Papers by Author: S.W. Boyd

Abstract: Digital image correlation (DIC) is an optical technique for full field deformation measurement. The spatial resolution and precision of the measurements are limited by the number of pixels within the image. The use of magnifying optics provides greater spatial resolution images, enabling smaller displacements to be observed with greater accuracy. Increasing the magnification of an image significantly changes the appearance of the non-periodic, stochastic speckle pattern which provides the grey scale contrast necessary for the image correlation method. In the paper a methodology is developed to evaluate the properties of different speckle pattern types under a range of resolutions up to 705 pixel / mm. Numerical deformation of the patterns is also undertaken to evaluate how the changes in the pattern properties affect the accuracy of the DIC measurements.

Abstract: The paper describes initial work on using 2D digital image correlation (DIC) and thermoelastic stress analysis (TSA) to obtain data from edge cracks in cross-ply laminates. It is demonstrated that detailed data related to the crack tip stresses can be obtained using TSA. The work reveals some of the limitations experienced when using DIC in applications where high spatial resolution is required. A detailed discussion is provided along with an outline for future work.

Abstract: The marine industry at present employs the use of aluminium extrusions in the construction of decks and superstructures that could be replaced with pultruded glass reinforced plastic (GRP) profiles. The length of the pultruded section is limited and therefore, efficient and economic jointing techniques must be developed that can withstand the loads applied to ship structures. This paper evaluates a novel means of adhesively bonded connection for GRP structures known as a finger joint. Various joint geometries are examined, load displacement behaviour is established and Thermoelastic Stress Analysis (TSA) is used to provide the full field stress distribution over the joint. The results of the TSA are compared with the load displacement behaviour. It is shown that by increasing fingertip angle there is a decrease in load carrying capacity, a decrease in shear stress and an increase in stress concentration factor at the finger joint tip.

Abstract: There are many instances where the use of weight saving composite materials for an entire structure is either; too complex, too expensive or unfeasible. In these circumstances the use of a hybrid structure can incorporate the benefits of traditional construction materials, for example steel, coupled with the advantages of composite materials in weight critical areas. In the present study, an investigation was undertaken into the fatigue life characterisation of a hybrid joint for marine application. In addition the residual strength of the joint, after a fixed number of fatigue cycles, was assessed under axial compression and bending loads. A progressive damage model was developed to predict the location of major stress concentrations, the path of damage and subsequent loss in stiffness of the joint under axial compression.