New Method to Measure Abrasion of Motorcyclist Protective Clothing

Motorcyclists often suff er severe injuries in accidents, especially at high temperatures when wearing thinner garments. Producing adequate protective clothing for them is therefore of great importance. Nevertheless, typical test procedures for protective clothing often cannot represent a real accident situation and scientifi c literature about this topic is scarce. Thus, in our project, a simple, inexpensive and realistic test setup was created. Experiments revealed signifi cant diff erences between typical motorcycle protective clothing materials under examination, indicating that especially those produced from man-made fi bres can lead to burns and worse injuries of motorcyclists, while some relatively inexpensive materials showed surprisingly high abrasion resistance. More importantly, the test results partly diff er from those performed with one of the standard testing devices, implying the importance of future tests to compare diff erent testing procedures with the results of real accidents.


Povzetek
Motoristi pogosto utrpijo hude poškodbe v nesrečah, še posebej pri visokih temperaturah, ko nosijo tanjša oblačila.Zato so ustrezna zaščitna oblačila zanje izjemno pomembna.Tipični postopki za preiskušanje zaščitnih oblačil pa pogosto ne odražajo realnih pogojev nesreče.Prav tako obstaja zelo malo znanstvene literature o tej temi.V nedavnem projektu je bila zato izdelana enostavna, poceni in realistična metoda, s katero so bile ugotovljene znatne razlike med tipičnimi proučevanimi materiali za zaščitna oblačila motoristov.Te kažejo na to, da zlasti materiali iz kemičnih vlaken lahko povzročijo opekline in poslabšajo poškodbe motoristov, medtem ko so se nekateri relativno poceni materiali pokazali presenetljivo visoko odpornost proti obrabi.Še pomembnejše je, da rezultati nedavnih testov deloma odstopajo od tistih, ki jih izvajajo na eni od standardnih preskuševalnih naprav, kar kaže na potrebo po nadaljnih primerjavah različnih metod z rezultati realnih nesreč.Ključne besede: zaščitna oblačila, motorist, odpornost proti obrabi, beton, asfalt on soft tissue injuries and other severe injuries was investigated as well, fi nding that protective clothing helped reducing the risk and severity of injuries [7,8].On the other hand, a large proportion of clothing failed in real accidents [7].Th erefore, the European standard EN 13595 "Protective clothing for professional motorcycle riders -Jackets, trousers and one piece or divided suits" was established in 2002.Recent publications have discussed the zone approach in this standard, defi ning diff erent levels of protection and diff erent test methods for the four zones, fi nding that this concept is generally suitable to defi ne the necessary degree of protection in diff erent garment areas [9,10].In one study, the relation between the protective level in EN 13595-1 "Part 1: General requirements" and the protection in a real accident was examined, fi nding that the standard allows for approximate estimating the real degree of protection, but also shows that more than a half of garments did not even meet the minimum requirements [1].Th is shows clearly the necessity to make more reliable tests available for the industry along with the whole production chain of protective clothing for motorcyclists.Th e testing of materials according to EN 13595-2 "Part 2: Test method for determination of impact abrasion resistance" was, depending on the protection zone, performed using the Taber® Abraser.Th is instrument was developed for accelerated wear testing.It produces a rub-wear action by rotating a test specimen in a horizontal plane against the sliding rotations of two abrading wheels rotating in vertical planes [11].Th e pressure of the rubbing wheels on the sample is usually 10 N. Such a combination of rolling friction and dynamic friction under low pressure, however, may not be an ideal representation of the situation in a motorcyclist's accident.Nevertheless, the number of rotations until a hole occurs is oft en depicted in motorcyclists' protective wear.Table 1 gives an overview of the range of Tab-er® Abraser breakthrough values, as it could be found in the literature.Apart from this test, in EN 13595-2, the seam burst strength is investigated using a burst tester and the impact cut is tested by measuring the maximum penetration of a defi ned blade through a fi xed test specimen.Another approach is suggested in [12], using a belt abrader instead of the rub-wear action used in EN 13595-2.Here, a static force of 49 N (consistent with the pressure of 25 kPa) is used.Th e sample falls from two diff erent heights -simulating the fi rst impact and the sliding aft erwards -onto a grid belt moving with 8 m/s, i.e. 28.8 km/h, resulting in 0.2-10 s abrasion times.Other test equipment, e.g.Martindale or linear abrasion testers, use low velocities, normally without the possibility of increasing the value.Consequently, in this research, a fast, simple and inexpensive test method was evaluated with respect to leather and man-made materials in protective garments for motorcyclists, which tries to combine the advantages of the methods described above.A micrometre caliper was used to measure the sample thickness at three positions along the radius between the middle and the edge of the abraded part before and aft er the testing.Usual textile thickness measurement instruments have signifi cantly larger measurement areas and are thus not suitable for measuring the varying thicknesses in these experiments.Th e values given here are thus underestimated in comparison with those measured with a textile thickness measurement instrument, especially in the case of the highly compressible knitted fabric.Areal weight was measured by cutting the samples into the size of 10 cm² (due to the sizes of available samples larger areas were not possible) and measuring the masses on an analytical balance (VWR).Th e last two fabrics are not suitable for protective purposes and are thus added for comparison.SuperFabric® has a surface structure similar to skate leather.Leather materials were soft and bendable, while the man-made materials were harder and stiffer.Since only small samples were provided, not enough material was available for cross-checking using the Taber® Abraser or a belt abrader.Instead, the few test results available in scientifi c literature, apart from the producers' own websites, are given here for comparison.
As an easy and well-available testing method, combining the pure dynamic friction of the belt abrader with the circular movement of the Taber® Abraser, a pillar drilling machine was used (Figure 1).Th e sample holder was taken from the Martindale abrasion tester (according to DIN EN ISO 12947), an instrument which is available in most textile institutes, using the standard setup with one standard Martindale spacer layer.Th e force between the sample in the sample holder and the abrading object below is controlled using the scales below the abrasion stone.
Since radial velocities increase from the middle to the border of the abraded area, this method enables creating a velocity profi le along the radius of each sample.Th e abraded sample area has the diameter of 28.65 mm.Using the force of 100 N, this results in the pressure of 95.7 kN/m² = 95.7 kPa.Th is value is about 4× the value used in the belt abrader test, simulating the sliding of a motorcyclist of 80 kg in weight on a circular area with the diameter of 82 mm, which is a typical order of magnitude of one knee, elbow or hand.
While overestimating this value in the test described here, the maximum frequency of the available pillar drilling machine resulted in the maximum velocity of 2.9 m/s = 10.4 km/h, which is clearly underestimated and even smaller than the value of a belt abrader.Nevertheless, this value -as well as the pressure on the sample -can be tailored to testing conditions closer to reality.Opposite to all other testing methods described above as well as the Martindale or linear abrader, the use of a pillar drilling machine allows for using real concrete, asphalt or similar materials as abrading objects.
In our research, we used a paving stone with a fi ne surface structure, similar to typical asphalt in Germany and other European countries.For the second test, a lawn edging stone was used with a courser surface structure.
For optical examination of samples, a digital microscope VHX-600D by Keyence (nominal magnifi cation 50×) and a camera were used.

Results and discussion
Th e samples were evaluated before and aft er the abrasion tests optically and by measuring the thickness.Th e fi rst idea to also take into account the masses before and aft er the tests was excluded due to the following reasons: fi rstly, it was not clear how to handle nearly completely torn off areas, whether they had to be cut away before weighing or not; secondly, since the outer area -which was not infl uenced by the test -would keep its mass, it would be hard to interpret the results by calculating a relative mass loss -even a completely abraded sample would still have the border area left so that the values like 100% loss of mass would not be possible; finally, during the experiments, it became evident that some of the man-made materials were molten together with the Martindale spacer layers on the sample holder aft er the tests, leading to even higher masses and thus distorting the results.Th e results of thickness measurements before and after both abrasion tests are depicted in Figure 2. Comparing all leathers, skate leather had the highest remaining thickness aft er the tests, apparently giving the highest security, due to its large original thickness.Nevertheless, most other leathers, including the softer and thinner calf leather and kangaroo leather for gloves, showed only small abrasive wear.Unexpectedly, in the thicker kangaroo leather for other garments, a hole was found for rubbing on a lawn edging stone, i.e. the material failed for the abrasion test.

Figure 2: Th icknesses of test samples before and aft er abrasion tests
Kevlar-ceramic with its smaller original thickness protects against abrasion on a paving stone, but not on a lawn edging stone -here, a standard deviation signifi cantly increased, meaning that the holes in the material cannot be excluded and were found during the test.Th e situation was similar in carbon-Kevlar, Cordura, Gore material and SuperFabric®.Here, in one or more cases, holes occurred during the tests on a lawn edging stone; for carbon-Kevlar and Cordura, even during the tests on a paving stone.Th is means that all synthetic materials failed the test on a rougher lawn edging stone, even at the low test velocity.Unexpectedly, carbon-Kevlar and Cordura, typical materials in motorcyclist protective clothing, failed even the test on the paving stone.
On the other hand, the knitted fabric 3a was not punctured during the abrasion test on a paving stone, but completely destroyed aft er the abrasion on a rougher lawn edging stone.Th e denim showed holes in both tests.
Interestingly, SuperFabric® gives the best results in the literature, followed by automotive leather with a special coating, Cordura, PES with epoxy resin plates (a similar idea as in SuperFabric®), fi sh leather and Kevlar/Nomex/PBI.Th is is in direct contrast to the fi ndings of our study, where the Super-Fabric® and Cordura were completely destroyed during the abrasion on a lawn edging stone, while the simple calf leather and the skate (fi sh) leather showed the smallest losses, even when without any additional coating.Apparently, the test methods diff er signifi cantly in their results, making it necessary to perform a follow-up study using diff erent test standards.
An optical examination of diff erent materials before and aft er the tests revealed more information about the infl uence of abrasion on the samples.Calf leather depicts the images of the four leather surfaces before and aft er the abrasion tests.While the skate leather showed strong abrasive wear of the nubs, the optical change of the thinner kangaroo leather was less eye-catching.On the thicker kangaroo leather, the original structure lost as well.A small hole -interestingly near to the middle, i.e. at lower velocities -was clearly visible.Th e calf leather showed the lowest optical deviation from the original state aft er the abrasion tests.Microscopic images of the same samples, taken with the nominal magnifi cation of 50×, are depicted in Table 4. Table 5 shows the results of the abrasion tests on man-made materials.In all materials, holes were visible at the abrasion against a lawn edge stone, for carbon-Kevlar and Cordura even at the abrasion against a paving stone.
In some cases, the fabrics were additionally stiff er aft er the tests, showing that parts of the material were molten and thus fused, partly also in connection with the Martindale spacer layer between the metal sample holder and the investigated sample itself.Th e microscopic images of these samples are depicted in Table 6.Finally, the test results of soft er fabrics, which are not suitable as protective clothing, are depicted in Table 7.While the dense knitted fabric with relatively low elongation and tight surface was not punctured by rubbing on a paving stone, the rougher surface of a lawn edge stone destroyed it.Th e denim was in both test setups destroyed.
Although denim, made from cotton, does not tend to melt and fuse together with objects around, it must be underlined that denim does not provide Calf leather any shelter, but is destroyed even in a less harsh test.Th e latter is also visible in the microscopic images in Table 8.Unexpectedly, this holds true also for two of the wellknown and oft en used man-made materials, while the leather materials mostly showed a much higher reliability to withstand abrasion on rough ground.Especially the calf leather, being oft en used and relatively inexpensive, showed a good abrasion performance.
On the other hand, it must be underlined that the results of the test used here do not exactly refl ect the real accident situation, in which mostly a linear movement occurs, similar to a belt abrader.Nevertheless, they indicate the importance of performing tests on motorcyclist protective clothing, ideally with a variety of diff erent experimental procedures which are capable of simulating diverse kinds of abrasive wear in an accident.

Conclusion and outlook
A new, simple test procedure for the motorcyclist protective wear against soft tissue injuries was developed and tested on 11 diff erent samples.While the leather samples in most cases showed only low abrasion, all samples from man-made fi bres were punctured by abrasion on rougher ground, some of them even by abrasion on a smoother stone.Th ese results -which are contrary to those found in the literature from Taber® resistance tests -clearly indicate the importance of testing all abrasion protec-tion garments with a reliable method, ideally using more than one test stand to simulate diff erent possible accident situations.Additionally, expanding this study to other materials, using also less abrasive materials as abrasion partners, would support the understanding of different eff ects of diverse abrasion testers, such as the Martindale or linear abrasion tester.
Acknowledgments Th e authors are grateful to Held Biker Fashion for providing all test samples.

Figure 1 :
Figure 1: Pillar drilling machine used for tests reported here (left panel) and sketch of sample holder taken from Martindale abrasion tester (right panel)

Table 8 :
Microscopic images of reference samples before (left panels) and aft er abrasion tests (middle panels: abrasion on paving stone; right panels: abrasion on lawn edging stone); nominal magnifi cation: 50×FabricsOriginal Paving stone Lawn edg.stone Knitted fabric 3a Denim Table7: Reference samples before (left panels) and aft er abrasion tests (middle panels: abrasion on paving stone; right panels: abrasion on lawn edging stone)

Table 1 : Taber® Abraser breakthrough values from the literature
Th e following samples, presented in Table2, were made available for investigations by the company Held Biker Fashion (Held GmbH, Burgber-Erzfl öße, Germany).

Table 2 :
Samples under investigation and available information about them

Table 3 Table 3 :
Leather samples before (left panels) and aft er abrasion tests (middle panels: abrasion on paving stone; right panels: abrasion on lawn edging stone)

Table 4 :
Microscopic images of leather samples before (left panels) and aft er abrasion tests (middle panels: abrasion on paving stone; right panels: abrasion on lawn edging stone); nominal magnifi cation: 50×

Table 5 :
Man-made samples before (left panels) and aft er abrasion tests (middle panels: abrasion on paving stone; right panels: abrasion on lawn edging stone)

Table 6 :
Microscopic images of man-made samples before (left panels) and aft er abrasion tests (middle panels: abrasion on paving stone; right panels: abrasion on lawn edging stone); nominal magnifi cation: 50×