system of the head is therefore more suitable.

Since in helmet tests based on measuring force and torque, certain difficulties can thus be expected in accessing the torque corresponding to simulated rotational force on the free-falling head, the alternative method with stationary head and drop weight has been proposed here as a more passable way. It would provide an opportunity for simpler and better simulation of reality, for example through, in this case, more predictable, in-room relatively stable axes of inertia during the shock process. The small angular changes due to deflections in question here can probably be considered negligible. Let us now turn to an analysis of this method. The anvil here corresponds to the end surface of the drop weight and the impact body laid out on the test object helmet, which with associated sensors vectorically measures the input impact force and torque on the helmet model head unit. Alternatively, the sensor can be mounted in the impact weight impact instead of on the loose impact body. Reaction forces and moments measured in the neck bracket counteract the impact forces caused by the impact and the moments on the model head and must therefore be subtracted from these measured results. corresponding acceleration values. As a consequence of this, with an idealized infinitely rigid neck and model head, one would get the acceleration zero for the model head because this becomes without movement and the entire input force is propagated to the neck. This is also the reason why in the case of a rigid neck bracket and stationary head, as in the testing of industrial helmets, the tests cannot be attributed to acceleration networking but must adhere to measured forces, which here too should be time-integrated averages or effective values of vector-measured results. With the new test method proposed here, the difference in measured force and torque values obtained after subtraction is thus the basis for calculating acceleration and damage indices. This could thus also be applied to the test method currently used on industrial helmets. It would be worth trying if this would provide acceptable accuracy even with the very stiff neck strap in this case.

A condition in this type of test is that the model head can be considered indefinable; an approximation that is also used in the current standard. In reality, however, this leads to higher result values than with a natural head and is therefore a stricter test with safer helmets as a result. 530 225 Due to the inertia resistance of the head, the continued compression of the helmet padding is limited to the point where all the kinetic energy of the drop weight is consumed and absorbed in the form of residual deformation, viscous damping, friction, heat and transferred residual kinetic energy. A small part of the opening is located in the rubber suspension of the neck bracket. The sensor of the neck bracket measures the damped force transmitted to the neck bracket via the helmet and model head, which is achieved during the shock pulse.

With the relatively low values for the stiffness of the natural neck, it can be expected that the forces of inertia measured in the impact body will dominate over the reaction forces measured in the neck attachment. The difference between these forces thus results in a movement of the model head which means a corresponding acceleration, which due to the low neck stiffness can be expected to have. a characteristic similar to the standard case with the free-falling head. The proposed test equipment can therefore alternatively also be used for direct measurements of maximum acceleration for comparison with the current standard and enable evaluation for selection of the best test method.

The proposed new test procedure thus seeks to achieve the advantage compared to the old standard that you get a more complete and reliable picture of the helmet's protective ability by the corresponding certification test includes both straight shock and rotational force. Since linear and rotational acceleration in tests on model heads with helmets can be assumed to be proportional to forces and torques acting on their common mass, it also seems justified with current types of iron-deformable model heads to base the calculation of damage criteria on helmet tests on measured forces and torques instead of to use measured values of maximum acceleration as in the current test standard. The advantage of this would be that it is easier and safer to measure and handle force and torque data than the corresponding maximum accelerations which in impact tests can show difficult-to-master nailing due to high-frequency resonant oscillations in the accelerometer. Finally, it can also be said that injuries are usually directly attributable to forces that have arisen.

With a transition to power and torque meshing, the practical possibility that the test standard can be extended to take rotational force into account in terms of production also increases. A special advantage lies in the fact that force sensors for forces and torques can be calibrated with easily accessible deadweight needles. This would contribute to better global compatibility between different laboratories and standards. In addition, to safer results with less spread than relying solely on accelerometers as in the current standard, where often large distances to the appropriate calibration lab for this sensor type means that the time intervals between control calibrations can be sparse, which means uncertain protection quality of certified marketed helmets.

The advantages of the proposed principle for impact testing of safety helmets here may also include that the test head with helmet is stationary mounted on a flexible mount, which provides a more realistic simulation with regard to the neck's mechanical properties in terms of stiffness and cushioning. With this arrangement, it can therefore be considered that the test environment is closer to the real human body than the simulation in the current standard. Because the natural frequency can be specified with a square root function, the choice of stiffness in the neck attachment becomes less critical, as does the effect of possible propensity to age in the damper. An important objection to the procedure with stationary head and serrated neck is that there are large differences in reaction force fl: between axial shock in head neck stiffness and shock across this direction.

However, it can be discussed whether the proposed method does not better simulate the natural condition of the human body than the current standard sample with a free-falling head that completely ignores the possibility of the effect of neck stiffness on the test results. Of course, this must be examined with practical tests to investigate the compatibility with the corresponding tests in the current standard.

The flexibility of the rig's neck attachment must also be adjusted to adapt to a more realistic full-body simulation. This would then rather mean a reduced stiffness in the neck bracket, which thus further distances itself from the current standard test. 530 225 lf) For comparison and complement, one can also alternatively use absorbed energy and obtained values of transmissibility. The use of the concept of transmissibility, here based on the relationship between energy uptake in the model head or helmet, would be a possible alternative test method to statistically more correctly assess safety helmets and have less spread in the result than to now only use acceleration measurements as gnmd. Because the requested energy, in addition to measured forces and torques, is also based on calculation with integration of measured acceleration to obtain the corresponding speed and displacement, this has a smoothing effect and makes the outgoing result less dependent on the acceleration of the acceleration than if maximum acceleration was used as Assessment basis - The general use of time-integrated averages, objective values or absolute values in the presentation of results in helmet tests would, for the same reason, mean a more reliable assessment of the protection quality of the helmets. This should be prescribed in the test standard, to be used in parallel with the current standard, which would be particularly justified insofar as only maximum acceleration is used for the assessment and not the accepted damage criteria, HIC and GSI, which are based on integration criteria. A change in the standard may, however, mean that a tolerance of the tolerance limits must be made, as the spike in the currently used maximum values means that the maximum values are higher than expected integrated average values.

Since in registered rotational acceleration the characteristic contains both positive and negative amplitude, this must be taken into account by character-independent calculations with, for example, absolute values or effective values.

Another possibility with the new method is that by measuring with an impedance head you can get an idea of the local ability for energy absorption in the event of an impact in different areas of the helmet.

The impedance head provides force and acceleration data, which after integration is used for the energy calculation and therefore, as before, has a smoothing effect on the result.

Yet another principle for helmet testing is the proposal with vibration excitation of helmet model heads, possibly with a clearance function for non-linear shock simulation. With the use of the concept of transmissibility, phase angle detection and dissipated energy, this method could constitute a simplified and convenient alternative or complement to the current test standard based on shock tests.

Equipment for vibration excitation of this dignity is extensive and expensive. If the method after evaluation proves to be practically useful, however, there is the possibility that it could be applied to larger test centers that already have such equipment, perhaps with spare capacity. There is also a need for research to develop conversion functions to harmonize this new method with current injury criteria and medically based tolerance thresholds for brain damage as a result of occasional shocks. To obtain a basis for this, a literature study and computer simulation of the method must first be done. after which this variant, as with other new methods, is tested in practice for comparison with the current standard case test. Further research may lead to a simplified, special vibration equipment for this type of test.

The various test methods listed here can be computationally linked to medical damage criteria for the brain. The most well-known criterion, the Wayne State curve, is based, as previously mentioned, on acceleration measurements in human heads, and is the basis for various damage indices such as HIC and GSI, which are included in the current test standard. for some helmets. However, all of these criteria, especially the tolerance limits now used for maximum acceleration, are, as already mentioned, incompletely substantiated and apply strictly only to central shocks and then only directly from above, so they should be revised.

As rotational violence is not covered in the current testing standard, and medically accepted criteria for this type of violence are not available, research funding should be allocated to develop experimentally and from the literature various damage criteria adapted to current needs for improved standard methods for testing head protection. 530 225 ll It should also be emphasized that an iron movement between old standard samples and new variants must be carried out in order to select the best method and gain acceptance for it. The research work required shall include investigation of both theoretical relationships and results from comparative practical tests on helmets.

The procedure for helmet testing shall include impact tests on current areas and directions relative to the test head, but shall also be supplemented with special tests for simulation of pure rotational force. The proposed rig is then suitably used, which can be adapted for acceleration as well as force, torque and energy measurement. Special fi injection tests shall be performed partly with and partly without the impactor body and partly with the installation of the impactor body integrated in the lower end of the push rod.

For production, the proposed type of test rig should be able to compete with the old one, as it allows for both easier and faster setting, including firing. An advantage is also that the new test equipment can be used for all types of safety helmets, including industrial helmets, and can also replace previously separate rigs for fall tests as well as penetration tests and tests on face protection.

Summary of proposed test principles.

There is a need to improve the current test standard for safety helmets with respect to both central shock and rotational force to the head. The current CEN and ISO standards contain only incomplete test regulations with central shock and have no regulations at all for tests with commonly occurring dangerous rotational force. Both of these two types of violence can be simulated in this proposed type of rig for impact testing with a helmet on a stationary model head, which is supported by a naturally flexible neck brace. Assessment of the helmet's protective capacity can, in addition to the current standard test with maximum acceleration and derived damage criteria, also be based on integrated mean, absolute and effective values for measured forces, torques, accelerations and absorbed energy, obtained from the vectorically registered shock pulse for both central and rotational force. . In addition, vibration tests with measured phase angles between force and displacement as well as values of corresponding transmissibility, regarding levels of dissipated energy, have also been proposed as a complementary measure of the helmet's protective ability.

Proposed alternative test principles in the above rig are as follows: 1) Vectorial registration of transferred forces and torques from a drop weight to helmet model head via fl er component component partly in the impact point of impact against the helmet and partly in the model head bracket on the foundation with coordinate system for forces and torques referred to the center of gravity of the model head, whether the calculation of the corresponding maximum care, integrated mean efficiency and absolute values for forces, torques, accelerations (linear and rotation), transmissibility and damage index can take place.

Compare with results from current standards and available damage criteria. 2) Vectorial registration via a three-axis accelerometer in the model head's center of gravity of Transferred linear acceleration from drop weight to helmet and model head, partly via six to nine accelerometers placed on the model head's surface to record the rotational acceleration of the model head.

Use measured vectorial values on the model head accelerations (linear and rotational), form max values, integrated mean, efficient; absolute values and damage index for comparison with current standards and available conventional criteria for the helmet's ability to protect. Compare with values obtained according to the previous point (1). 530 225 lål 3) Register vector forces and accelerations as well as locally Transferred energy to the helmet via an impedance head at the point of impact with measured torque arm in relation to the center of gravity of the model head with helmet. Also calculate Transmitted energy via measured forces, torques and accelerations on the model head. Use the total input energy (fall energy), the energy absorbed locally by the impedance head measured in the helmet, as well as the energy transferred to the model head and also form the corresponding transmissibility with regard to absorbed energy as a measure of the helmet's protective capacity. Compare with other tests. 4) Instead of impact tests, the helmet was subjected to local vibration excitation, possibly with a play function for non-linear impact characteristics. This provides opportunities for simulation corresponding to both linear central force and rotational force via a special adapter for pull and pressure against the helmet. Registered values of forces, torques, accelerations and energy transmitted from the helmet to the model head can then be expressed in the form of transmissibility with values that reflect the helmet's protective capacity. Also measured phase angle between the vectors for kra fi and displacement can be used here as a measure of the helmet's damping ability. The vibration method is compatible with the previously stated arrangement for stationary model head and simulated fl visible neck with instruments for vectorial measurement of accelerations and / or forces and moments, but could here be simplified by the possibility of hanging or free placement of model head with helmet. The method will initially be tested using an existing computer model. 530 225 few References [1] Lissner, H. R., Lebow, M. and Evans, F. G., "Experimental Studies on the Relation Between Acceleration and Intercranial Pressure Changes in Man," Surgery, Gynecology, and Obstetrics, Vol. III, 1960, pp. 329-338. [2] Hodgson VR and Patrick, LM, "Dynarnic Response to the Human Cadaver Head Compared to a Simple Mathematical Model," Proceedings, 13th Stapp Conference, Society of Automotive Engineers, 1969. [3] Gadd, CW, "Use of a Weighted Impulse Criterion for Estimating Injury Hazard, "Proceedings, Tenth Car Crash Conference Paper 660703, New York, Society of Automotive Engineers, 1966. [4] Ljung, C.," On Protection Criteria in Helmet Testing with Proposed Test Method for Recreational Helmets , "Technical Report SP-Rapp 1984-31, Borås, Sweden [5] Johnson, GI," Parameter study ang. Helmet testing, Parts 1 and 2, "Technical Report, MU-884, FFA, The Aeronautical Research Institute of Sweden, Stockholm 1974. [6] Aldrnan, B., Lundell, B., and Thorngren, L.," Helmet Attenuation of the Head Response in Oblique Impacts to the Groundj 'IRCOBY Conf, Lyon, 1979. [7] Johnson, GI, "Development of an Impact Testing Method for Protection Hehnets." Safety In Ice Hockey ". ASTM Publication Code Number 04-01050. Ann Arbor MI, 1989 [8] Margulies, SS, and Tibault, LE, "A Proposed Tolerance Criterion for Diffuse Axogonal Injuries in Man," Journal of Biomechanics, 1992, 25 917-923. [9] Halldin, P., Gilchrist , A. and Mills, NJ, "A New Oblique Impact Test for Motorcycle Helmetsj 'Woodhead Publishing Ltd, IJ Crash 2001, Vol 6 No l.

[10] Johnson, GI, "A Comparison of Results on Helmet Impact Testing", ASTM Journal of Testing and Evaluation, Volume 31, Number 1, January 2003. 530 225 Figure Description Figures 1 - 4 show principle sketches of a proposed test rig and details thereof for testing safety helmets. The details included in the och gures and their respective functions are shown in the corresponding detail numbers in the respective figure and the following designations with description.

Figure 1: \ Q O0 \] U \ (Jl «ß (J-) I \)> ~ 4 | 10 ll 12 Figure 2: 6 _ 6.1 6.2 6.3 7 7.1 11.1 - 11.2 Figure 3: Pl P2 P3 P4 - P5 P6 P7 P8 - P9 Figure 4: M1 - M2 Assembly of test rig Falling tower with four vertical pipes for controlling the fall weight Cross section of drop bar Coordinate table for positioning the drop tower in the xy plane Heavy base plate of eg steel, included in the coordinate table, provides stability to the drop tower Foundation Helmet with stop body and inner pedal head Model head with mounted helmet in outer position-horizontal axis with position adjustable in x-joint of model head with helmet in outer position-vertical axis with position adjustable in z-joint Model head neck bracket with six-component sensor for registration of forces and torques Neck bracket connected to the model head through a ball joint Rubber suspension for simulation of surrounding four pipes Release mechanism for drop weight Details of test rig Impact body in position for sample on helmet Impact body with impedance cap d, enlarged view with spherical abutment surfaces Impact surface with carved concentric circular pattern, simulates the roughness of the road surface Rubber strap for fixing abutment body Model head with helmet set up for testing Part of helmet in enlarged view Enlarged view of drop weight and abutment body type Alloy Pneumatic cylinder with piston rod and speedometer Quick-opening valve Container for pressure medium, lu fi or hydraulic oil Inlet valve Adjusting screws for vertical and horizontal movement of the pneumatic cylinder Instrumentcrad unit, helmet / model head installed with shaft in horizontal position Alternative model Helmet at the point of impact on the helmet Examples of principles for achieving an almost pure impact moment for testing the fitted helmet on. model head Torque in the head's vertical symmetry plane Torque in the head's horizontal reference plane 530 225 Appendix A1 Algorithms Forces, torques, accelerations and their directions.

Algorithms have been set up with a view to the best possible compatibility between current and possible test standards _ A) Calculation of quantities from measured forces and torques, The components (F) for resulting forces and torques are calculated from measured signals from a six-component sensor in the model head neck installation. In this case, the calibration matrix (m) of this sensor is used and the signal matrix (S) of the sensor according to F = m. S (1) Resulting requirement fi- (F) and torque values (M) are calculated from the obtained component values in the given orthogonal coordinate system (xyz) F = (2) M = «/ Mxz + My2 + Mä Resulting requirement fi direction is determined via the cosines for the angles ( cpF) between the resultant vector and the respective coordinate axis cpFx = acos Fx / F rpFy acos Fy / F (3) acos Fz / F <|> Fy In the same way the corresponding angles (qpM) are obtained for the direction of the torque resilient rpMx = acos Mx / M cpMy = acos My / M (4) mpMz = acos Mz / M The angles can be ironed for conformity. 530 225 Ha Now the momentary forces (F) and torque (M) arising at the impact are known in magnitude and direction.

Corresponding time sub-values integrated over the pulse time (T) are obtained from the resulting instantaneous forces and moments according to T Fave = (l / T), iF dt 0 (5) T Mave = (1 / T) IMdr 0 B) Calculation of quantities from measured components of linear and rotational acceleration In an analogous way as with requirements and torques, when accelerating from six measured components (a) in the coordinate system (xyz) corresponding values can be obtained for the acceleration partly the linear vector (aL) and partly rotational power (aR). = v <6) ak = and vector directions qøaLx = aeos aLx / aL rpaLz = aeos aLz / aL waRy cpaRz aeos aRy / aR (8) aeos aRzJ aR 530 225 Vi C) Conversion of measured forces and torques to corresponding accelerations Value head aL) and (aR) for linear and rotational motion can be obtained from the resultant for measured force fi and torque values (F) and (M) with knowledge of the mass (W) and moment of inertia (I) of the model head according to aL = F / w (9 ) aR = M / I Corresponding integrated time averages over pulse length (T) T aLave = (l / T), [F / w .dt 0 (10) T aRave = (l / T) IM / I .dt In the same way, by time integration over the pulse length, both calculated and directly measured quantities are processed.

Calculation of generated energy Total energy emitted (E) is obtained from the impact force (Fs), calculated with knowledge of the mass of the shock bar (drop weight) (ws), and measured speed (vs), summed over the pulse time (T). The friction of the push rod fi is set to be relatively small and negligible.

Fs = ws id (vs) / dt TE = I Fs vs dt OT Vs = ld (vs) / dt dt 0 Vs E = Iwsvs d (vs) = ws (vs) 2/2 (11) O 530 225 l ' The energy (Eimp) specified in the head is obtained from its acceleration (aimp) and demand values (Pimp) T Eimp = = jFimp aimptdt (12) 0 Linear energy (EL) dissipated in the model head and rotational energy (ER) are obtained from the measured instantaneous components of the neck sensor and their calculated results for linear and rotational acceleration (aLh) and (aR) respectively, as well as the corresponding recorded forces (Fmo) and torque (Mmo) T EL = jFmoaLtdt 0 (13) T ER = jMmoaRtdt 0 Calculation of transmissibility As a measure of the protection of a body against brain damage due to blows to the head, the helmet's transmissibility (Tr) is calculated, which means the proportion of helmet-transferred average values (Fave) and torque (Mave) transmitted from helmet to head, or alternatively Transmitted linear and rotational acceleration (aLave) or (aRave) and the like Transmitted linear and rotational energy (ELave) resp (ERa ve).

With respect to transmitted forces and torques TrF = Fave head / Fave helmet TrM = Abdominal head / Abdominal helmet (14) With respect to transmitted accelerations TraL = aLave head / aLave helmet 15 TraR = aRave head / aRave helmet () With respect to Transmitted energy TrEL / 16 ) TrER = ERave head / ERave helmet 530 225 1% Calculation of damage index Damage index GSI is obtained from the results of forces registered by the neck sensor (F) and torque (M) which are then converted to corresponding acceleration values. These can also be obtained from directly measured values of accelerations of linear and rotation type Calculation of (GSIL) for linear acceleration from recorded forces (F) and mass (Wmo) T osn. = hF / wf-f d: (17) 0 Analogy calculation of (GSIR) for recorded torque (M), model moment of inertia (l) and a conversion factor or transfer function (k) T Gs1R = 1 0 About linear and rotational acceleration (aL) and (aR) obtained by direct data recording, respectively, becomes T Gs1L = lpaLWar (19) 0 and T osm = 1 0 To ascertain the latency of rotational force in this simple way as in (18) and (20) can be used for the same type of algorithm as with straight shock, this must be substantiated with further research. 530 225 .lb Figure description Figures 1 - 4 show principle sketches of a proposed test rig and details thereof for testing safety helmets. The details included in the figures and their respective functions are shown in the corresponding detail numbers in the respective figures and the following designations with description.

Figure 1: Assembly of test rig 1 - Falling tower with four vertical pipes for controlling the fall weight 2 - Cross section of fallout 3 - Coordinate table for positioning the fallout in the xy plane 4 - Heavy base plate of eg steel, included in the coordinate table, gives stability to the fallout 5 - Foundation 6 - Helmet with impact body and impedance head 7 - Model head with mounted helmet in outer position-horizontal axis with position adjustable in x-joint 7.2 - Model head 8 - Alternative mounting of model head with helmet in outer position-vertical axis with position adjustable in z-joint 9 - Model head neck bracket with six-component sensor for registration of collars and torques Neck bracket connected to the model head by a ball joint 10 - Elastic suspension for simulation of flability in the human neck 11 - Fall weight with sliding surfaces, controlled by the fall tube's surrounding four tubes 12 - Release mechanism 2: Details of test rig 6 - Impact body in position for test on helmet 6.1 - Impact body with impedance head, enlarged v y with spherical abutment surfaces 6.2 - Impact surface with carved concentric circular pattern, simulates the roughness of the road surface 6.3 - Harness of elastic bands for fixing abutment body 7 - Model head with helmet set up for testing 7.1 - Part of helmet in enlarged view 11.1 - Enlarged view of drop weight 11 and abutment.2 - Drop weight Figure 3: Alternative type of test rig with pneumatic cylinder P1 - Pneumatic cylinder with piston rod and speedometer P2 - Quick-opening valve P3 - Container for pressure medium, air or hydraulic oil P4 - Inlet valve P5 - Adjusting screws for vertical and horizontal for pneumatic cylinders unit, helmet / model head installed with the axle in horizontal position P7 - Alternative vertical position for helmet / model head P8 - Helmet installed on model head P9 - Impact body installed at the point of impact on helmet Figure 4: Examples of principles to achieve an almost pure impact torque for testing of mounted helmet on model head M1 - Torque in the vertical plane of symmetry of the head M2 - The horizontal reference plane of the moment head

Claims (1)

Claim 1, method of testing safety helmets, comprising simulating various types of specified external force on the head, thereby ascertaining the helmet's ability to prevent the occurrence of brain injuries in the wearer in accidents with blows to his head, said method is characterized in that the test object helmet (7), is installed on an instrumented stationary model head (7.2), and is subjected to simulated force by a shock force generated from a movably adjustable device. method according to claim 1, characterized in that the impact force in the test is generated by releasing a drop weight (ll) with adjustable drop height and input energy from a movable drop blank (1), which with vertical longitudinal axis can be parallel in the horizontal plane with the possibility of aligning the desired point of impact on the helmet ( 7) by the vertical upright fall tower (1) being supported by an oscillation stabilizing heavy base plate (4) which is attached to a horizontal coordinate table (3) for screw adjustment of the fall inch (1) to the xy coordinates desired in the horizontal plane and thus the fall weight ( 1) the point of impact on the helmet (7) is determined in this plane and whose position coordinates (x) and (y) can be read by means of scales belonging to the screw setting Claim 3, method according to claim 2! that the impact force instead of via a drop weight here is provided by a device with pressure medium from a charging valve (P4) to a pressure tank (P3) connected via a short line with a quick-opening valve (P2) for firing to a pneumatic or hydraulic cylinder with a calibrated piston rod 031) which is adjustable via adjusting screws (P5) for impact in the desired hit area against the helmet (P8) installed on the model head (P6). Claim 4, method according to one of Claims 1 to 3, characterized in that the percussion device, which may be, for example, the drop weight (11) or the push rod (P1), exerts the impact force against the stationary helmet (7), via an intermediate like stationary abutment body, ( 6) or (P9), with a small mass and fastened by means of, for example, an elastic harness (6.3) in the desired position for the precise point of impact of the shock on the helmet (7) or associated part thereof, for example a face shield. Claim 5, method according to one of Claims 1 to 4, characterized in that the stationary model head (7.2) with mounted helmet (7) is attached to a foundation (5) via a simulated human neck (8), (9) which is closest to the foundation. an elastic damping element (10) to give the bracket a flexibility corresponding to the human neck, in addition to the bracket (8), (9) closest to the model head being instrumented to be able to vectorically measure the reactions of the forces, moments and accelerations due to of the shock impulse from the drop weight (5) is transmitted via the helmet (7) and the model head (72) to the sensor (5), whereby also the part of the input shock energy remaining from the model head can be obtained. Claim 6, method according to one of Claims 1 to 5, characterized in that adjustment of the point of impact of the impact on the helmet (7), in addition to the possibility of adjustment in the xy-plane, can be achieved by tilting the neck bracket in the vertical plane of symmetry of the test head with different attitude angles. , and in addition also adjusted with the possibility of the model head and helmet for movement with the roll angle (cp) about the longitudinal axis of the neck bracket, and further possibility of movement (island) along the longitudinal axis of this bracket, each with additional degrees of freedom can be obtained with the model head mounted on a ball joint. with the center of gravity of the model head. 530 225 .ll Claim 7, method according to any one of claims 1 - 6, characterized in that data can be registered with stationary fl component components for vector values of both accelerations and forces and moments in simulated force by impact against a stationary test head with a helmet, whereby the possibility of simplified data handling can be obtained for linear and rotational accelerations from registered forces and moments through known values of mass and moments of inertia, after which customary recalculation of obtained accelerations can take place to corresponding standardized damage indices such as HIC and GSI, as an assessment basis for the tested helmet. may allow for further simplification with a smaller number of vector components for acceptable results. Claim 8,. method according to claim 4, characterized in that of the two contact surfaces between the percussion device (11), (P1) and the abutment body (6), (P9) one is flat and the other is slightly convex (bombarded) (6. 1) for to avoid oblique loading of the impactor against the surface of the helmet (7.1). Claim 9,. method according to claims 3 and 4, characterized in that the stop body (6), (P9) with its sensor arrangement for both torque and accelerations functions as an impedance head for recording local energy absorption in the impact area on the helmet and that the method for recording energy absorption is also possible for the model head having similar instrumentation in the neck bracket (9).