Jacques Stolarz's research while affiliated with Mines Saint-Etienne and other places
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Publications (11)
Low cycle fatigue of porosity free Al-Si alloys containing between 11 and 18 wt.% Si and produced through directed solidification has been investigated. All alloys contain acicular Al-Si eutectic as the principal element of microstructure, completed by different amounts of primary (Al) and (Si) phases. Crack initiation and propagation modes have be...
The influence of microstructural parameters on low cycle fatigue damage in some single phase and biphasic stainless steels has been studied. In a single phase austenitic steel, the fatigue life increase with decreasing grain size is attributed to the positive effect of microstructural barriers in the bulk. In a metastable austenitic steel, the grai...
Duplex stainless steels (DSSs) produced by rolling have a significant anisotropy in mechanical properties. The present research deals with this anisotropy, paying particular attention to fatigue behaviour in the high-cycle fatigue regime. In doing so, the mechanical response of a 5 mm thick rolled plate of EN 1.4462 type duplex steel was characteri...
The fatigue short crack propagation in polycrystalline metals and alloys is strongly dependent on microstructure because of the presence of interfaces (grain, twin or phase boundaries) which cannot be crossed without additional energy supply. The conventional approach to the problem of microstructure exclusively considered as interfaces appears ins...
The martensitic transformation (γ→α′) induced by cyclic strains in a metastable austenitic stainless steel leads to significant modifications of fatigue mechanisms compared with stable alloys, in particular at the mesoscopic scale (short cracks). The present study has been carried out on a metastable high purity Fe–17Cr–13Ni steel with two differen...
The cyclic plasticity mechanisms in body-centred cubic (bcc) materials are strongly temperature and strain-rate dependent. At low temperatures, slip asymmetry (due to low mobility of screw dislocations) occurs and leads to changes of the grain shape, whereas above a temperature transition, symmetric slip is observed and the initiation sites are mai...
Low cycle fatigue (LCF) tests in air have been carried out on smooth specimens of several model binary Al–Si alloys with microstructures characterised by a high degree of homogeneity and the absence of casting defects, owing to the processing involving directed solidification. The elementary damage events, namely short crack nucleation at Al–Si int...
L'influence de la transformation martensitique, induite par deformation cyclique, sur les mecanismes d'endommagement en fatigue oligocyclique dans un acier inoxydable austenitique metastable, avec differentes tailles de grains, a ete etudiee. Pour cela, des mesures macroscopiques et des observations microscopiques des fissures courtes ont ete reali...
Depuis une dizaine d'années, les études de fatigue-corrosion de matériaux métalliques en milieux aqueux tiennent compte des interactions locales corrosion-déformation à l'origine de l'endommagement. Une courte revue de ces interactions est proposée: (a) effets des réactions électrochimiques (dissolution, décharge d'hydrogène) sur la plasticité cycl...
The damage of metals and alloys under cyclic straining occurs through the progressive development of surface roughness and short crack nucleation and growth before the beginning of fatal crack propagation in the hulk. During the major part of the fatigue lifetime (> 80% N F ), a development of short cracks preceeding the fatal crack propagation tak...
A new description of LCF damage evolution taking into account the two-dimensional nature of short cracks is proposed. It appears that random character of the damage process is limited to the short crack nucleation. In the stage of short crack growth, the parameters related to the crack population (crack density, crack lengths) have no significant i...
Citations
... The above controversy is mostly due to the fact that SIMT is implicitly correlated with macroscopic values of stress and strain. However, it is well documented [34] that, at a microscopic scale, SIMT sets off in zones with high stress concentrations which are generated by plastic deformation (intersection of slip bands under monotonic loading, interactions between slip bands and grain boundaries in fatigue). ...
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... This is in agreement with the observations made by Stolarz. 21 The higher fatigue life at lower strain amplitude is attributed to the increase in the yield strength of the ferritic phase as a result of the aging treatment. When the strain amplitudes are low, the plastic deformation is mostly confined to the austenitic phase and a microstructurally short crack propagating in the austenitic phase is obstructed at the phase boundary. ...
... The increased cooling employed on TW2 with an interpass temperature of 100 • C resulted in a phase balance of 36% ferrite and 64% austenite. This is consistent with previous work stating that increased cooling rates promote austenite, and fast cooling rates through T 12/8 increase the ferrite volume fraction content [2][3][4][26][27][28][29][30]. Additionally, these phase balance results for the two test samples quantify well the petroleum industry standards of 30-70% of ferrite-austenite balance based on ER2594. ...
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... However, it is worth-noting that the lowest value of V for HEA-B is encountered at pre-yield regime unlike the minimum value in the IFS material [46] being encountered at some high plastic strain, which leads to the formation of cellular structure hindering dislocation movement. Danie´lou et al. [58] have examined the activation volume in interstitial free steel and several ultra high purity irons doped with different amounts of interstitials at very low plastic strains using SRC experiments and found that the activation volume for these materials ranges between ~40-140 b 3 . ...
... The evolution of all three types of cracks was reported. It was documented by Stolarz (1997) that even if the density of initiated cracks is high, it is the in-depth growth of a semicircular crack that determines the kinetics of crack growth. Linkage with existing cracks is far less important. ...
... The crystallographic orientations always determine the slip system in the individual grain and the short crack tends to retard and deflect at the grain boundary. Numerous studies have shown that the grain size affects the short crack growth behaviour [8][9][10][11]. As reported, normally, the fatigue short crack growth rate tends to increase as the grain size becomes larger, as does the threshold value. In summary, the effect of grain size on short crack growth can be attributed to the weakening or enhancement of microstructural barriers. ...
... This might be one factor for the multidirectional forged sample having greater wear rates compared to SIMA processed alloy alloys. Moreover, it was also noted that the coarser primary silicon phase in hypereutectic Al-Si alloys often wears out faster than the finer primary and eutectic silicon phase because of a brittleness and micro crack propagation tendency [36][37][38][39]. ...
... As seen from Figure 13b,c, the adverse effect of surface and sub-surface pores is severe on HCF crack initiation and propagation, but the studies on LCF cracks have not shown a similar severity in Al-Si alloys. A study by Stolarz et al. [323] gave a concrete definition of how LCF crack initiation mostly occurs at the eutectic Al/Si interface, and fine porosity in the specimens do not significantly impact nucleation or growth mechanisms. Single and multiple cracking models created by the study showed that fatigue failure resistance increases if multiple microstructurally small cracks (MSCs) are present in the material. ...
... From studying the influence of the pH, it has been proved that pH directly influences the repassivation kinetics, i.e. passive film reconstruction generally is faster for lower values of pH [13] and therefore the unprotected material remains in contact with the corrosive solution for a shorter period of time. On the other hand, it must be taken into account that at low pH, H 2 -embrittlement processes can be active, contributing to enhanced crack propagation rates [13][14]. ...
