Lifetime Prediction for Ceramic Gas Turbine Components

Stürmer, G.; Schulz, Achmed; Wittig, Sigmar

doi:10.1115/1.2906688

Cited by 11 publications

(4 citation statements)

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“…(17). the integration of the above formula with respect to the cycle N results in the following formula, for volume flaw analysis, for the probability of fracture (or macrocracking) after subcritical crack growth, As suggested by Nemath, et al (15), the constant B in the above formula can be obtained from the cyclic fatigue test under uniaxial stress, such as the rotating beam fatigue test.…”

Section: Cyclic Fatiguementioning

confidence: 99%

An Approach for Fatigue Cracking Failure Prediction of Ceramic Rolling Elements under Hertzian Loading

Chiu

1999

Tribology Transactions

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In highly stressed rolling element contacts of ceramics, cracking along the edge of the rolling track is a well-recognized mode of failure. Using the maximum value of principal tensile stress which a material element experiences under the passage of the contact load as critical stress for failure, the failure probability of the ceramic rolling element is formulated according to Weibull probability theory using a volumetric flaw assumption. The formulation contains material parameters, such as fatigue exponent, crack growth constant and Weibull modulus, which are obtained previously from (static and cyclic fatigue) bending testing of two advanced silicon nitrides. For the two ceramic materials, the Hertz contact stress field is analyzed to determine the failure probability in terms of maximum tensile principal stress, aspect ratio and sliding friction coefficient. Numerical examples have been calculated for ceramic rods and balls with and without sliding friction. The strong effect of friction on failure probability indicates the need for good lubrication in reducing friction and increasing the reliability of the hybrid ceramic bearings.= semi-major axis = crack length = semi-contact width, semi-minor axis = crack growth constant = Young's modulus = friction coefticient = Mode -I stress intensity factor = fracture toughness, Mode I

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Section: Cyclic Fatiguementioning

confidence: 99%

An Approach for Fatigue Cracking Failure Prediction of Ceramic Rolling Elements under Hertzian Loading

Chiu

1999

Tribology Transactions

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“…42 Earlier, Der Stu¨rmer had proclaimed that nuns and monks only waited for the right moment to join forces with Jews so that they could exploit the Volk 'in the service of international powers'. 43 A caricature on the front page of the same issue depicted a nun in traditional habit being tempted with foreign currency by the devil depicted with a Star of David on his forehead.…”

Section: Foreign Exchange Regulations and The Campaign Against The Catholic Churchmentioning

confidence: 99%

The Bonds That Shame: Reconsidering the Foreign Exchange Trials of 1935–36 Against the Catholic Church in Nazi Germany

Cucchiara

2015

European History Quarterly

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This article reassesses the foreign exchange trials and concurrent propaganda campaign in 1935-36 against the Catholic Church in Nazi Germany. Scholars have had difficulties situating the foreign exchange trials within the church struggle because most have viewed the proceedings as legitimate and the impact on the church and the laity as negligible. The argument of an untainted justice system under National Socialism can of course no longer be sustained, and the Nazis routinely used specific crimes to persecute their enemies. The violation of Germany's complex foreign exchange laws became a signature crime favoured by the Security Service in the persecution of Jews. In 1935, the regime attempted to use accusations of foreign exchange violations in pursuit of the church. New evidence from the Vatican Archives reveals that the foreign exchange trials against the church were anything but legitimate proceedings on the margins of the church struggle. Instead, the regime pursued immediate and specific political goals with the trials at a crucial point in the conflict. In particular, the regime attempted to force the church to publicly capitulate on unresolved issues over Catholic lay associations. Hitler routinely interfered in the proceedings and lower-ranking officials soon joined in and used the trials to discipline bishops and religious orders within their respective spheres of influence. The bishops' often ill-considered response to the trials only escalated the crisis within the church, and evidence indicates that the regime delayed settlements for as long as possible to press church leaders to make further concessions to the regime.

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“…Note that Eq. (3) can be used to calculate σ Ieq,0 (ψ) directly for the special case when the material parameters N and B are invariant (constant) over the entire load history 16 , 17 . In this paper we show how to compute σ Ieq,0 (ψ) using Eq.…”

Section: Theoretical Developmentmentioning

confidence: 99%

Transient reliability of ceramic structures

Jadaan

Nemethm

2001

Fatigue Fract Eng Mat Struct

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Present capabilities of the NASA Ceramic Analysis and Reliability Evaluation of Structures/Life (CARES/Life) code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (SCG) (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time‐dependent reliability of ceramic structures subjected to simple time‐dependent loading. For example, in SCG type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time‐dependent loads, whereas for cyclic fatigue applications, it can account for various types of repetitive constant amplitude loads. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as engine start up and shut down and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and/or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time‐dependent reliability of components subjected to transient thermomechanical loads that take into account the change in material response with time. In this article, the dominant delayed failure mechanism is assumed to be SCG. This capability has been added to the NASA CARES/Life code, which has also been modified to have the ability of interfacing with commercially available finite element analysis codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.

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Lifetime Prediction for Ceramic Gas Turbine Components

Cited by 11 publications

References 0 publications

An Approach for Fatigue Cracking Failure Prediction of Ceramic Rolling Elements under Hertzian Loading

An Approach for Fatigue Cracking Failure Prediction of Ceramic Rolling Elements under Hertzian Loading

The Bonds That Shame: Reconsidering the Foreign Exchange Trials of 1935–36 Against the Catholic Church in Nazi Germany

Transient reliability of ceramic structures

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