National Repository of Grey Literature 71 records found  beginprevious55 - 64next  jump to record: Search took 0.01 seconds. 
Initial stages of fatigue failure of polycrystalline materials
Man, Jiří ; Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav
Geometry of persistent slip markings (PSMs) formed during cyclic loading of polycrystalline stainless steels and superalloy was studied using atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM-FEG). Internal dislocation structure was investigated using transmission electron microscopy (TEM). Persistent slip bands with dislocation structure corresponding to the cyclic strain localization were identified and correlated with PSMs observed on the specimen surface.
CYCLIC PLASTICITY AND DISLOCATION SUBSTRUCTURE OF ferritic STAINLESS STEEL
Petrenec, Martin ; Polák, Jaroslav
The cyclic plastic response of polycrystalline ferritic stainless steel with b.c.c. structure is analysed in terms of the general statistical theory of the hysteresis loop and cycled in the magnetic field. Simultaneously, the internal dislocation substructure developed in the material during cyclic straining is studied using transmission electron microscopy and Kikuchi lines. The inhomogeneous distribution of dislocations into the persistent slip bands can be correlated with the localization of the cyclic plastic strain. The analysis of the loop shape by plotting the first and the second derivative of the half-loop allows determining the effective stress and the probability density function of the critical internal stresses. Extra peak of the second derivative of the half-loop was explained by the inverse magneto-elastic effect.
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.
Effect oc surface carburizing on low cycle fatigue of 316L austenitic stainless steel
Obrtlík, Karel ; Polák, Jaroslav
Both surface carburized and untreated 316L stainless steel specimens were cyclically loaded with constant plastic strain amplitude. Characteristics of stress strain response and fatigue life were evaluated and surface relief evolution and crack initiation was studied.
Dislocation structure, effective and internal stresses of cyclically deformed ferritic stainless steel
Petrenec, Martin ; Polák, Jaroslav
The hysteresis loops were recorded and analysed by force of generalised statistical theory of the hysteresis loop to separate internal and effective stresses on X10CrAl24 steel. Values of effective elastic module,possibly saturated stress and the maximum of density function were estimated in dependence on number of cycles and were faced with examined dislocation structures.
The cyclic stress - plastic strain response comparing of stainless steels under asymmetry cycle
Petrenec, Martin ; Polák, Jaroslav
The hysteresis loops of 316L austenitic and X10CrAl24 ferriytic steel were analysed to separate internal and effective stresses and evaluate the influence of asymmetry cycle on them too.
Evaluation of short fatigue crack growth in feritic steel
Zezulka, Petr ; Polák, Jaroslav
The specimens were cycled in a computer-controlled electrohydraulic MTS machine. The feature is appreciation course growth of short fatigue cracks in ferritic stainless steel. Two different alternative for solution short fatigue crack growth are included.
Dislocation structure in the HAZ of the HSS steel after shot peening
Kruml, Tomáš ; Buirette, C. ; Degallaix, G. ; Polák, Jaroslav
The welds of a high strength C-Mn microalloyed steel with ferritic-bainitic microstructure were shot peened in order to improve the fatigue resistance. Since the weakest point was the heat affected zone (HAZ), the dislocation structure in two depth off the zone was investigated before and after shot peening. No specific dislocation arrangement was found neither in the initial state nor after shot peening and the arrangement can be characterised as random. The dislocation density was elevated in the initial state due to bainitic transformation. The shot peening resulted in appreciable increase of the dislocation density with a very strong gradient. The results were discussed in terms of the effect of surface hard layer induced by shot peening on the fatigue life of the weld and on the initiation and growth of fatigue crack in HAZ.
Fatigue life and short crack growth in plasma nitrided 316L stainless steel
Obrtlík, Karel ; Polák, Jaroslav
Cylindrical specimens with shallow notch of 316L austenitic stainless steel both with plasma nitrided and untreated surface were cyclically strained with constant plastic strain amplitude. Fatigue life, crack initiation, short crack growth and stress response were studied in both materials.

National Repository of Grey Literature : 71 records found   beginprevious55 - 64next  jump to record:
See also: similar author names
16 POLÁK, Jan
18 POLÁK, Jaroslav
5 POLÁK, Josef
4 Polák, Jakub
16 Polák, Jan
2 Polák, Jaromir
1 Polák, Jindřich
3 Polák, Jiří
5 Polák, Josef
2 Polák, Jozef
16 Polák, Ján
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