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# Experimental crack length measurement under variable temperature using a thin film AC potential difference technique

 dc.contributor.author Roberge, Douglas M. en_US dc.date.accessioned 2007-05-15T15:25:09Z dc.date.available 2007-05-15T15:25:09Z dc.date.issued 1997-05-01T00:00:00Z en_US dc.identifier.uri http://hdl.handle.net/1993/986 dc.description.abstract An alternating current (AC) potential drop (PD) method is developed for measuring crack length under combined thermal and mechanical loading. An insulated aluminum film deposited on the surface of center cracked 6061-T6 aluminum alloy test specimens provides a medium for the measurement of PD data used in calculating crack length. Experimental PD data is collected over a range of crack lengths and temperatures and compared against theoretical and numerical models. Potential difference data is found to be linear over a wide range of crack lengths. An analytical relationship is derived based on a theoretical model to provide a predicted crack length given potential difference and specimen temperature. Calculated crack lengths are compared to optically measured crack lengths for cracks 0 to 30 mm in length at temperatures up to 300$\sp\circ$C. Calculated values were found to be within $\pm$0.3 mm of measurement results over nearly all temperatures and crack lengths. Improvement of the accuracy of calibration equations and the sensitivity of the foil deposit is achieved through a numerical study of the film potential field in various configurations. Application of the technique to studies of creep and fatigue induced crack growth under varied thermomechanical loading suggested a resolution of 0.02 mm and accuracy within $\pm$0.09 mm using an excitation current of only 1.98 mA. en_US dc.format.extent 7041270 bytes dc.format.extent 184 bytes dc.format.mimetype application/pdf dc.format.mimetype text/plain dc.language en en_US dc.language.iso en_US dc.rights info:eu-repo/semantics/openAccess dc.title Experimental crack length measurement under variable temperature using a thin film AC potential difference technique en_US dc.type info:eu-repo/semantics/masterThesis dc.type master thesis en_US dc.degree.discipline Mechanical & Manufacturing Engineering en_US dc.degree.level Master of Science (M.Sc.) en_US
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