Behaviour of bioceramics under impact loading

[摘要] Stabbing incidents are of continued concern and the need to quantify the force required to cause a stab-wound is increasingly urgent. Only through an understanding of the mechanics of penetration of human tissue can forensic engineers and pathologists infer, after the event, whether any particular wound track is likely to have been due to homicide, suicide or accident. In stabbing incidents, the main resistance to knife penetration is provided by bone tissue. Structurally, bone is a complex material. It is neither as brittle as a monolithic ceramic nor as ductile as a polymer. Rather, it lies within an intermediate class of material that the author has called "near-brittle" and which exhibits limited damage evolution up to failure. A computational constitutive model of near-brittle bone must be benchmarked against experiments on the real material but it is prudent to perform preliminary static and impact tests on simpler model materials which mimic, in at least one aspect, the behaviour of bone. To bracket this behaviour, for which very little relevant data is available, experiments were therefore done on the two extreme cases, ie brittle monolithic ceramics and ductile polymers. At the same time, experience in computational constitutive modelling of a damaging material was gained using preexisting data on the static behaviour of a ceramic composite. Though quantitatively different from bone, this has a qualitatively similar near-brittle response. The experimental work on ductile materials raised the contentious question of the role of kinetic energy versus momentum during impact. While damage certainly increases with kinetic energy, there may also be a small increase with momentum. There is no simple explanation for any such effect and the results are not conclusive but they do point the way towards additional work. The computational modelling proved difficult. The damage model used by Gibson & Thomson (1995) is erroneous but attempts to devise an accurate substitute were hampered by the nature of the explicit finite element solver. The work concludes with experiments on real bone under static and impact loading, to generate data which is essential if this objective is to be eventually met.

[发布机构] University:University of Glasgow

[关键词] Materials science