Browsing by Author "Rickman, John M."

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    Cone cracking in human bone: a CT case review series
    (Elsevier, 2022-06-06) Christensen, Angi M.; Rickman, John M.
    Skeletal trauma analysis often involves the assessment of the types and patterns of fractures, followed by categorizing the trauma into one of several broad “mechanisms.” Trauma analysis ideally also involves understanding the underlying mechanistic basis for the bone's failure. Beveling in bone is one example of a fracture pattern that is often cited as evidence of a high-velocity projectile impact, but appears to be poorly understood in terms of both the mechanism for bevel production as well as the loading conditions responsible for its formation. It has recently been demonstrated that bone beveling results from a failure mechanism called cone cracking, which is also associated with lower velocity impacts. Many case reviews and instructional texts include imagery of beveled bone in association with projectile impacts, but present various other explanations (or no explanation) for the fracture mechanism responsible. Five cases are presented here involving cone cracking in human forensic cases. For each case, the associated fracture patterns are discussed, photographic and micro-CT imagery are shown, and a review of the cone crack is presented in cross-section. The diagnostic utility of CT examination of ambiguous perforations is also highlighted.
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    Forensic fractography of bone: fracture origins from impacts, and an improved understanding of the failure mechanism involved in beveling
    (University of Florida Press, 2021-06-25) Christensen, Angi M.; Rickman, John M.; Berryman, Hugh E.
    Fractography involves the study of fractures and cracks in a material in order to understand the cause of failure. Even as a complex, highly hierarchical composite, bone is a material that obeys physical laws, including cracking behavior. The fields of fractography and fracture mechanics, therefore, have much to offer in our understanding of bone’s response to loading and force. Here we discuss how fractography can be used in the assessment of fractures originating from impacts including those from projectiles. Fractures and fracture patterns frequently associated with impact trauma—including radial fractures, circumferential fractures, and beveling—are described and used interpretively in forensic analyses; however, the mechanisms for their production and arrangement are often underutilized in fully understanding the trauma event. These mechanisms are reviewed here from a fractography perspective. Furthermore, a review is presented of new data indicating that beveling in bone associated with impacts, especially with projectiles, is produced by cone cracking, a process that is also well documented in other brittle materials. This information can be used to enhance understanding of impact trauma in general, as well as in the context of specific forensic cases. Moreover, describing and interpreting skeletal trauma within the context of fracture mechanics and fractography has the advantage of aligning the nomenclature used in forensic anthropology with that used in other scientific fields, particularly those involved in the study of material failure. To facilitate this alignment, we provide discussion and definitions for various fractography-related terms.
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    A novel hypothesis for the formation of conoidal projectile wounds in sandwich bones
    (Springer, 2018-10-18) Rickman, John M.; Shackel, James
    When perforated by a projectile, sandwich bones typically exhibit wounds with a distinct conoidal morphology that is widely utilised both in wound diagnosis and trajectory determinations. However, the dynamic fracture mechanisms underlying this intriguing wound type have yet to be experimentally verified. The most frequently quoted hypothesis for their formation, plug and spall, is difficult to reconcile with the conoidal morphology exhibited by such wounds. The present article carries out a high-speed videographic and micro-computerised tomographic (μ-CT) analysis of perpendicularly produced projectile wounds induced from 139.15 to 896.84 metres per second (m/s) in pig scapulae. Fundamental data on energy absorption, wound shape and bevel symmetry are presented. Cross-sectional fracture morphology revealed by μ-CT raises the novel hypothesis that tensile stresses induced by the projectile in the outer cortex elicit cone crack formation and that this cone crack then propagates catastrophically through the entire sandwich structure. This process results in the momentary formation of a bioceramic conoid, a conoidal volume of bone consisting of all three sandwich bone layers separated from the parent bone by the internal bevel. Fragmentation of the separated volume leaves the conoidal wound behind as its counterpart. The significance of this hypothesis in terms of differential diagnosis and interpretation of bevel shape is discussed.
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    A scanning electron microscopy study of projectile entry fractures in cortical bone; genesis and microarchitectural features
    (Springer, 2021-12-13) Rickman, John M.; Painter, Jonathan; Hazael, Rachael
    The present paper presents a scanning electron microscope (SEM) analysis of the genesis and microarchitecture of experimentally induced cortical entry fractures in porcine scapulae impacted at velocities ranging from 54 to 897 m/s. SEM observation was conducted on polyurethane replicas cast from negative silicone moulds. Analysis of the sequence of fracture processes operative during projectile impact revealed the presence of ring cracks at the site of impact, confirming that penetration in sandwich bones is achieved by cone crack propagation. Despite impulsive loading, two forms of plastic deformation were identified in the cortical bone surrounding the entry fracture up to a maximum velocity of 871 m/s. Microscopic radial and concentric cracks were associated with projectile impact, and the role of pores and pits as stress concentrators was captured. Possible underlying mechanisms for the observed plastic deformation are described, and the diagnostic utility of SEM analysis is presented.