Investigation of crack growth behaviour under mixed mode loading

The crack growth resistance of different metals under mixed mode (I+II) and biaxial loading was investigated. Fracture pattern depends on the load ratio under different modes and their level. Criterial equation were proposed

Fracture resistance of shell-steel reactor steel with mixed deformation modes for justification of extension of nuclear power plants lifetime

Preliminary thermomechanical loading promotes increase of resistance to brittle fracture of heat-resistant steels with fractures and is the fundamental basis of the perspective method of increasing the resource for ensuring safe operation of power reactor corps. In existing standards for calculating the strength of equipment of nuclear power plants, the calculation for fracture toughness is performed only for plane opening mode of fracture (mode I), but the plane of the fracture can have an arbitrary orientation with respect to external forces. Aim: The aim of the research is an experimental study of the effect of the preliminary thermomechanical load under modes I and II on the fracture toughness for modes II and I of reactor steels, respectively, as well as the preliminary thermomechanical load under the I + III mode for the fracture toughness under the I + III mode. Materials and Methods: Experimental studies of static fracture resistance were performed on samples on four-point bending (mode II), on cylindrical specimens torsion (mode III), and on a modified compact sample with an oblique fracture (mode I + III) for 15Ch2NMFA(II) and 15Ch2MFA(II) steels. Results: It is shown that the fracture toughness characteristics for transverse and longitudinal displacements (modes II, III) are smaller than for normal detachment (mode I) at a test temperature exceeding the brittle-viscous transition temperature, and vice versa, more when the test temperature is lower. It was found that the preliminary thermomechanical load under mode II causes an increase in the fracture toughness under mode II and a reduction in the fracture toughness under mode I for tempering embrittlement reactor steels. Under these conditions, this index practically does not change for plastic reactor steels. The established patterns show the need to modify regulatory documents to assess the ultimate bearing capacity of structural elements with fractures, in particular, the shells of nuclear power reactors, equipment of the 1st and 2nd circuits, pipelines

Влияние эксплуатационных и конструкционных факторов на скорость роста усталостных трещин в жаропрочном никелевом сплаве корпуса камеры сгорания авиационного ГТД

 For scientific justification of operation of aviation gas-turbine engines on technical condition it is necessary to have information on the fatigue crack growth rate in material of details of engines from the initial cracks sizes to critical. This information, according to normative documents, is used at purpose of terms and volumes of carrying out scheduled tasks at maintenance of engines. Work purpose: the research fatigue crack growth rate in a high-temperature ni-base alloy of acombustion chamber casing of the aviation gas-turbine engine taking into account operational (temperatures) and constructional (a joint weld, product thickness) factors. Experimental procedure: the studies were performed on a flat specimens on tension (plate1.6 mmthickness) with a local cut by a standard ASTM E647 technique at temperatures of tests +550 °Cand +600 °C. Fatigue crack growth rate was investigated in the base metal, in a joint weld and in a zone of thermal influence apart23 mmfrom a joint weld. For this, a fatigue crack was initiated from a mechanically incised notch that was located in a corresponding place with respect to the welded seam: over the base metal, welded seam, and the zone of thermal influence. A linear portion of the fatigue crack growth diagrams is constructed and the coefficients of the Paris equation are obtained. Confidence intervals are also given, which illustrate the region where the results of the experiment hit the target with a probability of 95%. Conclusion: it is shown that taking into account statistical data interpretation on fatigue crack growth rate of the zone of thermal influence and the main metal differ slightly while fatigue crack growth rate in a joint weld increases in twothree times. Assessment of mechanical characteristics of studied alloy was performed, upon transition from the base metal through a zone of thermal influence to a joint weld. For this purpose were used measurements of hardness by Rockwell’s method. Results showed minor change of hardness that indirectly explains small difference (in borders of a statistical error) on the fatigue crack growth rate in the base metal and a zone of thermal influence. Исследована скорость роста трещин усталости в зоне термического влияния, в сварном шве и в основном металле жаропрочного никелевого сплава корпуса камеры сгорания авиационного газотурбинного двигателя при эксплуатационных температурах 550, 600 °С. Эксперименты выполнялись на плоских образцах на растяжение толщиной1,6 мм, что соответствует толщине корпуса камеры сгорания. Показано, что с учетом статистической обработки экспериментальных данных по кинетике роста трещин усталости зона термического влияния и основной металл отличаются незначительно, в то время как скорость роста трещин усталости в сварном шве увеличивается в два-три раза.