Claire Leppard

Radial deformation measurement of a cylinder under compression using multicore fibre

A multicore fibre (MCF) sensor to measure the radial deformation of a compliant cylinder under compression is presented. The sensor is connectorised and need not be permanently bonded to the test object. A differential measurement technique using FBGs written into the MCF makes the sensor temperature insensitive. FBG measurement of axial strain of a cylinder under compression is also reported.

On the thermal expansion hysteresis of a UK PBX

The linear coefficient of thermal expansion of a UK PBX has been measured over the temperature range -40 to +80 °C: (5.55 ± 0.05) ×10-5 K-1. A subtle but measurable hysteresis in length as a function of temperature was observed. This is attributed to a mismatch between the thermal expansion coefficients of its solid-fill and binder constituents. On heating or cooling this induces mechanical stresses within the binder system, which being viscous it can flow to relieve. A change in sample temperature results in an asymptotic relaxation to a mechanical equilibrium length. This is analogous to the type of stress relaxation and creep behaviour normally associated with the bulk response of viscoelastic materials when more conventional stresses are applied.

Visualisation of the three-dimensional structure of energetic polymer composite materials

A review of imaging techniques which can be used to acquire three dimensional data on polymer composite materials is presented. The techniques chosen utilise a variety of contrast forming mechanisms including x-ray, nuclear magnetic resonance and optical & electron microscopy. Discussion is illustrated with reference to a particular HMX based UK PBX. The achievable contrast and spatial resolutions are considered, with arguments relating to destructive and non-destructive methods of acquiring data. The eventual use of this work will be in computational modelling.

EVIDENCE FOR FRICTION BETWEEN CRACK SURFACES DURING DEFORMATION OF COMPOSITE PLASTIC BONDED EXPLOSIVES

The compressive strength has been found to increase linearly with hydrostatic pressure in a low pressure range in which work softening due to crack damage is observed. Analysis indicates that this linear increase can be attributed to friction between the surfaces of closed cracks and a friction coefficient is obtained from the linear slope and the measured angle of the failure plane. Analysis also indicates that the plane of maximum shear stress, the failure plane, is at an angle greater than 45 degrees when friction is present and a friction coefficient is also calculated directly from this angle. In addition, a relationship between the ratio of compressive to tensile strength and the friction coefficient has been given by Zuo and Dienes. The observed ratio is greater than the predicted value without friction and a friction coefficient is obtained from this relationship which is in agreement with the two values obtained as discussed above. This agreement of three independent measures of the friction coef...