Influence Of Torsional Stress Research Articles

Fatigue Damage Assessment to a Rigid Planar Jumper on Model Scale

A rigid jumper is an important part of a subsea production system, and it may experience significant vortex-induced vibrations (VIVs) if subjected to current. It has normally a non-straight geometry shape in three-dimensional space. Consequently, the response of a rigid jumper under VIVs is much more complicated compared with straight pipeline structures. Currently, there are very limited studies and design guidelines including methods on how to assess the fatigue damage of rigid jumpers under VIVs. The methodology used for straight pipelines is often applied by ignoring the non-straight geometry characteristics and the multiaxial stress states. However, both experimental and numerical results show that the torsional stress does exist besides the flexural stress for rigid jumpers under VIVs. The objective of this study is to do a fatigue assessment practice based on the state-of-the-art calculation methods to a rigid jumper on model scale. The VIV response is obtained from experimental tests and numerical calculations by either force or response model methods. The influence of torsional stress on fatigue assessment is studied. Two approaches have been investigated. In the first approach, the flexural and torsional stresses are evaluated separately. The second approach uses the first principal stress to calculate the fatigue damage; thus, the flexural and torsional stresses are evaluated together. It appears that the use of the first principal stress gives higher fatigue damage if the torsional stress contribution is significant. Furthermore, the principal stress method is also less time-consuming in processing the results.

Study on Blade Fatigue Life of Rotating Power Machinery

The linear damage model (LDM) is widely applied in engineering calculation, but it does not consider the relationship between damage variable and load parameters. Therefore, the life prediction based on LDM is not satisfied for the aero-engine blades. Besides, it easily brings about error in predicting fatigue life by common nonlinear damage model which neglect the influence of torsional stress. Hence, a modified nonlinear continuum damage model (CDM) is put forward based on Chaboche nonlinear damage model in this research. And to determine the damage and fatigue life of TC4 material used in aero-engine blades, axial tension and compression fatigue test is conducted. Compared with LDM results, the fatigue life prediction results of the modified CDM in this work show a good agreement with the tests data. So the correctness of the modified model is verified. Finally, the fatigue life of a certain aero-engine high pressure compressor blade is predicted by the modified nonlinear continuum damage model.

Abcès pulmonaires compliqués : chirurgie ou drainage ?

The influence of torsional stress on the asymmetric magnetoimpedance in a glass-coated negative magnetostrictive amorphous microwire due to bias current is studied theoretically. The longitudinal and off-diagonal impedance components are found assuming a simplified spatial distribution of the magnetoelastic anisotropy induced by the torsional stress. The asymmetry in the field dependence of the impedance components is attributed to the combination of the circular magnetic field produced by the bias current and a helical anisotropy induced by the torsional stress. The asymmetry in the magnetoimpedance and the low-field hysteresis are analyzed as a function of the bias current and torsional stress. It is shown that the application of torsional stress significantly changes the value of the bias current required to suppress the hysteresis effect. The results obtained may be useful for applications in magnetic-field and stress sensors.

Asymmetric magnetoimpedance in amorphous microwires due to bias current: Effect of torsional stress

The influence of torsional stress on the asymmetric magnetoimpedance in a glass-coated negative magnetostrictive amorphous microwire due to bias current is studied theoretically. The longitudinal and off-diagonal impedance components are found assuming a simplified spatial distribution of the magnetoelastic anisotropy induced by the torsional stress. The asymmetry in the field dependence of the impedance components is attributed to the combination of the circular magnetic field produced by the bias current and a helical anisotropy induced by the torsional stress. The asymmetry in the magnetoimpedance and the low-field hysteresis are analyzed as a function of the bias current and torsional stress. It is shown that the application of torsional stress significantly changes the value of the bias current required to suppress the hysteresis effect. The results obtained may be useful for applications in magnetic-field and stress sensors.

Torsion and magnetic field effect in the impedance of FeSiBNbCu soft magnetic amorphous wires

The magnetoimpedance (MI) effect (influence of magnetic field), torsion impedance effect (influence of torsional stresses) and a torsion magnetoimpedance (effect produced by torsion in the magnetoimpedance effect) are shown for Fe 73.5 Si 13.5 B 9 Nb 3 Cu 1 as-cast wires. The results can be explained by the influence of torsion induced anisotropy in the magnetization processes at the chosen drive current frequency of 1 MHz. Resistance and reactance responses of 40% and 48%, respectively are found.

Torsion dependence of giant magnetoimpedance in amorphous wires

The effect of stresses is known to modify the magnetic properties in magnetostrictive amorphous wires. A comparative study of the giant magnetoimpedance (GMI) for amorphous wires with compositions Fe 77.5Si 7.5B 15, Co 72.5Si 12.5B 15 and Co 68.15Fe 4.35Si 12.55B 15 and positive (30×10 −6), negative (−2×10 −6) and vanishing (0.1×10 −6) magnetostriction have been studied. The influence of torsional stress on hysteresis loops and GMI is also reported. Modifications of GMI response are ascribed to the magnetoelastic anisotropy induced by torsion.

Fracture of steel at different stages of hydrogen embrittlement

1. In places of segregation in a polycrystalline body hydrogen facilitates microplastic deformation under the influence of torsional stresses in the first stage and the formation of microcracks under the influence of normal stresses, which reduces the capacity of steel for even deformation and strengthening. 2. The susceptibility of steels to hydrogen embrittlement varies with the distribution of hydrogen, since local hydrogen weakening increases the sensitivity of steel to overloading and premature brittle failure. 3. In the second stage of reversible embrittlement the capacity of the steel for even strengthening is reestablished, although hydrogen bubbles begin to form, reducing the ductility, and the characteristic signs of the stage of irreversible embrittlement appear. 4. In conformity with the rate at which brittleness develops, the morphology of the fracture also changes. The original ductile fracture changes to typical brittle fracture during reversible embrittlement. With the development of irreversible embrittlement the fracture becomes mixed—brittle sections along with ductile sections. 5. The most even structure, chemical composition, fields of internal stress, distribution of structural components, and dispersity of structural components increase the resistance of steel to hydrogen embrittlement.

Influence of torsion on the magnetic properties of cylindrical CoP and CoNiP amorphous electrodeposited layers

The influence of torsional stresses on the magnetic properties of amorphous electrodeposited CoP and NiCoP layers has been investigated. The rectangularity of the hysteresis loop is improved by torsion and the coercive force, H C, decreases. The results indicate the presence of a weak perpendicular anisotropy.