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A rubberized impact absorbing pavement can reduce the head injury risk in vulnerable road users: a bicycle and a pedestrian accident case study
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.ORCID iD: 0000-0001-6923-4751
Department of Civil, Chemical, Environmental, and Materials Engineering, University of Bologna, Bologna, Italy.ORCID iD: 0000-0003-1565-1554
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Neuronic Engineering.ORCID iD: 0000-0002-0980-4051
Department of Civil, Chemical, Environmental, and Materials Engineering, University of Bologna, Bologna, Italy.ORCID iD: 0000-0003-1006-5935
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2022 (English)In: Traffic Injury Prevention, ISSN 1538-9588, E-ISSN 1538-957XArticle in journal (Refereed) Accepted
Abstract [en]

Objective: Vulnerable Road Users (VRU), including pedestrians and cyclists, are generally the leastprotected road users and are frequently missed in the planning process of preventive measures.Rubberized asphalt mixtures were originally developed as a possible environmentally friendly solutionto recycle the End-of-Life Tires while making the pavements more durable. The objective ofthe current study was to explore the effects of increasing the rubber content of the common rubberizedasphalt mixtures in reducing the head injuries risk for VRUs.Method: To achieve this purpose, four different sample series with 0, 14, 28, and 33 weight percentrubber in each were tested. A compressive test without permanent deformation and onewith failure were performed on each sample series. The mechanical behavior of each set wasmodeled using a MAT_SIMPLIFIED_RUBBER material model in LS-Dyna and validated against astandard Head Injury Criterion (HIC) drop test. Ultimately, previously low-speed accident reconstructedcases, a bicycle and a pedestrian one, were used to assess the effect of varying the rubbercontent on reducing the head injury risk.Results: In the bicycle accident case, the risk of skull fracture was reduced from 0.99 to 0.29 whencomparing the non-rubberized asphalt mixture with the 33% rubber mixture. In the same accidentcase, the risk of concussion, evaluated using the logistic regression method, was reduced from0.97 in the non-rubberized mixture to 0.81 in the 33% rubber mixture. The initial conditions, linearand rotational velocities, were lower for the pedestrian case compared to the bicycle case (thebicycle case was more severe compared to the pedestrian case), which led to lower strains in thepedestrian case. In the pedestrian accident case, the risk of skull fracture was reduced from 1.00in the non-rubberized mixture to 0.63 in the 33% rubber mixture, while the risk of concussion wasreduced from 0.64 to 0.07.Conclusion: The rubberized asphalt mixtures could reduce the head injury risk for the studiedcases when the rubber content in the asphalt mixture increases.

Place, publisher, year, edition, pages
2022.
Keywords [en]
Rubberized pavement; recycled rubber; head injury; bicycle accident; pedestrian accident; vulnerable road users
National Category
Applied Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-311602DOI: 10.1080/15389588.2022.2067990PubMedID: 35604793Scopus ID: 2-s2.0-85130924758OAI: oai:DiVA.org:kth-311602DiVA, id: diva2:1655140
Funder
Vinnova, 2013-04465
Note

QC 20220504

This work was supported by “BVFF – Bana v€ag f€or framtiden” underGrant number 2016-02; Sweden’s innovation agency, Vinnova underGrant number: D.nr.: 2013-04465); the SAFERUP! Project through theEuropean Union’s Horizon 2020 Research and Innovation programMarie Skłodowska-Curie under Grant number 765057.

Available from: 2022-04-30 Created: 2022-04-30 Last updated: 2023-06-08Bibliographically approved
In thesis
1. Biomechanical Analysis of Fall Injuries using Finite Element Modeling
Open this publication in new window or tab >>Biomechanical Analysis of Fall Injuries using Finite Element Modeling
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A fall is a serious health issue for the elderly. Among different fall types, the sideways fall is considered to be more severe concerning the injury outcome. When elderlies experience an unintentional sideways fall, they can either resist the impact forces with the soft tissue force attenuation capacity and femoral strength or need external protections to reduce the injury risk. In this thesis, these two aspects were investigated. Finite element whole-body models are valuable tools for analyzing fall biomechanics and investigating the possible preventive measures more conveniently. The whole-body models were developed to investigate traffic accidents; however, a sideways fall has different kinematics than the other types of accidents. Consequently, it is necessary to enhance the whole-body models according to the major fall parameters leading to severe injury cases before assessing the external protection capabilities.The current thesis attempted to advance these two critical aspects regarding fall-induced injuries. A finite element whole-body model was chosen to study three critical parameters in fall biomechanics: body posture, soft tissue, and femoral strength. The whole body model was positioned in different body configurations relevant for the sideways fall to evaluate the body posture that could lead to the highest internal forces on the femoral head. Next, different soft tissue constitutive material models and soft tissue thicknesses were investigated to find a material model that could accurately reproduce the experimental results according to an objective rating method named CORrelation and Analysis (CORA). Finally, the separate and combined effects of geometrical and mechanical properties change due to aging on femoral strength were assessed for the elderly males and females. In the second aspect of the thesis, the shock-absorbing rubberized asphalt pavements' preventive capacity was examined. First, different rubberized asphalt mixtures were implemented in a bicycle and a pedestrian accident reconstruction cases to evaluate the head injury risks. Later, the asphalt mixtures were studied in a sideways fall scenario to evaluate the hip fracture risk in an elderly male and female.

The first aspect of the thesis presented the results and methods to improve the sideways fall analysis, and the second aspect of the thesis focused on assessing the rubberized asphalt mixtures for injury prevention purposes. The sideways fall with the upright trunk and a slightly forward-tilted pelvis could lead to the highest internal forces. A nonlinear Ogden material model for muscle tissue and a Mooney-Rivlin material model for adipose tissue scored better among different soft tissue material models in the side impacts to the hip segments. The geometrical and mechanical properties change due to aging leading to a different behavior for males and females, where females experience a higher rate of strength loss due to aging. Moreover, it was indicated that a rubberized asphalt mixture could reduce the head injury risk for pedestrians and cyclists and the hip fracture risk for the elderly. The amount of rubber in the asphalt mixtures needs to exceed a specific limit to observe rubberized asphalts' preventive effects. Consequently, it is necessary to optimize the mixtures' rubber content to improve its prevention capacity.

In summary, the current thesis presented a method to improve the whole-body models according to the sideways fall requirements and assessed the protective capacity of the rubberized asphalt mixtures against head and hip injuries.

Abstract [sv]

Ett fall är ett allvarligt hälsoproblem för äldre. Bland olika falltyper anses fallet i sidled vara allvarligare vad gäller skadeutfallet. När äldre drabbas av ett oavsiktligt fall i sidled kan de antingen stå emot slagkrafterna med mjukvävnadskraftens dämpningsförmåga och lårbensstyrka eller behöva yttre skydd för att minska skaderisken. I denna avhandling har dessa två aspekter undersökts. Finite element helkroppsmodeller är värdefulla verktyg för att analysera falls biomekanik och lämpligt för att undersöka möjliga förebyggande åtgärder mer bekvämt. Helkroppsmodellerna utvecklades för att undersöka trafikolyckorna; ett fall i sidled har dock en annan kinematik än de andra typerna av olyckor. Följaktligen är det nödvändigt att förbättra helkroppsmodellerna enligt de viktigaste fallparametrarna, vilket leder till allvarliga skadefall, innan man bedömer de yttre skyddsförmågan.

Den aktuella avhandlingen försökte föra fram dessa två kritiska aspekter angående fallinducerade skador. En finite element helkroppsmodell valdes för att studera tre kritiska parametrar i falls biomekanik: kroppshållning, mjukvävnad och femoral styrka. Helkroppsmodellen placerades i olika kroppskonfigurationer som är relevanta för fallet i sidled för att utvärdera kroppshållningen som kunde leda till de högsta inre krafterna på lårbenshuvudet. Därefter undersöktes olika konstitutiva materialmodeller för mjukvävnad och mjukdelstjocklekar för att hitta en materialmodell som exakt kunde återge de experimentella resultaten enligt en objektiv klassificeringsmetod som heter CORrelation and Analysis (CORA). Slutligen utvärderades de separata och kombinerade effekterna av förändringar av geometriska och mekaniska egenskaper på grund av åldrande på lårbensstyrkan för äldre män och kvinnor. I den andra aspekten av avhandlingen undersöktes de stötdämpande gummerade asfaltbeläggningarnas förebyggande kapacitet. Först implementerades olika gummerade asfaltblandningar i rekonstruktionsfallen för en cykel och en fotgängarolycka för att utvärdera riskerna för huvudskador. Senare studerades asfaltblandningarna i ett sidledes fallscenario för att utvärdera risken för höftfraktur hos en äldre man och kvinna.

Den första aspekten av avhandlingen presenterade resultaten och metoderna för att förbättra analysen av sidledsfall, och den andra aspekten av avhandlingen fokuserade på att bedöma de gummerade asfaltblandningarna i skadeförebyggande syfte. Fall i sidled med upprätt bål, och ett något framåtlutat bäcken kan leda till de högsta inre krafterna. En ickelinjär Ogden-materialmodell för muskelvävnad och en Mooney-Rivlin-materialmodell för fettvävnad fick bättre poäng bland olika mjukdelsmaterialmodeller i sidokollisioner mot höftsegmenten. De geometriska och mekaniska egenskaperna förändras på grund av åldrande vilket leder till ett annorlunda beteende för män och kvinnor där kvinnor upplever en högre grad av förlust i styrka på grund av åldrande. Dessutom indikerades att en gummerad asfaltblandning kunde minska risken för huvudskador för fotgängare och cyklister och risken för höftfraktur för äldre. Mängden gummi i asfaltblandningarna behöver överskrida en specifik gräns för att observera gummerad asfalts förebyggande effekt. Följaktligen är det nödvändigt att optimera blandningarnas gummihalt för att förbättra dess förebyggande förmåga.

Sammanfattningsvis presenterade den aktuella avhandlingen en metod för att förbättra helkroppsmodellerna enligt kraven på sidledes fall och bedömde skyddsförmågan hos de gummerade asfaltblandningarna vid huvud- och höftskador.

Place, publisher, year, edition, pages
Sweden: KTH Royal Institute of Technology, 2022. p. 56
Series
TRITA-CBH-FOU ; 2022:29
Keywords
Fall induced injury, finite element analysis, rubberized asphalt mixture, shock-absorbing pavement, hip fracture, elderly, sideways fall, whole-body model
National Category
Applied Mechanics
Identifiers
urn:nbn:se:kth:diva-311606 (URN)978-91-8040-211-8 (ISBN)
Public defence
2022-05-23, Rappesalen, Alfred Nobels Allé 10, Huddinge, 14:00 (English)
Opponent
Supervisors
Note

The thesis was carried out at the Neuronic Engineering unit, KTH Royal Institute of Technology in Stockholm, Sweden. The thesis was funded by "BVFF – Bana väg för framtiden" (BVFF number 2016-025).

QC 2022-05-02

Available from: 2022-05-02 Created: 2022-04-30 Last updated: 2022-06-25Bibliographically approved

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Sahandifar, PooyaFahlstedt, MadelenKleiven, Svein

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