The article presents a new solution of child-resistant systems to improve the safety of children transported in motor vehicles subjected to a side impact during a vehicle crash. The proposed concept works by means of implementation of an energy dissipation mechanism acting between a child restraint system anchorage and a restraint system seat. The effectiveness of the proposed system is evaluated using numerical analyses of a simplified basic model as well as more complex mechanical design of the mechanism. The latter is analyzed as a part of the child restraint system (CRS) together with a deformable model of an anthropomorphic test device of Q3 series. Tests outcomes clearly show a positive effect of application of the proposed energy dissipation system resulting in reduction of head and thorax acceleration and influencing a lower factor (index) of the head injury criteria. The presented solution shows that there is still a room for improvement of young passengers safety. . . . . Keywords Crashworthiness Crash simulation Child-resistant systems Finite element analysis Side impact 1 Introduction that are still required to pay a special attention: constant mis- use of a CRS [6–8] and the number of injuries due to a side In 2005, costs associated with motor vehicle-related fatal and impact, or near-side impact collision [9, 10]. non-fatal injuries among 0–14-year-old children amounted to Fortunately, there are some organizations involved in child over 3.6 billion USD in the USA . The statistics show that safety which have undertaken the discussed problem. The motor vehicle crashes are the leading cause of death among most significant one is Australia’sChild Restraint children both in the USA and Canada [2, 3]. The same fact Evaluation Program (CREP) that started back at the end of applies to the European Region . Despite a mandatory use the twentieth century. It proved that systematic research can of various child restraint systems (CRSs) and the existence of reveal a vital set of guidelines for both rule makers and CRS such regulations as UN/ECE Regulation 44, this situation has makers . Although the CREP program have been imple- not changed over the last few years . Researchers investi- mented for some time, the Australian experience and method- gating the problem highlight the two most important issues ology have only recently received enough attention in the USA  with a provision proposed by the National Highway Traffic Safety Administration (NHTSA) . * Jerzy Malachowski In the European Union, recognition of the abovementioned firstname.lastname@example.org problems led to preparation and implementation of a new standard: UN/ECE Regulation 129 . According to the Department of Mechanics and Applied Computer Science, Faculty of commission, one of the major improvements provided by this Mechanical Engineering, Military University of Technology, Gen. S. document (compared to the predecessor, Regulation 44) is Kaliskiego 2 str., Warsaw, Poland better lateral impact protection achieved by means of a man- Department of Mechanical Engineering, Politecnico di Milano, via datory side impact test . La Masa 1, 20156 Milan, Italy For example, many reports point to the seatbelts misuse as Idap Technology, Jagiellonska 55 str., Warsaw, Poland one of the important issues affecting safety [7, 16, 17]; how- Automotive Industry Institute, Jagiellonska 55 str., Warsaw, Poland ever, presently, the only solution available on the market ad- dressing this problem is the active tensioning system (ATS) Department of Engineering Sciences, University of Agder, Gimlemoen 25A, Kristiansand, Norway introduced by Britax-Roemer. A side impact is also widely recognized as a very severe type of crash [15, 18, 19]. What University of Florence, Piazza San Marco 4, Florence, Italy 3926 Int J Adv Manuf Technol (2018) 97:3925–3935 proposition of a modification in the CRS design concept. A comparison of the basic (unmodified) CRS and the modified CRS concept are provided proving that the energy dissipation mechanism, with a principle of operation based on plastic deformation of a wire bent, reduces forces acting on a child body. In this study, finite element analyses (FEA), which have already proven their effectiveness in investigating many crash Fig. 1 Simple representation of CRS base and CRS seat scenarios, were adopted [10, 22–24]. Only numerical studies of the CRS concept with dissipation system are presented is alarming though is that so far the only “answer” for the new without any validation data. This is due to the fact that the requirements given by CRS producers is to add a portion of FE CRS model applied in the simulations was used to verify energy absorbing foam (a form of additional structural solu- the proposed concept of the energy dissipation system. It is tion) in the sideway zones of the CRS headrest, while the main also the end-result of one of the stages during the realization of concept of seat design remains still the same for years. Perhaps the project INNOTECH-K1/IN2/59/182901/NCBR/12 and the best illustration of the situation in research on CRS design other projects covering the CRS modeling and simulation. is the crash test conducted in 2009 in Sweden. It showed that Based on the results obtained from projects, the prototype, Toyota Yaris, model year 2008 and Volvo 945, model year which is much more complicated and has a completely differ- 1996, despite a 12-year difference, offer the same level of ent design, is being manufactured. Therefore, in this research, child protection, which is unacceptable in the case of adults a validation of two different CRSs is missing the target. (especially drivers) protection systems [20, 21]. The abovementioned crash test showed yet another issue related to the insufficient attention put on development of more safe CRS. It occurred that a normalized chest load of a 2 The concept of the new energy dissipation child dummy seated in Toyota was two times higher compared system to an adult driver dummy. Moreover, Kuppa et al. showed the results of a crash test leading to similar conclusion. The key concept of the currently produced CRS with ISOFIX In this paper, the authors present an innovative concept of a anchorage is similar to the idea of non-stretching seatbelts. new, ISOFIX-mounted, CRS design. It is aimed at improving During an impact event, a child starts to decelerate together child protection during a lateral impact crash scenario by a Fig. 2 Acceleration histories in the bodies representing CRS base and CRS seat Int J Adv Manuf Technol (2018) 97:3925–3935 3927 Fig. 3 CRS with energy dissipating elements with a whole car body due to the fixed connection between the CRS as multibody system consisted of two bodies connected car and CRS during the impact. This enables to benefit from each other with a kind of interface element—the concept has energy dissipation occurring in crumple zones and keeping the been already investigated in  and used to analyze vehicle child away from a contact with inner parts of a car (at least in a crashes [26–28]. In the presented case, the elements that con- frontal impact scenario). Staying with an adult seatbelts simil- trol the aforementioned relative movement of the base and the itude, the new idea can be seen as introduction of their more seat will be introduced. Figure 1 presents the simplest repre- sophisticated version. sentation of such a system. It is assumed that the connector Typical CRS for group 1 (the group designation according with inelastic properties placed between two bodies is used as to old Regulation 44) consists of a base, which is connected to an element responsible for energy dissipation. the car body via ISOFIX anchorage and a seat, mounted on the The influence of the connector was investigated using a base, where a child actually sits. The most fundamental as- simple model shown in Fig. 1. The left body of the model, sumption behind the new concept is that during impact, CRS with prescribed mass m = 1000 kg, represents the car body seat will be permitted to move independently to the base. with base of the CRS connected to the car using ISOFIX. The Therefore, the seat with a child and the CRS base can be right body, with prescribed mass m = 20 kg, represents a seat treated as separate bodies. This allows thinking about the of the CRS with a child sitting on it. The energy dissipation Fig. 4 a Test stand with a model of energy dissipation device and schematics of the device. b Typical force-displacement characteristic of energy dissipation device (the area under the curve represents the energy absorbed by the proposed mechanism in the test) (right) 3928 Int J Adv Manuf Technol (2018) 97:3925–3935 Table 1 Material properties with associated parts of the CRS  Density ρ (kg/m ) Young modulus E (GPa) Poisson ratio Yield stress Re (MPa) Tangent modulus ν (−) E (MPa) tan Steel 7850 210 0.3 400 1000 Polyamide 1130 3 0.3 85 100 Polypropylene (Tiplen) 900 1.3 0.45 7 (Table 2) Headrest foam 60 0.00025 –– (Table 3) Polystyrene foam 27 0.019 0.3 –– device was modeled using an inelastic spring element linking used energy-absorbing elements due their excellent perfor- two bodies. The connector had an elastic—perfectly plastic mance under axial loading, small initial impact force, or a long characteristic—an equivalent of the Hookean substance con- deformation process. Such structures have been extensively nected in a series with the Saint-Venant’s substance. In fact, studied by many researches [29–31]. On the other hand, cel- this model represents a principle of operation of the proposed lular elements with features such as outstanding properties in energy dissipation mechanisms. efficient energy absorption and excellent mechanical damping The prescribed velocity in time v(t) was applied to the body properties have been also investigated [32, 33]. Cutting dam- representing a base of CRS, as shown in Fig. 1. The velocity age of metal sheets, which shows that the work of friction profile history was obtained using integration of an accelera- forces and plastic deformation of the cut sheet can be used tion history taken from a side impact crash test of two cars. in a solution to dissipate energy, is also worth mentioning [34, Acceleration vs. time curves for the bodies representing 35]. “base” and “seat” are shown in Fig. 2. It can be seen that All the above-mentioned solutions were analyzed in terms introduction of an inelastic connector drastically reduces max- of possibilities for implementation in the CRS prototype. The imum acceleration of the second body. It can be stated that, modified CRS had to satisfy applicable standards. This meant somehow, a filter was applied for the acceleration history of that ISOFIX mount had to remain in place and CRS dimen- CRS attached to the car body. sions as well as total weight could not exceed certain values. Taken all above into consideration, it was decided to use a far more different solution: wire bent on a roll. In this case, the energy should be dissipated via plastic deformation of the 3 Implementation of the energy dissipation introduced dissipation element and, to a lesser extent, via solution into a real-world CRS plastic deformation of CRS parts. The schematics of the final layout incorporating the new idea are shown in Fig. 3.As the The basic principle of the dissipation systems is to transform basic model described above, in the new CRS design, two kinetic energy into plastic deformation and fracture of a struc- parts can be distinguished. The first part contains the ture. Metallic thin-walled structures are one of the most widely Fig. 5 a Test stand. b Stress-strain relationship for wide (1) and narrow (2) seatbelts Int J Adv Manuf Technol (2018) 97:3925–3935 3929 Table 2 Nonlinear characteristic of the plastic region of Tiplen (based of a child seat and its validation based on the test results. An on experimental data)  effect of modeling techniques and dynamic material behavior on the obtained results were also discussed. A methodology Effective plastic strains Effective stress (MPa) presented in the article was also used to develop FE model of 0.00 7.0 the CRS with a new concept of a dissipation mechanism. 0.019 17.0 Proper representation of kinematics of the structure re- 0.045 20.5 quired definition of 24 contact pairs. In fact, obtainment of 0.070 22.0 proper behavior of a contact algorithm was the most time- 0.150 23.5 consuming part of the numerical model development. In all analyses, the interaction between all parts of the model was simulated using the contact procedure implementing the pen- alty method. The principal of this method can be described as ISOFIX anchorage and, thus, it is rigidly connected to the car placing normal interface springs between all nodes that belong body. The second part, where a child is actually seated, can to a penetrating surface (“slave surface”) and their normal move to the sides relative to the first one. The movement is projections on the surface that is penetrated (“master surface”) controlled by elements responsible for energy dissipation. . The characteristic of a dissipation element was taken from The material properties for steel, polyamide, polypropylene experimental tests that were conducted at the Automotive (tiplen), seatbelts, and foams were acquired experimentally Industry Institute (see Fig. 4). In the FE analyses, the dissipa- and description of each test can be found in Baranowski et tion elements were modeled using springs elements with a al.  and Muszynski . Material characteristics and prop- nonlinear force-displacement characteristic applied from the erties associated with different parts of the CRS are listed in experiment performed. Table 1. During numerical modeling of a CRS, attention should be focused on the proper modeling of seatbelts. First, mechanical properties of the belt material were described based on the 4 Numerical simulation of improved CRS results obtained from uniaxial tension tests carried out for two different kinds of seatbelts . Seatbelts stress-strain The crashworthiness of a new design was virtually tested characteristics obtained from the experimental tests are pre- using the commercial code LS-Dyna . The software is sented in Fig. 5a. The data were entered into the selected based on the finite element method (FEM) and uses an explicit constitutive model that provides a correct description of the scheme for time integration of a system of equations describ- belt material behavior during analyses. The numerical model ing a motion. The FE model of the CRS consists of 146,599 of a harness system consisted of 2D elements, described using elements and 118,974 nodes. Most of the structure was a fabric constitutive model, combined with 1D elements modeled using four-node shell elements utilizing (seatbelt constitutive model). 2D seatbelt parts were finely Belytschko–Tsay formulation . A typical approach and meshed to accurately distribute contact forces between the all the necessary steps required to develop a correct FE model dummy and the belt itself. Slipping of the belts in the buckle of CRS can be found in Muszynski . The aforementioned was simulated using a special feature available in LS-Dyna paper presents detailed information on a numerical FE model code called “slipring.” No experimental data were available to match the friction parameters; therefore, a friction coefficient Table 3 Nonlinear characteristic of the headrest foam (based on experimental data)  of 0.2 was used (based on the recommendations of James K. Day from Livermore Software Technology Corporation this Volumetric strains Effective stress (kPa) value should usually be less than 0.3). The CRS was enriched with a Q3 ATD. An FE model of a 0.00 0 Q3 ATD represents a 3YO child weighting 14.5 kg. It consists 0.10 20 of 165 different parts. Fully deformable ATD models devel- 0.20 25 oped by Humanetics Innovative Solutions are recognized as 0.30 30 “standard” in crash test simulations. The company assures that 0.40 35 all numerical ATD models reproduce behavior of the ATDs 0.50 44 used in laboratory crash tests (Tables 2 and 3). 0.60 60 A general concept of the analysis was to perform a crash 0.70 112 test similar to the one described in UN/ECE Regulations 129, 0.80 275 however, without side wall imitating interior of a car. The 0.83 445 boundary conditions represent the situation when the child sits 3930 Int J Adv Manuf Technol (2018) 97:3925–3935 Fig. 6 FE model of CRS with child and applied boundary conditions on the far side of the impact (during such a scenario the CRS second model (test #2), the relative movement of the base and with the child moves toward the center of a car). Therefore, no seat was allowed and energy dissipating elements were acti- interaction with the vehicle body was assumed, and thus the vated. The second model can be seen as a design reproducing door was not included in the model. The investigation was the structural concept described in Section 2. possible by applying the deceleration curve compliant with Regulation 129 to the seat, backseat, and ISOFIX mounts. Additionally, the initial velocity of the whole CRS-ATD FE 5 Results and discussion model was defined as the maximum value of a curve (v = 6.775 m/s) according to the upper corridor curve defined in In Fig. 7, qualitative analysis is presented with the selected Regulation 129. Boundary conditions applied to the model are stage of the CRS with ATD FE model movement for both shown in Fig. 6. cases. The relative movement of the seat vs. the CRS base Numerical simulations were performed for two versions of can be clearly seen in the seat with the dissipation system. the CRS model. In the first one (test #1), the relative move- Also, noticeably smaller movement of the ATD’s head can ment between the base and seat was blocked. This model can be noticed. The main assumption of dissipation system oper- be assumed as a basic CRS, without any modifications. In the ation was that the energy should be dissipated via plastic Fig. 7 a Basic—standard CRS case. b CRS with energy dissipation mechanism during side impact simulation. The movement of the seat relative to the base can be noticed in (b) picture Int J Adv Manuf Technol (2018) 97:3925–3935 3931 Fig. 8 Internal energy graph of the CRS elements for both tests with the work of dissipation elements included deformation of the introduced dissipation element and to a of the CRS parts, including the work of dissipation elements lesser extent via plastic deformation of CRS parts. This is representing the steel wire. In test #1, a smaller amount of clearly confirmed in Fig. 8 showing an internal energy history energy was consumed by the CRS parts (max: 216 J), than Without dissipaon system With dissipaon system 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10 0,11 0,12 0,13 -100 Time [s] Fig. 9 Contact force between the ATD head and the CRS headrest in both tests H[ ead rest contact forceN] 3932 Int J Adv Manuf Technol (2018) 97:3925–3935 Without dissipaon system With dissipaon system 0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,09 0,10 0,11 0,12 0,13 Time [s] Fig. 10 Internal energy of the CRS headrest in both tests in test #2: max. 281 J. This is a result of a larger deformation contact force history between ATD’s head and the headrest is of the CRS parts and especially dissipation elements, the work presented. Due to the presence of dissipation system, the max- history of which is represented with a green line. In Fig. 9,a imum value of force acting on the ATD’s head is visibly Fig. 11 Resultant acceleration of the ATD’s head in both tests H[ ead rest internal energyJ] Int J Adv Manuf Technol (2018) 97:3925–3935 3933 Fig. 12 Resultant acceleration of the ATD’s thorax inbothtests smaller (test #2: 632 N), whereas in the basic CRS (test #1), #1: 58 g). From the obtained results, it can be concluded that the peak force is 761 N. It is also reflected by the fact that the in the side impact scenario, the presented system of energy headrest accumulated smaller amount of energy in test #2: dissipation is very effective. It is worth noticing that simula- 12 J comparing to 15 J in test #1 (Fig. 10). tions were conducted using Q3 ATD series. This series repre- Acceleration histories in ATD’s head for both cases are sents the most difficult case to protect a group of children. shown in Fig. 11. They clearly present that introduction of They are old enough to be transported in front-seated restraint an energy dissipating mechanism resulted in reduction of the systems; however, on the other hand, all the other bio- maximum acceleration value by 21% (form 38 to 30 g). One mechanical parameters of the body do not allow for imple- of the most popular injury index: the Head Injury Criteria mentation of seatbelts for adults. In Table 4, the maximum (HIC), given by (1), was calculated for both acceleration his- values of all discussed quantities are presented for a more tories based on the following formula: thorough analysis of the simulation results. From the end-user perspective, the introduced mechanism 2:5 makes CRS more complicated and heavier. On the other hand, HIC ¼ max ∫ atðÞdt ðÞ t −t ð1Þ 2 1 ðÞ t −t 2 1 improvement of a protection level compensates these draw- backs with a vengeance. where a(t) is the acceleration measured in head, t is the be- ginning of time interval, and t is the end of time interval. Table 4 Peak values of discussed quantities of two simulated cases The time interval for the HIC calculation presented below was 36 ms. According to NHCTSA, limiting the HIC limit CRS Head—CRS CRS Head res. Thorax res. value for this time interval is 1000 . As predicted, the HIC elements headrest headrest acceleration acceleration internal contact force internal value obtained for the case with the new energy absorbing energy energy system was smaller compared to the case of “basic” CRS. [J] [N] [J] [g] [g] The dropfrom173 g intest#1to100 g intest#2means a great improvement of head protection effectiveness by 42% Test 216 761 15 173 58 #- (see Fig. 11). Acceleration histories measured in the ATD’sthorax are Test 281 632 12 100 28 shown in Fig. 12. Again, introduction of dissipation system #- resulted in smaller peak acceleration values (test #2: 28 g, test 2 3934 Int J Adv Manuf Technol (2018) 97:3925–3935 Publisher’sNote Springer Nature remains neutral with regard to jurisdic- 6 Conclusions tional claims in published maps and institutional affiliations. Authors present the idea of a new system allowing for better protection of children transported in CRS during a side (lateral) References impact. In the first part, the basic concept of the solution is presented. A number of solutions was analyzed in terms of 1. Naumann RB, Dellinger AM, Zaloshnja E, Lawrence BA, Miller possibilities for implementation in the CRS prototype. It was TR (2005) Incidence and total lifetime costs of motor vehicle- decided to use a wire bent on a roll due to its simplicity and, at related fatal and nonfatal injury by road user type, united states. the same time, high efficiency. In this case, the energy is dissi- Traffic Inj Prev 11(4):353–360 2. National Highway Traffic Safety Administration (2014) Traffic pated via plastic deformation of the introduced dissipation ele- safety facts, U.S. department of Transportation, DOT HS 812 261 ment and to a lesser extent via plastic deformation of CRS parts. 3. Statistics Canada, major causes of death, Government of Canada, The numerical simulations reflecting a side impact proce- http://www.statcan.gc.ca dure described in UN/ECE Regulation 129 are described sub- 4. World Health Organization (2009) European status report on read safety. WHO Regional Office for Europe, Copenhagen sequently. In the FE analyses, the dissipation elements were 5. Arbogast KB (2014) A public health priority for only ten percent of modeled using springs elements with a nonlinear force- the car occupant population: why focus on children and how are displacement characteristic obtained from experimental tests. they different biomechanically? In: Proceedings of the International Detailed information on the material data and applied initial- IRCOBI Conference on the Biokinetics of Impact. Berlin, boundary conditions are provided. Finally, the results of simu- Germany, September 10–12 2014, 1–14. Available at: http://www. ircobi.org/wordpress/downloads/irc14/pdf_files/01.pdf lations comparing the classic CRS with a new solution are 6. Koppel S, Muir C, Budd L, Devlin A, Oxley J, Charlton J, presented. A comparison of obtained results shows a great po- Newstead S (2013) Parents’ attitudes, knowledge and behaviors tential behind the proposed energy dissipation system. The relating to safe child occupant travel. Accid Anal Prev 51:18–26 main assumption of dissipation system operation was con- 7. Skjerven-Martinsen M, Naess PA, Hansen TB, Staff T, Stray- Pedersen A (2013) Observational study of child restraining practice firmed in the internal energy history of the CRS parts. Due to on Norwegian high-speed roads: restraint misuse poses a major application of the dissipation elements, a larger amount of en- threat to child passenger safety. Accid Anal Prev 59:479–486 ergy was consumed. The peak acceleration values in the head 8. Jermakian JS, Klinich KD, Orton NR, Flannagan CAC, Manary andinthe thorax ofATDseatedin the newCRS were smaller MA, Malik LA, Narayanaswamy P (2014) Factors affecting tether than in case of ATD seated in the “basic” CRS. The same use and correct use in child restraint installations. J Saf Res 51:99– applies to the HIC value. What is also important, the presented 9. 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Available at: http://citeseerx.ist.psu.edu/viewdoc/ parameters” granted within the Mazowieckie Voivodeship ROP 7 “Smart download?doi=10.1.1.915.7651&rep=rep1&type=pdf Growth” PA 1.2 “Use of research and development activity in economy” 13. National Highway Traffic Safety Administration (2014) Notice of and the support of the Interdisciplinary Centre for Mathematical and Proposed Rulemaking: 49 CFR Part 571 Federal Motor Vehicle Computational Modeling (ICM) University of Warsaw under grant no Safety Standards; Child Restraint Systems— Side Impact GB65-19. This support is gratefully acknowledged. Protection, Docket No. NHTSA–2014–0012, RIN 2127–AK95 14. 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