Papers by Author: P. Ryan

Abstract: The liquid film re-growth behaviour resulting from pulsed laser surface melting (LSM) has been investigated for typical 2xxx, and 7xxx aerospace alloys, both on parent plate and friction stir welded (FSW) joints. In Zr free alloys, as a result of the high growth rate and steep thermal gradient, the melted layer re-grew with a stable front, epitaxially, from the parent subsurface grains. This caused a thin coarse grained solidified layer to form over the parent material, thermomechanically affected zone (TMAZ) and heat affected zone (HAZ), and fine columnar grains to develop over the FSW nugget zone of the same order in width as the nugget grain size. In the case of the Zr containing alloys, a very fine columnar grain structure was found over the entire surface, independent of the subsurface grain structure. This has been shown to occur by growth selection from a band of nanoscale Al grains epitaxially nucleated on Al3Zr dispersoids, at the melt solid interface, that had not fully dissolved in the melt.

Abstract: By combining modern surface strain measurement techniques with the traditional tensile test mechanical test, a method has been developed whereby the mechanical properties of a test sample with a heterogeneous microstructure such can be characterised in one test. In this paper the applicability to such a method of two such surface strain measurement techniques, image correlation (IC) and electronic speckle pattern interferometry (ESPI), is assessed. Two commercially available systems were used to monitor, simultaneously, the surface strain on tensile test specimens during testing. Measurements on homogeneous samples were compared with measurements made using strain gauges and excellent agreement was found. Elastic modulus and proof stress values measured in these standard samples showed that the uncertainty in the measurements was below 10%. The method was then applied to an inertia friction weld, whose strength varied linearly as a function of distance from the weld line. The values of proof stress obtained were compared with micro-hardness measurements.