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Autoradiography-Based Differential Wear Scar Mapping, 03-R9592

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Principal Investigators
Douglas Eberle
Martin Treuhaft
Craig Wall

Inclusive Dates:  11/28/05 – 03/28/06

Background - SwRI has long been a leader in Radioactive Tracer Technology (RATT®) and has an active program serving the needs of engine manufacturers and others who require sensitive and convenient measurement of wear processes. Such measurements typically involve making the objects that are subject to wear radioactive and then detecting and quantitating the radioactive wear debris to evaluate the amount of wear that has occurred and to correlate that wear with the specific conditions under which the wear took place. In addition to quantitative information regarding wear rates, it is becoming increasingly important, in the particular case of diesel engine liners, to know the shape of the wear scar at top ring reversal on at least a qualitative basis. By taking advantage of a client-sponsored project using surface layer activated liners in a diesel engine wear test, an idea was conceived to develop a convenient method for obtaining this information through autoradiography.

Approach - The objective of this program was to develop a convenient method for creating a two-dimensional qualitative mapping of diesel engine liner wear scars as well as to investigate techniques for converting these to representative three-dimensional quantitative images. Liners in a modern diesel engine were surface layer activated at the top ring reversal. Baseline autoradiographs were obtained by exposing x-ray film in direct contact with the radioactive wear surfaces for a controlled period of time. The liners were then installed in an engine and subjected to wear. At the end of the engine wear test, the liners were removed, and autoradiographs were retaken over the worn activated areas. The sets of autoradiographs were digitized using a scanner, which converted the images to matrices of grayscale values. Using a freely available open source image processing program, the images were positionally indexed to each other and then subtracted to obtain a matrix of grayscale values representing a two-dimensional image of the wear scars. These images were then transformed into three-dimensional representations.

Autoradiograph Images of Surface Before and After Scratch

3-D Representation of Scratch

Accomplishments - Baseline and post-test autoradiographs were successfully completed of the engine liner surface layer activated areas. These autoradiographs were digitized, indexed, and subtracted to obtain two-dimensional qualitative images of wear scars. Because of likely inconsistencies in film emulsions, exposures, and digitization, however, conversion to three-dimensional surface representations revealed some skewing. It is felt the current method can successfully provide useful wear scar location and images of the scar shape and that further work may be able to develop techniques to prevent or correct this skewing to make a three-dimensional quantitative image.

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