Abstract: A method of operating on a workpiece comprises offering a probe of material harder than the workpiece material to a continuous surface of the workpiece causing relative cyclic movement between the probe and the workpiece while urging the probe and workpiece together whereby frictional heat is generated as the probe enters the workpiece so as to create a plasticized region in the workpiece material around the probe, stopping the relative cyclic movement, and allowing the plasticized material to solidify around the probe. This technique, which we refer to as "friction plunge welding" provides a very simple method of joining a probe to a workpiece. The method can be used for repairing cracks and the like within a workpiece or for joining members, such as studs or bushes, to a workpiece.

Abstract: A method of monitoring a structure comprising the steps of:(a) transmitting a burst of acoustic energy through the structure from a transducer coupled to it,(b) detecting a received wave resulting from the burst at one or more transducers coupled to the structure, and(c) monitoring for any change in the structure after a given time (or event) by repeating the steps (a) and (b) with the coupling of the transducers being essentially unaltered, to detect a further received wave or waves; comparing the further received wave or waves with a corresponding reference received wave or waves; and determining for each comparison whether the received wave differs from the reference, any difference being indicative of the formation or growth of a defect in the overall acoustic path travelled by the acoustic energy.

Abstract: A method and apparatus of monitoring the resistance characteristics of a circuit carrying an alternating current or a current having an alternating component is described. The apparatus includes first integration or averaging means for integrating or averaging the potential drop for the period between instants when the instantaneous current has the same value in a current loop; and display means for displaying a value representative of the output from the integration or averaging means.

Abstract: A method and apparatus for short-circuit MIG welding is described. The apparatus comprises a power supply electrically connected with electrode wire and a workpiece in use; and electrode wire feed means. Monitoring means is provided for monitoring the ratio (M) of one of the mean and successive integral of the arc duration to the corresponding one of the mean and the successive integral of the short-circuit duration. The welding process can be monitored by monitoring the ratio (M).