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【演講公告】106/03/15 Prof. Kobayashi (Department of Mechanical Engineering, University of Washington)
Dynamic Fracture

A Photomechanic Study



Albert S. Kobayashi

University of Washington

Department of Mechanical Engineering

Seattle Washington 98195



This presentation will summarize the author’s studies on dynamic fracture based on photomechanics. During the early stage of our studies, high speed photography was used to record the rupture of pressurized thin-walled steel pipes and a numerical model of the rupturing pipe was developed. This model was used successfully to predict the rupture experiments of full-scale pipes. Moiré interferometry together with high-speed photography and the generation phase of dynamic finite element analysis were then used to determine the dynamic fracture toughness of 7075-T6 and 2024-T3 aluminum specimens. A high temperature moiré interferometry was developed and the fracture toughness of alumina at temperature up to 1000̊ C was recorded. A two-dimension finite element (FE) models with postulated grain/fiber bridging models in the fracture process zone of ceramic matrix composite were used to estimate the energy dissipated during fracture. Postulated crack bridging models were adjusted through an inverse analysis to match the computed crack opening displacement (COD) with the measured surface COD via moiré interferometry. Fracture behavior of carbon fiber/carbon matrix (C/C) composite was analyzed with a 2-D finite element (FE) model of a single edged notch bend (SENB) specimen subjected to a series of re-notching tests. The irregular transverse cracking in the wide frontal fracture process zone (FPZ) of the machined notch tip was represented by an idealized distribution of crack bridging stress (CBS) along an idealized straight crack. The CBS was obtained through an inverse analysis by matching the FE computed and moiré measured crack opening displacement (COD) during the re-notching process. This FE model was used to estimate the equivalent strain energy release rate, Geq, and the equivalent stress intensity factor, Keq, of the zig-zagged crack
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