Changes in residual stresses in anodically produced oxide films on duralumin D16T subjected to cyclic loads

During their operational use the aeronautic structures can be submitted to relatively moderate cyclic loads and more rarely to stern loads. These last can generate residual stress field, which will influence the in-service behaviour. Otherwise, residual stress field can be created in a voluntary way by a specific treatment (compressive stresses). They permit to improve fatigue tolerance behaviour. This illustrates the importance of the study of the structure behavior under residual stresses, and the need to consider them in numerical simulations. The objective of this work is to develop a numerical method, based on the boundary element method and the principle of superposition, to assess the influence of residual stresses on fracture mechanics parameters.

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A Direct Method on the Analysis of Steady State Residual Strains in a Steel Joint Subjected to Cyclic Loads

Seismic Engineering ◽

10.1115/pvp2003-2113 ◽

2003 ◽

Author(s):

C.-C. Yu ◽

C.-T. Wu ◽

T.-P. Chang

Keyword(s):

Steady State ◽

Residual Stresses ◽

Direct Method ◽

Direct Analysis ◽

Cyclic Loads ◽

Pipe Length ◽

Study Results ◽

Residual Strains ◽

Residual Stresses And Strains ◽

Fixed End

The thick plate element of Mindlin type combined with the plane stress element is adopted in the direct analysis method. The numerical process is pretty efficient with respect to the speed of the calculation of final steady state residual quantities resulted in by cyclic loads. Two pipes joined together with a concentric reducer are employed as an example. The steady state residual stresses and strains after pipes experience cyclic anti-symmetric deflections, simulating the seismic loads, are illustrated. The diameter, the length of the pipes, and properties of material are the parameters evaluated in the present study. Results indicate that shorter pipe has higher shear effect at the fixed end. The ratio of pipe diameter to pipe length does not significantly differ the residual profile while the existence of a concentric reducer disturbs the distribution of the residual stresses and residual plastic strains dramatically.

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The Effect of Temperature and Load Cycling on the Relaxation of Residual Stresses

Advances in X-ray Analysis ◽

10.1154/s0376030800011915 ◽

1976 ◽

Vol 20 ◽

pp. 309-319 ◽

Cited By ~ 1

Author(s):

J. M. Potter ◽

R. A. Millard

Keyword(s):

Residual Stress ◽

Residual Stresses ◽

Cyclic Load ◽

Stress Measurement ◽

Thermal Exposure ◽

Effect Of Temperature ◽

Cyclic Loads ◽

Load History ◽

Stress Concentrations ◽

Aircraft Structures

The Fastress automatic residual stress measurement system was used to measure residual stress in unnotched shot peened 7075-T6 aluminum alloy specimens for a study of the effect of load and thermal exposure on residual stresses. Cyclic loads at zero and high mean stress conditions at stress levels in excess of those used in aircraft structures gave no apparent change in residual stress. Thermal exposure above 200°F resulted in significant changes in residual stress; at 225°F, 30 to 50 hours were required to cause the residual stress to reduce to onehalf the original value and less than 15 hours at 250°F was sufficient to cause a 50Z reduction. The data indicate that the cyclic load history that may be expected in aircraft structures is not sufficient to cause residual stress relaxation in areas remote from fasteners and other stress concentrations but that thermal exposure can cause significant relaxation.

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The Effect of Film Stress on Indentation Modulus/Hardness for Silicon Oxide Films

MRS Proceedings ◽

10.1557/proc-563-225 ◽

1999 ◽

Vol 563 ◽

Author(s):

Brad Sun ◽

Jin Lee ◽

Patrick Kofron ◽

Qing Ma

Keyword(s):

Residual Stress ◽

Residual Stresses ◽

Elevated Temperatures ◽

Silicon Oxide ◽

Oxide Films ◽

Sio2 Film ◽

Indentation Modulus ◽

Rf Power ◽

Appreciable Change ◽

Steel Substrates

AbstractA controlled experiment was performed to determine whether residual stresses in silicon oxide films affect the apparent modulus and hardness of the films measured using microindentation. A set of wafers, each with a SiO2 film of different residual stress, were produced by PECVD deposition using different RF power settings. Residual stresses, determined by curvature measurement, were shown to become more compressive with the increase of the RF power. Correlation between indentation modulus/hardness and residual stress was established because the modulus was also observed to be trending with the RF power. To determine whether the residual stress change is the cause for the change of indentation modulus/hardness, one of the wafers was cut to pieces and bonded to steel substrates of different thickness at elevated temperatures. Because of the thermal mismatch between silicon and steel, the silicon pieces were stressed by the steel substrates and therefore provided additional stresses to the SiO2 film on the top surface. The applied stresses were determined using Raman piezospectroscopy. Micro-indentation tests performed on these samples showed no appreciable change of modulus/hardness due to additional stresses. It was concluded that the material change, such as density, was behind the correlation between indentation modulus and residual stress.

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Structural characteristics and residual stresses in oxide films produced on Ti by pulsed unipolar plasma electrolytic oxidation

The Philosophical Magazine A Journal of Theoretical Experimental and Applied Physics ◽

10.1080/14786430801968603 ◽

2008 ◽

Vol 88 (6) ◽

pp. 795-807 ◽

Cited By ~ 46

Author(s):

R.H.U. Khan ◽

A.L. Yerokhin ◽

A. Matthews

Keyword(s):

Residual Stresses ◽

Plasma Electrolytic Oxidation ◽

Structural Characteristics ◽

Oxide Films ◽

Electrolytic Oxidation ◽

Plasma Electrolytic

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Resolving Crystallites in Zirconium Oxide Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100062610 ◽

1969 ◽

Vol 27 ◽

pp. 140-141

Author(s):

R.A. Ploc

Keyword(s):

Electron Microscope ◽

Inelastic Scattering ◽

Zirconium Oxide ◽

Oxide Films ◽

Optic Axis ◽

Objective Lens ◽

Microscope Objective ◽

Linear Optic ◽

A Current ◽

Microscope Objective Lens

The optic axis of an electron microscope objective lens is usually assumed to be straight and co-linear with the mechanical center. No reason exists to assume such perfection and, indeed, simple reasoning suggests that it is a complicated curve. A current centered objective lens with a non-linear optic axis when used in conjunction with other lenses, leads to serious image errors if the nature of the specimen is such as to produce intense inelastic scattering.

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