CRITERIA FOR HEAD IMPACT PROTECTION BY MOTORCYCLE HELMETS

Transcription

1 CRITERIA FOR HEAD IMPACT PROTECTION BY MOTORCYCLE HELMETS E Shuller, W Köni, and G Beier t Institute for Leal Mediine, Urüversity of Munih MPA, University of Stuttart Abstrat he objetive of this study is to establish riteria for head impat protetion to be required for optimal peiformane of motoryle helmets Head injury severity sustained in real aidents was ompared with test results obtained by laboratory droptests aordin to ECER, onsiderin residual damae ofprotetive paddin as an indiator for head impat loadin 5 interal helmets were olleted from real motoryle rashes providin basi imponant aident data onemin head injury and head impat harateristis For new helmets similiar to those used in the real aident sample, omparable damae was simulated in laboratory droptests usin various anvils and impat areas and applyin step by step inreasin impat veloities Comparin deeleration proflies from drop tests representin a best as possible approximation of residual aident damae with orrespondin head injury severity (AIS), the followin prinipal results and onlusions were obtained: ) Inreasin head injury severity is not losely related to inreasin residual deformation of the enery absorbin liner ) Critial head injury (AIS 5) may our for impats whih are related to rather low translational head deeleration of approximately 5 or lower measured in the ECER headform Hih rotational aeleration miht be deisive in these paniular aident ases 3) Test results suest that ECER Limits should be sinifiantly redued to optimize head impat protetion Introdution In ommon pratie, ie as required in national and international standards, the performane of protetive helmets for motoryle riders is evaluated predominantly by enery absorption test results Aordin to the test proedure from ECER [ l ], helmets equipped with an instrumented headform have to be dropped from ertain heihts (5 m7 m/s and 4 m m/s) on a fixed flat or hemispherial anvil Tue impat deeleration within the headform has to be reorded triaxial versus time Tue resultant deeleration urve has to be evaluated with respet to peak value and duration Tue ability of shok absorption and therefore the performane of helmets is onsidered to be the better, the less a resultant deeleration is reorded Test proedures established for helmet standards are desined for ood reproduible measurements as well as a simple as possible experimental setup As a onsequene, basi differenes have to be onsidered when omparin results obtained from laboratory test proedures, e aordin to ECER, and real aident onditions In partiular, these are the followin aspets: Tue headform is similar to the human head only in shape and weiht, but annot simulate the omplex bioloial struture of the human head 3

2 The impat enery transfer in droptests is determined only by the mass of the headform and the helmet, and not influened by the riders whole body mass whih in real aidents possibly is reatin a different speifi effetive head mass 3 Real aident biomehanial effets onernin the headnek juntion (e dampin and osillations) annot be simulated in the droptest 4 Loadin of the ervial spine and base of the skull annot be measured 5 The fixed anvils to be used represent only a limited number of the reat variety of possible impated strutures in real aidents Therefore, it is evident that headform deelerations obtained from ECER droptests are not neessarily equivalent to head deelerations ourin for idential impat veloities in real aidents Thus, droptests are representin predominantly omparative testin of material and onstrution properties for different helmets under dynami loadin onditions Objetive of the Study Bein aware of these limitations onemin laboratory droptests, nevertheless, it is assumed that residual deformation of the protetive paddin ould be at least to a ertain extent an indiator for dissipated impat enery both in reality and in laboratory droptests Then, headform deeleration measured for that partiular droptest whih is simulatin the real aident residual deformation of the protetive paddin should be a suitable physial parameter to estimate head impat loadin (f [], [3]) Therfore, the study onsisted of two parts: Heimets olleted from a well doumented real aident sample were examined for damae, in partiular for residual deformation of the protetive paddin From aident files and aident reonstrution for eah ase harateristi aident parameters were determined, suh as rider kinematis, impat situation et, and related to head injury type and severity For new helmets seleted as far as possible to be of the same kind as aident helmets, droptests were arried out applyin various impat veloities and anvil types, in order to determine the relationship between impat enery, resultant headform deeleration and residual deformation of protetive paddin lf the residual deformation of the protetive paddin produed in a defined laboratory test is assumed to estimate the biomehanial head loadin for the aident ase, the laboratory test results may be appliated to predit head injury risk and to establish riteria for head impat protetion to be required for optimal performane of motoryle helmets Furthermore, these findins may also suest improvements or hanes for test proedures and performane requirements in standards Aident Heimets and lnjury From aident ases investiated at the Munih Institute for Leal Mediine, 5 interal helmets were seleted for this investiation The motoryle riders wearin these helmets sustained head injury of severity AIS to AIS External damae of helmets indiated impats aainst various strutures haraterized by various impat areas and impat diretions Table summarizes relevant data for the real aident sample, ie helmet type, head injury type and severity, impated struture, impat area, impat diretion and helmet damae Altoether, the aident ases are overin a wide rane of the real motoryle aident sene 4

3 Riders who sustained ritial and fatal head injury (AIS 5 and AIS ) predominantly were exposed to lateral impats in the temporal reion and oipital impats Those impats oured aainst various strutures, but for 5 out of the total of ases linear impat sins were observed on helmets A stron orrelation between extemal damae of helmets and injury severity is not evident 5 head injury oured, Certainly, in eneral, helmet damae tends to inrease alon with injury severity, but, for example, in ase No, ritial AIS observed althouh no sinifiant helmet damae ould be Dynami Tests for New Heimets ) MPA Stuttart were arried out on five helmet types (interal Laboratory investiations of the helmets), testin helmets for eah type (f Table The test helmets were seleted to be as best as possible similar to the orrespondin aident helmets, ie with respet to size, onstrution, material of the shell and the protetive paddin The new helmets were tested for impat veloities ranin from 44 m/s up to : m/s and usin the followin anvil types: flat, hemisperial, rail, kerbstone, semiylindrial Impat areas on helmets are illustrated in Fi frontal (B), lateral (), parietal (P), and oipital (R) For eah droptest headform deeleration was reorded triaxial aainst time and residual deformation produed in the protetive paddin was measured Fi shows two harateristi resultant deelerationtime urves reorded whih are to be interpreted as follows: The helmet tested provides ood performane for an impat aainst a flat anvil with a veloity of 44 m/s (resultant headform peak deeleration 74 ) and almost no 35 ) performane, ie failure of the shok absorbin liner, for an impat aainst a hemispherial anvil with Fis 3 m/s (resultant headform peak deeleration are presentin diarams of resultant headform peak deeleration versus impat veloity measured for new helmets whih were impated to various anvils and impatareas Failure of the protetive paddin, ie a steep inrease of deeleration, oured for rown impats (impat area P) aainst flat anvils at hiher impat veloities as ompared to irumferene impats (impat areas B,, R) and to impats aainst more puntate anvils Residual deformations of protetive paddin measured in laboratory tests were analyzed with respet to headform peak deelerations As an example, for impat area B (frontal) and for flat and hemispherial anvil types the variation ranes for these data are demonstrated in Fi 7 Fi presents the orrespondin perentae residual deformation of the protetive paddin related to the inertial thikness On pratial appliation of the diarams from Fi 7 and Fi sometimes diffiulties may arise, beause for steep urve sements small inauraies onemin the measurement of residual deformation will result in rather hih variations for the related peak headform deelerations 5 (5 Nevertheless, the followin estimation is onsidered to be possible: Residual deformations of the 5, protetive paddin lower than than mm % ) are orrelated to peak headform deelerations lower mm residual deformations (7 % ), headform 3 will not be exeeded independant of anvil types used Up to deelerations of Therefore, the loal residual deformation of protetive paddin an be onsidered as an indiator, whether the aident onditions have been stroner or milder than ECER test onditions If residual deformation of the protetive paddin is exeedin mm (7 % ) the orrespondin headform deelerations annot be obtained reliable from the overall presentation in Fis 7 and 5

4 But, for these ases a speial analysis may be suessfull, if the speifi aident parameters are onsidered, suh as helmet onstrution, impat area and the impated struture This proedure was arried out for aident ase No 9 (f Table ): Aident files reported a ollision of the motoryle with an onomin passener ar The years old female passener of the motoryle was thrown on the road surfae without any vehile ontat Extemal helmet damae indiated an oipital impat The youn women sustained ritial head injury (skull fratures and brain ontusion) and died 5 days after tbe aident The residual deformation of the protetive paddin ( mm) appeared not to be produed by a flat struture rather than by a rounded or eded struture of linear extension, suh as a kerbstone to be found at the aident loation Applyin diarams from Fi 7 and Fi, the residual deformation of mm would be related to a peak deeleration of to 3 (flat anvil) and to (hemispherial anvil) In order to reprodue the residual deformation for helmet No 9 as best as possible, drop tests were arried out usin a flat and rail type anvil, in order to simulate impats on the road surfae and the kerbstone Best aproximation for the residual deformation of the aident helmet ould be ahieved under followin onditions: Anvil type Impat area Impat veloity Peak deeleration Residual deformation HIC 5 ms deeleration rail oipital 7 m/s 9 9 mm 7 5 These data are loated in the enter of the variation rane for the hemispherial anvil in Fi 7 and Fi The experiments applyin a flat anvil did not produe suh a ood aproximation of real aident residual deformation of the protetive paddin A 9 mm residual deformation ould be ahieved for hiher impat veloties and hiher peak deelerations, ie 7 and resp The residual deformation pattern of helmet No 9 ould be simulated under onditions, whih meet the requirements from ECER If it is onsidered to be true, that headfonn peak deeleration measured in drop tests and real head impat loadin, ie translational head deeleration, are almost of the same order, a test result meetin the standards does not uarantee that ritial head injury of AIS 5 will be avoided, even when impat onditions are sinifiantly milder than the required 3 in the ECEReulation Disussion The investiation of helmets impated in real aidents and orrespondin experimental laboratory impat tests simulatin the residual deformation of the protetive paddin suest, that headfonn deelerations measured in droptests indiate real aident head loadin, ie at least translational head deeleration The orrespondin relationship evaluated in this study is presented in Fi 9 For aident ases head injury severity (AIS) is plotted versus atual residual defonnation of the protetive paddin, distinuishin helmet shells made of Polyarbonate () and GlassReinforedPlasti (GFRP) In the same way, the upper limit of the variation rane for headform peak deelerations shown in Fi 7 is plotted versus residual deformation of protetive paddin of new helmets produed experimentally Applyin laboratory test results to aident helmets leads to the result, that half of the aident ases representin ritial and fatal head injury (AIS 5 and AIS ) oured under impat onditions whih are related to headform peak deelerations lower than 5 measured in

5 laboratory droptests The aident sample inludes not a sinle ase related to beadform peak deelerations more than 3 Fi 9 also indiates that there exists no stron orrelation between bead injury severity and residual deformation of protetive paddin observed for aident belmets (e 7 mm is related to AIS 3 ), and, as a onsequene, no lose relationship between head injury severity and headform peak deeleration (e AIS 3 for deelerations < 5 ) For speifi aident situations, e for ase No 9, it is evident, that hih rotational head aeleration may have been oured as a onsequene of an oipital impat This ould be an explanation that, in fat, rather low translational head deeleration did our, as indiated by the orrespondin laboratory test, and a hih rotational head aeleration, not measured in the fallin headform, was additionally responsible for the AIS 5 head injury sustained in the real aident A review of biomehanial head impat tolerane data from the literature [4] presented in Fi indiates that severe head injury is to be expeted either for hih translational or for hih rotational aelerations (f solid marks in Fi ) Beause of the head nek anatomy both omponents appear not to be independant from eah other Aordin to Fi head injury severity AIS > ould be expeted even for rather low translational aeleration ( < 5 ), if rotational aeleration exeeds krad/s However, as far as rotational and translational omponents are onsidered not to be independent, translational aelerations < would not ause rotational aelerations > krad/s whih appear not be ritial aordin to Fi Conlusion The results of the study soest that rotational head aeleration ould be important in real aident impat situations To inlude this as a performane riterium in a test proedure for Standards would be very diffiult and probably not neessary, beause, as demonstrated above, a sinifiant redution of limit for the translational headform deeleration, e up to, would exlude ritial rotational head aeleration in real impat situations Referenes [] ECEReulation : Uniform Provisions Conernin the Approval of Protetive Heimets for Drivers and Passeners of Motoryles [] tte D P Jessl, and EG Suren: Impat Points and Resultant Injuries of MotorCylists Involved in Aidents, with and without Heimets Pro of the 94 IRCOBI Conferene [3] Hope PD and BP Chinn: The Correlation of Damae to CrashHeimets with Injury, and the Impliations for Injury Tolerane Criteria Pro of the 99 IRCOBI Conferene [4] Data olleted in partiular from: a) Proeedins of the Stapp Car Crash Conferene, annually published sine 9 (loth, llth et) by SAE (Soiety of Automotive Enineers), Warrendale, Pennsylvania, USA, b) Proeedins of the IRCOBI Conferene (International Researh Committee on Biokinetis of Impats), annually published sine 973 (lst, nd et) by IRCOBI Seretariat, 9 Rue Salvador Allende, 95 Bron, Frane [5] Newman J A: A Generalized Aeleration Model for Brain Injury Threshold (GAMBIT) Pro of the 9 IRCOBI Conferene Aknowledements This investiation was funded by the Bundesanstalt für Straßenwesen (BAST), Projet No FP 7 7

6 TABLE : Aldent Heimet # r f the Real Aident 5 amoie Shell Material / Protetlve Paddln PU /PU PU Skull AIS Head 5f 5 5f 3 lnlurv Brain other body sements ISS 3 7 5f f () () () () () () 75 () lmpated Struture solid deformable fixed [\) vaulted plane movable flat linear () () () () lmpatarea x frontal oipital parietal lateral hin () () () () () () () Impat Diretlon radial oblique tanential () Shell Damae laeration breakin destrution abrasion < 3 5 < < Protetlve Paddln Damae residual deformation (mm) 4 breakin () < Polyarbonate, Polystyrole, GlassReinforedPlasti, PU Polyurethane, f Fatal evidene, () estimated, no positive proof 4

7 TABLE : New H ei mets Se eted for Lab oratorv D roptests Heimet Type Size M A B M M D M E M T** M Prod Year Shell Mat Certlfi Protetive Paddina 4mm 3mm 3mm ABS 3mm 4mm 4mm ECE ECE ECE ECE ECE ECE 3539mm, 3 all 337mm, 37 a/i 73mm, 3 all 374mm, 45 a/i 33mm, 9 all 3mm, 7 a/i PA Polystyrole, Polyaronate, PA Polyamide, ABS ArylnitrileButadieneStyrole, GlassReinforedPlasti, for Case No 9 only Fiqure : Impat areas Impat area Helmet type B 9 Anvil Veloty B rlat 4 4 n/s $ i '_, L' I ' ' l t _ tt ' I HIH Helmet type B Impat area B hemspherial Anvil m/s Veloity oo ' H toih t I H u o Fiqure : Charateristi deelerationtime urves 9

8 N <O Flure &l Ql eq) Heimet C Heimet E x Hmet fflmel I Hol A o a rlat aritft am,o r, 3: Hlmet [ " " t P m/ /,,:: }" lpat area Velodty Fllln9 headfo,,, tests, ' Holmol C Holmol + Holmol O &, hemlspmni _ o Heimet A 7 J 5on <4' <4 / " 3? lr;::' I, / m/s Veloity soo,,r, Fiure Q) Qj u q) Q) Qi u Q) 4 9 Heimet H+lmI [ " " Fallinq headfo"" tts, HolmC + Hof D o ph a Heimet A, flot aftyll lmparl r lmpat area! 7 5 e <4 3 o m/ Veloity! :! l 7 fl Yi'f/ 5!:': e 4 N / 3 / /t Ä o m/s Veloity

9 N to " Q son vvv lll 7 J lmt A Holmot [ Kdnet D Hol E JC D +! D Mo!A Hei met Mmltph lul ""'4d + o Ktlm l A Heimet C O net ff; rn,kt ' Veloity ' rr,ys t Fiure Cl) 5: Fellin hendfor tes t s, impot oro Veloily H,Ys ::::: 4 ' :', 3 L+ +tt7, Cl) Qj u GI 7 5 e '!7 NJ ' 3 V ]_/ ::::E!:Y'""7 I, onlt hmlsphertol onll: t'oll M,, I :!'::: onwh: ktfinlon x ony4t: flot _ ftpod Veloity 5!, f;' /,/ /, : r7// I I,Ys t lal om:kort Fntlin 4 o n'f'll rou tmped,_ Veloity ( = :;,Ys _J _ rlif feront onvils heodfol"lll teste, impat oreo B ond rear, : :LLJdl_: 'r"'t::j_ I ' ' t o 7 : J! 5, rt++;l _JJ ""T" eoo ro::i Fiure : o ClJ e Q Cl) Qj CD 7 J

10 7 +: e Q) a; u Q) Cl Fiure +: e Q) a; u Q) Cl 5 5 Deformation mm 5 et, 7 Deelerationdeformation satter bands, 7: F i ure : 3 4 Deformation 5 Deelera t iondeforma t ion satter bands, irnpat area B, helrnet A E 9

11 5 ytest helmets: upper urve for impot test 4 in the front oreo :;: e 3 Q,) Q) Q,) Cl x E fw",,, t t Fi Deformation mm aide nt helmets Vl 4: 4 9: 4 Comparison of I n j ury Deformation O = GrRC l!i = mm Max imum Headform Peak Oeeleration and Head severity AIS Related to Residual Test and Aident Helmets D e f ormation o f { GFRC and P C see Text ) 93

12 \) u:> a: Q) Q) < CU "t:j CU ( Cl) ""' N, + V "' < /:i D \ GAMBIT= D D a /:i /:i ms Transl Aeleration [] AIS o AIS t AIS AIS > Fi O : Translational a n d R o ta tional A e leration and H e a d lnjury S e v e rity AIS ( f [4], [5])