MATERIALD SAN SCIENC SPORTN EI S Editedby: F.H. (Sam) Froes andS.J. Haake Dynamics Shock Absorbing Effectivenesf so Hockey Helmet Liner Foams After Exposure to Repeated Impacts SpyrouE. T.B.and Hoshizaki Pgs. 199-209 TIMS 184 Thorn Hill Road Warrendale 15086-751A P , 4 (724) 776-9000 SHOCK ABSORBING EFFECTIVENES HOCKEF SO Y HELMET LINER FOAMS AFTER EXPOSURE TO REPEATED IMPACTS E. Spyrou and T.B. Hoshizaki Sport Maska Inc. Department of Research and Development 600 Boul. Industriel St-Jean-sur-Richelieu, Quebec 4S7B J3 ,, Canada Abstract hockee ic e yTh helme consideres i t multiplda e impac nature game tth d th devic o f et an e o e edu the prolonged use of helmets by players. The liner foam is one of the many variables that influence impact absorption of a helmet. The purpose of this study was to investigate how inner liner foams, use hocken di y helmets, perfor mtermn i energf so y attenuation, following exposure repeateo t d impacts. Foam samples use thin di s experimen typesto wertw f :eo vinyl nitrile (VN) and expanded polypropylene (EPP) and measured 100 x 100 mm and were 12.5 mm thick. There were two phases to this experiment. In the first phase, which also served as the conditioning phase for the second, twenty impacts were performed repeatedly (1 minute between impacts) on thre level o e(C2J foamtw 0 f impacf energy1 e s)o o eacr th d sfo f d an ho t )an severitO (C J 5 y( liner type. In the second phase, a control set (Co) of foams (3 samples / liner type), not exposed to prior impact, along with the two sets of foams conditioned in phase I were tested once with an impact of 20 J. A monorail drop test was used to evaluate the foams. The type of liner foam and the severity of multiple impacts were both found to substantially affect liner impact absorption properties. Overal bese th l t performanc foamP observes EP e,e wa althoug th mors y db wa e N hV efficien absorbinn i t g impac t lowea t r energies. Such informatio e verb yn e nusefuca th n i l design of helmets and can possibly help prevent injuries. Materials and Science in Sports Edited by F.H. (Sam) Froes (ThS IM e Minerals, Metal Materials& s Society), 2001 200 Introduction With contact sport activities there exists a certain risk of injury - the game of ice hockey is no exception. The environment of play presents many chances for collision with the boards (e.g. wood, meta glass)& l , metal goal posts surfacee ic , , hockey sticks pucke th , , skate othed an s r equipment, as well as with the players of the opposing team. Consequently, ice hockey has a high rate of injury, frequently to the head and face (1,2,3,4,5,6,7). Priority, therefore, has been causee studgivee th th f heayf o no t s o d injurie meand san protectionf so hockee ic e yTh . helmet has improved protection to the head since its use became mandatory. The insurgence though of concussions recently promptes ha , d renewed attentio helmeo t n t designt no t quicA .bu k- necessaril bese y th solutio - t problee th o nt m woul tougheo t e d b performanc e nth e requirements set in certification standards. Certification standards have been a determinant factor of helmet performance and thus have influenced design to a great extent. It has been suggested that helmets be designed specifically for the unique conditions of each sport and all conceivable conditions shoul e consideredb taked dan n into accoun helmen i t t design r (8)feasibilitFo . y purposes, standard limitee sar scopen di , therefore overlooking importane somth f eo t conditions under whic game hth s playedei e sucOn h. conditio helmety nwa usee e woular sy th db e db players and how helmet performance is affected by the frequency and severity of blows that it is subjected to, during its lifespan. majoo Tw r type heaf so d protective devices exist firse Th .t type singla , e impact device uses i , d in very high energy impacts. Such impacts generally occu racn i r e car, motorcycle bicycld an , e accidents wher helmee eth t provides protection agains singla t e considere s i cras d han d unfio t t further protect the wearer following the crash. The second type, a multiple impact device, usually withstands impacts of less energy but is more durable. It is more effective in handling multiple impact situations. The ice hockey helmet falls under the second type of protective devices. This is due to the likelihood of less severe repetitive impact situations in the game of hockey. Initial research and development of ice hockey helmets was based on fundamental studies of human injury tolerance measures (9,10,11,12). In particular, linear acceleration levels have been shown to be a principal variable implicated in skull and cerebral injury. In general, the safety 2 threshol r headfo d impact s considerei s z (wheraroune 9.8= g b z 10 o g dt m/s1 de30 ), with minimal risk of skull fracture below 300 g; however, the relationship between linear acceleration and cerebral damage such as concussioz n in not well understood. As a result, the ultimate goal of helmets has been to reduce the energy transferred to the head. The extent of energy reductio s boti n a hfunctio e magnitudth f o n f deformatioo e e resultinth d an ng force proportiona lineae th o rt l deceleration achievo T . e this, helmets typically consis shela f o tl (outer covering) cushionina , g material (also calle liner)chinstrape a dth d an ,maio Tw n. type f foaso m deformation exist: plastic and elastic. The plastic material will not recover to its original shape following impact whereas elastic material will recover firse th t n casI . kinetie eth c energa f yo striking object is completely absorbed when the material has been fully compressed. Under a plastic deformation materiae th , l sustain deformatioa s n whic s beyonhi e elastidth c limid an t permanent damage is done. When the load is released, the material will not regain its original shap wilt distortee bu lb mechanica s it d dan l properties deformatiowile differene th lb o t e du tf no the materia moleculae th t la r seconlevele th n .I d case importane ,th t featur thas ei t while maximum force develope t affectedno s d i time th pea,o e t k forc doubleds ei . Unde elastin ra c deformatioe nth material can return to its original shape without any permanent damage. The bulk of material display both elastic and plastic properties to a certain degree. Depending on the use of the helmet, the material it is composed of, should possess more or less of the two material properties discussed (elasti . plastic)cvs r exampleFo . hocken i , y wher possibilite eth repeatea f yo d impact scenario 201 exists, material with more elastic properties woul suitable db e since recover materiae th f yo s i l crucial in dealing with subsequent impacts. Bishop indicates that these material consist of medium density resilient foams (13). Predicting impact absorption characteristics of helmets has proven to be difficult given the numerous material, geometric, and environmental factors and their interactions (14). The purpos f thio e so investigat t stud s wa y e effec th ef inne o t r liner typd environmentaan e l conditions (i.e. energy of impact and multiple impacts) on the impact attenuating characteristics of ice hockey helmets. To avoid confounding factors resulting from whole helmet testing, flat sectional samples representing typica hockee lic y helmet materials were evaluated (12,15). Methods Samples Liner samples were constructed possessing common construction characteristic f hockeo s y helmets presentl ymarkete use th squar m n di m sampl A .0 e line10 ex rconsiste 0 tha10 ta f do was 12.thick typem o 5m innef Tw .so r liner material were used: expanded polypropylene (EPP) an d5 kg/m 9 viny d 3an l a densitlinernitrilN 5 6 d V f ha sd eo y an (VN P ) EP foam e Th . respectively. Instrumentation Monorail System. The impact testing apparatus used was a monorail or guided-fall system (Figure 1), which consisted of a cylindrical metal guide supported from a beam anchored to a cement block at the lower end. This arrangement provided stability and uniform movement of the aluminum spherical impactor (calibration ball, diameter = 14.605 mm, mass = 4005 ± 5 grams) used to impact the samples (16). A carriage assembly supported the spherical impactor, universae th f o y lb ybalwa l joint combinee Th . d impacto e masth f so carriagd an r e assembly was 5.15 kg. Rotational movement of the spherical impactor was prohibited during impact. Given that this is the standardized impactor required for system calibrations, it was chosen to permi resulte th t thif so s studappliee industriab e o yth t n di l setting. An adjustable remote release mechanis uses m frecarriago wa e dt eth e assembly wit initiao hn l velocity. This release mechanis adjustee heighb y n an m achievt ca o t ta d desiree eth d impact energy level e surfacTh . e upon whic samplee hth s were positione r impacflaa dfo s t steewa t l anvil with a surface area of 0.09 m2.