Simple Flow Theory Research Articles

Elastic-plastic buckling of buried pipelines by seismic excitation

A quasi-bifurcation theory of dynamic buckling and a simple flow theory of plasticity are employed to analyze the axisymmetric, elastic-plastic buckling behavior of buried pipelines subject to seismic excitations. Using the seismic records of the 1971 San Fernando earthquake, a series of numerical results have been obtained, which show that, at strain rates prevalent in earthquakes, the dynamic buckling axial stress or strain of a buried pipe is only slightly higher than that of static buckling.

On the Hydrodynamic Derivatives for the Directional Stability of Ships in Following Seas

The maneuverability of ships in a seaway may be considered from various aspects which include small and favorable wave motion. Especially, it is well known that the most dangerous condition of a ship at sea developed when the ship is in a following sea or quartering sea.In order to investigate the directional stability of ships under such circumstances, in this paper the linearized equations of motion of ship are carried out taking into account the hydrodynamic forces which act on the ship due to the presences of waves. These hydrodynamic forces are calculated using the Froude-Kriloff hypothesis and according to the conception of simple flow theory of the slender body and the quasi-static theory and the assumption that width and draft of the ships are of the small in camparison with the wave length. So as to consider stationary condition of the surging motion, herein the ship travels with the propagating velocity of waves at any position of the ship relative to the waves.On the other hand, a method is shown that these hydrodynamic derivatives of the model ship are experimentally measured by operating the planar motion mechamism behind the wave making board realizing stationary following sea conditions.

Biaxial Plastic Stress-Strain Relations of a Mild Steel for Variable Stress Ratios

Abstract The main objective in the study reported in this paper was to provide further experimental checks on the validity of the simple flow theory of plasticity. In this investigation, biaxial stresses were produced by subjecting tubular specimens to internal pressure and axial tension. The tests were made on specimens machined from cold-drawn seamless-steel tubing. Most of the tests were performed under variable biaxial-stress ratios but in order to provide the necessary control data and basic biaxial strength properties, a series of constant stress-ratio tests also was conducted. Eight different types of variable stress-ratio tests were devised to determine the validity of the simple flow theory. The results of these tests do not support the theory. A test also was made to check the validity of the distortion-energy criterion as used in the simple flow theory. The differences between the theoretical and experimental results for this test were too great to be explained as due to experimental error or material anisotropy. A special variable stress-ratio test also was conducted to compare certain requirements of both the slip and simple flow theory. The results from this test were in poor agreement with the simple flow theory and in approximate agreement with the slip theory. An investigation was made to determine the validity of the so-called “loading function” as required by the various plasticity theories. These test results do not agree with the concept of the isotropic expansion of loading functions.

Triaxial plastic stress-strain relations for an aluminum alloy 14S-T4

This paper gives the results of an investigation on the plastic stress-strain relations of an aluminum alloy 14S-T4 subjected to triaxial stresses. In addition to providing information on the triaxial plastic stress-strain relations, this study serves to provide a further check on the validity of the theories of plasticity used to predict plastic stress-strain relations for combined stresses. The triaxial stresses considered consisted of two equal compressive principal stresses and a third tensile principal stress. The stresses were produced by subjecting a solid cylindrical specimen to radial hydraulic pressure in addition to axial tension. Two types of triaxial stress tests were made. In one type of test the loads were applied so that the ratio of the principal stresses remained essentially constant during the test. For these constant stress-ratio tests, the influence of the stress ratio on the plastic stress-strain relations was investigated. In a second type of test the ratio of the principal stresses was varied during the test. The variable stress-ratio type test was conducted in order to provide a further check on the validity of the simple flow theory. The constant stress ratio tests for various principal stress ratio showed good agreement between the test results and the predictions of the simple flow theory of plasticity. However, the variable stress-ratio test results did not agree with the predictions of the theory.