Abstract: The entire contents of these applications are incorporated herein by reference. A method and apparatus for detecting and monitoring fractures in a structure by monitoring acoustic energy transmitted within the structure by receiving continuously over a period of time electrical signals from a plurality of acoustic tranducers carried by the structure in a pulse processor to form data bursts from pulses in the signals and deriving, for each of a plurality of the data bursts, delta-t values representing the differences between burst arrival times at each sensor, the delta-t values forming a delta-t pattern, and generating a damage indication signal when the delta-t pattern is repeated to a predetermined degree.

Abstract: Apparatus and a method for inspecting a topology of a surface (2) of a structural member (1) are provided. The degree to which a known type of stress has been applied to the member may be ascertained using a Moiré grid (8). The method involves providing a range of calibration samples of structurally equivalent members, the samples each having been subject to the known type of stress to a differing respective degree. Measurements taken using the apparatus and method of the invention are then compared with measurements taken from a calibration sample to determine the amount of stress which has been applied.

Abstract: A method and apparatus for detecting and monitoring fractures in a structure by monitoring acoustic energy transmitted within the structure by receiving continuously over a period of time electrical signals from a plurality of acoustic tranducers carried by the structure in a pulse processor to form data bursts from pulses in the signals and deriving, for each of a plurality of the data bursts, delta-t values representing the differences between burst arrival times at each sensor, the delta-t values forming a delta-t pattern, and generating a damage indication signal when the delta-t pattern is repeated to a predetermined degree.