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  • 1.
    Aare, Magnus
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Kleiven, Svein
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Halldin, Peter
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Injury tolerances for oblique impact helmet testing2004In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 9, no 1, p. 15-23Article in journal (Refereed)
    Abstract [en]

    The most frequently sustained severe injuries in motorcycle crashes are injuries to the head, and many of these are caused by rotational force. Rotational force is most commonly the result of oblique impacts to the head. Good testing methods for evaluating the effects of such impacts are currently lacking. There is also a need for improving our understanding of the effects of oblique impacts on the human head. Helmet standards currently in use today do not measure rotational effects in test dummy heads. However rotational force to the head results in large shear strains arising in the brain, which has been proposed as a cause of traumatic brain injuries like diffuse axonal injuries (DAI). This paper investigates a number of well-defined impacts, simulated using a detailed finite element (FE) model of the human head, an FE model of the Hybrid III dummy head and an FE model of a helmet. The same simulations were performed on both the FE human head model and the FE Hybrid III head model, both fitted with helmets. Simulations on both these heads were performed to describe the relationship between load levels in the FE Hybrid III head model and strains in the brain tissue in the FE human head model. In this study, the change in rotational velocity and the head injury criterion (HIC) value were chosen as appropriate measurements. It was concluded that both rotational and translational effects are important when predicting the strain levels in the human brain.

  • 2.
    Brolin, Karin
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Hedenstierna, Sofia
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Halldin, Peter
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Bass, Cameron
    Center for Applied Biomechanics, University of Virginia, Charlottesville.
    Alem, Nabih
    US Army Aeromedical Research Laboratory, Fort Rucker.
    The importance of muscle tension on the outcome of impacts with a major vertical component2008In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 13, no 5, p. 487-498Article in journal (Refereed)
    Abstract [en]

    The hypothesis that muscle tension protects the spine from injuries in helicopter scenarios was tested using a finite-element model of the human head and neck. It was compared with cadaver crash sled experiment with good correlation. Then, simulations were performed with a sinusoidal velocity (5-22 G) applied at T1 60° to the horizontal plane. The model with relaxed muscle activation had delayed and decreased peak head rotation compared with passive properties only. Full muscle activation decreased the injury risk for the 13.5-22 G impacts. A sensitivity study of the impact angle showed a very slight variation of the resulting neck flexion, and 1° change affected all ligament injury predictions less than 4%. Finally, simulations with helmets resulted in increased ligament and disc strains with increasing helmet mass and with an anterior or inferior shift of the centre of gravity. It is concluded that the hypothesis seems to hold.

  • 3.
    Halldin, Peter
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Gilchrist, A.
    Mills, N. J.
    A new oblique impact test for motorcycle helmets2001In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 6, no 1, p. 53-64Article in journal (Refereed)
    Abstract [en]

    A new oblique impact test for motorcycle helmets is described, simulating a fall from a motorcycle on to the road surface or the windshield of a car. An instrumented headform falls vertically to impact a horizontally moving rigid rough or deformable surface. Both the impact site on the helmet, and the vertical and horizontal velocities, can be varied, while the headform linear and rotational accelerations are measured. The rig was used to compare a new helmet design with current helmets, which are designed to pass impact tests in which the impact force is perpendicular to the helmet surface. The new design, which has a low friction layer between the shell and the liner, reduced, by up to 50%, the rotational acceleration of the head compared with conventional designs.

  • 4.
    Ho, Johnson
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Automatic generation and validation of patient-specific finite element head models suitable for crashworthiness analysis2009In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 14, no 6, p. 555-563Article in journal (Refereed)
    Abstract [en]

    A method to automatically generate finite element (FE) head models is presented in this paper. Individual variation in geometry of the head should be taken into consideration in future injury-prediction research. To avoid inter- and intra-operator variation due to manual segmentation, a robust and accurate algorithm is suggested. The current approach utilises expectation maximisation classification and skull stripping. The whole process from geometry extraction to model generation is converted into an automatic scheme. The models that are generated from the proposed method are validated in terms of segmentation accuracy, element quality and injury-prediction ability. The segmentations of the white matter and grey matter are about 90% accurate and the models have good element quality, with 94% of the elements having a Jacobian above 0.5. Using the experimental data from post-mortem human subject heads, nodal displacements were compared with the data collected from the simulations with the FE head models. The results are promising, indicating that the proposed method is good enough to generate patient-specific model for brain injury prediction. Further improvement can be made in terms of geometry accuracy and element quality.

  • 5.
    Juntikka, Rickard
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Optimization of single skin surfaces for head injury prevention - a comparison of optima calculated for global versus local injury thresholds2004In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 9, no 4, p. 365-379Article in journal (Refereed)
    Abstract [en]

    This paper describes optimizations of material properties for a bonnet-like plate using finite element calculations and the Euro-NCAP pedestrian head impact test. Four different head models were used for the impact simulations, a Euro-NCAP dummy head, a Hybrid III dummy head and two biomechanical head models exhibiting different mechanical properties for the brain tissue. The objective function was to minimize the displacement of the bonnet plate while satisfying constraints on the head injury criterion (HIC), the resultant contact force and, for the human head models, the strain in the brain tissue. An investigation was also conducted of the kinematics of the head models during impact, evaluating the energy distribution and the apparent mass. The analysis gave at hand that optimization of the plate with respect to impact with the Euro-NCAP and Hybrid III head models reached substantially, different results compared to impact with the biomechanical head models. For the latter case, the stiffness of the brain tissue influenced which constraints were active in the final solution. The investigation of the kinematics at impact showed that a substantial portion of energy was confined within the brain during impact for the biomechanical head models. The apparent mass at impact coincided with the actual mass for the rigid dummy heads while for the human head models it was roughly the mass of the skull only.

  • 6.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Evaluation of head injury criteria using a finite element model validated against experiments on localized brain motion, intracerebral acceleration, and intracranial pressure2006In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 11, no 1, p. 65-79Article in journal (Refereed)
    Abstract [en]

    The objective of the present study was to analyze the effect of different load directions and durations following impact using a finite element (FE) model of the human head. A detailed FE model of the human head was developed and validated against available cadaver experiment data for three impact directions (frontal, occipital, and lateral). Loads corresponding to the same impact power were imposed in different directions. Furthermore, the head injury criterion (HIC), the recently proposed head impact power (HIP) criterion, as well as peak angular acceleration, and change in angular and translational velocity were evaluated with respect to the strain in the central nervous system (CNS) tissue. A significant correlation was found between experiments and simulations with regard to intracranial pressure data for a short-duration impulse and intracerebral acceleration characteristics for a long-duration impulse with a high-angular component. However, a poor correlation with the simulations was found for the intracranial pressures for the long-duration impulse. This is thought to be a result of air introduced to the intracranial cavity during experimental testing. Smaller relative motion between the brain and skull results from lateral impact than from a frontal or occipital blow for both the experiments and FE simulations. It was found that the influence of impact direction had a substantial effect on the intracranial response. When evaluating the global kinematic injury measures for the rotational pulses, the change in angular velocity corresponded best with the intracranial strains found in the FE model. For the translational impulse, on the other hand, the HIC and the HIP showed the best correlation with the strain levels found in the model.

  • 7.
    Lanner, Daniel
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Halldin, Peter
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Iraeus, Johan
    Epsilon, Göteborg, Sweden.
    Holmqvist, Kristian
    SAFER, Chalmers University of Technology, Göteborg, Sweden.
    Mroz, Krystoffer
    Autoliv Research, Vårgårda, Sweden.
    Pipkorn, Bengt
    Autoliv Research, Vårgårda, Sweden.
    Jakobsson, Lotta
    Volvo Car Corporation, Göteborg, Sweden.
    Backlund, Maria
    Volvo Car Corporation, Göteborg, Sweden.
    Bolte, John H.
    The Ohio State University, Ohio, USA.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Evaluation of finite element human body models in lateral padded pendulum impacts to the shoulder2010In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 15, no 2, p. 125-142Article in journal (Refereed)
    Abstract [en]

    Lateral impacts are of great concern for occupant safety. In order to design side protective systems, it is of importance that the timing of the body and the head should be well predicted. Today, experimental and numerical Anthropometric Test Devices (ATDs) are used as human substitutes to predict the human kinematics. As a complement to the ATDs, numerical Human Body Models (HBMs) are used as research tools. The objective of this study is to compare the loading and kinematics of the shoulder complex in three different HBMs with published biological experiments. This study also compares the models with each other and with two numerical ATDs. The results indicate that no HBM can be used for detailed prediction of the kinematics of the human shoulder complex. However, in the presented statistical analysis, all HBMs show a better overall correlation to experiments compared to the numerical ATDs.

  • 8. Prus, C.
    et al.
    Vinuesa, Ricardo
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, School of Engineering Sciences (SCI), Mechanics, Stability, Transition and Control. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Tembras, E.
    Mestres, E.
    Ramirez, J. P. Berro
    Impact simulation and optimisation of elastic fuel tanks reinforced with exoskeleton for aerospace applications2017In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 22, no 3, p. 271-293Article in journal (Refereed)
    Abstract [en]

    The main subject of the study is the impact simulation of an elastic fuel tank reinforced with a polymer exoskeleton. Thanks to its lightweight and failure resistance, this type of design shows potential to be used in aerospace applications. The simulation emulates a drop test from the height of 20 m on a rigid surface, in accordance with Military Handbook testing guidelines for fuel tanks. The focus is on providing an example of modelling and solving this type of problems. The computational methods are tested on a generic model of a rectangular prismatic tank with rounded edges. The walls of the tank are made of orthotropic fabric reinforced polymer. The simulation is performed for a 70% and a 100% water-filled tank. All calculations are performed using the Altair HyperWorks 13.0 software suite, in particular, the nonlinear RADIOSS solver and OptiStruct Solver and Optimiser. The fluid inside the tank is modelled using the SPH (Smoothed Particle Hydrodynamics) approach. The model serves as a basis for establishing a design optimisation procedure, aiming at reduction of mass of the tank components while ensuring structural integrity. The main insights of the current study are the successful modelling of the liquid and the air inside the tank by means of smoothed-particle hydrodynamics elements, and the structural optimisation methodology of a composite fuel tank.

  • 9. Zou, H.
    et al.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Schmiedelera, J. P.
    The effect of brain mass and moment of inertia on relative brain-skull displacement during low-severity impacts2007In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 12, no 4, p. 341-353Article in journal (Refereed)
    Abstract [en]

    Traumatic brain injury is the leading cause of death in automobile crashes. The sensitivity of human brain injury prediction to small parameter changes is a critical element of both experimental and mathematical work yet to be adequately investigated. This work proposes a new analytical human brain injury model to determine the parameters to which injury prediction is most sensitive. The trajectory sensitivity analysis explicitly indicates that injury prediction is most sensitive to brain mass moment of inertia, followed by brain mass. A number of finite element (FE) simulations were executed with various brain sizes. The maximum relative brain motions decrease with decreased brain size, and they are very close in the FE and analytical models. We conclude that brain mass moment of inertia, primarily, and brain mass, secondarily, should be varied in focused experimental and FE modeling work to ensure that conclusions are not drawn from individual data points at which injury predictions are highly sensitive to small parameter changes.

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