The work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip set of experiments was carried out using specimens with pre-grown centered fatigue crack. An original mathematical algorithm for experimental data treatment was developed to obtain a power of heat source caused by plastic deformation at crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. Based on the results of mathematical data treatment, we proposed a way to estimate the values of J-integral and stress intensity factor for cracks with pronounced the plastic zone.
The presented work is devoted to the experimental study of heat dissipation process caused by fatigue crack propagation. To investigate a spatial and time temperature evolution at the crack tip, set of experiments has been carried out using plate titanium specimens with pre-grown centred fatigue crack. An original mathematical algorithm for experimental data treatment has been developed to obtain the power of heat dissipation caused by plastic deformation at the crack tip. The algorithm includes spatial-time filtration and relative motion compensation procedures. The time dependence of the stored energy was calculated as the difference between work caused by plastic deformation near the crack tip and heat dissipation energy obtained from experimental data. As a result, it has been shown that the stored energy has to accumulated during the fatigue test and has to be equal to zero when the crack reaches the critical length corresponding to the failure of sample.
The work is devoted to the experimental study of heat dissipation caused by plastic deformation and failure processes taking place in a titanium alloy Ti-4.2Al-1.6Mn. To investigate the spatial and time evolution of temperature, a set of experiments has been carried out on plane titanium smooth specimens and specimens with pre-grown centered fatigue cracks. The original mathematical algorithm for experimental data processing has been applied to obtain the rate of heat dissipation generated by plastic deformation and stored energy. It is shown that the stored energy is accumulated in titanium specimens undergoing fatigue tests, and at the time of damage to fracture transition it is equal to zero.
Reliable operation of steam boilers is maintained by periodic in-service cleanings of the internal surfaces of the steam-water path. Such cleanings can be made with traditional and new acid cleaning agents. The nec-essary condition for developing an effective chemical cleaning program is predicting its required duration taking into account the properties of the detergent used and the contamination of the metal surface. Insufficient duration of this operation leads to increased residual contamination, while excessive duration – to metal dissolution. Traditionally, the required time for chemical cleaning is evaluated according to the results of laboratory experiments. The aim of this study is to obtain analytical dependencies and characteristics describing the kinetics of the acid stage of steam boiler chemical cleaning. The laboratory studies of the acid stage of chemical cleaning of samples of high-pressure steam boiler generating tubes were performed by the chemical etching method. The rates and completeness of the removal of lumpy and uniform deposits by acid reagents were also determined. The method of mathematical modeling was used to obtain the kinetic equation. The conditional purification rate constants for this equation were found by the methods of statistical processing of laboratory results. A description of the scale removal rate from the inner surface of the steam generating tubes is proposed as a first-order kinetic equation depending on their specific contamination and reagent washing solution acidity. The equation allows calculating the required duration of chemical cleaning for providing a given value of specific residual contamination of the metal surface. According to the results of the laboratory studies, the conditional rate constants of purification were determined using proven detergent reagents and types of scale. The adequacy of the obtained results is ensured by their consistency with real-life data. The results of the study can be used to select the technology of acid stages of chemical cleaning of lumpy and uniform deposits and justify their duration for providing standard values of specific residual contamination of the surface of steam generating tubes of drum boilers.
This work is devoted to theoretical and experimental study of energy balance in titanium alloys under plastic deformation and failure. It is shown that infrared thermography can give a unique opportunity to investigate the thermodynamics of plastic deformation and failure of metals. The energy balance in titanium alloy OT-4 was studied in smooth samples under quasi-static loading and at fatigue crack tip under crack propagation. Extending previous results of the research group in Perm, we coupled the experimental investigation of temperature evolution with a statistical description of the mesodefect ensemble. It allowed us to propose a thermodynamic internal variable model of heat dissipation in metals.
Traditional and new washing acid reagents are used for chemical cleaning of internal surfaces of steam-water pipes of boilers. In previous studies, the rate of removal of lumpy and uniform deposits in the evaporative pipes of high-pressure steam boilers depending on the type of cleaning solution and the duration of cleaning was obtained. However, during chemical cleaning, removing deposits is accompanied by corrosion processes of the metal pipes, which leads to their loss. In the scientific and technical literature there are practically no data characterizing this process when using new detergent reagents. The aim of the study is to obtain experimental data on the corrosion rate of steels during the acid stage of chemical cleaning with the use of new cleaning reagents such as Antirzhavin, Deskam and Auge Pro AC 60. The gravimetric method of determination of metal corrosion rate of evaporative pipes is used. The samples of corrosion in cold and heated washing solutions during chemical cleaning from deposits by etching are employed. The laboratory testing has revealed the dependences of corrosion rate of carbon steel of boiler evaporative pipes and corrosion indicating plates in heated and not heated washing solutions of the inhibited hydrochloric acid and acid reagents on cleaning duration. It has been found that the corrosion rates of carbon steel are reduced during the cleaning process and at the end of the acid stage in solutions of inhibited hydrochloric acid and reagent solutions have values exceeding the maximum permissible corrosion rate in a cold inhibited technical solution of hydrochloric acid. However, they are less than those for pure metal and metal with scale. The experimental data obtained can be used in the selection of a chemical reagent for acid cleaning and its optimal duration, as well as in the selection of the method of steel corrosion control during cleaning.
Состояние вопроса. Одним из основных факторов, влияющих на срок службы испарительных труб паровых котлов, является состояние их внутренних поверхностей нагрева. Для предотвращения повреждений испарительных труб проводятся периодические химические очистки этих поверхностей от отложений. В настоящее время для проведения таких очисток предлагается ряд новых моющих реагентов. При этом недостаточно данных о влиянии состава моющего раствора, его температуры и длительности очистки на техническую эффективность очистки, скорость и полноту удаления отложений. В связи с этим необходимо провести исследования по определения скорости очистки поверхности экранных труб от эксплуатационных отложений при использовании различных моющих реагентов и условий ее проведения. Материалы и методы. Исследование образцов испарительных труб паровых котлов проведено с применением метода травления в условиях нагрева и без него. Для химической очистки использованы ингибированная соляная кислота, Антиржавин, Дескам, Auge Pro Ас. Определения удельной загрязненности и химического состава отложений проведены согласно требованиям СО 34.37.306-2001. Результаты. В ходе лабораторного исследования получены зависимости скорости удаления бугорчатых и равномерных отложений, а также скорости коррозии металла испарительных труб от вида моющего раствора реагента, температуры и длительности очистки. Установлено, что скорость очистки образцов труб от равномерных и бугорчатых эксплуатационных отложений в кислотных растворах исследованных реагентов на 15-30 % больше, чем в растворе ингибированной соляной кислоты. Выводы. Полученные экспериментальные данные могут быть использованы при выборе технологии проведения кислотной очистки, для снижения ее продолжительности с обеспечением наименьшей остаточной удельной загрязненности поверхности металла в условиях, наиболее приемлемых для промышленных объектов.
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