Search

The alternate load path method for progressive collapse analysis ignores the cause and mechanism of member failure and its influence on the dynamic effect of the remaining structures. It must assume the location of member failure, which is unsuitable for grid structures with many members. In this paper, by using the double broken line follow-up strengthening model and the proposed VUMAT material constitutive model, taking the member instability and material failure as the member failure criteria and considering the geometric nonlinearity and material nonlinearity, the instantaneous member removal method for deleting the failure member in real time was proposed. On this basis, nonlinear dynamic analysis for a three-layer space truss was used to compare the effects of different member failure criteria on the structural responses, such as the member failure sequence and the occurrence time of the continuous structural collapse. The results show that when considering the instability of members, the initial member failure and the final progressive collapse occur earlier than when using the material failure criterion, which is more similar to the actual situation. Furthermore, the proposed VUMAT material constitutive model can apply to study the progressive collapse behavior of space truss structures. [ABSTRACT FROM AUTHOR]

Establishing a quantitative prediction model for the SCC crack growth rate of dissimilar metal welded joints at the safe end is very important for the safety evaluation of nuclear power structures. However, the SCC growth process is closely related to crack tip creep. In this paper, uniaxial tensile creep experiments under different stress are carried out on nickel base alloy 600, and the constitutive creep equation of nickel base alloy 600 is established. At the same time, the SCC crack tip creep field is analyzed using finite element software, and the effects of crack tip creep variables, creep rates, and material creep properties on the crack tip field are analyzed. Results show that nickel base alloy 600 occurs creep under high stress, and the creep rate in the crack tip region decreases with the crack inclination angle and the distance from the crack tip. The peak values of creep and creep rate appear directly in front of the crack propagation direction. Research results lay a foundation for establishing a quantitative prediction model of SCC. [ABSTRACT FROM AUTHOR]

The mechanical properties of the crack tip are vital for material safety evaluation. The weld material of welded joints is prone to work hardening during processing and installation, which changes the material mechanical properties and seriously affects the safety assessment of nuclear power welded joints. At the same time, nuclear power pipelines will creep under high temperatures and cause changes in the mechanical field at the crack tip. This paper obtains the mechanical properties of nickel-based alloy 182 in a nuclear power water environment. With the help of ABAQUS software, the change rules of the crack tip stress field and creep field under different hardening degrees are analyzed, and then the influence on crack tip creep and crack propagation rate is analyzed. Results show that increasing pre-hardening will increase the Mises stress around the crack tip, and the creep around the crack tip is expressed under pre-deformation, indicating that pre-hardening can accelerate the cracking of stress corrosion to a certain extent. Research has shown that the work hardening induced by the pre-deformation has an important influence on the creep rate at the crack tip, and the high creep zone is mainly concentrated in the direction of crack propagation. Under a certain work hardening rate, the crack growth will be accumulated. [ABSTRACT FROM AUTHOR]

Correction to: Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Rice-Tracey-Huang models. Chirkov should read: "Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Rice-Tracey-Huang models. In Strength of Materials, 54, No. 5, 767-775 (2022), the title of the paper "Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Reiss-Tracey-Huang models. [Extracted from the article]

The paper presents the results of the application of the refined calculation guidelines to the analysis of the stress-strain state and fracture resistance of the equipment elements of the NPP primary circuit system with WWER reactor, in particular, the cylindrical part and the zone of the reactor pressure vessel inlet nozzle, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft under the operating and emergency modes of thermomechanical loading. The calculation methodology is based on the use of the modern models and methods of solution to the nonlinear boundary tasks of non-isothermal thermal viscoplasticity and tasks of fracture mechanics using the refined mixed schemes of the finite element method with increased accuracy. They allow one to obtain reliable solutions to the tasks considering the deformation history of thermomechanical loading, modern concepts of fracture mechanics and approaches to the modeling of brittle-viscous fracture defects, irradiation swelling and creep of metal, as well as as the structural elements, under the conditions of elevated temperature, intensive neutron irradiation and nonstationary modes of thermomechanical loading. The authors obtained and analyzed the calculation results for the cylindrical part and zone of the inlet nozzle of the WWER-1000 reactor pressure vessel, coolant collector welded joint in a steam generator, baffle, and reactor internals' shaft using the proposed guidelines. The results imply the possibilities of the proposed recommendations and make it possible to analyze some general tendencies and features of the application of the refined calculation models to justify the strength and life extension of the NPP structural elements under investigation. [ABSTRACT FROM AUTHOR]

Correction to: Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Rice-Tracey-Huang models. The Reiss-Tracey model" by O.Y. Chirkov should read: "Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Rice-Tracey-Huang models. The online version of the original article can be found at https://doi.org/10.1007/s11223-022-00410-6 In Strength of Materials, 54, No. 3, 345-357 (2022), the title of the paper "Validity analysis of elastic-plastic deformation mechanics problems considering the growth of pores in the material via the Reiss-Tracey-Huang models. [Extracted from the article]

This study proposed a model describing the kinetics of short fatigue crack growth from a smooth surface and from the top of a blunt notch. The driving force of the fatigue crack is the effective stress intensity factor (SIF), which is defined as the difference between the applied "external" and "internal" SIFs, characterizing the material resistance to crack growth. The model makes it possible to calculate the kinetic diagram of the growth rate of a short fatigue crack from the notch and estimate the fatigue life (number of load cycles) from the moment of crack initiation until it reaches a certain size at a constant range of applied nominal stresses. The total fatigue life is divided into the crack initiation stage (stage 1) and crack growth stage (stage 2). In addition to the load parameters and notch's geometric dimensions, the input data for the calculation are the static strength characteristics (elastic modulus, Poisson's ratio, and macroyield initiation stress) determined via short-term tensile tests of standard specimens of this material, and microstructural characteristics (grain size, grain misorientation angle, Taylor's factor, and Burgers vector) determined from the microstructural analysis of the initial material. The calculations based on the proposed model of the kinetic curve of the crack growth rate and total fatigue life of the tested specimens made of steel 45 show good agreement with the experimental ones. [ABSTRACT FROM AUTHOR]

The effects of the dip angles of the echelon notches on the acoustic emission (AE) are studied under uniaxial compression. For this comprehensive analysis, discrete-element simulations are used. Therefore, model dimensions of 150×150 mm were specially prepared. These models contained three echelon cracks with different lengths of 4.5, 3, and 1.5 cm, and a 2 mm vertical distance between the cracks. The inclination angles of the middle crack varied as 0°, 15°, 30°, 60°, 75°, and 90° in the specimens containing echelon cracks with different configurations. Two neighboring cracks were perpendicular to the middle cracks. Twelve different models were designed and tested under uniaxial compression. It was observed that the failure process and crack propagation patterns in the rock-like material specimens were affected by changes in cracks' angles and their configurations. The AE events in the loaded specimens grew rapidly during the initial loading phase. Numerous AE events showed a decline in the induced stresses at the peak load states. [ABSTRACT FROM AUTHOR]

A methodology for theoretically estimating the endurance limit of a material for conditions of multicycle fatigue is proposed. The estimation is based on the fact that under these conditions, a nonpropagating surface fatigue crack of one grain size exists at the level of the applied stress range equal to the endurance limit. In this regard, the tools of linear-elastic fracture mechanics were used in the development of the methodology, but with corrections for the size and geometry of a short fatigue crack. The methodology allows for estimating the endurance limit of smooth specimens under symmetric and positive stress ratios of the loading cycle. The initial data for the estimation are the characteristics of the static strength and microstructure of the material. The reliability of the proposed estimation is confirmed by experimental fatigue data for structural alloys of various classes taken from the literature. [ABSTRACT FROM AUTHOR]

The stress corrosion cracking (SCC) crack propagation behavior of nuclear power structural materials in a high temperature water environment can be regarded as oxide film rupture and regeneration under the interaction of material, corrosive environment, and mechanical micro- environment. To understand the influence of the passivation process of the shape around the crack tip over time on the creep field, the change of oxide film curvature value is used to represent the passivation process of the shape around the crack tip. The finite element software ABAQUS is used to simulate and analyze the crack tip creep field and its distribution law of the oxide film at the crack tip under different curvatures. Results show that different oxide film curvatures will affect the size and distribution of stress and strain around the crack tip. With the increase of oxide film curvature, the creep amount, creep rate, and crack growth rate of the base metal all show an increasing trend. [ABSTRACT FROM AUTHOR]

Results of complex experimental investigations on the determination of energy characteristics of fracture propagation in Charpy specimens cut in three different directions during impact bending tests for heat-resistant 15Kh2NMFA steel are presented. Tests were conducted over a wide temperature range on an instrumented vertical coping equipped with a high-rate data logging system. According to the test results, load diagrams were obtained. Total strain and fracture energy and its components were determined: crack nucleation energy, ductile crack growth energy, brittle crack propagation energy, and ductile final rupture energy. The use of quantitative fractography methods made it possible to determine both the specific strain and fracture energies, their components, and the average propagation rates of brittle and ductile cracks in the specimens' material. Critical brittle fracture temperatures were determined by two methods. The cutting direction of specimens significantly influenced the fracture energy characteristics and crack propagation rates in the material, which might affect the accuracy of strength and resource estimation of the NPP first contour components. [ABSTRACT FROM AUTHOR]