Quantitative fractography techniques have been in use at the Aeronautical Research Laboratory (ARL), Melbourne, Australia, for more than 15 years, and they have been developed into a specialized facility for deriving crack growth histories from fracture surfaces. This capability has played a fundamental role in a number of pioneering life extension programs which have permitted the continued operation of several aircraft types in current service with the Royal Australian Air Force (RAAF). The increasing RAAF demand for advanced fractography has required the development over a number of years of computer-based semiautomated data acquisition and data processing facilities for fractographic analysis; these developments have permitted a significant improvement in the speed with which fracture surfaces may be analyzed and are now used routinely in ARL's quantitative fractography.
This paper describes current ARL activities in the use and further development of quantitative fractographic techniques and the specialized facilities employed to derive and process data from fracture surfaces observed by both scanning electron microscopy and optical microscopy. The results able to be obtained are illustrated by reference to case histories of defects in components from service aircraft, from full-scale component tests, and from laboratory test samples. Procedures for minimizing or overcoming some of the difficulties associated with interpretation of fracture surface markings are discussed. The paper also describes the way in which fracture mechanics concepts need to be used in conjunction with fracture surface analysis to achieve a correct understanding of the crack growth history. In particular, some empirically based approaches developed for interpolation and extrapolation of incomplete crack growth histories may now be understood by reference to fracture mechanics concepts. Finally, current and future developments in fracture surface analysis are discussed, with particular reference to the benefits to be gained by the introduction of modern image processing and image enhancement techniques.