The SHARP testing brings together some of the best aspects from the standards currently in use around the world and has defined more rigorous tests and assessments than are currently in use for Regulation. SHARP tests protection across a much wider range of speeds.
In developing the tests as well as looking at impact energy management the areas of the helmet most likely to be struck and the risk of brain injury from that impact were also considered. Analysing in-depth real world accident studies allowed the linking of specific laboratory impacts with real world injury, therefore the tests address specific risk of head injury. Helmets are impacted against anvils to represent both flat surfaces and kerbstones, testing protection over the whole helmet not just specific points.
A suite of enhanced test procedures and assessment criteria for helmets have been developed, so that a helmet performing well when assessed against them will offer real and significant increases in head protection. The tests are:
Linear impact tests - Energy absorption tests. The helmet is placed onto a test head form and dropped from a certain height onto different types of anvils. Acceleration is measured at the centre of gravity of the head form as is the energy absorbed by the helmet at various locations and speeds.
Oblique impact tests - Rotational acceleration by friction. The helmet is placed onto a test head form and dropped from a certain height against an inclined anvil with a very rough surface. Rotational acceleration is measured in the test head form. Limit values allow the risk of brain and neck injury to be assessed.
The results from 22 different impacts are combined into a single easy to understand star rating and published to provide consumers with comparative information to assist them in making informed purchase decisions.
Test Protocols:
The linear test is designed to measure the energy absorption characteristics of the motorcycle helmet shell and liner. When carrying out the linear impact test a twin wire guided test apparatus is used. This equipment is similar to that used in the British Standard BS 6658:1985.
Before commencing the test, the helmet is placed onto an appropriately sized head form and this is placed onto the guided carriage. The carriage is raised to a certain height above the anvil and released. The helmet, head form and carriage accelerate to impact upon a fixed anvil. On impact, the lateral and rotational motion is controlled by the tensioned wire and the carriage. This reduces the potential for a proportion of the impact energy to be dissipated through rotation. Pitch, roll and yaw motion of the helmet is controlled during the impact.
Research has shown that this method of linear impact is better suited for the SHARP performance rating than the free motion test apparatus, which allows the helmet to slide and rotate on the anvil, thus reducing the measured peak acceleration. [Mellor et al, 2007]
Research has shown that the twin wire guided test method provided the most repeatable helmet tests and the most accurate results, especially when compared with the free motion prescribed in the UN ECE Regulation 22.05. [Mellor et al, 2007]
The oblique impact test is designed to measure the rotational acceleration of a helmet and head form caused by friction. The results of this test can be used to monitor the risk of brain or neck injury caused on impact with the road.
Within the current European legislation, there are two methods of testing oblique impacts. The differences between the two methods are numerous - they are based on different principles - but are intended to identify similar helmet performance. Research has recently been completed which evaluates both Methods (A and B) and determines their suitability. Previous research had determined that Method B was more stringent, but this was based on a number of approximations involving non-linear energy transfer and complex loading mechanisms which is too simplistic in nature. Indeed recent evidence suggests that Method A is more stringent than Method B for surface friction.
For oblique impact testing Method A, as described in UN-ECE Regulation 22.05, is being used. Method A more closely simulates real world accident dynamic loading conditions, and provides a numerical (non-binary) result, as opposed to a simple pass/fail. Method A has its foundations in British Standard BS 6658:1985 and prescribes a test based on the peak tangential forces resulting from an oblique impact between the helmet and abrasive surface.
The helmeted head form is guided onto an oblique rigid anvil at a velocity of 8.5m/s. UN ECE Regulation 22.05 compliant abrasive inclined anvil test apparatus is used to assess surface friction. For this assessment, tests will be carried out using a size J head form only, with the results being applied for all helmet sizes.
Surface friction may be determined at any point on the helmet shell but for consistency tests are performed on both sides of the helmet with the helmet facing forwards (wherever possible). Impact sites are as near as possible to those identified as point X within UN ECE Regulation 22.05. The impact velocity will be 8.5 m/s, with a tolerance of -0 / +0.15m/s.
Should an unusual or standard geometric feature or fitting be within the impact site and be deemed likely to influence the result, then the site may be redefined to a suitable area.
In order to carry out tests in a manner which most accurately reflects the real world distribution of frequency and direction of helmet impacts impact sites have been selected.
To ensure that the protection offered by helmets to riders is appropriate, it is necessary to ensure the impact conditions are representative of those experienced in real life. Data suggests that the impact sites currently used in UN ECE Regulation 22.05 are appropriate and these sites will be tested as specified. The side of the helmet is the most frequently impacted area - 53%. Therefore an additional side impact test will be completed meaning that both sides of the helmet will be tested. Helmet impact sites will be marked using the methods and criteria described in UN ECE Regulation 22.05 (paragraph 7.3.4.2 and annex 4 (fig 3)). A test area has been defined, over which the helmet can be tested, to prevent helmet optimisation and ensure a higher level of protection of the whole of the helmet.
The test protocols do not include an impact on the chin guard of full faced helmets (impact site S). Proposals have been made for testing chin guards at 5.5m/s with 275g limit and this was incorporated into the latest revision of UN ECE Regulation 22.05. Thus, all new helmets conforming to UN ECE Regulation 22.05 will incorporate effective chin guard protection, based upon the very latest research.
An enhanced high and low speed test method was specified, based upon head injury severity. The COST 327, 2001 report recommended that impact velocity be raised from the current UN ECE Regulation 22.05 value of 7.5m/s to 8.4m/s, but to ensure that helmet performance was not compromised in the lower velocity impacts a 6.0m/s test was added. Performance limits would be strengthened and a new enhanced baseline level of performance formed. SHARP will test between 6.0m/s and 8.5m/s. To be consistent with the oblique impact test speed 8.5m/s has been selected, rather than the 8.4m/s proposed by COST.
Research indicated a strong recommendation to use 9.5m/s as the upper impact velocity. This may be too severe for many current production helmets. To ensure that protection at this velocity does not reduce, the performance of helmets at this test speed is being monitored.
Helmets are fitted to an appropriately sized instrumented head form prior to testing. It is essential that each helmet is tested with a size of test head form that most appropriately and closely fits the helmet.
Variable mass head forms are used, which are the same as those used in UN ECE Regulation 22.05 testing. These most closely represent real world conditions. Evidence also suggests that the motorcycle helmet industry is converging on the use of these head form masses.
Testing uses head forms of the following masses and geometry (profile):
Head Form 'A' – 3.1kgs with 500mm geometry
Head Form 'E' – 4.1kgs with 540mm geometry
Head Form 'J' – 4.7kgs with 570mm geometry
Head Form 'M' – 5.6kgs with 600mm geometry
Head Form 'O' – 6.1kgs with 620mm geometry
For the future it is hoped that a child head form will be developed to evaluate the most popular child helmets. At present UN ECE Regulation 22.05 does not specify a head form to test child helmets.
