|
Наведено оригінальні методики випробувань на малоциклову втому циліндричних лабораторних зразків зі сталі 10ГН2МФА за контролю амплітуди деформацій ( ) при температурах 20oС та 270oС. Показано, що при кімнатній температурі метал проявляє властивості, які характерні для циклічно знеміцнених сталей. При температурі випробувань 270oС метал проявляє властивості, які характерні для циклічно зміцнених сталей. Зміна циклічних властивостей металу (від циклічно знеміцнених до циклічно зміцнених) призводить до збільшення у понад 2 рази циклічної довговічності внаслідок підвищення до 47% значень умовної границі текучості при циклічному зміцненні.
This paper presents the special procedures for low-cycle fatigue testing of cylindrical laboratory specimens of steel 10GN2MFA under strain amplitude control ( ) at temperatures of 20oС and 270oС. It is shown that at room temperature the metal demonstrates the properties characteristic of cyclically hardened steels (an increase in the width of the elastic-plastic hysteresis loop and a decrease in the cyclic stress amplitudes). High values of the strain amplitude correspond to higher values of the cyclic stress amplitude and lower values of the cyclic yield stress. With an increase in the values of the strain amplitude, the intensity of the decrease in the cyclic stress amplitudes is lowered, followed by their further stabilization approximately within the yield stress limits. In this case, with decreasing values of the strain amplitude, an increase occurs in the cyclic yield stress values, which become stable after a certain number of loading cycles. At the test temperature of 270oС, the metal demonstrates the properties characteristic of cyclically hardened steels (a decrease in the width of the elastic-plastic hysteresis loop and an increase in the amplitudes of cyclic stresses). Lower values of the cyclic yield stress correspond to higher values of the strain amplitude, and the metal is cyclically hardened approximately up to the ultimate strength limits. As the strain amplitude values increase, a decrease in the hardening intensity occurs, and after a certain number of loading cycles, the values of the cyclic stress amplitude become stable. With decreasing values of the strain amplitude, the increase in the cyclic yield stress values occurs, together with a simultaneous reduction in the width of the elasto-plastic hysteresis loop (the amount of plastic deformation per cycle), and after a certain number of loading cycles, the amount of plastic deformation per cycle is less than 0,2%, which, later on, will make it impossible to determine the cyclic yield stress values. An increase in the test temperature from 20oС to 270oС gives rise to a change in the cyclic properties of the metal, which results in the increase in the cyclic life by more than twice due to the 4% increase in the yield stress values determined in static tension, and due to the cyclic hardening which causes the increase by up to 47% in the values of the cyclic yield stress determined from low-cycle tests. In this case, the cyclic hardening of the steel at a temperature of 270oС gives rise to the approximate 30% increase in the amplitude of cyclic stresses relative to similar values obtained at room temperature. |
