Contact pressure distribution in circular tube expansion using a conical plug

The technique of evaluating contact pressure distributions along a plug metal interface by measuring the deformations in terms of plug surface strains using electrical resistance strain gauges has been explored. To relate the unknown pressure distributions to the strain gauge readings, a finite element model of a plug was used assuming that the normal and shear pressures can be represented as a linear combination of generalized distributions, which have the form of polynomials up to the fourth order.This technique has been suitably applied to a thin brass tube expanding process for a single expansion ratio, and a single conical hollow plug with and without lubricant. To ensure good accuracy in the results, particular care was given to technological plug design and the choice of a number of appropriate strain gauged points on the inside surface of the plug.The more adequate polynomial representations of the normal and shear contact pressures were found by analyzing the degree of randomness in the distribution of the residuals. A comparison was made between experimental pressure distributions and those predicted by the slab method. Results obtained were compared with those derived from the use of a polynomial curve fitting method, besides assuming an average coefficient of friction at the interface.