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Toughening Mechanisms in Biological Hard Tissues.

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Final rept. May 91-May 94,

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We have studied toughening mechanisms in mineralised tissues. We have demonstrated the importance of microdamage as a universal toughening mechanism. This is clear from all the mineralised tissues we have examined. The tougher tissues have a variety of mechanisms to increase elongation before fracture, and these are rather different in antler and in dentine. Antler has fibers that behave telescopically and also has a structure that forces microcracks to depart from the most dangerous orientation dentine has a structure that initially induces yield at 450 to the loading direction, whatever that is, but at higher strains induces clouds of microcracks in the direction of the loading, and finally the macrocrack is diverted by the predominant fiber direction. We have examined such toughening mechanisms by a combination of mechanical testing, including static, impact and fatigue loading optical examination, scanning confocal microscopy, acoustic emission, fractal analysis of fracture surfaces, and some finite element analysis. The work on the grant has resulted in 5 papers published or in press in refereed journals, two chapters in books published or in press, and one large paper on fatigue which has just been submitted. We expect two more papers based on AFOSR work to appear.

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  • Anatomy and Physiology

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