This research was driven by the capability of the Ultrasonic Consolidation (UC) manufacturing process to create smart metal matrix composites for use within high value engineering sectors, such as aerospace. The UC process is a hybrid additive/subtractive manufacturing process that embeds fibres into metal matrices via the exploitation of a high plastic flow, low temperature phenomenon encountered at ultrasonic frequency mechanical vibrations. The research concerned an investigation of the use of the UC process for embedding Nickel-Titanium alloy (NiTi) shape memory alloy (SMA) fibres into Aluminium (Al) matrices which could potentially be used as vibration damping structures, stress state variable structures, as well as other future smart material applications.
It was hypothesised that the fibre volume fraction within a UC matrix was limited due to a reduction in foil/foil bonding, caused by increased fibre numbers, as opposed to the total level of plastic flow of the matrix material being insufficient to accommodate the increased fibre numbers.
This hypothesis was tested by increasing the NiTi SMA fibre volume fraction, within an Al 3003 (T0) metal matrix, beyond that of previous UC work. The metal matrix and the fibre matrix interface of these samples was then microscopically analysed and the overall UC sample integrity was tested via mechanical peel testing. It was found that a fibre volume fraction of ~9.8% volume (30 X Ø100 μm SMA fibres) was the maximum achievable using an Al 3003 (T0) 100 μm thick foil material and conventional UC fibre embedding.
A revised hypothesis was postulated that the interlaminar structure created during UC was affected by the process parameters used. This interlaminar structure contained areas of un-bonded foil and the increase of UC process parameters would reduce this area of un-bonded foil. Areas of this interlaminar structure were also thought to have undergone grain refinement which would have created harder material areas within the structure. It was suggested that maximum plastic flow of the matrix had not been
reached and thus the use of larger diameter NiTi SMA fibres were embedded to increase the effective SMA fibre volume fraction within Al 3003 (T0) UC samples. It was suggested that the embedding of SMA fibres via UC had an abrasive effect on the SMA fibres and the SMA fibres had an effect on the Al 3003 (T0) microstructure. It was further suggested that the activation of UC embedded SMA fibres would reduce the strength of the fibre/matrix interface and the matrix would impede the ability of the SMA fibres to contract causing a forceful interaction at the fibre to matrix interface, weakening the UC structure.
This thesis is confidential until 1st June 2016. A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.