Application of failure assessment diagram methods to cracked straight pipes and elbows

Engineering and Physical Sciences Research Council (EPSRC) grant EP/K007815/

Metalų mechaninių savybių kitimo priklausomai nuo eksploatacijos trukmės tyrimas

A long-term operating influence on mechanical properties variation of constructional materials is analysed in this article. During the exploitation of structures and pipelines the consistent surrounding influence causes corrosion of the structures materials. Beside the surrounding influence of the constant stress state affects structures too. For constant stresses mechanical properties of structural elements are variable and the metal is ageing. The article presents experimental researches of hot-water pipelines material. From 20 - 40 years exploited pipelines specimens were cut and tension test was fulfilled. The test results disclosed that material strength stress increased minutely. The value of materials yield stress in exploited specimens showed up later if compared with new material. In the best way the changed materials plasticity properties were exposed by specimens relative elongation, which characterizes materials fragility. Linear materials mechanical properties dependenty on lifetime is presented in the article. According to this linear law it is possible to calculate materials mechanical properties of a structure, which is exploited, and assess safety of this structure

Metalų mechaninių savybių kitimo priklausomai nuo eksploatacijos trukmės tyrimas

A long-term operating influence on mechanical properties variation of constructional materials is analysed in this article. During the exploitation of structures and pipelines the consistent surrounding influence causes corrosion of the structures materials. Beside the surrounding influence of the constant stress state affects structures too. For constant stresses mechanical properties of structural elements are variable and the metal is ageing. The article presents experimental researches of hot-water pipelines material. From 20 - 40 years exploited pipelines specimens were cut and tension test was fulfilled. The test results disclosed that material strength stress increased minutely. The value of materials yield stress in exploited specimens showed up later if compared with new material. In the best way the changed materials plasticity properties were exposed by specimens relative elongation, which characterizes materials fragility. Linear materials mechanical properties dependenty on lifetime is presented in the article. According to this linear law it is possible to calculate materials mechanical properties of a structure, which is exploited, and assess safety of this structure

Dynamic J-Integral Evaluation of Three-Point-Bend Beams with Various Geometrical Dimensions

J-Integral is the main effective and commonly used tool for cracked elastic-plastic material resistance assessment. Determination of fracture toughness under impact loading conditions is related with problems of crack length measurement. Nevertheless, current experimental techniques restrict the specimen’s geometry taking into account span and height ratio, which is equal to four. Evaluation of fracture toughness estimation method which requires only experimental load-line displacement curve of single specimen is research object of dynamic fracture mechanics. This article proposes an approach of impact fracture toughness determination of elastic-plastic steel from single any size specimen test. Load-line displacement data obtained from three-point-bending tests of rectangular cross section specimens with V form single edge notch was used for J-integral calculation. Five series of specimens with different geometry were manufactured from ductile steel and tested

Quantification of hydrogen trapping in multiphase steels:Part I – Point traps in martensite

We quantified systematically the H trap density in martensite resulting from the presence of dislocations, grain boundaries and retained austenite through a combination of detailed microstructural characterisation, H permeation, thermal desorption and diffusion modelling. This thorough analysis allowed for the first time to deconvolve key microstructural constituents affecting H diffusion in multi-trap martensite. Three microstructures were investigated – as-quenched, tempered at 300 °C and tempered at 450 °C. The first two microstructures had identical dislocation densities and grain size, while the as-quenched one also contained 3.5 vol.% of retained austenite. The two tempered microstructures showed a large difference in dislocation density with few other microstructural differences. The as-quenched microstructure exhibited over an order of magnitude lower H diffusivity and increased H trapping due to retained austenite, while the tempered samples exhibited very similar diffusivities, indicating that dislocations have a limited effect on H trapping. Trap density scaling laws were successfully identified and validated through diffusion simulations and experiments. It was also shown that in martensite and heavily deformed ferrite, where the average grain size is small, grain boundaries are more effective trapping sites than dislocations. Our results also show that retained austenite cannot be effectively modelled as a point trap under the local equilibrium assumption, which is frequently used to model its effect on H diffusion, and that bulk trapping must be considered at least in two dimensions, which is addressed in part II of this series. © 2020 Acta Materialia Inc