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  • 1. Aare, Magnus
    et al.
    Kleiven, Svein
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Evaluation of head response to ballistic helmet impacts using the finite element method2007In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 34, no 3, p. 596-608Article in journal (Refereed)
    Abstract [en]

    Injuries to the head caused by ballistic impacts are not well understood. Ballistic helmets provide good protection, but still, injuries to both the skull and brain occur. Today there is a lack of relevant test procedure to evaluate the efficiency of a ballistic helmet. The purpose of this project was (1) to study how different helmet shell stiffness affects the load levels in the human head during an impact, and (2) to study how different impact angles affects the load levels in the human head. A detailed finite element (FE) model of the human head, in combination with an FE model of a ballistic helmet (the US Personal Armour System Ground Troops' (PASGT) geometry) was used. The head model has previously been validated against several impact tests on cadavers. The helmet model was validated against data from shooting tests. Focus was aimed on getting a realistic response of the coupling between the helmet and the head and not on modeling the helmet in detail. The studied data from the FE simulations were stress in the cranial bone, strain in the brain tissue, pressure in the brain, change in rotational velocity and translational and rotational acceleration. A parametric study was performed to see the influence of a variation in helmet shell stiffness on the outputs from the model. The effect of different impact angles was also studied. Dynamic helmet shell deflections larger than the initial distance between the shell and the skull should be avoided in order to protect the head from the most injurious threat levels. It is more likely that a fracture of the skull bone occurs if the inside of the helmet shell strikes the skull. Oblique ballistic impacts may in some cases cause higher strains in the brain tissue than pure radial ones.

  • 2.
    Balieu, Romain
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Lauro, F.
    Bennani, B.
    Haugou, G.
    Chaari, F.
    Matsumoto, T.
    Mottola, E.
    Damage at high strain rates in semi-crystalline polymers2015In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 76, p. 1-8Article in journal (Refereed)
    Abstract [en]

    A specific damage characterization method using Digital Image Correlation for semi-crystalline polymers is proposed for a wide range of strain rates. This damage measurement is an extension of the SEE method [16] which was developed to characterize the behaviour laws at constant strain rates of polymeric materials. This procedure is compared to the well-known damage characterization by loss of stiffness technique under quasi-static loading. In addition, an in-situ tensile test, carried out in a microtomograph, is used to observe the cavitation phenomenon in real time. The different ways used to evaluate the damage evolution are compared and the proposed technique is also suitable for measuring the ductile damage observed in semi-crystalline polymers under dynamic loading.

  • 3.
    Juntikka, Rickard
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Hallström, Stefan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Weight-balanced drop test method for characterization of dynamic properties of cellular materials2004In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 30, no 5, p. 541-554Article in journal (Refereed)
    Abstract [en]

    A novel weight-balanced drop rig used to evaluate the response of cellular materials subject to dynamic compression is presented. The testing method utilizes approximately constant velocity throughout the major part of the compression phase and the results compare well with results from other methods, reported in the literature. The repetitiveness is excellent, the rig is simple and the results are easily extracted. The applicability of the method for determination of elastic modulus is however limited to materials with relatively low stiffness. Accurate modulus measurements for stiff materials at high strain-rates require a very rigid and lightweight test set-up.

  • 4. Karthikeyan, K.
    et al.
    Kazemahvazi, Sohrab
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures. Engineering Department, University of Cambridge, Trumpington Street, Cambridge, United Kingdom.
    Russell, B. P.
    Optimal fibre architecture of soft-matrix ballistic laminates2016In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 88, p. 227-237Article in journal (Refereed)
    Abstract [en]

    Soft-matrix ballistic laminates (such as those composed of fibres of Ultra High Molecular-Weight Polyethylene, e.g. Dyneema® HB26 and Spectra Shield) find extensive use as catching type armour systems. The relationship between the lay-up of these laminates with respect to the observed failure mechanisms has not been empirically investigated in the open literature, and is the subject of this work. Lay-ups are characterised by two parameters: (i) sequencing (or interply lay-up angle) θ¯ and (ii) in-plane anisotropy β, and can be mapped on to θ¯-β space. Four geometries that lie at the extrema of this parameter space are designed, built and tested. Testing is through ball bearing impact on circular clamped plates. The anisotropy (β) is coupled to the macroscopic response of the plates, while sequencing (θ¯) is coupled to the microscopic response. Penetration velocity is strongly affected by pull-out at the boundary, and in the present study this is shown to account for two-thirds of the ballistic resistance. The results have implications for validation testing on scaled samples, predictive modelling and simulation, and armour design.

  • 5.
    Tilert, Dan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics.
    Svedbjörk, Göran
    Ouchterlony, Finn
    Nilsson, Bruno
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics.
    Temun, Attila
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics.
    Mattsson, Lars
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Metrology and Optics.
    Measurement of Explosively Induced Movement and Spalling of Granite Model Blocks2007In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 34, no 12, p. 1936-1952Article in journal (Refereed)
    Abstract [en]

    Charges of high explosives have been buried (countersunk) in granite blocks and detonated. This article describes the measurement and evaluation of the shock wave propagating through the granite blocks. It also demonstrates how the shock wave data can be used to improve computer simulations of granite's behaviour. The overall goal has been to investigate how granite withstands penetrating weapons, that first penetrate the ground and then detonates within the created cavity. Several variables have been investigated. It is shown that water content of the granite can increase the shock wave amplitude with up to a factor 2, and a crack in the granite often attenuates the shock wave amplitude with a factor 4 or more. Also, the granite block thickness needed to prevent internal crack formation has been investigated.

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