Hydrostatic stress

About: Hydrostatic stress is a research topic. Over the lifetime, 1568 publications have been published within this topic receiving 37773 citations.

The nucleation of high temperature brittle intergranular fracture in 2.25cr-1mo steel

Abstract: An investigation of brittle intergranular crack nucleation at high temperatures in 2.25Cr-lMo steel is presented. A series of tests was designed to allow the independent variation of segregating impurities (e.g., sulfur and phosphorus) and locally applied stress levels to determine the effects of applied stress on impurity enrichment and fracture of grain boundaries in as-quenched material. The study utilized blunt notched specimens with suitable finite element stress analyses, together with high resolution Auger electron surface analysis techniques. It is shown that the imposition of a tensile hydrostatic stress enhances the segregation of elemental sulfur to grain boundariesprior to the nucleation of high temperature brittle intergranular cracks. The location of enriched grain boundaries relative to the peak stress regions in notched specimens is discussed, and possible mechanisms for the observed sulfur enrichment presented.

Finite element analysis of sucker rod couplings with guidelines for improving fatigue life

Abstract: The response of a variety of sucker rod couplings to an applied axial load was simulated using axisymmetric finite element models. The calculations investigated three sucker rod sizes and various combinations of the slimhole, Spiralock, and Flexbar modifications to the coupling. In addition, the effect of various make-ups (assembly tightness) on the performance of coupling was investigated. An axial load was applied to the sucker rod ranging from {minus}5 ksi to 40 ksi, encompassing three load cycles identified on a modified Goodman diagram as acceptable for indefinite service life of the sucker rods. The simulations of the various coupling geometries and make-ups were evaluated with respect to how well they accomplish the two primary objectives of preloading threaded couplings: (1) to lock the threaded coupling together so that it will not loosen and eventually uncouple, and (2) to improve the fatigue resistance of the threaded connection by reducing the stress amplitude in the coupling when subjected to cyclic loading. Perhaps the most significant finding in this study was the characterization of the coupling parameters which affect two stress measures. The mean hydrostatic stress, which determines the permissible effective alternating stress, is a function of the coupling make-up. Whereas, the alternating effective stress is a function of the relative stiffnesses of the pin and box sections of the coupling and, as long as the coupling does not separate, is unaffected by the amount of circumferential displacement applied during make-up. The results of this study suggest approaches for improving the fatigue resistance of sucker rod couplings.