Sobrecargas en crecimiento de grietas por fatiga biaxial

El presente trabajo se centra en el estudio de grietas de fatiga bajo cargas biaxiales. Se presenta una nueva metodología para evaluar el efecto de las sobrecargas basada en la evaluación experimental del factor de intensidad de tensiones efectivo y de la apertura de la grieta (Crack Opening Displacement, COD). El estudio se ha realizado en probetas cilíndricas de acero de bajo contenido en carbono sometidas a cargas de tracción y torsión. Los datos experimentales se han obtenido mediante la técnica de correlación de imágenes digitales. Se ha comparado la evolución de la grieta con y sin sobrecarga. Además, se ha utilizado un procedimiento de detección de carga de apertura. Dicho procedimiento se había desarrollado previamente en fatiga uniaxial para el caso biaxial. Dicho procedimiento permite poner de manifiesto el cambio originado por un ciclo de sobrecarga.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

A review of non-destructive testing techniques for the in-situ investigation of fretting fatigue cracks

© 2020 The Authors Fretting fatigue can significantly reduce the life of components, leading to unexpected in-service failures. This phenomenon has been studied for over a century, with significant progress being made during the past decade. There are various methods that have been used to study fretting fatigue cracks in order to gain a greater understanding of the effects of fretting fatigue. Destructive methods are traditionally used to observe fretting fatigue cracks. Although useful in determining crack location, crack length, crack propagation modes, crack path and shape, it is not efficient or reliable for time based measurements. Non-destructive testing has developed in recent years and now in-situ monitoring can be used during testing in order to increase the understanding of fretting fatigue. This paper presents a review of non-destructive testing techniques used in-situ during fretting fatigue testing, which are compared in order to conclude the suitability of each technique. Recent developments in non-destructive techniques that could be also applied for fretting fatigue tests are also discussed, as well as recommendations for future research made

Multi-parameter fracture mechanic analysis of fatigue crack propagation by digital image correlation

The effect of these parameters on the SIF evaluation are then tested for stable and accurate SIF estimation. The method showed a great stability for continuous evaluation of SIF under static and cyclic loads. It was also successfully applied on cylindrical samples under biaxial loading and the results showed good agreement between analytical and experimental evaluation of SIF. Finally, the methodology was also employed successfully to detect crack closure effects. Fecha de lectura de Tesis Doctoral: 07/06/2019.Accurate evaluation of the fracture parameters is crucial for estimating the behaviour of the mechanical components in service condition. Experimental observations are extremely useful to provide accurate and reliable information for modern structural integrity analysis. The stress intensity factor (SIF) is a key parameter for understanding the fatigue crack propagation behaviour of structures prone to linear elastic failure. The SIF has been widely studied and a number of experimental, numerical and analytical methods have been developed and continue being developed to improve the estimation of the SIF for different loading conditions and component geometries. Digital Image Correlation (DIC) is a simple and versatile method for full-field quantification and can be used to measure experimentally the displacement data from a surface of a component being strained. By combining the experimentally evaluated displacement data with analytical solutions such as Westergard's, Muskhilishvili's and Williams' series, one is able to evaluate the SIF in cracked components. However, the selection of the experimental parameters and the limitations of the approach (e.g. the maximum permitted plasticity at the crack tip) are still a controversial concept. This work concentrates on three main topics: optimization the experimental DIC parameters for SIF evaluation, continuous measurement of SIF by DIC and evaluation of crack tip field under complex loading conditions (biaxial loading) with and without the presence of overloads. A multipoint over-deterministic method is employed to combine an elastic model based on Williams' solution for displacement distribution around the crack tip with the experimentally full field measurement of displacement at the crack tip by DIC. Different parameters such as number of terms in Williams' series, size of the field of view and the best location of the area of interest are examined in the optimisation stage

The Effect of Overload on Crack Growth Behaviour in Biaxial Fatigue

This paper focus on the study of biaxial fatigue cracks based on a methodology that enables evaluation of the overload effect in fatigue. The methodology is based on the experimental evaluation via full-field technique of digital image correlation of the effective stress intensity factor and the crack opening displacement (COD). The tests were performed on cylindrical specimens made of low carbon steel subjected to tension-tension and a combination of tension and torsion loads. The experimental data was used to compare the crack growth behaviour with an overload cycle under uniaxial and biaxial loading. A hybrid method was also employed to evaluate the value of the Stress Intensity Factor (SIF) before and after applying the overload. The results showed a reliable estimation of closure level and SIF for both uniaxial and biaxial loading condition. A new procedure previously developed for uniaxial loads was adapted to the study of biaxial loads. This new procedure was used to identify important differences produced by the overload event

The Effect of Overload on Crack Growth Behaviour in Biaxial Fatigue

This paper focus on the study of biaxial fatigue cracks based on a methodology that enables evaluation of the overload effect in fatigue. The methodology is based on the experimental evaluation via full-field technique of digital image correlation of the effective stress intensity factor and the crack opening displacement (COD). The tests were performed on cylindrical specimens made of low carbon steel subjected to tension-tension and a combination of tension and torsion loads. The experimental data was used to compare the crack growth behaviour with an overload cycle under uniaxial and biaxial loading. A hybrid method was also employed to evaluate the value of the Stress Intensity Factor (SIF) before and after applying the overload. The results showed a reliable estimation of closure level and SIF for both uniaxial and biaxial loading condition. A new procedure previously developed for uniaxial loads was adapted to the study of biaxial loads. This new procedure was used to identify important differences produced by the overload event