Now showing 1 - 4 of 4
  • Publication
    Measuring knife stab penetration into skin simulant using a novel biaxial tension device
    This paper describes the development and use of a biaxial measurement device to analyse the mechanics of knife stabbings. In medicolegal situations it is typical to describe the consequences of a stabbing incident in relative terms that are qualitative and descriptive without being numerically quantitative. Here, the mechanical variables involved in the possible range of knife-tissue penetration events are considered so as to determine the necessary parameters that would need to be controlled in a measurement device. These include knife geometry, in-plane mechanical stress state of skin, angle and speed of knife penetration, and underlying fascia such as muscle or cartilage. Four commonly available household knives with different geometries were used: the blade tips in all cases were single-edged, double-sided and without serrations. Appropriate synthetic materials were used to simulate the response of skin, fat and cartilage, namely polyurethane, compliant foam and ballistic soap, respectively. The force and energy applied by the blade of the knife and the out of plane displacement of the skin were all used successfully to identify the occurrence of skin penetration. The skin tension is shown to have a direct effect on both the force and energy for knife penetration and the depth of out of plane displacement of the skin simulant prior to penetration: larger levels of in-plane tension in the skin are associated with lower penetration forces, energies and displacements. Less force and energy are also required to puncture the skin when the plane of the blade is parallel to a direction of greater skin tension than when perpendicular. This is consistent with the observed behaviour when cutting biological skin: less force is required to cut parallel to the Langer lines than perpendicularly and less force is required to cut when the skin is under a greater level of tension. Finally, and perhaps somewhat surprisingly, evidence is shown to suggest that the quality control processes used to manufacture knives fail to produce consistently uniform blade points in knives that are nominally identical. The consequences of this are that the penetration forces associated with nominally identical knives can vary by as much as 100%.
    Scopus© Citations 74  748
  • Publication
    A combined experimental and numerical study of stab-penetration forces
    The magnitude of force used in a stabbing incident can be difficult to quantify, although the estimate given by forensic pathologists is often seen as 'critical' evidence in medico-legal situations. The main objective of this study is to develop a quantitative measure of the force associated with a knife stabbing biological tissue, using a combined experimental and numerical technique. A series of stab-penetration tests were performed to quantify the force required for a blade to penetrate skin at various speeds and using different 'sharp' instruments. A computational model of blade penetration was developed using ABAQUS/EXPLICIT, a non-linear finite element analysis (FEA) commercial package. This model, which incorporated element deletion along with a suitable failure criterion, is capable of systematically quantifying the effect of the many variables affecting a stab event. This quantitative data could, in time, lead to the development of a predictive model that could help indicate the level of force used in a particular stabbing incident.
      792Scopus© Citations 35
  • Publication
    Head Impact Biomechanics Simulations: A forensic tool for reconstructing head injury?
    Establishing the cause of death in forensic investigations can be facilitated by in-depth knowledge of the mechanics of skull fracture and associated lesions to intracranial tissue. Deformation of the skull arising from mechanical impact can lead directly to various soft tissue brain injuries. Advanced simulation techniques, as used in aerospace design and automotive safety, can usefully serve to quantify levels of force associated with skull fracture and with levels of strain or stress associated with brain trauma. Such simulations require physical material failure data so as to ensure predictions are accurate both in relative terms and in absolute quantitative terms. Computer simulations based on multibody dynamics and the finite element method can be used to reconstruct the mechanics of head injury in order to establish the causes of occurrences of skull fracture and TBI.
      479
  • Publication
    Toward a Predictive Assessment of Stab-Penetration Forces
    (Ovid Technologies (Wolters Kluwer) - Lippincott Williams & Wilkins, 2014-04) ; ; ;
    Collaborative research between the disciplines of forensic pathology and biomechanics was undertaken to investigate the hyperelastic properties of human skin, to determine the force required for sharp instrument penetration of skin, and to develop a finite element model, which reflects the mechanisms of sharp instrument penetration. These studies have led to the development of a "stab metric," based on simulations, to describe the force magnitudes in stabbing incidents. Such a metric should, in time, replace the crudely quantitative descriptors of stabbing forces currently used by forensic pathologists.
    Scopus© Citations 11  331