The use of SE(T) specimen fracture toughness for FFS assessment of defects in low constraint conditions

AbstractDue to the loss of constraint, shallow cracked specimens can ‘absorb’ more energy than deeply cracked specimens commonly used to define the critical value to fracture and therefore exhibit a higher fracture toughness. The increase in energy absorption allows a reduction in the inherent conservatism when assessing components in low constraint conditions. This study addresses the benefit of using shallow cracked SE(T) fracture toughness specimens in fitness for service (FFS) assessment of defects under low constraint conditions, e.g. blunt defects or shallow cracks. Tearing resistance curves (J-R curves) have been constructed by means of a virtual test framework to determine crack initiation and propagation for shallow cracked SE(T) specimens and parametric notched C(T) specimens. The effect of constraint level on J-R curves is compared. It is observed that most of the blunted C(T) specimens analysed exhibit the same or a lower toughness value than that of a shallow cracked SE(T) specimen. The results are used to show how reduced conservatism can be made in defect assessment of blunt defects or in cases in which reduced constraint conditions can be demonstrated

Simulation of stress-assisted localised corrosion using a Cellular Automaton Finite Element approach

In this paper, the overall corrosion damage process is modelled sequentially using cellular automata (CA) to describe the localised corrosion component, and finite element analysis (FEA) to account for the mechanical component resulting from the stress concentration effect of the corrosion defect (pit). Synchronous execution of the CA and FEA, and provision of feedback between both provides a good approximation of stress-assisted pit development. Qualitative and quantitative comparison of simulation results with experimental measurements show good agreement. In particular, the model shows that mechanical effects, notably plastic strain, accelerates the rate of development of localised corrosion

Pit to crack transition and corrosion fatigue lifetime reduction estimations by means of a short crack microstructural model

Article number 109171A microstructural model is presented to assess pit-to-crack transition and corrosion fatigue strength in pitted components in different environments. The model is first validated using available experimental data in the literature for pitting corrosion fatigue strength and S-N curves for both carbon and stainless steels. The value of the method proposed and its applicability is then shown by the development of fatigue knock down factor maps to the in-air S-N curve. Finally, the influence of pit local topology on pit-to-crack transition damage tolerance and the links to the NDE methods quantitative resolution necessary to account for defect shape or acuity in structural integrity assessments are discussedMinisterio de Educación DPI2014-56904-PMinisterio de Educación DPI2017-84788-PConsejo de Investigación de Ingeniería y Ciencias Físicas del Reino Unido EP / S012362 /

An iterative technique to assess the fatigue strength of notched components

Incluído en: Vol. 28 Procedia Structural IntegrityThe present work provides an efficient formulation to assess the growth of short fatigue cracks in metallic components. The proposed technique consists on the iterative combination of a micromechanical short-crack growth model and the Finite Elements Method. The interaction of the crack with the microstructure of the material is evaluated through the dislocations distribution technique. The finite elements analysis of the problem is needed to obtain the stress gradient ahead of the notch. The division of the main problem into simpler scenarios makes the resolution of the method easier since cases with known solutions are required exclusively. The iterative method formulation is properly described and application examples are given in order to show its usefulness.Ministerio de Educación y Ciencia (España) y Junta de Andalucía DPI2014-56904-PMinisterio de Educación y Ciencia (España) y Junta de Andalucía DPI2017-84788-PMinisterio de Educación y Ciencia (España) y Junta de Andalucía P18-FR-430