This article presents a design development for the ring expansion test as an alternative technique of burst test to determine the mechanical properties of circular homogeneous thin-walled tubes in the hoop direction where it is supposed to fail. This is done by replacing the internal fluid pressure in burst test by a solid mandrel partitioned into an equal number of pieces. The numerical analyses were carried out using the commercial finite element method (FEM) package ABAQUS/CAE. The testing system consists of a multispecies mandrel assembled with two identical cones from top and bottom, and the ring specimen circumscribes the mandrel, which expands radially as a result of the cone’s axial displacement. The FEM was used to optimize the proposed design in terms of the minimum number of pieces in use. In addition, the effects of friction between the cones/the mandrel and between the ring/the mandrel are investigated. The FEM revealed that eight mandrel pieces or more are needed to preserve a uniform hoop stress throughout the ring circumference. Moreover, the FEM results in conjunction with theoretical formulas revealed that eight mandrel pieces at a minimum are required to minimize the power dissipated because of friction to a nuance value of 2 %. It is concluded that the higher the number of pieces used, the more uniform the hoop stress generated in the ring specimen. Moreover, it can effectively decrease friction effect at the ring/mandrel interface. The FEM also makes a great contribution in estimating the friction coefficients as it is restricted to be evaluated experimentally.
Background The ring expansion technique is a non-standardized material testing used to evaluate round tubes’ mechanical properties such as burst pressure and stress-strain behavior, however, this technique has limitations such as lack of suggested specimen geometry, strain measurement technique, and friction coefficient(s) estimation. Objective This study primarily aims to evaluate the stress-strain property in the hoop direction for seamless pipes with a further correlation with the tensile stress-strain curve. Moreover, investigating the specimen’s geometry effect on the results was also considered throughout the study. Methods Experimental, simulation, and analytical techniques were carried out and through their conjunction, it was applicable to estimate hard-to-measure coefficients, identify and evaluate new correction factors, and validate the simulation and analytical results. Results Experimental strain measurements were performed by derived analytical equation rather than an external measuring device, novel evaluation of the hoop stress correction value (K) was performed by the comparison between experimental and simulation work, in addition to a convenient similarity between the standard tensile test and the non-conventional proposed technique results. Conclusion The ring expansion test is a promising technique to evaluate the seamless pipes' burst pressure, stress-strain behavior, and other mechanical properties. Furthermore, the authors recommend future work regarding estimating both pressure dissipation factor (α) in terms of friction coefficients and hoop stress correction value (K) in terms of ring’s geometry.
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