Mat. Res. Bull. Vol. 6, pp. 153-162, 1971. Pergamon Press, Inc. Printed in the United States. THE MECHANICAL PROPERTIES OF ANODICALLY FORMED ALUMINIUM OXIDE FILMS D. G. Brandon and D. Eliezer Department of Materials Engineering Technion - Israel Institute of Technology Haifa, Israel (Received December 29, 1970; Communicated by R. W. Douglas) ABSTRACT The mechanical properties of amorphous aluminium oxide films formed by anodising were determined using a bulge test. The bi- axial modulus, the fracture strength, the fracture strain and in- ternal stress, and the reduced bursting pressure were measured. The results were consistent with previous data and confirmed that the bulge test is a rapid and easily reproduced method of de- termining the mechanical properties of thin films. Introduction Considering the present commercial importance of thin films, re- markably little previous work has been published on their mechanical prop- erties. In spite of, or perhaps because of, the great variety of techniques available for determining these properties, results to date are both incom- plete and contradictory (1-4). In a previous paper it was shown how a differential-pressure ("bulge") test could be used to determine the biaxial stress-strain curve for a thin film (5). This test has the overwhelming advantage of being easy to repro- duce and simple to perform. Moreover, the results are readily interpreted in terms of the conventional parameters used to describe bulk properties. Anodically-formed oxides constitute a class of thin films of increas- ing practical importance; as corrosion resistant layers, as transparent win- 153