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Publications (5)1.41 Total impact

  • Daisuke Murakami · Seiichi Kobayashi · Toshikazu Torigaki · Richard Kent
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    ABSTRACT: Thoracic trauma is the principle causative factor in 30% of road traffic deaths. Researchers have developed force-deflection corridors of the thorax for various loading conditions in order to elucidate injury mechanisms and to validate the mechanical response of ATDs and numerical human models. A corridor, rather than a single response characteristic, results from the variability inherent in biological experimentation. This response variability is caused by both intrinsic and extrinsic factors. The intrinsic factors are associated with individual differences among human subjects, e.g. the differences in material properties and in body geometry. The extrinsic sources of variability include fluctuations in the loading and supporting conditions in experimental tests. Recent studies have considered the intrinsic factors, especially the material-level response of the rib, which can be modified over a limited range within, e.g. a finite element (FE) model in order to fit a gross overall thoracic response corridor. Studies typically do not, however, consider uncertainty due to extrinsic factors. The purpose of this work was to estimate the contribution of selected extrinsic factors to the uncertainty in a response corridor by using a thorax FE model. The sensitivity of twelve response corridors to the relative positioning of the thorax, the loader and the test fixture was analyzed. Reasonable ranges of experimental uncertainty were established for loader angle, loader location, and thorax orientation, and response variability was analyzed for three tissue states (intact, denuded, and eviscerated) with four different loaders (hub, distributed belt, single diagonal belt, and double diagonal belts). Of the variables considered here, the thorax orientation has the largest effect on the force-deflection response, which increases and decreases the effective stiffness up to 20%. The simulation work isolated the extrinsic contribution from the corridor and indicated model deficiencies and refinements, which have the potential to improve model accuracy, particularly modeling the soft tissues and the costal cartilage.
    No preview · Article · Dec 2006 · Stapp car crash journal
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    ABSTRACT: This article assesses the position-dependent injury tolerance of the hip in the frontal direction based on testing of eight postmortem human subjects. For each subject, the left and right hemipelvis complex was axially loaded using a previously developed test configuration. Six positions were defined from a seated femur neutral condition, combining flexed, neutral, and extended femur positions with abducted, neutral, and adducted positions. Axial injury tolerances based on peak force were found to be 6,850 +/- 840 N in the extended, neutral position and 4,080 +/- 830 N in the flexed, neutral position. From the flexed neutral orientation, the peak axial force increased 18% for 20 degrees abduction and decreased 6% for 20 degrees adduction. From the extended, neutral orientation, the peak axial force decreased 4% for 20 degrees abduction and decreased 3% for 20 degrees adduction. However, as there is evidence that increases in loading may occur after the initiation of fracture, the magnitude of the peak force is likely related to the extent of injury, not to the initial tolerance. Using the axial femur force at the initiation of fracture (assessed with acoustic crack sensors) as a potentially more relevant indicator of injury may lower the existing injury criteria. This fracture initiation force varied by position from 3,010 +/- 560 N in the flexed, neutral position to 5,470 N in the extended, abducted position. Further, there was a large position-dependent variation in the ratio of fracture initiation force to the peak axial force. The initiation of fracture was 83% of the peak axial force in the extended, abducted position, but the ratio was 34% in the extended, adducted position. This may have significant implications for the development of pelvic injury criteria by automobile designers attempting to mitigate pelvis injuries.
    No preview · Article · Oct 2006 · Traffic Injury Prevention
  • Seiichi Kobayashi · Daisuke Tomii · Kazuyuki Shizawa
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    ABSTRACT: Ductile fracture of a polymer plate due to craze growth is characterized by a failure in the front of propagating neck. In this paper, the elastoviscoplastic constitutive equation, that explicitly represents the effect of craze, is rigorously derived. Through a thermodynamic discussion about arguments of craze rate function, a new craze evolution equation is proposed so as to express the craze concentration on the boundary between the oriented molecular region and the glassy one, and the craze annihilation in the oriented region, with a hydrostatic stress criterion of craze generation. Additionally, an evolution law of mean plastic strain affecting the craze growth is numerically identified for a polymer block with some circular holes. A finite element simulation is carried out in order to verify this model. The craze propagation and annihilation are visualized, and the possibility of failure prediction based on this model is also discussed.
    No preview · Article · Jun 2004 · Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A
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    ABSTRACT: Polymeric materials have various characteristics of deformation, e.g., strain rate dependence (viscoplasticity) at room temperature, strain localization just after initial yielding and propagation of a localized region with strain hardening. Viscoplasticity has been usually represented by a constitutive equation of plasticity with a hardening law including a plastic strain rate. However, such a modeling is not thermodynamically consistent with the hardening law dependent on strain rate. In this paper, a strain rate tensor is introduced into free energy and a thermodynamic force conjugate to this rate is newly defined. On the basis of the principle of increase of entropy and one of maximal entropy production rate, a non-coaxial constitutive equation of viscoplasticity is derived as a flow rule in which a dissipation function plays the role of plastic potential. It is shown that a strain rate dependent constitutive equation must be always non-coaxial in a thermodynamically consistent theory.
    No preview · Article · Apr 2002 · Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A
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    ABSTRACT: In the previous paper, a strain rate tensor is introduced into free energy and a thermodynamic force conjugate to this rate is newly defined. On the basis of the principle of increase of entropy and one of maximal entropy production rate, a non-coaxial constitutive equation associated with a plastic deformation rate is derived as a flow rule in which a dissipation function plays the role of plastic potential. Material moduli in this equation, however, are still not expressed as functions of hardening law. In this paper, the constitutive equation is newly generalized into corner theory which permits an existence of a vertex on dissipation surface. A non-coaxial angle of a plastic deformation rate is related to the non-coaxial angle of a stress rate by use of strain rate sensitivity. Furthermore, a finite element analysis is carried out for a plane strain tension of homopolymer. Some remarkable numerical results of strain localization for homopolymer are discussed in detail.
    No preview · Article · Apr 2002 · Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A