Evaluación de resultados de fatiga con alto y ultra alto número de ciclos mediante un modelo de regresión de Weibull

El modelo de fatiga de regresión de Weibull, propuesto por Castillo-Canteli, representa una alternativa posible y adecuada para la evaluación y predicción de vidas de fatiga ultra altas (VHCF). Este modelo proporciona una definición probabilística del campo S-N para los posibles mecanismos de rotura determinantes, basada en distribuciones de Weibull de mínimos, así como la existencia de un límite de fatiga asintótico y la propiedad de reducir todo el campo SN a una única función de distribución mediante la variable normalizada V=(log N-B)(log Δσ-C). De este modo, el doble mecanismo de rotura, interno y superficial, que caracteriza las vidas altas (HCF) y ultra altas (VHCF) en fatiga puede ser satisfactoriamente tratado como distribuciones independientes en este particular y complejo caso de muestras con resultados concurrentes, conocido como problema de datos confundidos. Una vez estimados los parámetros de ambas funciones de distribución se procede a la combinación y reconversión de ambas como campo S-N conjunto. El modelo permite establecer una estrategia para optimizar la programación de los ensayos. Por último se presentan dos ejemplos de aplicación, uno de un programa externo experimental y otro de resultados simulados, ambos con ultra alto número de ciclos y dos posible mecanismos de rotura.The fatigue Weibull regression model proposed by Castillo-Canteli represents a possible and adequate alternative for the assessment and prediction of very high cycle fatigue (VHCF) lifetimes. This model provides a probabilistic definition of the S-N field for the two determining failure mechanisms based Weibull distributions for minima, as well as the existence of an asymptotic fatigue limit and the capability to reduce the S-N field to a single cumulative distribution function by considering the normalized variable V=(log N-B) (log Δσ). In this way, both dual fracture mechanisms, i.e. the internal and the surface ones, characterizing the HCF and VHCF data can be adequately interpreted and handled as independent distributions in such a particular and complex case of concurrent populations, known as a confounded data problem. Once the model parameters of both normalized cumulative distribution functions are independently estimated for both failure mechanisms and subsequently combined and reconverted to a joint S-N field whereby. The model allows a test strategy to be established for optimizing the the fatigue program planning. Finally, two examples of application are presented, the first related to an external experimental program, and the second to simulated data both for VCCF with twofold failure mechanisms

Bruchmechanischer Festigkeitsnachweis nach der FKM-Richtlinie - 4. erweiterte Ausgabe

Der Artikel gibt einen Überblick über die FKM-Richtlinie Bruchmechanischer Festigkeitsnachweis für Maschinenbauteile, deren Kern die Bewertung fehlerbehafteter Bauteile bei statischer und zyklischer Beanspruchung ist. Es wird insbesondere auf Änderungen und Anpassungen in der 4. erweiterten Ausgabe 2018 eingegangen. Diese betreffen vor allem neue Entwicklungen und Aktualisierungen in der nationalen und internationalen Normung, die Berücksichtigung der lokalen Spannungsmehrachsigkeit an der Rissspitze (Constraint), verbesserte Prozeduren für die Bewertung von Bauteilen mit Sekundärspannungen, die Aktualisierung der Werkstoffdaten sowie erweiterte Lösungen für Spannungsintensitätsfaktoren, Grenzlasten und \u1d447-Stress

FKM-Richtlinie "Bruchmechanischer Festigkeitsnachweis für Maschinenbauteile"

The German guideline "Fracture Mechanics Proof of Strength for Engineering Components" [1, 2] has been released 2001 as a result of activities sponsored by the Research Committee on Mechanical Engineering (FKM), task group "Component Strength". The guideline describes basics for the integrity assessment of cracked components subjected to static or cyclic loading and provides a step-by-step computational procedure for the use in engineering practice. The guideline was formulated based on a number of national and international reference documents, in particular SINTAP P], R6 [4], BS 7910 [5] and DVS-2401 [6], recent research results and some own key aspects. Since 2004 it is also available in English. The procedures and solutions of the guideline are implemented in the computer program FracSafe [7]. The latest 3rd edition of the guideline (2006) includes several new topics. These allow for the consideration of special effects at cyclic loading, mixed mode loading, dynamic (impact) loading, stress corrosion cracking and probabilistic aspects in fracture mechanics calculations. There is a compendium of stress intensity factors and limit load solutions and a compendium of material data. A lot of examples and case studies are included to demonstrate the application of the procedure to engineering problems. This paper gives an overview of the guideline Ill