Analysis of structural problems with the aid of scale models constructed in low–modulus thermoplastic materials such as Perspex, Vybak and Darvic is now well established. Measurements of strain and deflexion are complicated, however, by the structure creeping under load and by the effects of changes in ambient conditions of temperature and humidity. Experience shows that these difficulties can usually be overcome by the use of suitable testing techniques, but strain measurements using resistance strain gauges are sometimes regarded critically because these measurements are said to be influenced by the heating effect of the bridge current and the low thermal conductivity of thermoplastics. One aspect of this could be a softening of the model material with heat causing a variation in the value of Young's modulus. At the Naval Construction Research Establishment, Dunfermline, thermoplastic model testing has for many years been a feature of the work in support of structural and theoretical analyses and the information derived from this work shows that the criticisms are unjustified.

Present sensor designs are critically examined and their commonly encountered problems are assessed. A sensor design is detailed and its performance characteristics are examined showing that the problems have either been eliminated or minimised.

Results are described of a theoretical and experimental investigation of the effects of collision damage in the form of elasto-plastic lateral bending and local indentations, on the stiffness and strength of tubular steel bracing members. Full-scale tests have been carried out on two pairs of nominally identical braces obtained from the BP West Sole Platform, recently removed from the North Sea following completion of service. One tube from each pair was tested to collapsl under compres sive load in an initially undamaged condition while the second was tested to collaple following application of simulated collis:·.on dama,.:,e, thus providing a direct indication of damage effects. Results were found to correlate satisfactorily with theoretical analysis and with four tests on small-scale tUbes representing as closely as possible the fullscale experiments. The relationship between collision loads and damage deformations was examined.

Methods for measuring residual stresses and distortions in welded structures are described and initial results are given of a suwey being carried out during manufacture of warship hull sections. The stresses are determined by measuring the elastic strain induced in the plate and stiffeners due to contraction of the stiffener welds, and profiles of the stiffener and plating after welding have been obtained. The survey is intended to provide information for use in future design calculations of the buckling strength of ship hulls.

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