Experimental Investigation Into Plugging of Open Ended Piles

This paper presents the results of a model pile test in a transparent photoelastic medium. This medium is composed of crushed glass particles in a refractive index matching liquid. The test setup allows for quantitative photoelastic measurements. For the measurement of the photoelastic data the phase stepping technique is used. Stresses in the granular medium located next to and in the plug were recorded at varying installation depths of the pile during monotonic jacking of the transparent pile in combination with the pile head load. The horizontal stress ratio in the plug for this particular test is found to be equal to the vertical stress. A distinct stress arch below the pile base is observed during penetration. The high local stress increase in and below the plug move with the pile as the plug travels downward into the soil and do not change much in absolute magnitude.

An overdetermined phase-stepping strategy for the capture of high-quality photoelastic data

An overdetermined extension to the phase-stepping approach to digital photoelasticity is described in order to obtain high-quality photoelastic data for use in the examination of contact problems. A framework is adapted from earlier work by Ambirajan and Look and is applied to the generalization of existing phase-stepping strategies and the synthesis of new overdetermined variants on the method. The optimality of these strategies is demonstrated computationally, and the influence of errors in quarter-wave plate orientation and assumed isoclinic angle is explored. Sample experimental results are presented, which demonstrate the excellent performance of the system when used with narrow-bandwidth filters to approximate the use of monochromatic light. When the internal filters integral with the colour camera were used, the results were also of high quality up to a relative retardation of around 4.5 measured on the green channel, but measurements of higher fringe orders were progressively degraded owing to the broad bandwidths of the camera's internal filters.

A review of automated methods for the collection and analysis of photoelastic data

Photoelasticity is one of the most widely used full-field methods for experimental stress analysis. However, the collection of photoelastic parameters can be a long and tedious process. The advent of automated photoelastic systems has allowed the experimentalists to speed up the rate of analysis and to perform more complex investigations. This paper provides a survey of recent methods of automated photoelasticity developed in the last 20 years, i.e. methods of the fringe centres, half-fringe photoelasticity, phase-stepping photoelasticity, methods based on the Fourier transform, spectral content analysis (SCA) and RGB (red, green, blue) photoelasticity.

Computer aided photoelastic stress analysis of a variable-pitch lead screw

Three-dimensional stress-freezing photoelasticity is applied to analyse the stress in a variable-pitch lead screw at contact with two conical meshing elements. A PC-based image-processing system and the relevant digital techniques are used to collect the photoelastic data, and the cubic technique is used to evaluate the effective stress at the contact region. The model-making and computer aided data collection procedures are described. Contour plots of the effective stress at the contact regions are presented. It was found that the highest effective stress values on the two contact thread surfaces are approximately the same, although the exerting forces are quite different.