Clive Siviour - Academia.edu (original) (raw)

Papers by Clive Siviour

Conference proceedings of the Society for Experimental Mechanics, Sep 8, 2016

Journal of Biomechanics, 2012

Materials

This research utilises a novel heat stage combined with a Zeiss scanning electron microscope to i... more This research utilises a novel heat stage combined with a Zeiss scanning electron microscope to investigate phase changes in iron alloys at temperatures up to 800 ℃ using SE and EBSD imaging. Carbon steel samples with starting structures of ferrite/pearlite were transformed into austenite using the commercial heat treatment process whilst imaging within the SEM. This process facilitates capturing both grain and phase transformation in real time allowing better insight into the microstructural evolution and overall phase change kinetics of this heat treatment. The technique for imaging uses a combination of localised EBSD high temperature imaging combined with the development of high temperature thermal-etching SE imaging technique. The SE thermal etching technique, as verified by EBSD images, enables tracking of a statistically significant number of grains (>100) and identification of individual phases. As well as being applied to carbon steel as shown here, the technique is part...

This dissertation examines the high strain rate mechanical properties of polymers, polymer bonded... more This dissertation examines the high strain rate mechanical properties of polymers, polymer bonded explosives and solders. In addition, it examines experimental developments that will allow more detailed investigation of these properties in the future. The split Hopkinson pressure bar is a standard apparatus used to measure the mechanical strength of materials at strain rates between 500 and 10,000 s- 1 � Measurements are performed by dynamically loading a small cylindrical specimen between two rods that are instrumented with strain gauges. The data from these strain gauges are used to calculate stress and strain in the specimen as functions of time. Chapter two contains an account of the Hopkinson bar system and its application. The advantages and limitations of the system are presented and discussed. Once of these limitations, the time taken for the specimen to reach mechanical equilibrium, is examined in detail in chapter three. In chapter four the variation of strength with strain rate of two polymers, polycarbonate and polyvinyladine difluoride, is investigated. It is shown that at high stain rates their mechanical strength is increased by freezing out of low order molecular relaxations. Chapter five presents data from measurements made on polymer-bonded explosives. The effect of crystal size on the mechanical properties of the mixture is examined, and it is shown that the strength of the material varies as the inverse square root of crystal spacing. In chapter six measurements of the high strain rate properties of different solder materials are presented. These measurements were made to provide high quality experimental results for the development of material models for solder at high strain rates. Chapter seven presents results from the application of speckle metrology, a wellestablished technique for making optical measurements of displacements, to the Hopkinson bar system. Along with a line laser device for measuring specimen radius this allowed accurate measurements of the Poisson's ratio of Hopkinson ba [...]

Crystallographic texture in polycrystalline HCP and cubic materials, often developed during therm... more Crystallographic texture in polycrystalline HCP and cubic materials, often developed during thermomechanical deformations, has profound effects on properties at the macroscopic or component level; given the respective natures of current detection techniques, a non-destructive, three-dimensional bulk texture detection method for these materials is yet to be developed. This thesis tries to achieve this goal through systematic studies on the relationship between ultrasonic wave velocity and texture. The feasibility of such development is firstly reviewed via the combination of computational and experimental studies on exemplary HCP materials. Numerical results obtained via a representative volume element (RVE) methodology reveal that the wave speed varies progressively and significantly with changing texture, and experimental ultrasound studies combined with EBSD characterisation demonstrate distinguished velocity profiles for samples with different textures. Thus the possibility of the development is proved by the combined results. A novel convolution theorem is then presented, which couples the single crystal wave speed (the kernel function) with polycrystal orientation distribution function to give the resultant polycrystal wave speed function. Firstly developed on HCP and then successfully extended to general anisotropic materials, the theorem expresses the three functions as harmonic expansions thus enabling the calculation of any one of them when the other two are known. Hence, the forward problem of determination of polycrystal wave speed is solved for all crystal systems with verifications on varying textures show near-perfect representation of the sensitivity of wave speed to texture as well as quantitative predictions of polycrystal wave speed. More importantly, the theorem also presents a solution to the long-standing inverse problem for HCP and cubic materials, with proof of principle established where groups of HCP and cubic textures are recovered solely from polycrystal wave velocities through the theorem and the results show good agreements with the original textures. Therefore the theorem opens up the possibility of developing a powerful package for bulk texture measurement and wave propagation studies in HCP, cubic materials and beyond.

EPJ Web of Conferences, 2021

The Photon Doppler Velocimetry (PDV) technique is used to capture simultaneously propagating elas... more The Photon Doppler Velocimetry (PDV) technique is used to capture simultaneously propagating elastic waves of longitudinal and shear nature in a Tension-Torsion Hopkinson Bar (TTHB) apparatus. The system uses a pair of probes per velocity measurement, which were taken on the opposite sides of the TTHB bar with a laser irradiated spot size of ~35 µm. The collected data were compared to the measurements obtained from the conventional strain gauge technique, and were in good agreement. The PDV method was effective in separating longitudinal and rotation signals even when they were superimposed on each other at the gauge location. This approach is also shown to be effective in detecting and accounting for the presence of bending waves in the TTHB bars.

Experimental Mechanics, 2020

Background Understanding the mechanical response of elastomers to applied deformation at differen... more Background Understanding the mechanical response of elastomers to applied deformation at different strain rates and temperatures is crucial in industrial design and manufacture; however, this response is often difficult to measure, especially at high strain rates (e.g. > 100 s− 1), and more predictive methods to obtain constitutive relationships are required. Objective The objective of the research described in this paper is to develop such methods. Method The paper outlines a novel approach combining quasi-static monotonic tests in tension and compression, quasi-static cyclic tests in tension, and high strain rate tests in compression, with dynamic mechanical analysis and time-temperature superposition. A generalized viscoelastic model incorporating continuum damage is calibrated. Results The results show that a model calibrated using data from quasi-static compression and dynamic mechanical analysis can be used to adequately predict the compressive high strain rate response: he...

Review of Scientific Instruments, 2020

$Research paper thumbnail of Predicting the high strain rate response of plasticised poly(vinyl chloride) using a fractional derivative model$

EPJ Web of Conferences, 2018

Polymers are frequently used in fields as diverse as aerospace, biomedicine, automotive and in-du... more Polymers are frequently used in fields as diverse as aerospace, biomedicine, automotive and in-dustrial vibration damping, where they are often subjected to high strain rate or impact loading. Poly(vinyl chloride) (PVC), and its plasticised variants (PPVC), are just two examples of this broad category of materi-als. Since many polymers exhibit strong rate and temperature dependence, including a low temperature brittle transition, it is extremely important to understand their mechanical responses over a wide range of loading con-ditions.PVC with 60 wt% plasticiser is used in this study, as its highly rubbery nature lends itself well to being used in various load mitigation and energy absorption applications. It is challenging to obtain high strain rate data on rubbery materials using conventional techniques such as the split-Hopkinson (Kolsky) bar. Therefore, alternative approaches are required. Based on previous work developing a framework to predict high rate re-sponseusing a fract...

EPJ Web of Conferences, 2015

AIP Conference Proceedings, 2017

Journal of Dynamic Behavior of Materials, 2015

Materials Science and Engineering: A, 2016

Chemical Science, 2016

We report a non-cytotoxic supramolecular polyurethane network whose mechanical properties can be ... more We report a non-cytotoxic supramolecular polyurethane network whose mechanical properties can be recovered efficiently (>99%) at body temperature.