Structural behavior of large-scale triangular and trapezoidal threaded steel tie rods in assembly using finite element analysis
Abstract Pre-stressed steel tie rods are used extensively as load carrying components in structures like suspension bridges, steering systems in automotive vehicles, wings and fuselage of aircrafts, spokes of Ferris wheels, etc. The governing variables for the bearing strength of a large-scale steel tie rod (of diameter usually larger than 60 mm) include the mechanical strength of the tie rod body, geometric configuration of the thread teeth and the number of turns of thread engagement. The optimal number of turns of threaded connections of large scale steel tie rods has been predicted by full scale rupture experiments and reported previously by the authors. This paper builds up further on that work and investigates the structural behavior of the two types of threaded connections of steel tie rods, viz. (i) the triangle threaded connection, and (ii) the trapezoidal threaded connection, using finite element analysis in ANSYS. The axial displacement, equivalent stress distribution, interfacial contact pressure and sliding distance on the engaged thread teeth under different axial loads are presented and analyzed. The numerical simulations verify and expound the results of full-scale tensile rupture experiments. The concordant comparison between experimental measurements and finite element analysis provides working guidelines and support for the design and fabrication of steel tie rods in practical operations.
Experimental and numerical study of expandable threaded connections and proposal of a new design
This paper investigates the behaviour of a flush oilfield premium connection during the cold expansion process. The objective has been to validate, through experimental tests of make up and expansion on prototypes designed traditionally, the numerical simulation generated to reproduce and interpret the mechanism that occurs during the whole process. A finite element model, able to understand the expansion mechanics, to explain the damages caused on the expanded prototypes and to define design changes in order to improve the mechanical strength and hydraulic seal, has been set up. Taking advantage of the calculation procedure, a new expandable connection has been developed, at first on the basis of numerical simulation, then assessed by means of experimental tests. The new connection has shown definitely better behaviour about the hydraulic seal, withstanding the maximum internal pressure of 5050 psi.
An analysis of strong discontinuities in multiplicative finite strain plasticity and their relation with the numerical simulation of strain localization in solids
Abstract This paper presents an analysis of strong discontinuities in inelastic solids at finite strains. Solutions exhibiting this type of discontinuities, characterized by a discontinuous displacement field, are shown to make physical and mathematical sense in a classical multiplicative plasticity continuum model if the softening modulus is reinterpreted as a singular distribution.Physically, the strainsoftening is localized along the discontinuity. Conditions for the appearance of strong discontinuities in the geometrically nonlinear range are characterized, as it is the response of the material during localization. In addition, these analytical results are exploited in the design of a new class of finite element methods. The proposed methods fall within the class of enhanced strain methods, and lead to solutions independent of the mesh size and insensitive to mesh alignment, without requiring any regularization of the solutions by numerical parameters like a characteristic length.