Modelos fractomecánicos para la estimación del crecimiento de fisuras cortas y la evaluación de la resistencia a la fatiga

The fatigue strength assessment of metallic components containing manufacturing defects is currently analysed by applying fracture mechanics-based methodologies. This work begins by dealing with the recently published paper entitled “Short crack propagation analysis and fatigue strength assessment of additively manufactured materials: an application to AISI 316L”, Int J Fatigue 151 (2021) 106396, by Bergant, Werner, Madia, Yawny and Zerbst, where IBESS approach and Chapetti´s short crack growth threshold models were imple-mented for assessing the fatigue strength of laser powder bed fusion processed AISI 316L stainless steels. The application of the Chapetti´s model is carried out here in the way its author thinks it should be made, and results show clear differences when comparing with the results of the referenced paper. Analyses of the sources of discrepancy are also carried out. Some discussions associated with other recent applications of the available fracture mechanics models and hypotheses, or their combinations, are added in order to optimize future analysis when using them for short crack growth threshold estimations. Later, several analyses are made by making gen-eral observations associated with the prediction models, their hypotheses, their combinations and their relation-ship to the Kitagawa-Takahashi diagram. Finally, it is shown that when applying the fracture mechanics models special attention is necessary when comparing intrinsic strengths of the analysed material and that of materi-al-defect combinations, particularly when the defects used in the analysis are artificial and/or are relatively large comparing with the microstructural dimension.Fil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Prediction of the fatigue limit of blunt-notched components

A prediction of the fatigue limit of blunt-notched components of a low carbon steel was made on the basis that the fatigue limit of polycrystalline metals represents the critical conditions for the propagation of nucleated cracks. An expression for the material resistance to crack propagation as a function of the crack length is obtained for the first part of the short crack regime, which defines the blunt notch sensitivity to fatigue. The material resistance curve is modeled from a depth d, given by the position of the strongest microstructural barrier to microstructurally short crack propagation, which defines the plain fatigue limit. A microstructural threshold, ΔKd, is suggested as an intrinsic material resistance to microstructurally short crack propagation, defined by the plain fatigue limit Δσe0 and the position of the strongest microstructural barrier d. The modeled notch sensitivity fits reasonably well the experimental results for a low carbon steel.Fil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Analysis of the influence of defects on fatigue resistance of metallic components

The influence of defect on fatigue resistance of components is carried out by using a propagation threshold approach to estimate the high cycle fatigue resistance of components from data of intrinsic properties of the material. The Chapetti´s threshold curve for fatigue crack propagation is used, which includes the short crack regime. The approach accounts for the effective driving force applied to the crack as the difference between the total driving force applied to the component, ΔK, and the threshold for fatigue crack propagation of the material, ΔKth. Application to analyze the influence of plate thickness on fatigue resistance of welded joints is presented.Fil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación En Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentin

Fracture mechanics based prediction of undercut tolerances in industry

Undercuts are geometrical discontinuities or grooves along the toe of a weld caused by loss of the parent material that remain unfilled by weld metal. Regardless of their causes, undercuts can be found in structures and components, in the majority of joints and most of the welding processes. Due to their frequency of appearance in welded structures and their detrimental effects on component life, undercut acceptance criteria had to be regulated by construction codes and standards. Depending on the area where the component is in service, specific tolerances must be satisfied in order to accept or reject the part. In general, undercut depth is considered to be the limiting parameter for this kind of imperfection. However, there is currently in industry no agreement about which value of depth is tolerable for a desired fatigue strength. The purposes of the present paper are twofold. First, to summarise the state of art associated to undercut tolerances in different codes, standards and recommendation documents, for different industries and applications. Secondly, to employ a fracture mechanics based methodology to predict safe undercut dimensions for butt welds subjected to fatigue. Predictions are in good agreement with experimental results from literature, and proposed method proved to be helpful for assessing weld discontinuities.Fil: Steimbreger, Ceferino. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Undercut tolerances in industry from a fracture mechanic perspective

Fatigue is an important damage mechanism that particularly affects welded components, since they are likely to present residual stresses, inhomogeneities and stress raisers. Assessment of cyclic load effects on welds has concerned both industries and scientist for decades; unexpected failure must be prevented and at the same time, structures must withstand design loads with minimum requirements of material. All these facts together with economic issues have lead to the creation of normative that rule designing and construction of welded components. Particularly, toe undercuts are generally found in large structures, and large scatter and disagreement exists towards their significance and effects. Documents usually limit only their depth without considering radius, width or length, and there is currently no explanation to that fact. Understanding the damaging process will also help to set less conservative tolerances, with consequent cost reduction due to less demanding inspection. The present paper deals with a fracture mechanic approach that uses the Resistance Curve concept to predict fatigue limit of welded components with undercuts. Results revealed that depth is the most influencing variable, and it can be used as the limiting parameter in design regulations. Moreover, good correlation was obtained with FAT values normally assigned to this kind of defect.Fil: Steimbreger, Ceferino. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

A simple expression to estimate the fatigue endurance of welded joints

A simple expression is proposed to estimate the fatigue endurance of welded joints that can be used to understand and analyze in a simple way the influence of the main geometrical, mechanical and material effects (weld geometry, local geometry, material properties, residual stresses and size of defects). The proposed expression was derived from the results of the analysis of the fatigue strength of welds studied by means of a fracture mechanics approach that takes into account the fatigue behavior of short cracks by using the resistance curve method. For that purpose numerical simulation of transversely stressed butt, T and cruciform joints were performed.Fil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Steimbreger, Ceferino. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Fatigue behavior prediction of welded joints by using an integrated fracture mechanics approach

Current fracture mechanics methods for fatigue assessment of welded joints are based on long crack behavior. The present work introduces a method to predict the fatigue strength of welded joints by means of an integrated fracture mechanics approach (IFMA) that takes into account the fatigue behavior of short cracks. This methodology estimates the fatigue crack propagation rate as a function of the difference between the applied driving force and the material threshold for crack propagation, function of crack length. Firstly, the proposed fracture mechanic method is introduced and compared with the traditional fracture mechanic approach, used mainly for fitness for purpose assessment of welded joints with cracks or other crack-like defects. Then, the method is used for several theoretical and parametric applications to show its ability to predict the influence of different mechanical, geometrical and microstructural parameters in the definition of the fatigue resistance of welded joints. The influence of plate thickness, initial crack length and reinforcement angle on fatigue strength of butt-welded joints has been analysed and results show good agreement with experimental trends. Finally, the method is applied to predict and analyze the fatigue behavior of butt welded and non-load-carrying transverse fillet welded joints, and estimated and experimental results are analysed and compared.Fil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Jaureguizahar, Leandro Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Fatigue of NiTi shape memory wires

In the present work, an innovative methodology for characterizing structural fatigue of NiTi superelastic wires is proposed. It consists in, firstly, performing low speed nearly isothermal pseudoelastic cycles in a limited region of the wire specimen. This results in the stabilization of the pseudooelastic behavior accompanied by a decrease in the stresses for forward and reverse transformations which allows obtaining an equivalent to a geometric dog-bone shaped specimen due to the reduced transformation stresses in the pre-cycled region. In a second stage, by limiting the transformation active zone to the pre-cycled region, the deformation speed can be increased to practical values avoiding any transformation activity outside that region. In that way, grip induced failures resulting in artificially shorter fatigue lives might be completely avoided thus allowing an accurate characterization of the true structural fatigue. Additionally, strain controlled experiments on wires in fully austenite and fully martensite states have been performed. Resulting fatigue lives in these cases were at least two orders of magnitude higher compared with the pseudoelastic fatigue indicating the decisive role played by the stress induced transformation in determining fatigue life. The influence of testing temperature and deformation rate on fatigue life has also been evaluated.Fil: Jaureguizahar, Sebastian Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; ArgentinaFil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Yawny, Alejandro Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comision Nacional de Energía Atómica. Gerencia de Área Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Física de Metales; Argentina21st European Conference on FractureCataniaItaliaEuropean Structural Integrity Society ESI

Static strengthening and fatigue blunt-notch sensitivity in low-carbon steels

The influence of four different static strengthenings on the fatigue blunt-notch sensitivity of a low-carbon steel with a ferrite–pearlite microstructure was analyzed and modeled. The analysis was made using a model previously derived which estimates the fatigue limit of blunt notched components by means of the parameter ktd defined as the stress concentration introduced by the notch at a distance d from the notch root surface equal to the distance between microstructural barriers. While the distance d between microstructural barriers is kept constant by keeping constant the grain size, the effective resistance of the microstructural barriers to crack propagation is increased by static strengthening. The analyses have shown the influence of the distribution and effective resistance of the first two or three microstructural barriers on fatigue blunt-notch sensitivity.Fil: Chapetti, Mirco Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Katsura, N.. Nagoya University. Material Science and Engineering; JapónFil: Tagawa, T.. Nagoya University. Material Science and Engineering; JapónFil: Miyata, T.. Nagoya University. Material Science and Engineering; Japó

Fatigue propagation of long cracks in metastable austenitic stainless steels

Fatigue crack growth of a metastable austenitic stainless steel was investigated in thin specimen under positive stress ratio. Annealed and Co l d rolled conditions were used to test the influence of the microstructure. The influence of load ratio and load history on propagation behavior was analyzed using the Elber`s closure approach, the Donald and Paris partial crack closure and the empirical Kujawski (∆K•Kmax) α parameter. Results show that load ratio effects could be explained by two parameters concepts . It see ms that the amount of martensite transformation is responsible for the observed differences in fatigue crack growth resistance.Postprint (published version