Christopher Shearwood

Mechanical properties and interfacial characteristics of carbon-nanotube-reinforced epoxy thin films

Multiwalled carbon nanotubes (MWNT) reinforced epoxy composite thin films were prepared by a microfabrication process and their elastic modulus was determined using a shaft-loaded blister test and linear and nonlinear elasticity models. Compared to net resin thin films, a 20% increase in elastic modulus was seen when 0.1 wt % MWNTs were added, suggesting MWNT alignment by spin coating. Electron microscopic observations of the fracture surfaces suggested high interfacial shear stress between MWNTs and the epoxy matrix, a result supported by both molecular mechanics simulation and micromechanics calculations.

Characterization of spark plasma sintered Ag nanopowders

The low temperature sintering behaviour of nanocrystalline Ag powder (with an average size of 70 nm) was characterized. Using spark plasma sintering (SPS), the Ag nanopowders can be successfully sintered at low pressure for only 5 min without external heating, and the sintering density increases and porosity decreases significantly with increase in the sintering temperature. Nanoindentation has been used to characterize the SPS sintered Ag samples. The mechanisms of the low sintering temperature behaviour of the nano-Ag powder and the nanoscale mechanical performance have been discussed. Compression tests were also used to characterize the mechanical properties of the sintered Ag sample with a maximum strain up to 15%.

Spark plasma sintering of TiNi nano-powders for biological application

Nano-sized TiNi powder with an average size of 50 nm was consolidated using spark plasma sintering (SPS) at 800 ◦ C for 5 min. A layer of anatase TiO2 coating was formed on the sintered TiNi by chemical reaction with a hydrogen peroxide (H2O2) solution at 60 ◦ C followed by heat treatment at 400 ◦ C to enhance the bioactivity of the metal surface. Cell culture using osteoblast cells and a biomimetic test in simulated body fluid proved the biocompatibility of the chemically treated SPS TiNi.

A shaft-loaded blister test for elastic response and delamination behavior of thin film-substrate system

The elastic response of a thin film of photoresist deposited on a silicon wafer is studied by using a shaft-loaded blister test method developed recently. Experiment data are compared with an analytical solution. Results demonstrated that under shaft loading, the thin film underwent a pure bending mode at small deformation and gradually transformed to a pure stretching mode at larger deformation. The effect of residual stress on elastic response is also studied. The delamination of thin film from substrate can be successfully measured under displacement control mode by the shaft-loaded blister test.

Proposal for Micromachined Accelerometer, Based on a Contactless Suspension With Zero Spring Constant

In this paper, a micromachined accelerometer, based on a contactless suspension with a zero spring constant is proposed. The sensor provides the possibility of a significant increase in resolution. Minimization of the spring constant of the contactless suspension is achieved by combining inductive and electrical contactless suspensions. To study the conditions required to eliminate the spring constant of the suspension and achieve stable levitation of the accelerometer proof mass, a mathematical model of the suspension is developed. It is shown that such a suspension can be developed in principle.

Proposal for a Micromachined Dynamically Tuned Gyroscope, Based on a Contactless Suspension

In this paper, the operating principle of a micromachined, dynamically tuned gyroscope, based on a contactless suspension is discussed and its mathematical model is derived. Dynamical analysis based on this mathematical model for the case in which the contactless suspension provides “hard” electrical springs is conducted. The analysis shows that such a gyroscope can be created in principal and provides a value for the gyroscope gain to measuring angular rate which is several orders of magnitude greater in comparison with existed prototypes of the micromachined gyroscope based on a contactless suspension.

Spark plasma sintering of TiNi nanopowders

Nano-size TiNi powder prepared by electro explosion of TiNi wire process as processed by spark plasma sintering for 5 minutes at variable temperatures between 700 and 1000°C. The shape memory effect and crystallagraphy of both the powder and the sintered TiNi specimens were extensively characterized. The specimen sintered at a temperature of 700° showed high porosity and partial densification, but with apparent shape memory effect. By contrast, the specimens sintered at higher sintering temperatures above 900°C showed high density, but experienced extensive oxidation with teh resulting loss of the shape memory effect. High temperature sintering resulted in significant solid-state inter-diffusion of atoms and thus the formation of different intermetallic phases, such as NiTi2 and Ni3Ti. The phase transformation temperatures and enthalpies for the samples sintered at 700 and 800°C increased with increasing temperature. In addition, the differences between the start and finish transformation temperatures for the sintered specimens appear to be significantly narrower compared to those of the nano-powder.

AN ANALYTICAL MODEL OF MICROMACHINED ELECTROMAGNETIC INDUCTIVE CONTACTLESS SUSPENSION

The paper presents an analytical model of a micromachined electromagnetic inductive contactless suspension, which describes the dynamics of a levitated disk shaped proof mass in space, near an equilibrium point. The proof mass is levitated in an electromagnetic field created by a ring shaped coil. The model derives from the analysis of the set of Lagrange - Maxwell equations obtained for the proof mass - coil system in a general form. Also the condition for the stable levitation of the proof mass in space is developed and expressed in terms of coefficients of the quadratic form of a function of mutual inductance between the disk shaped proof mass and ring shaped coil.

Influence of the Elastic Properties of the Spring Element on the Rotor Tuning Condition of a Rotor Vibratory Gyroscope

This paper considers the dependence of the rotor tuning condition of a rotor-vibratory gyroscope on the elastic properties of the spring element which has, in particular, additional angular deflection along an axis perpendicular to the output axis of gyroscope. As a consequence of this dependence, the limitations to the performance of the rotor tuning condition are examined and a mathematical equation describing the rotor tuning error, dependent on variations in the gyroscope parameters, is obtained. Analysis of the equation of rotor tuning error allows us to formulate the condition needed for minimization of this error against temperature change.

Spark plasma sintering of silver nanopowder

The spark plasma sintering behaviour of silver nanopowder prepared by the electro-explosion method was investigated. Consolidation was carried out from 50°C to 800°C for 5 mins at 34 MPa with differential scanning calorimetry indicating a sintering onset temperature as low as 160°C and an activation energy of 86±1 kJ/mol. Near full density resulted from treatment at 300°C, and at higher temperatures a normal Hall-Petch relation is obeyed. The enhancement of Vickers hardness to 1000MPa for materials sintered at 300°C is three times greater than for silver annealed in a conventional way. While polysynthetic twinning contributes to superior hardness, the primary cause is the sub-micron grain size.