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Damaging Processes of Gas Pipelines in a Long-Time Operation
Gajdoš, Lubomír
The individual types of damage, which can occur during operation of gas pipelines, are assessed from the mechanical point ofview. Besides description of particular damaging processes,taking place in gas pipelines during operation, quantitative definitions of damage in faatigue, stress corrosion, general corrosion and pitting corrosion are proposed. Further a determination of critical parameters for individual kinds of damage is presented.
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Quantitative assessment of the surface relief in fatigue using AFM
Man, Jiří ; Obrtlík, Karel ; Polák, Jaroslav
Atomic force microscopy (AFM) was applied to study the early stages of fatigue damage in polycrystalline copper and stainless 316L steel. The analysis of the image formation using an AFM tip reveals the lateral distortion of the extrusions and intrusions in case of high extrusions and deep intrusions. The true extrusion height can be obtained in direct observation and the depth of intrusions using replica technique. The evolution of the shape and the height of extrusions allowed to judge the activity of the persistent slip bands (PSBs) during fatigue life.
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The effect of V-notch on the propagation rate of fatigue crack
Hutař, Pavel ; Knésl, Zdeněk
The rate of a fatigue crack propagating in a vicinity of a V-notch is studied. To assess the influence of the constraint on the rate of the propagation, two parameter constraint based linear elastic fracture mechanics is used. The corresponding values of the T-stress are calculated and values of the effective stress intensity factor Keff controlling the rate of a crack propagation are estimated as a function of the V-notch opening angle. The results obtained are compared with those for a crack emanating from nonsingular U- notch concentrator.
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The influence of T-stress on the characteristics of a fatigue crack
Hutař, Pavel
The influence of the T-stress values on the propagation of fatigue cracks is analyzed. The parameters of the plastic zone are studied at two levels of applied stress, i.e. loading and unloading. The CTOD parameter and rp (plastic zone size) in the crack grow direction are discussed as a driving parameter of a fatigue crack propagation rate. The three ways of determination of propagation rate of a fatigue cracks are compared. Recommendations for applications of these methods are discussed.
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