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• The failure mechanism of TBCs samples was analyzed based on SEM. • A modified model is developed to evaluate the fatigue life of TBC pistons in high-power engines. • The piston TBCs thermal shock test rig was built and life tests were conducted. • Piston TBCs lifetime good correlation was achieved between the prediction model and the actual experimental results. • The research result can reduce the probability of engine accidents caused by coating damage, guide the process design of piston TBCs, and improve the reliability of high-power engines. Thermal barrier coatings (TBCs) have been widely used in high-power engine components because of their excellent thermal insulation properties. In this study, microcrack growth and fatigue life analysis of TBCs were carried out based on thermal shock tests of TBCs samples. Scanning electron microscopy (SEM) was used to observe the spallation and vertical crack growth behavior of TBCs during the tests. The fatigue life prediction model applied to piston TBCs was developed by modifying the Paris equation with the sintering of the coating and the effect of a thermally grown oxide (TGO) layer being considered. The model was calibrated by conducting tests on piston TBCs, and the forecasting error was less than 15%, indicating that the prediction model is both practical and effective. The results of this study provide a service life evaluation and test method for TBCs on pistons, which can be utilized to guide piston TBCs design. [ABSTRACT FROM AUTHOR]

• A theoretical model for service life analysis of auxetic honeycomb/substrate structures under thermal cycling is developed. • The auxetic structures have lower stress concentration than non-auxetic structures of the same density. • Lower relative density can increase the service life of the structures. • Auxetic structures possess much higher service life than non- auxetic structures. This paper studies the fatigue behavior of auxetic honeycomb layer/substrate structures due to interfacial delamination damage. First, the interfacial thermal stress and cyclic interfacial thermal stress intensity factor (ITSIF) at the free ends of the structure are determined in terms of the thermal shock time, relative density, aspect ratio, and internal cell angle of the honeycomb. Then, a theoretical model for the service life analysis of the structures is established based on Paris's law. The results show that the auxetic structures have a lower ITSIF level and a longer service life compared with those of the non-auxetic structures. Another interesting finding is that a reduction in the relative density of the honeycomb layer will increase the service life of the structures. This confirms the significance of applying auxetic materials in re-usable structures for thermal protection purposes. This research is the first attempt to evaluate the service life of the auxetic honeycomb layer/substrate structures under thermal cycling. [Display omitted] [ABSTRACT FROM AUTHOR]

• Oxidation in thermal shocks was comparably analyzed to isothermal oxidation. • Cracks in thermal shocks were initiated by thermal stress and propagated following Paris's Law. • The cracking behavior during thermal shocks is oxidation-accelerated cracking. • The oxidation behavior during thermal shocks is stress-assisted and crack-accelerated oxidation. Oxidation and cracking behavior during thermal-shock experiments of a new Co-based alloy were analyzed in the present work. Comparing to the static conditions, the oxidation behavior during thermal shocks is stress-assisted and crack-accelerated. Cracks during the thermal shocks were initiated from the sample surfaces and their growth are driven by various stresses, including those induced by volume change, mismatch of coefficients of thermal expansion (CTEs), and temperature gradient between the matrix and the internal oxides. It is found that the crack propagation correlates to these stresses in the classic Paris' law. [ABSTRACT FROM AUTHOR]

This paper presents a damage tolerant approach assessment of corner cracks in small nozzle process penetrations in the pressure vessel of the small modular reactor CAREM-25 subjected to mechanical and thermal shock loadings during certain operation events. Fracture mechanics analyses were performed following ASME XI guidelines considering a representative geometry and specific loading conditions. Stress distributions in the uncracked component were calculated by finite element techniques, while fracture driving forces were estimated using closed form solutions. Maximum allowable corner crack sizes were calculated using linear elastic fracture mechanics and failure assessment diagram (FAD) approaches. The onset of stable crack growth and crack instability were considered as failure conditions. Additionally, fatigue crack growth estimations during the service life were performed integrating a Paris law up to the maximum allowable crack sizes. The results indicate that it seems unlikely that pre-existing cracks reach allowable sizes during the reactor's service life. • Criteria from ASME XI are applied to small process nozzles of the CAREM-25 reactor. • Fracture mechanics and fatigue crack growth analyses for corner cracks are presented. • Very low probability that a crack became unacceptable due to fatigue crack growth. • It seems unlikely that cracks reach allowable sizes during the reactor's service life. • In-service inspection of corner regions is not justified in small CAREM-25 nozzles. [ABSTRACT FROM AUTHOR]