Motor vehicle accidents are statistically the major cause of accidental severe injuries for pregnant women and fetuses fatality. Volunteers, post mortem human surrogates, anthropomorphic crash test devices and computational occupant models are used to improve human safety in motor vehicle accidents. However, due to the ethical issues, pregnant women and their fetuses cannot be used as volunteers or post mortem human surrogates to investigate the effects of crashes on them. The only anthropomorphic test device representing pregnant women is very limited in design and lacks a fetus. There is no computational pregnant occupant model with a fetus other than 'Expecting'. This thesis focuses on understanding the risk of placental abruption for pregnant drivers involved in road accidents, hence assessing the risk to fetus fatality. An extensive review of existing models in general and pregnant women models in particular is reported. The time line of successive development of crash test dummies and their positive effect on automotive passive safety design are examined. 'Expecting', the computational pregnant occupant model with a finite element uterus and a multibody fetus, is used in this research to determine the strain levels in the uteroplacental interface. External factors, such as the effect of restraint systems and crash speeds are considered. Internal factors, such as the effect of placental location in the uterus, and the inclusion and exclusion of a fetus are investigated. The head of the multibody fetus is replaced with a deformable head model to investigate the effects of a deformable fetus head on strain levels. The computational pregnant driver model with a fetus offers a more realistic representation of the response to crash impact hence provides a useful tool to investigate fetus safety in motor vehicle accidents. Seat belt, airbag and steering wheel interact directly with the pregnant abdomen and play an important role on fetus safety in motor vehicle accidents. The results prove that the use of a three-point seat belt with the airbag offer the greatest protection to the fetus for frontal crash impacts. The model without a fetus underestimates the strain levels. The outcome of this research should assist automobile manufacturers to address the potential safety issues at the design level.

Traumatic brain injury (TBI) is a worldwide public health problem. It is often caused by impacts to the head, which can cause translational and rotational motions. During impacts to the head, the neck serves as one of the boundary conditions for determining its kinematic response. In today’s helmet assessment standards, the dynamics of the neck are not included, and in most standards only translational accelerations are examined within a short time interval around 20- 30 ms. However, to understand the risk of brain injury, it is also important to account for the rotational motions and the influence of the neck on head kinematics.  In this thesis the influence of the neck on head kinematics was investigated by comparing 5 different finite element (FE) models of the human. By using finite element analysis, simulations of four different accident scenarios were conducted. Most models are produced for the automotive industry and are not validated in vertical impacts with forces acting on the head. The accident scenarios included vertical and horizontal impacts to the head with different striking objects. The models included two anthropomorphic test devices (ATD) and three human body models (HBM). Furthermore, an isolated head was also used. The models were equipped with an industrial safety helmet, with and without a low friction layer (LFL). Additionally, the helmet versions were used to investigate how the various FE models predict the difference in rotational kinematics.  The head kinematics showed considerable disparities between the ATDs and the HBMs. The ATDs mostly showed a stiffer, spring-like behavior with higher translational accelerations and lesser rotational motions. Furthermore, the HBMs showed responses that were assumed to have been in better proximity to biofidelic responses. The incorporation of the LFL led to a reduction in peak resultant rotational velocity (PRV) in most models and accident scenarios. Furthermore, the results were highly influenced by the choice of duration. It was seen that the differences between the models increased over time, as the boundary effects could influence the kinematics to a larger extent. Hence, the neck had more influence on head kinematics at longer time durations.  This thesis contributes to a comparison of different FE models and how various boundary conditions affect the kinematics of the head. The Hybrid III should only be used in cases involving pure flexion-extension. The attachment of the KTH neck to the Hybrid III torso led to large differences in kinematic responses to the other models, and therefore it should not be used in virtual testing. Due to the resemblance between head-only and the HBMs, as well as the short duration in bicycle helmet assessment, the use of only a headform is probably a better approximation as the ATD necks that could be used are not good representations of biofidelity. Before implementing surrogate necks in helmet assessment, more investigations on the influence of the neck on head kinematics are necessary as well as the development of neck models with high biofidelity. / Traumatiska hjärnskador är ett globalt folkhälsoproblem. Traumatiska hjärnskador orsakas ofta av slag mot huvudet, vilket kan orsaka både translations- och rotationsrörelser av hjärnan. Vid slag mot huvudet verkar halsen som ett av randvillkoren som styr kinematiken av huvudet. I dagens hjälmstandarder är halsens dynamik inte inkluderad och i majoriteten av standarder är det endast translationsaccelerationer som undersöks samt inom en kort tidsram, runt 20-30 ms. För att förstå risken för hjärnskador behöver man även beakta rotationsrörelser och då blir halsens inflytande på huvudets kinematik av vikt, liksom att utvärdera kinematiken under en längre tid.  I detta examensarbete studeras halsens inverkan på huvudets kinematik genom att jämföra fem olika finita element (FE) modeller av människan. Genom att använda finita elementmetoden, genomfördes simuleringar av 4 olika olycksscenarior. Olycksscenariorna inkluderade vertikala och horisontella islag med olika objekt. De modeller som användes var två krockdockor och tre humanmodeller samt ett isolerat huvud. De flesta modeller är framtagna för bilindustrin vilket påverkar dess användningsområde genom begränsade valideringar av vertikala slag med krafter som verkar direkt på huvudet. Alla modeller var utrustade med en industrihjälmsmodell, med respektive utan ett lågfriktionslager. Dessutom användes hjälmmodellerna till att undersöka hur de olika FE modellerna förutspådde skillnader i rotationskinematik.  Kinematiken av huvudet visade på signifikanta skillnader mellan krockdockorna och humanmodellerna. Krockdockorna hade generellt ett stelare, fjäderliknande beteende med högre translationsacceleration och mindre rotationsrörelse. Vidare hade humanmodellerna ett beteende som var mer likt den förväntade mänskliga responsen. Användandet av lågfriktionslagret ledde till reduktion i resulterande peak rotationshastighet bland de flesta modeller och olycksscenarior. Resultatet påverkades nämnvärt av valet av tidsintervall. Vid längre tidsintervall var skillnaderna i beteende större mellan modellerna. Därför hade halsen större inverkan på huvudets kinematik vid längre durationer.  Detta examensarbete bidrar till en jämförelse av olika FE modeller och förståelse för hur olika randvillkor påverkar huvudets kinematik. Hybrid III borde endast användas för horisontella islag med enbart flexion-extensions rörelser. Infästningen av KTH halsen till Hybrid III gav stora skillnader i kinematiken jämfört med de andra modellerna, och därför ska den inte användas vid virtuella tester. På grund av de likheter som sågs mellan enbart huvud och humanmodellerna samt på grund av de korta islagen vid cykelhjälmsbedömningar, är troligtvis användandet av ett isolerat huvud en bättre approximation än användandet av de tillgängliga krockdockornas halsar. Innan man använder halsmodeller vid hjälmbedömningar, krävs fler studier på halsens inverkan på kinematiken samt framtagande av halsmodeller med mer människoliknande respons.