Grsp-48-21 (48th grsp, 7 10 December 2010, agenda item 12) fia foundation/ghvi proposal Objective of the Proposal



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6.2  Test headforms


A headform, capable of accepting an accelerometer mounted at its centre of gravity and conforming to the requirements of a three quarter headform as defined in EN 960:2006, shall be used. Headforms used for impact testing shall be rigid and be constructed of low resonance K–1A magnesium alloy. The headform and supporting assembly shall have a total combined mass as described in the following table, with the supporting assembly contributing to no more than 25% of the total mass.

Table 1. Test headforms



Headform label

Size Designation

Mass

A

495mm

3.10 kg +\- 0.10 kg

E

535mm

4.10 kg +\- 0.12 kg

J

575mm

4.70 kg +\- 0.14 kg

M

605mm

5.60 kg +\- 0.16 kg

O

625mm

6.10 kg +\- 0.18 kg


6.3  Marking the test line


A reference headform that is firmly seated with the basic plane horizontal shall be used for reference marking. The complete helmet to be tested shall be placed on the applicable reference headform whose circumference is not greater than the internal circumference of the headband when adjusted to its largest setting, or, if no headband is provided, to the corresponding interior surface of the helmet.

The helmet shall be positioned on the reference headform and a static force of 50 N shall be applied normal to the apex of the helmet. The helmet shall be centered laterally and seated firmly on the applicable reference headform according to its helmet positioning index. If the HPI and corresponding headform size are not available from the manufacturer, the test technician shall choose the headform and HPI value.


Maintaining the force and position described above, a test line shall be drawn on the outer surface of the helmet coinciding with that on the headform as shown in Figure 2.

6.4  Test schedule


Helmet samples shall be tested according to the test schedule shown in Table 2. The sequence of testing shall be as follows:


  1. Peripheral vision test (if applicable)

  2. Penetration resistance test (if applicable)

  3. Effectiveness of retention system test (if applicable)

  4. Strength of retention system test

  5. Shock absorption test

Table 2. Test schedule



Sample

Peripheral Vision Test

Penetration Resistance Test

Effectiveness of Retention System Test

Strength of Retention System Test

Shock Absorption Test

Helmet 1 – Ambient Temperature

X

X




X

X

Helmet 2 – Low Temperature










X

X

Helmet 3 – Elevated Temperature










X

X

Helmet 4 – Water Immersion










X

X

Helmet 5 – Ambient Temperature







X






6.5  Peripheral vision test


Position the helmet on a reference headform in accordance with the HPI and place a 50N preload ballast on top of the helmet to set the comfort or fit padding. (Note: peripheral vision clearance may be determined when the helmet is positioned for marking the test lines). Peripheral vision is measured horizontally from each side of the median plane around the point K (see Figure 3). Point K is located on the front surface of the reference headform at the intersection of the basic and median planes. The vision shall not be obstructed within 105 degrees from point K on each side of the median plane. Measurement may be performed with a physical measuring device (i.e. peripheral vision template or a test headform with point K clearly marked) or with laser measurement equipment.

6.6  Penetration resistance test

6.6.1 Apparatus

The apparatus for the penetration test shall include a full size reference headform that meets the requirements of EN960:2006.
6.6.2 Method

Position the helmet on a reference headform in accordance with the HPI and place a 50N preload ballast on top of the helmet to set the comfort or fit padding. Using a metal test dowel with a diameter of 20mm (see Figure 4) attempt to make contact with the headform by trying to enter any part of the metal dowel end through all of the openings of the helmet. Record the location of any metal dowel to headform contact.



6.7  Retention system effectiveness test

6.7.1 Apparatus

The apparatus for the retention system effectiveness test shall include a full size reference headform that meets the requirements of EN960:2006.
6.7.2 Method

Secure the reference headform to a fixture that will prevent headform movement when a tangential force is applied to the helmet. Position the helmet on a reference headform in accordance with the manufacturer’s instructions. A flexible strap and hook mechanism shall be attached to the front lower edge of the helmet such that it is in line with the mid-sagittal plane. The total mass of the falling weight guide apparatus shall be 3 ± 0.1 kg and shall be able to accommodate drop heights up to 100 cm. A 10 ± 0.1 kg drop weight shall then be raised to a height of 50 cm ± 0.5 cm and released (see Figure 5).


This procedure shall be repeated with the hook mechanism attached to the rear edge of the helmet.

6.8  Retention system strength test

6.8.1 Apparatus

The retention system strength test device consists of both an adjustable loading mechanism by which a static tensile load is applied to the helmet retention assembly and a means for holding the test headform and helmet stationary. The retention system test device shall allow the retention assembly to be fastened around two freely moving rollers, both of which have a 12.5 mm diameter and a 75 mm center-to-center separation, and which are mounted on the adjustable portion of the tensile loading device (see Figure 6).

6.8.2  Method


Place the subject helmet on the test headform such that the basic plane is normal to the force of gravity and adjust it in accordance with the manufacturer’s HPI. Securely fasten the retention system around the two freely moving rollers in a manner that avoids contact between the rollers and helmet’s buckle. Apply a preliminary load of 45 ± 3 N in the direction normal to the basic plane to the retention system and hold for a minimum of 30 seconds. Record the displacement measurement on the moveable test device.
Increase the load to 500 ± 5 N and maintain this load for 120 seconds, + 0 seconds, - 10 seconds by adjusting the load applied to the retention system as necessary. After 120 seconds (+0 seconds, -10 seconds) at full test load, measure and record the displacement measurement of the retention system. The maximum elongation shall be the difference between the initial measurement and the measurement taken after 120 seconds.


6.9  Shock absorption test

6.9.1 Apparatus

The test apparatus for the shock absorption test shall consist of the following:

(a) The headform employed in this test shall conform to all requirements under Clause 6.2.


(b) The test headform shall be mounted on a guided freefall system as shown in Figure 7 with an adjustable mounting for the helmeted headform to permit impacts to be delivered to any location on the helmet at or above the test line. A monorail guided freefall system shall also be acceptable. The total mass of this support assembly shall not exceed 25% of the combined mass of the drop assembly (i.e., supporting assembly plus the test head-form). The centre of gravity of the drop-assembly unit shall lie within a cone having a vertical axis and forming at most a 10 degree included angle with the vertex as the point of impact.
(c) A linear accelerometer shall be placed at the centre of gravity of the test head-form and its sensitive axis shall be aligned to within 5 degrees of the vertical when the helmet and headform are in the impact position. The accelerometer shall be capable of withstanding a maximum acceleration of 1000 g without damage and shall have a frequency response of at least 5 to 900 Hz. A triaxial accelerometer with identical performance specifications is also acceptable.
(d) The flat anvil shall be made of steel or another similar rigid metal and shall be firmly attached to the base of the drop assembly. The impact face shall have a minimum diameter of 150 mm.
(e) The hemispherical anvil shall be made of steel or another similar rigid metal and shall be firmly attached to the base of the drop assembly. The hemispherical anvil shall have a hemispherical impact surface with a radius of 48 ± 1 mm.

(f) The rigid mount for the anvils shall consist of a solid mass of at least 135 kg, the upper surface of which shall consist of a steel plate with a minimum thickness of 12 mm and minimum surface area of 0.1 m2.


(g) The data acquisition system shall be capable of collecting impact data at a rate of not less than 10 kHz per channel. The acceleration data channel and filtering shall comply with SAE Recommended Practice J211 DEC2003, Instrumentation for Impact Tests, Requirements for Channel Class 1000. All equipment shall conform to all requirements of SAE J211:2003.


6.9.2 System verification


The shock absorption test instrumentation shall be verified before and after each series of tests (at least at the beginning and end of each test day) by dropping a spherical impactor onto a modular elastomer programmer (MEP) test surface.

The spherical impactor shall be a device made of low resonance material (for example, magnesium), aluminum alloy, or stainless steel that couples mechanically with the ball arm connector of the drop assembly in place of the impact test headform. When mounted, the device presents a spherically machined impact face with a radius of 73 mm on its bottom surface. All radii from the center of the curvature of the impact face to its outer edge shall form angles of no less than 40° with the downward vertical axis. The center of curvature shall be within 5 mm of the vertical axis drawn through the center of the ball arm. The total mass of the spherical impactor drop assembly shall be 5.0 ± 0.1 kg.

The MEP shall be 152 mm in diameter and 25 mm thick, and shall have a durometer of 60 ± 2 Shore A. The MEP shall be affixed to the top surface of a flat 6.35 mm thick aluminum plate. The geometric center of the MEP pad shall be aligned with the center vertical axis of the accelerometer.
The impactor shall be dropped onto the MEP at an impact velocity of 5.44 m/s ± 2% as measured within the last 40mm of free fall of the impactor. Typically, this requires a minimum drop height of 1.50 metres plus a height adjustment to account for friction losses. Six impacts, at intervals of 75 ± 15 seconds, shall be performed at the beginning and end of the test series (at a minimum at the beginning and end of each test day). The first three of six impacts shall be considered warm-up drops, and their impact values shall be discarded from the series. The second three impacts shall be recorded. All recorded impacts shall fall within the range of 380 g to 425 g. The mean of the 3 post-test results shall not differ by more than 5% from the mean of the pre-test results. Otherwise, the results shall be discarded and the tests repeated with new samples after the source of this difference has been rectified.

The components of the data acquisition system, including all transducers shall be calibrated to traceable national reference standards at an interval of not greater than five years.


6.9.3 Helmet impact test locations

Each helmet shall be tested at four impact locations on or above the test line described in Clause 6.3. Each impact location shall be a distance of at least one-fifth of the circumference of the test headform from any prior impact location on that helmet.


6.9.4 Method

6.9.4.1  


The helmet it shall be placed on the appropriate headform according to the manufacturer’s helmet positioning index (HPI). The helmet shall be dropped onto the flat anvil with an impact velocity of 6.0 m/s ± 3%. Typically, this requires a minimum drop height of 1.83 metres, plus a height adjustment to account for friction losses. The helmet shall be dropped onto the hemispherical anvil with an impact velocity of 5.2 m/s ± 3%. Typically, this requires a minimum drop height of 1.38 metres, plus a height adjustment to account for friction losses. The impact velocity shall be measured during the last 25 mm of free-fall for each test. Following impact, the drop assembly shall be raised and the headform shall be oriented to another impact site.

6.9.4.2


The first impact shall be made not more than 60 s after the helmet has been removed from the conditioning environment. Following testing, the helmet shall be immediately returned to its conditioning environment for a minimum of 15 min before another impact test is conducted.
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