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Title: Interlaminar bonding in ultrasonic consolidation
Authors: Edmonds, Hannah
Keywords: Ultrasonic consolidation
Ultrasonic additive manufacture
Bauschinger effect
Surface effect
Volume effect
Plastic deformation
Interlaminar porosity
Sonotrode
Surface texture
Additive manufacturing
Issue Date: 2012
Publisher: © Hannah Catherine Edmonds
Abstract: Ultrasonic Consolidation (UC) is a solid state additive manufacturing process which fabricates three-dimensional objects by ultrasonically joining metal foils together, layer-by-layer, to form a solid part. The aim of this research was to investigate the effect of different UC operating parameters, specifically; sonotrode weld surface texture, UC substrate surface texture and foil surface texture, on interlaminar bonding so that appropriate process parameters can be selected to produce parts with different properties for a range of different applications. Within the investigation white light interferometry was used to characterise the weld surface texture of three sonotrodes and statistical analysis was used to quantify the significance of their effect on UC substrate average surface roughness (Sa) and bond strength over a range of processing conditions. Topology transfer between the different sonotrode weld surfaces and UC substrate surface textures was the examined and the subsequent effect on interlaminar porosity, bond strength and microstructure was measured using optical microscopy, peel testing and Focussed Ion Beam (FIB) microscopy. Stock foil was textured prior to processing by sonotrode rolling (without the ultrasonics engaged) and a comparison of the topology transfer, interlaminar porosity, bond strength and microstructure of samples fabricated using pre-textured foils was conducted compared to samples made with standard stock foil. Sonotrode weld surface Sa was identified as the most significant factor in determining the resulting substrate surface Sa and interlaminar peel strength in UC, followed by sonotrode oscillation amplitude and weld speed, while weld force did not appear to have a measurable effect over the range of processing conditions examined. The transfer of weld surface texture characteristics from sonotrodes to the samples they produced was observed. Sonotrode weld surface texture and the plastic deformation it generates through contact with the foil surface during processing emerged as factors that appear to effect interlaminar porosity, bond strength and grain morphology in UC. A relationship between the degree of sonotrode-induced deformation and the apparent level of interlaminar recovery and grain growth was proposed and discussed in relation to existing UC bonding theory, including the influence of the surface, volume and Bauschinger effects. UC samples manufactured with pre-textured foils exhibited increased interlaminar porosity but exhibited higher resistance to delamination compared to samples made with stock foil. The change in interlaminar bond characteristics was attributed to the plastic deformation experienced by the foil during the modification process.
Description: This thesis is restricted access until 22nd November 2017. A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
Version: Closed Access
URI: https://dspace.lboro.ac.uk/2134/10999
Appears in Collections:Closed Access PhD Theses (Mechanical and Manufacturing Engineering)

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