Numerical Dolly Rollover Evaluation Using a Damping-Harmonic System with a Low Back Booster to Reduce Injuries in a Six-Year-Old Child
, Mario Alberto Grave-Capistrán 2, Elliot Alonso Alcántara-Arreola 2, Carlos Alberto Espinoza-Garcés 2 and Christopher René Torres-SanMiguel 2,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript aims to test mechanical coupling with a low back booster in a 6-year-old child during a dolly rollover test. The reviewer thinks it is worthy of investigation. The reviewer has just a few comments:
1. A variety of test scenarios are required considering different speeds, vehicle types, etc. to make a solid conclusion about the mechanical coupling with a LBB.
2. In the current scenario, the child is located on the right side. Would the result be different if the child's location differs?
Comments on the Quality of English LanguageSome awkward expressions can be improved.
Lines 35-36: "such poor roads, human factors, and sudden vehicle breakdowns". Replace it with "such poorly designed and maintained roads, human errors, vehicle breakdowns"
Author Response
REPLY TO REVIEWERS
Ms. Ref. No.: safety-2658100
Title: Numerical evaluation of mechanical coupling with a low back booster in a 6-year-old child during a dolly rollover test
Journal: Safety
Date of reply: 16/12/2023
Author for correspondence: Christopher René Torres San Miguel
Email address: ctorress@ipn.mx
We thank the reviewers for their valuable remarks.
Please find below the replies to the reviewers' comments.
Reviewer 1
- A variety of test scenarios are required considering different speeds, vehicle types, etc. to make a solid conclusion about the mechanical coupling with a LBB.
Reply: We thank your valuable comment. Unfortunately, we cannot conduct new numerical simulations because our workstation is not able to perform this kind of simulation in a brief period. We spent about seven days to achieve the current rollover test. However, the numerical rollover was performed under normative according to FMVSS 208 for this motor vehicle crash. Additionally, according to Rivara et al [1] "the risk of death was not statistically different for children involved in crashes in SUVs compared to passenger vehicles." in the article, Rivara established a speed interval where the rollover is more common, resulting in the speed selected is within the highest probability range. We explained, in accordance with your recommendation in the section "Discussion," the possibility of performing more simulations in a work in progress, including more crash scenarios.
[1] Rivara, F.P. Injuries and Death of Children in Rollover Motor Vehicle Crashes in the United States. Injury Prevention 2003, 9, 76–80, doi:10.1136/ip.9.1.76.In the current scenario, the child is located on the right side. Would the result be different if the child's location differs?
Reply: We appreciate your observation; we decided on the right rear seat position because it is the most common position selected by parents in day-to-day life. It is essential to mention that the CRS with mechanical coupling in the middle or left position is going to be performed, considering if the child is positioned on the far side or near side according to the roll direction. This consideration will be treated for a more detailed article in a posterior work.
Comments on the Quality of English Language
Reply: We thank your valuable comment. We have improved the redaction, and we have rewritten some paragraphs for better comprehension. The corrections are marked with yellow highlighting.
Reviewer 2 Report
Comments and Suggestions for Authors“Stay safe and well !”
Thank you for giving me the opportunity to review this wonderful manuscript. I was interested in this paper, which it was assessed quantitatively the performance of the machanical coupling with LBB (Low Back Booster) in the context of a dolly rollover crash test. Also, it was very interested in the results which were revealed differences in kinematic behiviour and injury patterns.
Major Comments:
No comments. I think this paper has a good research design. I think that the fact that the main author and his research team reported various previous research results on the numerical evaluation of low back boosters for children and infants may have had a positive impact on this paper.
Minor Comments:
Although I am pleased that the study was well designed, I think that comparing the results of this study with the main author's previous research results is somewhat limited. I hope you try to compare the results of this study with another studies by other researchers. I think that it would make the main author’s points more logical.
Author Response
REPLY TO REVIEWERS
Ms. Ref. No.: safety-2658100
Title: Numerical evaluation of mechanical coupling with a low back booster in a 6-year-old child during a dolly rollover test
Journal: Safety
Date of reply: 16/12/2023
Author for correspondence: Christopher René Torres San Miguel
Email address: ctorress@ipn.mx
We thank the reviewers for their valuable remarks.
Please find below the replies to the reviewers' comments.
Reviewer 2
Although I am pleased that the study was well designed, I think that comparing the results of this study with the main author's previous research results is somewhat limited. I hope you try to compare the results of this study with another studies by other researchers. I think that it would make the main author's points more logical.
Reply: We fully agree with your comment. Through a comparison with other authors, the research acquired a more robust validation. We searched the literature for a similar motor vehicle crash where a Child participates in a rollover crash, but unfortunately, we did not find a representative case where the child is involved. However, the injury values reported are within the limits established in the FMVSS 208. Thus, the research guarantees that the case studies are applicable.
Reviewer 3 Report
Comments and Suggestions for AuthorsDetailed questions to the authors:
line 45 - please use official name of R66 regulation and please make another check of manuscript against other typos (there are at least two more).
line 56 - instead of (or besides) self-citations please cite original, widely recognized sources. Taking into account vast bibliography in this topic, it would be good to add a few more references.
line 62-71 - please rephrase this passage, as it seems inconsistent at the moment. It contains contradictory information. If you say that none of CRS reduce or prevent injuries during rollover, please support this statement with the research results.
line 106 and below - please explain if the rear seat was modelled by you or it was part of the Toyota FEM model from NCAC. It is not clearly formulated. Please provide more detailed information about "unidimensional" and "bidimensional" elements used in the FE models. There is about 50 different formulations of "bidimensional" elements in LS-Dyna. Which of them were used and why? How exactly anchorage of seatbelts was modelled. Did slipring element were used? Did you apply pretension? How the model of Hybrid III was obtained? Was is developed internally or it was acquired? Is there any description of this model available?
line 154 and below - please provide more information about constitutive modeling. Again, there is well above 100 different material models in LS-Dyna. Which were used and where. Graphics showing application of different materials together with tables where material models and corresponding parameters is present could be a better way to explain adopted constitutive modelling. Please describe also the kind of contact procedure and contact parameters used in the model. Coefficients of friction are just two of many and they are not necessarily the most important one. Please provide graphics where boundary and initial conditions will be summarized.
line 203 - does numerical model in the reference can be directly compared with the FE model presented in the article? Does the same modeling techniques and parameters were used? It is not stated clearly in the text.
Figure 5 - please refer to the fact that some parts of the dummy go beyond the outline of the vehicle (500 ms and later). Compared to the full size test (dummy located in the car) this fact changes kinematics of the dummy. How this affect comparison with NHTSA criteria later in the article?
A general note on the results section: additional results should be presented to confirm the validity of the numerical model: energy balance, lack of penetration at contact interfaces, contact forces due to pre-tensioning of safety belts, etc. Does stress in the coupling interface is low enough? The energy dissipated by the coupling mechanism should also be evaluated and discussed. As it was mentioned earlier in the introductory section, the energy dissipated by the coupling mechanism is the main principle of its operation.
line 274 - if the phenomena of seatbelt sliding is that important, corresponding contact modelling in this pair should be discussed. It should be clear from the article that seatbelt slippage can really be related to the kinematics/dynamics of the simulated phenomena, and not due to the numerical modeling techniques used.
Author Response
REPLY TO REVIEWERS
Ms. Ref. No.: safety-2658100
Title: Numerical evaluation of mechanical coupling with a low back booster in a 6-year-old child during a dolly rollover test
Journal: Safety
Date of reply: 16/12/2023
Author for correspondence: Christopher René Torres San Miguel
Email address: ctorress@ipn.mx
We thank the reviewers for their valuable remarks.
Please find below the replies to the reviewers' comments.
Reviewer 4
4.1.- line 45 - please use official name of R66 regulation and please make another check of manuscript against other typos (there are at least two more).
Reply: We appreciate your observations. We correctly modified the regulation's official name that you mentioned in the manuscript.
The Dolly rollover test is performed under some regulations according to the country. Among the most common are the Federal Motor Vehicle Safety Standard (FMVSS) 208, CMVSS 220 (Rollover protection), the Regulation No. 111 of the Economic Commission for Europe of the United Nations (UN/ECE) for categories vehicles N and O regarding rollover stability and the UN-ECE regulation 66.
4.2.- line 56 - instead of (or besides) self-citations please cite original, widely recognized sources. Taking into account vast bibliography in this topic, it would be good to add a few more references.
Reply: We fully agree with your comment. We reviewed the bibliography, modified the mistake committed, and added some recognized bibliographic sources.
In Motor vehicle crashes, children are the most exposed to high injury probability due to the anthropometric impact location and vehicle type, and another factor is the unsafe practice of being seated without following any safety regulations [1–5].
4.3.- line 62-71 - please rephrase this passage, as it seems inconsistent at the moment. It contains contradictory information. If you say that none of CRS reduce or prevent injuries during rollover, please support this statement with the research results.
Reply: We fully appreciate your comment, so we rewrite the phrase.
Enhancing children's safety is challenging due to the wide range of children's ages, sizes, and different body properties. A Child Restraint System (CRS) offers a way to increase child safety during crashes. CRS available in the market cannot isolate a significant amount of energy produced during the rollover crash. Some CRS devices have incorporated improvements such as springs or shock absorber mechanics to dissipate energy through the sliding movement coupling systems, while others include new materials to absorb the impact energy [6–12]. The mechanical coupling with the LBB system is a significant proposal to reduce the number of child injuries or fatalities in a variety of crash scenarios. Currently, the proposal model has been tested under frontal and rollover crash scenarios.
4.4.- line 106 and below - please explain if the rear seat was modelled by you or it was part of the Toyota FEM model from NCAC. It is not clearly formulated. Please provide more detailed information about "unidimensional" and "bidimensional" elements used in the FE models. There is about 50 different formulations of "bidimensional" elements in LS-Dyna. Which of them were used and why? How exactly anchorage of seatbelts was modelled. Did slipring element were used? Did you apply pretension? How the model of Hybrid III was obtained? Was is developed internally or it was acquired? Is there any description of this model available?
Reply: We thank your valuable comment. We modified these observations in the section "Methods and materials."
A numerical rollover crash test (figure 1) is established to obtain the acceleration pulses that are implemented in the simplified mechanical coupling test (figure 2). The catapult is designed with the dimensions specified in the FMVSS 208. The tetrahedral mesh applied consists of 10,650 nodes, 6,750 elements, and a mesh size of 8 mm. Table 1 shows the parameters for the numerical rollover developed.
Table 1.- Numerical rollover test conditions.
|
Test Speed |
13.34 m/s |
|
Time interval |
1-1000 ms |
|
Car |
Toyota Yaris 2010 |
|
Car weight |
1100 kg |
|
Roll direction |
Right passenger side |
Figure 1.- Dolly rollover test
Figure 2.- Acceleration pulses obtained from the numerical rollover test.
The simplified case for the mechanical coupling performance in a rollover test is composed of the vehicle's back seat, a 3-point seatbelt, a LBB, the F.E. model of Hybrid III 6yo provided under license from LS DYNA ® (Figure 3), and the acceleration pulses to represent the vehicle crash behavior during the rollover. The model components mesh specifications are summarized in Table 2.
Figure 3.- Dolly Rollover assembly test setup.
The vehicle's back seat was designed with the accurate dimensions of the Toyota Yaris 2010®. The rear seat consists of 3 parts: steel support, the padding, and the polypropylene connector between the seat backrest and the seat cushion. All the parts were meshed with a tetrahedral formulation for the seat backrest consisting of 30,852 nodes, 92,118 elements, 183,855 nodes, and 827,071 elements for a seat cushion.
The 3-point seatbelt is designed in LS-DYNA® software using unidimensional and bidimensional elements. The seat belt dimensions are 47 mm in width by 1 mm in thickness. For unidimensional (1D) elements, the LS DYNA default configuration for the safety belt was assigned with a mass pull of [13]. For bidimensional elements, the tetrahedral mesh size is 8mm, with 667 nodes and 1168 elements. A shell section with a Belytschko-Tsay element formulation with a thickness of 1 mm was selected. Nylon was set with a density of , Young's modulus of 5.333 GPa, yield strength of 0.08 GPa, and Poisson's ratio of 0.3. Loading and unloading curves to represent the axial force as a function of the seat belt were implemented [14]. No retractor and slipping were applied for the case study.
The LBB model is based on the Evenflo® model for groups 2 to 3 (adjustable 3-11 years or 18-49.8 kg). It consists of a support material, in this case, polypropylene, and the LBB cushioning with foam DAX 55.
Table. 2- Mesh components properties.
|
Component |
Subcomponent |
Mesh Formulation |
Type elements |
Element formulation |
Nodes |
Elements |
|
LBB |
Support material |
Tetrahedral |
Solid |
Constant stress solid element |
21,156 |
92,028 |
|
LBB cushioning |
Tetrahedral |
Solid |
Constant stress solid element |
3,510 |
10,028 |
|
|
Seatbelt |
Lap belt and shoulder belt |
Tetrahedral |
Shell (Bidimensional) |
Belytschko-Tsay |
667 |
1168 |
|
Seat |
Steel support |
Tetrahedral |
Solid |
Constant stress solid element |
30,852 |
92,118 |
|
Seat cushioning |
Tetrahedral |
Solid |
Constant stress solid element |
183,855 |
827,071 |
|
|
Mechanical Coupling |
Cartesian mechanism box |
Hexahedral |
Solid |
Constant stress solid element |
|
|
|
Suspension box |
Hexahedral |
Solid |
Constant stress solid element |
240,294 |
|
4.5.- line 154 and below - please provide more information about constitutive modeling. Again, there is well above 100 different material models in LS-Dyna. Which were used and where. Graphics showing application of different materials together with tables where material models and corresponding parameters is present could be a better way to explain adopted constitutive modelling. Please describe also the kind of contact procedure and contact parameters used in the model. Coefficients of friction are just two of many and they are not necessarily the most important one. Please provide graphics where boundary and initial conditions will be summarized.
Reply: We fully appreciate your valuable comment. We applied your recommendation for a better explanation of the constitutive model and its mechanical properties in the section "Methods and materials". The contact procedure selected was AUTOMATIC SURFACE TO SURFACE because it is a low-cost time strategy to represent the interaction between two parts or components that is widely used in numerical motor vehicle crashes. We modified these observations in the section "Methods and Materials as follows:
Numerical dolly rollover crash test analysis was performed using LS-Dyna®. The mechanical properties were established according to the component and subsystem, and they are located in Table 2. The rear seat support, the rigid rods ISOFIX, the support guide, and the catapult are assigned with steel. Polypropylene mechanical properties for LBB and connector. Foam DAX 55 was selected for seat, and LBB cushioning; the constitutive model assigned is shown in Table 3. The material was selected to avoid an indirect effect (structural materials are more stiffness) during the interaction child-seat.
J1, J2, C, and T parts from the Cartesian mechanism box and suspension box use the mechanical properties of aluminum 1100-H14. M1 and M2 parts implemented structural ASTM A36 steel. Table 4 shows the spring and damper characteristics based on commercial catalogs. Concrete was considered as a rigid body, and a rigid constitutive material modeled it since only the vehicle's structure is of interest and the concrete generation or propagation of microcracks is not significant for the rollover test.
Table. 3- Material properties.
|
Material |
Constitutive model selected in LS-DYNA |
Density |
Young's modulus (GPa) |
Yield Strength (GPa) |
Poisson's ratio |
|
Steel |
RIGID (020) |
210 |
0.6 |
0.3 |
|
|
Polypropylene [15] |
ELASTIC (001) |
1.35 |
0.036 |
0.312 |
|
|
Foam DAX 55 [16] |
LOW_DENSITY_FOAM (057) |
--- |
0.31 |
||
|
Aluminum 1100-H14 [17] |
ELASTIC (001) |
70 |
0.095 |
0.33 |
|
|
ASTM A36 steel [18–20] |
PLASTIC_KINEMATIC (003) |
200 |
0.25 |
0.32 |
|
|
Concrete[18] |
RIGID (020) |
29 |
--- |
0.15 |
Constraints are set on the nodal elements for the rear seat and the LBB to behave as a single body. The contacts established are shown in Table 5. The CONTACT_AUTOMATIC_SURFACE_TO_SURFACE card was selected to eliminate possible penetrations between the components during the interaction with a segment-based penalty formulation.
A static friction coefficient of 0.3 and dynamic friction of 0.2 between the rear seat, the LBB, and the Hybrid III 6yo are defined for the contacts [21]. The static and dynamic coefficients between the vehicle and the concrete are both 0.85 [22].
Table 5.- Contacts between components assigned for the test.
|
Subsystem 1 |
Subsystem 2 |
LS DYNA CARD selected |
|
Tires |
Catapult |
CONTACT_AUTOMATIC SURFACE TO SURFACE |
|
Vehicle |
Floor |
CONTACT_AUTOMATIC SURFACE TO SURFACE |
|
Rear seat |
Child dummy |
CONTACT_AUTOMATIC SURFACE TO SURFACE |
|
Seatbelt |
Child dummy |
CONTACT_AUTOMATIC SURFACE TO SURFACE |
|
Mechanical coupling |
Child dummy |
CONTACT_AUTOMATIC SURFACE TO SURFACE |
|
Mechanical coupling |
Rear seat |
CONTACT_AUTOMATIC SURFACE TO SURFACE |
4.6.- line 203 - does numerical model in the reference can be directly compared with the FE model presented in the article? Does the same modeling techniques and parameters were used? It is not stated clearly in the text.
Reply: We thank your valuable comment. We modified these observations in the section "Discussion."
The seat, the Hybrid III six-years-old, and the LBB are modeled with the same techniques and parameters used by Cruz et al. [23]. The mechanical coupling-LBB and the LBB-ISOFIX rollover test considered no slipping and retractor for the seatbelt.
4.7.- Figure 5 - please refer to the fact that some parts of the dummy go beyond the outline of the vehicle (500 ms and later). Compared to the full size test (dummy located in the car) this fact changes kinematics of the dummy. How this affect comparison with NHTSA criteria later in the article?
Reply: We thank your valuable comment. Your observation is correct; the simplified case study reproduces the kinematics quite well, but the simulations present some irregularities, such as the possibility of the upper limbs' interaction with the vehicle's structure. The incorporation of a lateral door and the roof will make the model more realistic.
In accordance with the article's objective, only some injury criteria are essential to acquire; for the current test, we are focusing on the head, neck, and thorax. For future work, we will perform in full size to study the kinematics and be able to compare it with the simplified rollover test study. Additionally, we searched the NHTSA databases, and there is no similar rollover study that includes a children's dummy. Evaluate full rollover crash can not result in less than 10 days due to the more elements and nodes used.
4.8.- A general note on the results section: additional results should be presented to confirm the validity of the numerical model: energy balance, lack of penetration at contact interfaces, contact forces due to pre-tensioning of safety belts, etc. Does stress in the coupling interface is low enough? The energy dissipated by the coupling mechanism should also be evaluated and discussed. As it was mentioned earlier in the introductory section, the energy dissipated by the coupling mechanism is the main principle of its operation.
Reply: We appreciate your valuable comment. We want to follow your recommendation for a more robust explanation of our numerical test. However, our LS-DYNA license expired on November 31st, and we will be able to add the required additional parameters after our license is reactivated on January 20th. Some advice that you recommended was discussed in the article as follows:
"Constraints are set on the nodal elements for the rear seat and the LBB to behave as a single body. The contacts established are shown in Table 4. The CONTACT_AUTOMATIC_SURFACE_TO_SURFACE card was selected to eliminate possible penetrations between the components during the interaction with a segment-based penalty formulation".
"the mechanical coupling-LBB and the LBB-ISOFIX rollover test considered no slipping and retractor for the seatbelt".
4.9.- line 274 - if the phenomena of seatbelt sliding is that important, corresponding contact modelling in this pair should be discussed. It should be clear from the article that seatbelt slippage can really be related to the kinematics/dynamics of the simulated phenomena, and not due to the numerical modeling techniques used.
Reply: We thank your valuable comment. We modified these observations in the section "Discussion."
The increment in the neck and thorax values occurred as the seatbelt slid across the child's shoulder during lateral movement along the z-axis and vertical movement along the y-axis. Children's Restraint System effectiveness is related to several factors. The actual mechanical coupling configuration used in the numerical rollover crash test doesn't allow a correct interaction of the vehicle's seatbelt with the thorax because the mechanical coupling increases the height of the child, so the shoulder belt is positioned over the sternum, which increases the slipping seat belt risk to the neck and significant injury severity. This behavior is shown during the kinematics results obtained by the rollover test. An alternative way to reduce child injuries is the mechanical coupling embedded into the rear seat. With this modification, a shoulder belt positioning may result in an optimal belt geometry setting.
Author Response File: 
Author Response.docx
Reviewer 4 Report
Comments and Suggestions for AuthorsThe paper investigated injuries sustained by a six-year-old child in a rollover crash involving a mechanical coupling with a Low Back Booster (LBB). The mechanical coupling adhered to the R129 standard, allowing adjustments for different age groups using Child Restraint Systems. The study has the potential to contribute valuable insights to child safety in road traffic accidents. The experimental design provides sufficient details for reader comprehension. I recommend that the author elaborate further on the study's limitations, including details about the types of testing vehicles used, and provide recommendations for future research.
Author Response
REPLY TO REVIEWERS
Ms. Ref. No.: safety-2658100
Title: Numerical evaluation of mechanical coupling with a low back booster in a 6-year-old child during a dolly rollover test
Journal: Safety
Date of reply: 16/04/2024
Author for correspondence: Christopher René Torres San Miguel
Email address: ctorress@ipn.mx
We thank the reviewers for their valuable remarks.
Please find below the replies to the reviewers' comments.
Reviewer 5
- The paper investigated injuries sustained by a six-year-old child in a rollover crash involving a mechanical coupling with a Low Back Booster (LBB). The mechanical coupling adhered to the R129 standard, allowing adjustments for different age groups using Child Restraint Systems. The study has the potential to contribute valuable insights to child safety in road traffic accidents. The experimental design provides sufficient details for reader comprehension. I recommend that the author elaborate further on the study's limitations, including details about the types of testing vehicles used, and provide recommendations for future research.
Reply: We thank your valuable comment. We have improved the discussion section according to the recommendation, and we have added a paragraph to explain the limitations of the numerical evaluation for better comprehension. The corrections are marked with yellow highlighting.
"Some limitations included that the test was performed only in a sedan vehicle (Yaris 2010) and a six-year-old child, additional test needed to be performed with different vehicles such as SUVs or trucks and with another child ATD as a three-year-old to assess the feasibility of its use with different age groups of children according to the UN/ECE R129."
Author Response File: 
Author Response.pdf
Reviewer 5 Report
Comments and Suggestions for AuthorsComments for authors of the paper:
Numerical evaluation of mechanical coupling with a low back 2 booster in a 6-year-old child during a dolly rollover test.
Ivan Lenin Cruz-Jaramillo, Jose Luis Torres-Ariza, Mario Alberto Grave-Capistran, Elliot Alonso Alcántara Arreola, Carlos Alberto Espinoza-Garces and Christopher Rene Torres-SanMiguel
Major issues:
Regarding material properties and modelling, in the manuscript, there are only linear elastic properties. Considering that we are dealing with road accidents and with different materials like polymeric foams, were all the materials modelled as linear elastic?
The number of elements vs the number of nodes seem odd, please confirm it. Also, tetrahedral elements are solid, not shell type. For shell elements the mystery of more nodes than elements is even stranger.
Finally, is there any form of validation? How reliable is this model?
Minor issues:
Units in figure 2
Comments on the Quality of English LanguageMinor editing of English language required
Author Response
REPLY TO REVIEWERS
Ms. Ref. No.: safety-2658100
Title: Numerical evaluation of mechanical coupling with a low back booster in a 6-year-old child during a dolly rollover test
Journal: Safety
Date of reply: 16/04/2024
Author for correspondence: Christopher René Torres San Miguel
Email address: ctorress@ipn.mx
We thank the reviewers for their valuable remarks.
Please find below the replies to the reviewers' comments.
Reviewer 6
Major issues:
- Regarding material properties and modelling, in the manuscript, there are only linear elastic properties. Considering that we are dealing with road accidents and with different materials like polymeric foams, were all the materials modelled as linear elastic?
We thank your valuable comment. We address these observations in the section "Materials and Methods". We provided more information about the constitutive material for the components. Some components were modeled with a linear elastic consideration. Still, other components, such as the foam for the rear seat, were modeled as a viscoelastic material, and the structure was modeled with an elastic-plastic behavior applying steel A36, as follows:
Numerical dolly rollover crash test analysis was performed using LS-Dyna®. The mechanical properties were established according to the component and subsystem and are located in Table 2. The rear seat support, the rigid rods ISOFIX, the support guide, and the catapult are assigned with steel. Polypropylene mechanical properties for LBB and connector. Foam DAX 55 was selected for seat and LBB cushioning; the constitutive model set is shown in Table 3. The material was selected to avoid an indirect effect (structural materials are more stiffness) during the interaction child-seat.
J1, J2, C, and T parts from the Cartesian mechanism box and suspension box were modeled with the mechanical properties of aluminum 1100-H14. M1 and M2 parts implemented the structural ASTM A36 steel. Table 4 shows the spring and damper characteristics based on commercial catalogs. Concrete from the floor was considered a rigid body. A rigid constitutive material was assigned to it since only the vehicle's structure is of interest. The concrete generation or propagation of microcracks is not significant for the rollover test.
Table. 3- Material properties.
|
Material |
Constitutive model selected in LS-DYNA |
Density |
Young's modulus (GPa) |
Yield Strength (GPa) |
Poisson's ratio |
|
Steel |
RIGID (020) |
210 |
0.6 |
0.3 |
|
|
Polypropylene [30] |
ELASTIC (001) |
1.35 |
0.036 |
0.312 |
|
|
Foam DAX 55 [31] |
LOW_DENSITY_FOAM (057) |
--- |
0.31 |
||
|
Aluminum 1100-H14 [32] |
ELASTIC (001) |
70 |
0.095 |
0.33 |
|
|
ASTM A36 steel [33–35] |
PLASTIC_KINEMATIC (003) |
200 |
0.25 |
0.32 |
|
|
Concrete[33] |
RIGID (020) |
29 |
--- |
0.15 |
- The number of elements vs the number of nodes seem odd, please confirm it. Also, tetrahedral elements are solid, not shell type. For shell elements the mystery of more nodes than elements is even stranger.
Reply: We appreciate your valuable comment. We modified and rechecked these observations in the section "Materials and Methods."
Table. 2- Mesh components properties.
|
Component |
Subcomponent |
Mesh Formulation |
Type elements |
Element formulation |
Nodes |
Elements |
|
LBB |
Support material |
Tetrahedral |
Solid |
Constant stress solid element |
21,156 |
92,028 |
|
LBB cushioning |
Tetrahedral |
Solid |
Constant stress solid element |
3,510 |
10,028 |
|
|
Seatbelt |
Lap belt and shoulder belt |
Linear Triangle |
Shell (Bidimensional) |
Belytschko-Tsay |
667 |
1168 |
|
Seat |
Steel support |
Tetrahedral |
Solid |
Constant stress solid element |
30,852 |
92,118 |
|
Seat cushioning |
Tetrahedral |
Solid |
Constant stress solid element |
183,855 |
827,071 |
|
|
Mechanical Coupling |
Cartesian mechanism box |
Hexahedral |
Solid |
Constant stress solid element |
106,147 |
69,199 |
|
Suspension box |
Hexahedral |
Solid |
Constant stress solid element |
240,294 |
208,335 |
- Finally, is there any form of validation? How reliable is this model?
Reply: We thank your valuable comment. The injury values obtained by the HDS-LBB were compared with the values injury values by another configuration denominated LBB-ISOFIX by Cruz et al [25] to assess the effectiveness of the model proposed
Minor issues:
- Units in figure 2
Reply: We thank your valuable comment. Your observation is correct, we decided to represent the units employed in the numerical test following the consistency units selected in LS-DYNA: mm, ms, kg and kN. Figure 2 has been updated according to your recommendations.
Author Response File: Author Response.pdf
Reviewer 6 Report
Comments and Suggestions for AuthorsReview of numerical evaluation of mechanical coupling with low back booster in 6 year old child during a dolly rollover test
· I am receiving this paper as v2 having never reviewed v1 and with highlighted changes throughout. I don’t see questions or responses from the first review. I don’t know why changes were made or in response to what..
· This is a case report, the title makes it look like it is test or regulatory focused, my view is the title should distinguish it as a case report. It is examining injuries. What was the funding source for the work, and any potential CoI, i.e. were the authors doing it as consulting or purely research work? This should be reported.
o Ok upon reading it is not a case report, and significant confusion is introduced by talking about ‘injuries’ vs ‘metrics’ and ‘injury risk’ as appropriate. This must be revisited throughout.
· A dolly is introduced, but in the abstract not clear what it is, what is the ‘dolly’ being referred to.
· The abstract refers to ‘injury rates’ but I think means to say ‘injury risks’.
· The authors need to be very clear about what is experimental and what is computational in their work, the abstract is confusing as to which is which.
· In the abstract it is not clear what the ‘mechanical proposal’ is.
· It is not clear what ‘injuries sustained remained below NHTSA established threshold’. Risks remained below? Are there real injuries as the first sentence indicates?
· Line 64 I think this should say ‘injured body regions’?
· Line 67 I don’t know where the statement comes from ‘crs in the market cannot isolate’… it is clear they can protect the occupant if coupled well with the vehicle and the occupant and well designed.
· Line 74 ‘harmonic oscillator?’
· Line 79 ‘principal factors to reach? ‘guarantee is under normative’? I am sorry I do not understand.
· The authors have reported in Figure 2 a remarkably small amount of temporal information with a sample rate of around 5 to 10 ms. Should report at least 1 kHz data, perhaps use nodout, there is a lot more information there.
· It looks like someone has requested more information about the numerical test setup, but perhaps more information about the version # of the models used could be employed.
· It looks like the authors have developed and proposed a shock absorbing box. To show the efficacy of their design, they should compare the output to the results from a test without the box in place. That is the key here and should be done. The abstract could also address this. Why is it called a ‘suspension’ box vs another name? what is being ‘suspended’?
o Wait I see they are doing this. Perhaps show a test matrix up front showing that with and without is going to be tested. A test matrix is typically a simple table.
· Line 213… so the mechanics of the vehicle frame are modeled but not the ground, correct? Rigid ground, deforming frame? What was the deformation of the frame, and what was the acceleration time history of the seat?
· Line 249 I don’t think ‘careful ‘is the right word here. Perhaps ‘highest’ or ‘most severe’?
· It would be valuable to report risk from the hic and nij, because differences there can be vanishingly small when considered in the context of risk.
· Some consistent terminology around ‘with or without’ ‘mechanical coupling’ would be helpful. It feels like there is a countermeasure here, the new device between the booster and the car, and with/ without that would be helpful terminology. Both are mechanically coupled… and I’d inherently assume that the better coupling to vehicle frame would give lower loads and accels.
· A careful analysis and presentation of flail or movement envelope is important here. Sometimes, higher loads but better coupling are preferred to more occupant movement b/c of the possibility for subsequent interactions, etc.
· Could the seat of the vehicle deform?
· So line 308, ‘increase in injuries’ should shift to ‘injury risk’. Come to think of it, the results really need a table of peak injury risks in the two scenarios for quick and simple comparison. This would facilitate writing the discussion also.
· A lot is driven by shoulder belt positioning, but when a child is strapped in a vehicle often there is an option to adjust the shoulder belt location depending on height. This exists in rear and front of many vehicles. How was that height chosen and did the authors consider putting shoulder belt height a consistent location relative to shoulder rather than allowing the device under the booster to change it??
· Again in 317 ‘significant injury severity’ is used again but this needs an AIS or other information / /qualifier – what risk to what risk? Or, AIS 2 to 3? Else I must recommend just to speak about relative risk and not go further than this using words like ‘significant’.
· Line 322 – again a 72% ‘increase in thorax injury’ may be a 72 % increase in metric, which might be 1% increase in risk depending on where on the risk curves. Further evidence the whole paper needs to be recast in this light.
Overall a decent job. Some clarifying info is added. The authors should revisit the paper, significant English language editing is needed, adjust language to focus on ‘metrics’ from the dummy as appropriate and ‘injury risk’ from risk curves derived from the metrics, but never ‘injury.’ This is very important. Also, please abandon use of ‘mechanical coupling’, as all conditions are mechanically coupled, and discuss perhaps as a ‘countermeasure’ for between the seat and the booster. Last, add more detailed accel trace definition (1 ms vs 5 or 10), a table of injury metrics and risks by body region. Also, add plots of the accel and rotational velocity of the rigid portion of the seat of the buck (vehicle model), and the booster seat with and without the ‘countermeasure’ as this is the main input driving the results / output.
Overall, authors can get there but need a significant amount of effort. Paper needs a new title and abstract. Thanks.
Comments on the Quality of English LanguageThe authors should revisit the paper, significant English language editing is needed, adjust language to focus on ‘metrics’ from the dummy as appropriate and ‘injury risk’ from risk curves derived from the metrics, but never ‘injury.’ This is very important. Also, please abandon use of ‘mechanical coupling’, as all conditions are mechanically coupled, and discuss perhaps as a ‘countermeasure’ for between the seat and the booster.
Author Response
REPLY TO REVIEWERS Ms. Ref. No.: safety-2658100 Title: Numerical evaluation of mechanical coupling with a low back booster in a 6-year-old child during a dolly rollover test Journal: Safety Date of reply: 19/04/2024 Author for correspondence: Christopher René Torres San Miguel Email address: ctorress@ipn.mx We thank the reviewers for their valuable remarks. Please find below the replies to the reviewers' comments. Reviewer 7 Review of numerical evaluation of mechanical coupling with low back booster in 6 year old child during a dolly rollover test I am receiving this paper as v2 having never reviewed v1 and with highlighted changes throughout. I don't see questions or responses from the first review. I don't know why changes were made or in response to what. This is a case report, the title makes it look like it is test or regulatory focused, my view is the title should distinguish it as a case report. It is examining injuries. What was the funding source for the work, and any potential CoI, i.e. were the authors doing it as consulting or purely research work? This should be reported. Reply: We thank your valuable comment. Our article is purely research work. Ok upon reading it is not a case report, and significant confusion is introduced by talking about 'injuries' vs 'metrics' and 'injury risk' as appropriate. This must be revisited throughout. Reply: We thank your valuable comment. Your observation is correct, but previous reviewers recommended changing injury risk to injury metrics. A dolly is introduced, but in the abstract not clear what it is, what is the 'dolly' being referred to. We thank your valuable comment. We defined the dolly rollover test in our research. The abstract refers to 'injury rates' but I think means to say 'injury risks'. Reply: We thank your valuable comment. Your observation is correct, but previous reviewers recommended to change injury risk to injury metrics. The authors need to be very clear about what is experimental and what is computational in their work, the abstract is confusing as to which is which. In the abstract it is not clear what the 'mechanical proposal' is. Reply: We appreciated your valuable observation; we have rewritten the abstract: Abstract: This study examined injuries sustained by a six-year-old child dummy in a numerical dolly rollover crash using a Toyota Yaris 2010. A harmonic dynamic system (HDS) composed of spring, dampers, and masses with a Low Back Booster (LBB) is denominated as HDS-LBB model. The HDS-LBB was designed to allow damping movements along three Cartesian axes (X, Y, Z) to reduce the energy transferred to the child by a motor vehicle accident and avoid a high injury risk. The HDS-LBB incorporates springs into the vertical axis to decrease the vertical movement during the rollover. The numerical analysis was conducted using LS-Dyna® software for 1 second, and the boundary conditions were set by the Federal Motor Vehicle Safety Standard (FMVSS) 213 for child restraint recommendations and the FMVSS 208 for a dolly rollover procedure. Data on head and thorax decelerations, neck flexion-extension, and thoracic deflection were acquired at a rate of 2 milliseconds. The injury values obtained by the HDS-LBB were compared with the values injury values by another configuration denominated LBB-ISOFIX by Cruz et al. [25] to assess the effectiveness of the model proposed. The results show a higher rate of injury value in the neck and thorax because of seatbelt displacement across the child's shoulder. Nevertheless, despite these seatbelt displacements, the injuries sustained remained below the Injury Assessment Reference Values (IARVS). It is not clear what 'injuries sustained remained below NHTSA established threshold'. Risks remained below? Are there real injuries as the first sentence indicates? Reply: We thank your valuable comment. We have added NHTSA IARVS and others IARVS from an European report in table 6 and this was discussed: Table 6 Injury reference values according to different reports. Case Injury criteria (injury metrics) HIC15NijNeck force (Fz)Neck moment (My)"Chest deflectionThorax acceleration ------(N)(Nm)(mm)(G) HDS-LBB 144 404.41 26.86 14 58 LBB-ISOFIX 156 0.443 TE 5 25 NHTSA threshold [41] 700 1 2800 T 2800 C 93 F 39 E 40 60 EEVC [42] UN R94 986 --- 1,824 94 42 --- AIS>-3 20% LR1,083---2,10111833--- AIS>-3 50% LR1,389---2,30414349--- T- Neck Tension Force; C- Neck Compression Force; F- Neck moment in flexion; F- Neck moment in extension Table 6 shows the IARV values established by different regulators and the values obtained. In both scenarios, the LBB-ISOFIX and the HDS-LBB remained below the IARVs established by the NHTSA and the European Enhanced Vehicle-Safety Committee (EEVC) [41,42]. According to the results, the head and thorax do not present the possibility of suffering a higher injury risk than AIS 3. The injury risk reported has some limitations because these were reported from data obtained by frontal accidents, and IARVs do not exist for a rollover crash. However, body regions such as the head and thorax can be evaluated with these IARVs due to HIC15 is measured in X, Y, Z axes, and chest deflection can be measured in the direction of interest. Nij was not considered in this case because the values reported by the HDS-LBB show small values since during the rollover, the head-neck region has a non-linear trajectory, so the forces applied to the neck do not only have an extension and flexion movement. The forces and moments are in several axes. Thorax acceleration represents an AIS injury risk lower than AIS 3 as a result of NHTSA IARVS limits. Line 64 I think this should say 'injured body regions'? Reply: We thank your valuable comment. We changed this text according to your recommendations: "The highest probability of injured body regions is the head [15]" Line 67 I don't know where the statement comes from 'crs in the market cannot isolate'… it is clear they can protect the occupant if coupled well with the vehicle and the occupant and well designed. Reply: We appreciate your valuable comment. We rewrote the paragraphs as follows: "The several CRSs available in the market follow the FMVSS 213 or the European UN/ECE R66 or R129 standard. However, these standards evaluate frontal or lateral protection, and the CRS's performance has not been evaluated during the rollover crash, so the manufacturers do not prove the effectiveness of CRS during rollover." Line 74' harmonic oscillator?' Reply: We appreciate your valuable comment. We explained that the harmonic oscillator, due to the proposal, has the behavior of restoring its equilibrium position after it is displaced. The system designed applied a restoring force proportional to the displacement experimented in the X-axis and Y-axis due to the springs and dampers. Line 79' principal factors to reach? 'guarantee is under normative'? I am sorry I do not understand. Reply: We appreciate your valuable comment. We rewrote the paragraph for better comprehension as follows: The proposal system is designed on the principles of a Harmonic Oscillator and follows the requirements established in ISO 13216 (International Organization Standard). Springs (provide restoring force) and dampers (reduce the system velocity) are used through the X, Y, and Z axes to absorb kinetic energy and protect the child's body during the motor vehicle crash [24]. The use of ISO 13216 provides the dimension and general requirements for anchoring the CRS. It establishes that the M-coupling was designed appropriately following the standard and does not represent a model with unsafe areas that can represent a higher injury risk due to possible interactions with the vehicle interior. The authors have reported in Figure 2 a remarkably small amount of temporal information with a sample rate of around 5 to 10 ms. Should report at least 1 kHz data, perhaps use nodout, there is a lot more information there. We thank your valuable comment. We changed the graphic according to your recommendation. It looks like someone has requested more information about the numerical test setup, but perhaps more information about the version # of the models used could be employed. We thank your valuable comment. We added more information about the models employed. The simplified case for the mechanical coupling performance in a rollover test is composed of the vehicle's back seat, a 3-point seatbelt, a LBB, the F.E. model of Hybrid III 6yo provided under license (Annual license) from LS DYNA ® version LSTC_H3_6YO.150202_V0.104.BETA (Figure 3), and the acceleration pulses to represent the vehicle crash behavior during the rollover. The mesh specifications of the model components are summarized in Table 2. From LS-DYNA ® the Prepost version 4.8 was used with the solver version 12. It looks like the authors have developed and proposed a shock absorbing box. To show the efficacy of their design, they should compare the output to the results from a test without the box in place. That is the key here and should be done. The abstract could also address this. Why is it called a 'suspension' box vs another name? what is being 'suspended'? Wait I see they are doing this. Perhaps show a test matrix up front showing that with and without is going to be tested. A test matrix is typically a simple table. Reply: We thank your valuable comment. We added a comparative matrix as your recommendation for a better explanation. Table 6 Injury reference values according to different reports. Case Injury criteria (injury metrics) HIC15NijNeck force (Fz)Neck moment (My)"Chest deflectionThorax acceleration ------(N)(Nm)(mm)(G) HDS-LBB 144 404.41 26.86 14 58 LBB-ISOFIX 156 0.443 TE 5 25 NHTSA threshold [41] 700 1 2800 T 2800 C 93 F 39 E 40 60 EEVC [42] UN R94 986 --- 1,824 94 42 --- AIS>-3 20% LR1,083---2,10111833--- AIS>-3 50% LR1,389---2,30414349--- T- Neck Tension Force; C- Neck Compression Force; F- Neck moment in flexion; F- Neck moment in extension Line 213… so the mechanics of the vehicle frame are modeled but not the ground, correct? Rigid ground, deforming frame? What was the deformation of the frame, and what was the acceleration time history of the seat? Reply: We thank your valuable comment. The rigid material was used for the ground since it was not relevant to obtain the damage generated on it. The rigid material allows the transmission of energy towards the vehicle. For the frame and the roof, piecewise linear plasticity materials type was used. The deformation in the roof and side frames is shown in the figure and did not generate inclusion of the structure towards the interior of the passenger compartment, so the infant did not hit against any area of the frame of the vehicle structure. The resulting accelerations are the same for the vehicle seat of both analyses with and without the device, so only one graph of this is shown. By not implementing only the Lbb, a reduction of the acceleration transmitted by the vehicle seat is generated. By implementing the device, this decreases notably because the device dissipates the energy transmitted by the shock absorbers and springs of the system in the 3 Cartesian axes, depending on the direction in which the deceleration is generated, reducing the decelerations that will be transmitted to the infant. However, the seat belt, when anchored with the vehicle seat, carries the decelerations of the vehicle seat. The Lbb, when mounted on the device lower, causes higher deceleration peaks in the head and thorax by this variation, so it is necessary to analyze the device with a system such as CRS where the belt carries the same decelerations as the device, allowing to examine the damage to the infant when both the seat and the belt restraint move simultaneously. The following graphic shows the global acceleration in Lbb, seat, and HDS. Line 249 I don't think 'careful 'is the right word here. Perhaps 'highest' or 'most severe'? Reply: We thank your valuable comment. We changed the word careful to severe: "The most severe accelerations start at 400 ms when the vehicle begins to rotate". It would be valuable to report risk from the hic and nij, because differences there can be vanishingly small when considered in the context of risk. Reply: We thank your valuable comment. We added a comparative matrix as your recommendation for a better explanation. Table 6 Injury reference values according to different reports. Case Injury criteria (injury metrics) HIC15NijNeck force (Fz)Neck moment (My)"Chest deflectionThorax acceleration ------(N)(Nm)(mm)(G) HDS-LBB 144 404.41 26.86 14 58 LBB-ISOFIX 156 0.443 TE 5 25 NHTSA threshold [41] 700 1 2800 T 2800 C 93 F 39 E 40 60 EEVC [42] UN R94 986 --- 1,824 94 42 --- AIS>-3 20% LR1,083---2,10111833--- AIS>-3 50% LR1,389---2,30414349--- T- Neck Tension Force; C- Neck Compression Force; F- Neck moment in flexion; F- Neck moment in extension Some consistent terminology around 'with or without' 'mechanical coupling' would be helpful. It feels like there is a countermeasure here, the new device between the booster and the car, and with/ without that would be helpful terminology. Both are mechanically coupled… and I'd inherently assume that the better coupling to vehicle frame would give lower loads and accels. Reply: We thank your valuable comment. We rewrote the paragraph in the result section for a better comprehension. Also, we have mentioned along the article with the abbreviations for every model. "The time applied for the rollover test was 1 s, with data recording every 1 ms. A comparative kinematics behavior study is carried out between the numerical test by Cruz et al. [25], which considered a six-year-old child positioned in a rear seat with a Low Back Booster (LBB) and anchored with an ISOFIX system (LBB-ISOFIX) and the proposal HDS coupling with a LBB denominated as "HDS-LBB". Both studies start at "t=0 ms" and end at "t=1000 ms" . Figure 6 shows the kinematics difference between both numerical rollover test". A careful analysis and presentation of flail or movement envelope is important here. Sometimes, higher loads but better coupling are preferred to more occupant movement b/c of the possibility for subsequent interactions, etc. Could the seat of the vehicle deform? Reply: We appreciated your valuable observation; the seat of the vehicle can be deformed due to this being modeled by applying a viscoelastic constitutive model. So line 308, 'increase in injuries' should shift to 'injury risk'. Come to think of it, the results really need a table of peak injury risks in the two scenarios for quick and simple comparison. This would facilitate writing the discussion also. Reply: We appreciated your valuable observation. A more detailed paragraph was written in the discussion section as follows. Table 6 Injury reference values according to different reports. Case Injury criteria (injury metrics) HIC15NijNeck force (Fz)Neck moment (My)"Chest deflectionThorax acceleration ------(N)(Nm)(mm)(G) HDS-LBB 144 404.41 26.86 14 58 LBB-ISOFIX 156 0.443 TE 5 25 NHTSA threshold [41] 700 1 2800 T 2800 C 93 F 39 E 40 60 EEVC [42] UN R94 986 --- 1,824 94 42 --- AIS>-3 20% LR1,083---2,10111833--- AIS>-3 50% LR1,389---2,30414349--- T- Neck Tension Force; C- Neck Compression Force; F- Neck moment in flexion; F- Neck moment in extension Table 6 shows the IARVs values established by different regulators and the values obtained. In both scenarios, the LBB-ISOFIX and the HDS-LBB remained below the IARVs established by NHTSA and the European Enhanced Vehicle-Safety Committee (EEVC) [41,42]. According to the results the head and thorax do not present the possibility of suffering a higher injury risk than AIS 3. The injury risk reported have some limitations because these were reported from data obtained by frontal accidents, and IARVs does not exist for a rollover crash. However, body regions such as head and thorax can be evaluated with this IARVS due to HIC15 is measured into X, Y, Z axis and chest deflection can be measured in the direction of interest. Nij was not considered in this case due to the values reported by the HDS-LBB shows small values due to during the rollover the head-neck region have a non-linear trajectory, so the forces applied to the neck does not only have extension and flexion movement and the forces and moments are in several axis. Thorax acceleration represents an AIS injury risk lower of AIS 3 as a result of NHTSA IARVS limits. The increment in the neck and thorax values occurred as the seatbelt slid across the child's shoulder during lateral movement along the z-axis and vertical movement along the y-axis producing that the effectiveness of the CRS can be affected. The HDS-LBB configuration used in the numerical rollover crash test does not allow a correct interaction of the vehicle's seatbelt with the thorax because the seatbelt height can be corrected in the Toyota Yaris Sedan 2010, so the numerical model looks to imitate this behavior. The height increment by the HDS-LBB originate that the shoulder belt can be positioned over the sternum increasing the slipping seat belt risk to the neck and increasing the injury risk for some body regions. This behavior is shown during the kinematics results obtained by the rollover test. An alternative way to reduce child injuries is the HDS-LBBB was embedded into the rear seat. With this modification, shoulder belt positioning may result in an optimal belt geometry setting. A lot is driven by shoulder belt positioning, but when a child is strapped in a vehicle often there is an option to adjust the shoulder belt location depending on height. This exists in rear and front of many vehicles. How was that height chosen and did the authors consider putting shoulder belt height a consistent location relative to shoulder rather than allowing the device under the booster to change it?? Reply: We appreciated your valuable observation. We have explained this observation according to your recommendations in the discussion section. "The increment in the neck and thorax values occurred as the seatbelt slid across the child's shoulder during lateral movement along the z-axis and vertical movement along the y-axis producing that the effectiveness of the CRS can be affected. The HDS-LBB configuration used in the numerical rollover crash test does not allow a correct interaction of the vehicle's seatbelt with the thorax because the seatbelt height can be corrected in the Toyota Yaris Sedan 2010, so the numerical model looks to imitate this behavior. The height increment by the HDS-LBB originate that the shoulder belt can be positioned over the sternum increasing the slipping seat belt risk to the neck and increasing the injury risk for some body regions. This behavior is shown during the kinematics results obtained by the rollover test. An alternative way to reduce child injuries is the HDS-LBBB was embedded into the rear seat. With this modification, shoulder belt positioning may result in an optimal belt geometry setting". Again in 317' significant injury severity' is used again but this needs an AIS or other information / /qualifier – what risk to what risk? Or, AIS 2 to 3? Else I must recommend just to speak about relative risk and not go further than this using words like 'significant'. Reply: We appreciated your valuable observation. We have explained before this observation according to your recommendations. A more detailed paragraph was written in the section discussion. Line 322 – again a 72% 'increase in thorax injury' may be a 72 % increase in metric, which might be 1% increase in risk depending on where on the risk curves. Further evidence the whole paper needs to be recast in this light. Reply: We appreciated your valuable observation. We have rewritten the paragraphs, as follows: The HDS-LBB model resulted in a 72% increase in the peak value of the thorax injury, the Clip3m measured a value of 55.12 G's, while the deflection reached 16 mm. Overall a decent job. Some clarifying info is added. The authors should revisit the paper, significant English language editing is needed, adjust language to focus on 'metrics' from the dummy as appropriate and 'injury risk' from risk curves derived from the metrics, but never 'injury.' This is very important. Also, please abandon use of 'mechanical coupling', as all conditions are mechanically coupled, and discuss perhaps as a 'countermeasure' for between the seat and the booster. Last, add more detailed accel trace definition (1 ms vs 5 or 10), a table of injury metrics and risks by body region. Also, add plots of the accel and rotational velocity of the rigid portion of the seat of the buck (vehicle model), and the booster seat with and without the 'countermeasure' as this is the main input driving the results / output. Reply: We appreciated your valuable observation. We have rewritten some paragraphs according to your previous observations. Overall, authors can get there but need a significant amount of effort. Paper needs a new title and abstract. Thanks. Reply: We appreciated your valuable observation; we have rewritten the title: Numerical dolly rollover evaluation using a damping-harmonic system with a Low Back Booster to reduce injuries in a six-year-old child.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe reviewer agrees to accept the manuscript.
Comments on the Quality of English LanguageAcceptable
Author Response
The authors thank the reviewers for encouraging the quality of our research presented.
Reviewer 2 Report
Comments and Suggestions for AuthorsYou worked hard to complete this paper, reflecting the opinions of the reviewers.
Congratulations :D
Author Response
The authors thank the reviewers for encouraging the quality of our research presented.
Reviewer 3 Report
Comments and Suggestions for AuthorsThank you for your thorough answers.
Author Response
The authors thank the reviewers for encouraging the quality of our research presented.
Reviewer 4 Report
Comments and Suggestions for AuthorsMy comment has been addressed
Author Response
Thanks
Reviewer 5 Report
Comments and Suggestions for Authorsall remarks addressed
Author Response
Thanks
Reviewer 6 Report
Comments and Suggestions for Authors· I still see only one occurrence of injury metrics in the paper and many occurrences of injury risk particularly in abstract. Change risk to metrics then if the other reviewer has asked for this.
· We show some longer duration things up to one minute but the graphic the new one with seat, lbb, HDS only goes out to 75 ms and it looks like there could still be some increased acceleration. And, the 50 g’s is quite high, perhaps add some head or torso g’s to this for comparison?
· The authors did not answer this question
o A careful analysis and presentation of flail or movement envelope is important here. Sometimes, higher loads but better coupling are preferred to more occupant movement b/c of the possibility for subsequent interactions, etc.
· I don’t understand the modeling of the seat as ‘viscoelastic’ or rate dependent. Elastic or elastic plastic would be enough to allow deformation. Please say bit more about the mechanics of the seat and the motion / deformation of the seat.
· Table 6 needs units where appropriate. Be sure all tables of values with units include them. Table 6 also shows ‘injury metrics’ as ‘injury criteria’ the two are different. Are they metrics, which can be compared to IARVs. I don’t think they are criteria. I also suggested putting risks, but the authors have not calculated risks. Where possible, it would be helpful.
o I see now they have some metrics, and some iarv / criteria. Please distinguish the metrics vs the iarv / criteria by row titling or rework the table to be clearer vs just putting 2 diff titles at the top (injury criteria ( injury metrics ) ) for clarity.
· I like the new title. Thanks.
Comments on the Quality of English LanguageA little better. a lot of effort here to address concerns.
Author Response
REPLY TO REVIEWERS
Ms. Ref. No.: safety-2658100
Title: Numerical evaluation of mechanical coupling with a low back booster in a 6-year-old child during a dolly rollover test
Journal: Safety
Date of reply: 06/06/2024
Author for correspondence: Christopher René Torres San Miguel
Email address: ctorress@ipn.mx
We thank the reviewers for their valuable remarks.
Please find below the replies to the reviewers' comments.
Reply V3
- I still see only one occurrence of injury metrics in the paper and many occurrences of injury risk particularly in abstract. Change risk to metrics then if the other reviewer has asked for this.
Reply: We thank your valuable comment. We have changed the terms according to the reviewer’s recommendation.
- We show some longer duration things up to one minute but the graphic the new one with seat, lbb, HDS only goes out to 75 ms and it looks like there could still be some increased acceleration. And, the 50 g’s is quite high, perhaps add some head or torso g’s to this for comparison?
Reply: We appreciate your observation. We have checked the graphs, and the time interval is 1000 ms for all the graphs.
- I don’t understand the modeling of the seat as ‘viscoelastic’ or rate dependent. Elastic or elastic plastic would be enough to allow deformation. Please say bit more about the mechanics of the seat and the motion / deformation of the seat.
Reply: We appreciate your observation. We applied a viscoelastic constitutive material MAT_LOW_FOAM (57) for the seat due to the seat having padding that is a foam, and according to other articles, the LS DYNA card “MAT (57)” is used to solve this material. The seat was modeled in three parts: The seatback, the cushion, and the supports. Some paragraphs were added for a better explanation.
“The vehicle's back seat was designed with the accurate dimensions of the Toyota Yaris 2010®. The rear seat consists of 3 parts: steel support, the padding, and the polypropylene connector between the seat backrest and the seat cushion”.
“The rear seat vehicle has a contact CONTACT_AUTOMATIC_SURFACE_TO_SURFACE between the seat back and seat cushion structure with the padding (foam). The polypropylene connector connects the seatback with the seat cushion using a Constrained Nodal Rigid Body (CNRB)”
Table 6 needs units where appropriate. Be sure all tables of values with units include them. Table 6 also shows ‘injury metrics’ as ‘injury criteria’ the two are different. Are they metrics, which can be compared to IARVs. I don’t think they are criteria. I also suggested putting risks, but the authors have not calculated risks. Where possible, it would be helpful.
Reply: We appreciate your observation. We have checked Table 6, and we have changed the structure for better comprehension.
Table 6 Comparative Injury Assessment Reference Values (IARVs) according to different reports and the values obtained in the numerical simulations.
|
|
|
Injury metrics |
IARVS |
||||
|
|
Units |
Values from the numerical simulations performed |
NHTSA threshold [41] |
EEVC [42] |
|||
|
HDS-LBB |
LBB-ISOFIX |
UN R94 |
AIS>-3 20% LR |
AIS>-3 50% LR |
|||
|
HIC15 |
--- |
144 |
156 |
700 |
986 |
1,083 |
1,389 |
|
Nij |
--- |
0.833 TE |
0.443 - TE 0.660 - TF 0.510 - CE 0.594 - CF |
1 |
--- |
--- |
--- |
|
Neck force (Fz) |
N |
404.41T |
|
2800 T 2800 C |
1,824 |
2,101 |
2,304 |
|
Neck moment (My)" |
Nm |
26.86E |
|
93 F 39 E |
94 |
118 |
143 |
|
Chest deflection |
mm |
14 |
5 |
40 |
42 |
33 |
49 |
|
Thorax acceleration |
G’s |
58 |
25 |
60 |
--- |
--- |
--- |
T- Neck Tension Force; C- Neck Compression Force; F- Neck moment in flexion; F- Neck moment in extension
- I see now they have some metrics, and some iarv / criteria. Please distinguish the metrics vs the iarv / criteria by row titling or rework the table to be clearer vs just putting 2 different titles at the top (injury criteria ( injury metrics ) ) for clarity.
Reply: We appreciate your observation. We have modified Table 6 according to your observations.
- I like the new title.
Author Response File: Author Response.pdf
Round 3
Reviewer 6 Report
Comments and Suggestions for AuthorsThanks for responding to my comments.
Comments on the Quality of English LanguageAcceptable.
