MATEC Web of Conferences 184, 01007 (2018) https://doi.org/10.1051/matecconf/201818401007 Annual Session of Scientific Papers IMT ORADEA 2018

Study regarding the influence of deployment on the occupant injury level during a frontal vehicle collision

Alexandru Ionut Radu1,*, Corneliu Cofaru1, Bogdan Tolea2 and Dragoș Dima1

1Department of Automotive and Transport, Faculty of Mechanical Engineering, 500091 University “TRANSILVANIA” of Brasov, Romania 2Department of Mechanical Engineering and Automotive, 410610 University of Oradea, Romania

Abstract. The aim of this paper was to analyse the influence of airbag deployment delay upon the head of the occupant in the case of frontal collision using in PC Crash and MADYMO dummy as the occupant. The study will also take into account the pretension delay of the seat-belt which is activated along with the airbag. Frontal on both the passenger and the driver were analysed including the occupant kinematics during the collision. Also, to validate the , a comparison was done with a real . We predict that by increasing the delay of deployment, the head will increase due to the fact the head travels close to the instrument panel/, and the force of the airbag will generate a significant acceleration upon the head. To better assess the potential injury of the occupant, the head injury criteria (HIC) will be calculated and correlated with the Abbreviated injury scale (AIS) code.

1 Introduction corn-starch) [7]. There are multiple types of airbags (front, sides, knee and curtains) [8]. The increasing number of vehicles during the last decades The head injury can be assessed by a parameter called in the urban area, as well as the intensification of HIC (Head Injury Criteria), defined by a mathematical congestions in intersections has led to considerable road- formula. The HIC criterion is a way of assessing the risk accident recordings [1]. Road traffic accident research has of a cranial trauma injury as a result of an accident. The been conducted over the years in order to study of the HIC criterion is the maximum standard value of the dynamic and kinematic behaviour of the occupant in the integral of the head acceleration. Depending on the impact phase as well as the injury assessment [2]. Since interval for which it is calculated, the HIC criterion is: the introductions of airbags, lots of lives have been saved - Unlimited - HIC; in motor vehicles crashes [3]. The airbag provides a good - 36 ms maximum - HIC36; protection for all kinds of crashes (side and frontal) that - 15 ms maximum - HIC15. could seriously injure or kill the occupants of the vehicle In order to predict the injury level of the occupant, the [4]. Huere has shown in a study that airbags can reduce HIC formula takes into account the head acceleration on head injuries by up to 82% for the 56-65 km / h range. the occupant’s head. The HIC formula is presented below Using the airbag, it was demonstrated that in 85% of [9], [10] cases, head injuries were classified as minor injuries [5]. Airbags have been demonstrated to reduce t2 1 2.5 (1) HIC36  max[(t2 t1)( a(t)dt) accident mortality by 19%, and reduce morbidity from t1,t2 t t  facial fractures and chest injuries. In purely frontal 2 2 t1 crashes, airbags reduce the fatality risk by 34% [6]. Where: t2 – final time value (s), t1 – initial time value (s), Airbags inflates when an electrical current provided a(t) – head acceleration resultant (g) by the airbag control unit is distributed to the detonator. The acceleration value, according to the impulse The ignition starts a chemical reaction that produces duration, shows a maximum limit of 40 g for the head. In nitrogen gas which rapidly inflates the nylon fabric bag. the case of pedestrians the situation is more dangerous, at After the airbag has been fully inflated, the nitrogen gas the impact with the ground, much higher head is released through small vent holes at the side when the (120 - 200 g) can cause severe injuries. The occupant’s head hits and compresses the airbag. The small head injury assessment is done using the HIC (Head holes are constructed specifically in a size and spaced out Injury Criteria) criteria in a time interval of 36 to reduce the volume of the airbag at a different rate, milliseconds for the occupant, respectively 15 ms for the depending on the type of vehicle. This gas is released pedestrian [11], [12]. alongside with dust particles that are from the material used to lubricate the airbag (typically talcum powder and

* Corresponding author: [email protected]

© The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). MATEC Web of Conferences 184, 01007 (2018) https://doi.org/10.1051/matecconf/201818401007 Annual Session of Scientific Papers IMT ORADEA 2018

The inur probabilit chart shown in ig. . the main characteristics of the airbag are presented in Fig. represents the correlation of the I scale code with the 2. HIC alue as discoered b lberto .

Fig. 2. Driver airbag technical specifications [16].

The inflation of the airbag are mm in length and mm in width. The total duration of inflation is ms during this time the massflow reaches Fig. 1. Injury potential according to HIC 36 value in correlation with the AIS scale code. . gs in the first ms then it drops to in the net ms. The mass of the airbag epands from to g in The graph presents the eolution of the probabilit cures ms. for I inur based on HIC alue. od tolerance In ig. the technical specifications of the passenger according to the HIC criterion is and corresponds to airbag are presented in the similar wa as the drier. It is a probabilit of of the I inur. This to mention that on the passenger side the airbag is much increases to for HIC . The probabilit of larger. death for the occupant indicate an I and occurs at HIC aboe . ances researched the effects of airbag dela on the nec . He obsered that the pea tension force and etension moment in nec are well below the nec inur critical intercept alues of and etension moment of m proposed discoered b HT. In contrast in the case of late airbag deploment the pea tension and etension moment are well aboe the nec inur tolerance. This suggests the high probabilit of serious Fig. 3. Passenger airbag technical specifications [16]. nec inur with late deploment airbag. n analsis b rieder and umar using accident The inflation dimensions of the passenger airbag are simulations with a irtual occupant model reealed that mm in length mm in width and mm in height. HIC alues of the irtual dumm increased with the uring inflation the massflow goes from to . gs in increase in airbag deploment dela. It was obsered a the first ms then it drops to almost in the net ms. percentage increase of the HIC alue b up to in The mass of the airbag epands from to g in the eent of an airbag deploment dela of ms. If the ms. It can be obsered that the passenger airbag is time dela was ms the gas force inside the airbag throws larger that the drier side. The technical characteristics of the occupants head in the rear and it comes in contact with the airbags are fied and cannot be modified in the the head restraint causing inur b increased acceleration program howeer there are some e parameters that can alues of the head . The stud at hand follows up this be adusted such as the ignition time of the airbag and analsis and test new ariants including passenger inur seatbelt pretention. ris a seatbelt pretensioning sstem. sing this screen the ignition time could be set to a specific alue maing this stud possible. lso the airbag and seatbelt could be either set as actie or one or 2 Occupant Model both set as inactie. There are other settings can set be se The occupant is represented b a multibod dumm male such as the seatbelt configuration onl shoulder belt or th percent model integrated in C Crash lap belt and if the current crash simulation is a side used to simulate the inematics of the occupant . impact. namic simulation were conducted before in order to analse the occupant behaiour using the 3 Methods Used model . using mathematical models of the human bod the moement of the bod elements can be The method inoles running simulations in CCrash imprinted etensiel . using the model where the ignition time of the Using this model, airbag deployment and kinematics airbag is modified in order to analse the dela time and can be analysed for both the driver and the passenger the occupant inematics. lso to alidate the simulation along with the seatbelt pretension system. For the driver, a frontal crash test will be conducted where the airbag and seatbelt are used. The crash test inoles a stationar

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ehicle H where an occupant dumm is positioned euipped with an accelerometer to measure the head acceleration and a striing ehicle H accelerated at mh.

Fig. 4. Crash test configuration.

The crash test was filmed with a high speed camera in order to analse the occupant inematic. In ig. . the inematic analsis is presented. lso the comparison with Fig. 6. Vehicles variation during the collision. the simulation was done. The elocit ariation shows that at mh both ehicles had the same elocit afterwards one ehicle slightl accelerates and the other tends to come to a stop. H reached a elocit of about mh during the first ms of the impact then coming to a complete stop at the time of . seconds. H registered a rapid decrease of elocit in the first ms of impact from to mh afterward coming to a complete stop at . seconds. In ig. . the head acceleration comparison of the occupants test and simulation is presented.

Fig. 5. Occupant kinematic comparison between the crash test and MADYMO model.

The crash was diided into phases the first phase consists the preimpact phase when the ehicles mae first contact. hase is the impact phase when the deformation of the ehicles tae place the energ is transferred and also the airbag and seatbelt pretention are deploed and limit the moement of the occupant. In phase the vehicles detach and occupant’s head rebound back and hits the headrest. It can be obsered a good inematic Fig. 7. Head acceleration comparison for the occupants. similarit between the crash test dumm and the The results of the simulation showed that the ariation in occupant. the head acceleration resulted in two peas the first being the contact between the head and the airbag and the 4 Results second one between head and head restraint. The data obtained from the comparatie analsis between the In ig. . the ehicle elocities are presented during the simulation and the eperimental test indicated a high collision. It can be seen that ehicle H was standing degree of similarit between them with a error. still while H was accelerated to the impact elocit ollowing the alidation of the irtual occupants of mh. behaiour with the actual collision test the effects of the delaed airbags on the head were analsed. In order to assess the seerit of inuries suffered b motor ehicle occupants due to delaed deploment of the airbag it was necessar to carr out simulations. In all these situations the occupant did not hae the but onl the airbag. o passie safet sstem has been used in one of the simulations. In ig. the occupant moement is presented for the the airbag trigger time has aried at the time of ms of the collision. The analsis was performed up to the ms dela alue. The acceleration reference alue ms corresponds to the ms time.

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the siulations a coparative analsis o the head acceleration as perored i

Fig. 8. Occupant kinematics at 100 ms of the collision when Fig. 10. Comparative head acceleration for the different airbag the airbag trigger time was modified. delay times.

t can be observed that the lack o passive saet sstes ro the diara analsis it as concluded that ater the results in collision o the occupants torso ith the steerin airba trier dela tie o s the acceleration value heel he s dela is the ideal situation here the at the head level doubles due to the epansion orce o the airba is ull epanded at the oent o contact beteen airba that is transitted to the occupants head n the the occupant and the airba inor dierences occur ith unavourable situation here the belt and the airba are delas o and s but ater s it can be seen that issin there as an increase in acceleration value o the position o the occupant approaches the situation o calculate the risk o inur o the occupant the here there are no passive saet sstes t s the head inur criteria as calculated occupant coes into contact ith the steerin heel and the airba deploent produces a head ipact orce urther analsis o the occupant oveent as done b observin the conseuences at the tie o and s presented in i

Fig. 11. HIC values for the different airbag delay times.

ead inur criteria values have been used to epress the occupants inur potential b correlatin the ith the severit scale ince the aiu values ere belo the threshold o the inur potential is considered to be lo inor inuries o i presents the likelihood o occurrence o lesions or the related stud

Fig. 9. Occupant kinematics at 100 ms and 200 ms of the collision when the airbag trigger time varied.

t can be seen that at s or the trier ties o and s the orce o the epandin airba is so reat

that it repels the occupant to the back o the seat eneratin and etra acceleration or the head olloin

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Fig. 12. The rate of occurrence of AIS-1 type lesions depending on the airbag deployment times.

The data revealed that the delay in triggering the airbag can induce the increase in head acceleration by 46%, directly affecting the risk of injury. The explanation is due to the fact that the distance between the head and the steering wheel is reduced if the airbag is delayed by 80- 100 ms, and at the moment of triggering, all the force generated by the expansion of the volume of gas inside the airbag is transmitted directly to the occupant's skull. The proper operation of the airbag (0 ms delay) requires that at the moment of contact between the head and the airbag, the airbag has reached the maximum expanded volume. Fig. 14. Comparative head acceleration for the different airbag delay times (passenger). This study also contains analysis for the passenger airbag trigger delay. Using the same procedures as above, With the seatbelt and airbag, the head acceleration is 3 simulations were performed (airbag and seatbelt with no pretty low, with the value of 45 m/s2. When only the delay, only the airbag with no delay and only the airbag airbag is present, with no delay, the acceleration increases with the delay of 40 ms). In Fig. 13 the occupant by 44% and when the trigger time is delayed with 40 ms, kinematics are presented at the collisions time of 100 and the acceleration increases even further by 144%. To 200 ms for the situations mentioned. evaluate the injury potential in the similar way for the driver, HIC was calculated and presented in Fig. 15. The HIC values are very low in this case, the maximum value being 11 when the airbag was delayed. In Fig. 19 the injury potential is presented in regards to the AIS scale.

Fig. 13. Passenger occupant kinematics at 100 ms and 200 ms Fig. 15. The rate of occurrence of AIS-1 type lesions of the collision when the airbag trigger time varied. depending on the airbag deployment times (passenger).

t can be seen that hen the airba and seatbelt are used Based on the AIS scale, the injury potential is very low the occupant is ell protected hen onl the airba is set (AIS-1) with the procent of 0.5% when the seatbelt and with no delay, the occupant impact the airbag when it’s airbag are present and increases a bit, to 3.67% when the copletel inlated ith the dela o s at s delay of the airbag was 40 ms. These results show that tie the airba orce hits the occupant but has lesser airbag delay times does increase the injury potential for eect than the driver due to the act that the distance both the driver and passenger, but the passenger has a beteen the head and the instruent panel is reater than lesser chance of injury. in the case o the driver the steerin heel is closer to the Further simulations were carried out to study the head n i the head acceleration coparison is delay in triggering the seat belt pretensioner. Using the presented same impact configuration as in the previous analysis, it was intended to use only the seatbelt and varying the lag time when triggering it. The values for the delay times were: 0 ms, 10 ms, 20 ms and 30 ms. In Fig. 16 the occupant's movement is presented for the related study.

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obtained. In this case, the increase of acceleration was of only 3.67% witch is considered negligible. The results of the seatbelt pretensioning delay study showed that there were no major differences in head Fig. 16. The kinematics of the occupant according to the delay acceleration values due to the fact that the seat belt secures times when the pretensioner is triggered. the occupant well in the seat regardless of the pretensioning system. From the point of view of the occupant's behavior, small differences were found in all situations except for the 20 and 30 ms times where the movement was identical. The References comparative analysis of head acceleration is shown in Fig. 1. Oţăt, ni ib 1;67(1), 17. 2. Oţăt, umitru, Oţăt, n , 823, , 3. httpswwwnhtsagoeuipmentairbags, 4. ceely r, orab, ais and egyi, , 121(4) , 5. ure, oretruno and aeron, n Proceedings: International Technical Conference on the Enhanced Safety of Vehicles 2001, , 6. oganel, and oica, n IOP Conference Series: Materials Science and Engineering, 252(1) , Fig. 17. Head acceleration comparison for different delay times 7. endall, , of the seatbelt pretentioner. 8. httpwwwleomanscommanguidehtml, From the analysis of the obtained data, it was noted the accessed, existence of small value differences for the 4 analysed 9. cenry, ead nury riterion and the , situations, thus concluding that the delay of the pretensioning system does not have a massive impact on 10. ppinger, un, anda, aner, the degree of injury of the occupant. haewpong and altese, , 11. ang, oon, im, hoi, n 5 Conclusions Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Following the study regarding the influence of airbag Engineering 229(7 , deployment delay on the occupant injury potential, the 12. ramer, 74(10), following conclusions were drawn. It has been found that by increasing the delay of the airbag deployment time in the event of a frontal impact, 13. httpwwwbiomeccanicaorensecomcriteridi the probability of injury to the occupant's head increases alutaionedeltraumacranicohtml, by up to 46%. Reducing the distance between the 14. ances, umaresan, roadhead and occupant's head and the / steering wheel when eiss, n Proceedings of the 2003 Summer the airbag ignites would result in a force expansion of the Bioengineering Conference, gas that is transmitted to the occupant’s head generating 15. rieder, and umar, n ASME 2007 Summer an extra acceleration and also throws back the occupant Bioengineering Conference, , increasing the injury potential due to the impact between 16. atentechni, , the head and headrest. Thus, an increase in injury probability of 8% was observed in the 0 ms delay of the 17. O. Oţăt, astraete and V. Oţăt, n Proceedings airbag deployment, while a 100 ms delay resulted in a of the European Automotive Congress EAEC-ESFA 54% increase in the head acceleration value. So the role 2015, , of the airbag is reversed, it no longer has the role of 18. rusca, enea, oica and arulescu, n cushioning the collision, but to generate injuries. 2nd WSEAS Intrenational Conference on In the case of the passenger, similar results were Multivariate Analysis and its Application in Science obtained, although a lower overall injury risk was and Engineering MAASE09,

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