The goal of the present paper is to propose a criterion to predict the fatigue strength of hard m... more The goal of the present paper is to propose a criterion to predict the fatigue strength of hard metals under conditions of multiaxial, non-proportional loadings. It is very simple to compute, but still provides very good results for a wide range of in-phase and out-of-phase cycling loads.
An experimental and analytical study of the effect of varying contact stress fields on the initia... more An experimental and analytical study of the effect of varying contact stress fields on the initiation life of fretted specimens is conducted for two high strength alloys commonly used in the aerospace industry, namely Al4%Cu and Ti-6Al-4V. The experiments reveal there is a contact size effect in fretting fatigue life. Two critical plane models are used to predict the observed experimental lives. The results show that these models may provide over-conservative life estimates for fretting tests subjected to more rapidly varying contact stress fields. The existence of a critical stressed layer, or volume, is used to explain these results qualitatively, and averaging methods are then developed to allow the extension of the critical plane approach to cases of rapidly varying contact stress fields. It is shown that a critical averaging dimension of the order of the grain size of the material appears to give realistic estimates of fatigue life and predicts the observed size effect reported in the experimental work.
This paper summarises an attempt to propose a methodology suitable for estimating high-cycle fati... more This paper summarises an attempt to propose a methodology suitable for estimating high-cycle fatigue strength of cylindrical contacts under a partial slip regime. In particular, Taylor’s point method, usually applied to predict fatigue limits of notched components, was used in conjunction with the Modified Wöhler Curve Method allowing us to formulate a novel fretting fatigue prediction methodology. The devised procedure takes as its starting point the idea that to correctly estimate fatigue damage under fretting fatigue two different aspects must be taken into account: stress gradients and degree of multiaxiality of the stress field damaging the fatigue process zone. The first problem was addressed by using the Theory of Critical Distances, whereas the latter by using an appropriate multiaxial fatigue criterion. In order to check the accuracy of the proposed methodology, a number of tests on cylindrical contacts were selected from the technical literature for two high strength alloys commonly used in the aerospace industry, namely Al4%Cu and Ti–6Al–4V. The performed analyses showed a sound agreement between estimations and experimental data. In particular, the proposed method correctly predicted failures in the medium-cycle fatigue regime, allowing the high-cycle fatigue estimations to fall within an error interval of about ±20%. This result is very interesting, especially by the light of the fact that such an approach is based on the use of linear-elastic stresses, making it suitable for being used in situations of practical interest by post-processing linear-elastic finite element results.
A series of fretting fatigue experiments are described in which the fatigue life is found to vary... more A series of fretting fatigue experiments are described in which the fatigue life is found to vary with contact size. There exists a critical contact size, where fatigue lives are longer than 107 cycles. Short crack methodologies based on the Kitagawa–Takahashi diagram are developed and used to predict the critical contact size in the experiments. Good agreement is found between experimental and predicted results. A discussion regarding the appropriate fundamental material parameters for cases where the stress field is non-uniform is also undertaken.
In this paper, a new multiaxial high cycle fatigue endurance criterion is proposed within the set... more In this paper, a new multiaxial high cycle fatigue endurance criterion is proposed within the setting of situations where the mechanical component is subjected to iso-frequency in-phase or out-of-phase sinusoidal multiaxial loadings. It considers, as measures of fatigue solicitation: (i) a new function of the shear stress amplitude, which is capable to account for the nonproportional character of the loading history and (ii) the maximum principal stress along the stress history. Assessment of the resulting criterion shows that it compares very well with experimental data published in the literature.
The goal of the present paper is to propose a criterion to predict the fatigue strength of hard m... more The goal of the present paper is to propose a criterion to predict the fatigue strength of hard metals under conditions of multiaxial, non-proportional loadings. It is very simple to compute, but still provides very good results for a wide range of in-phase and out-of-phase cycling loads.
An experimental and analytical study of the effect of varying contact stress fields on the initia... more An experimental and analytical study of the effect of varying contact stress fields on the initiation life of fretted specimens is conducted for two high strength alloys commonly used in the aerospace industry, namely Al4%Cu and Ti-6Al-4V. The experiments reveal there is a contact size effect in fretting fatigue life. Two critical plane models are used to predict the observed experimental lives. The results show that these models may provide over-conservative life estimates for fretting tests subjected to more rapidly varying contact stress fields. The existence of a critical stressed layer, or volume, is used to explain these results qualitatively, and averaging methods are then developed to allow the extension of the critical plane approach to cases of rapidly varying contact stress fields. It is shown that a critical averaging dimension of the order of the grain size of the material appears to give realistic estimates of fatigue life and predicts the observed size effect reported in the experimental work.
This paper summarises an attempt to propose a methodology suitable for estimating high-cycle fati... more This paper summarises an attempt to propose a methodology suitable for estimating high-cycle fatigue strength of cylindrical contacts under a partial slip regime. In particular, Taylor’s point method, usually applied to predict fatigue limits of notched components, was used in conjunction with the Modified Wöhler Curve Method allowing us to formulate a novel fretting fatigue prediction methodology. The devised procedure takes as its starting point the idea that to correctly estimate fatigue damage under fretting fatigue two different aspects must be taken into account: stress gradients and degree of multiaxiality of the stress field damaging the fatigue process zone. The first problem was addressed by using the Theory of Critical Distances, whereas the latter by using an appropriate multiaxial fatigue criterion. In order to check the accuracy of the proposed methodology, a number of tests on cylindrical contacts were selected from the technical literature for two high strength alloys commonly used in the aerospace industry, namely Al4%Cu and Ti–6Al–4V. The performed analyses showed a sound agreement between estimations and experimental data. In particular, the proposed method correctly predicted failures in the medium-cycle fatigue regime, allowing the high-cycle fatigue estimations to fall within an error interval of about ±20%. This result is very interesting, especially by the light of the fact that such an approach is based on the use of linear-elastic stresses, making it suitable for being used in situations of practical interest by post-processing linear-elastic finite element results.
A series of fretting fatigue experiments are described in which the fatigue life is found to vary... more A series of fretting fatigue experiments are described in which the fatigue life is found to vary with contact size. There exists a critical contact size, where fatigue lives are longer than 107 cycles. Short crack methodologies based on the Kitagawa–Takahashi diagram are developed and used to predict the critical contact size in the experiments. Good agreement is found between experimental and predicted results. A discussion regarding the appropriate fundamental material parameters for cases where the stress field is non-uniform is also undertaken.
In this paper, a new multiaxial high cycle fatigue endurance criterion is proposed within the set... more In this paper, a new multiaxial high cycle fatigue endurance criterion is proposed within the setting of situations where the mechanical component is subjected to iso-frequency in-phase or out-of-phase sinusoidal multiaxial loadings. It considers, as measures of fatigue solicitation: (i) a new function of the shear stress amplitude, which is capable to account for the nonproportional character of the loading history and (ii) the maximum principal stress along the stress history. Assessment of the resulting criterion shows that it compares very well with experimental data published in the literature.
Uploads
Papers by Jose Araujo