Probabilistic constitutive relationships for material strength degradation models

Boyce, L.; Chamis, Christos C.

doi:10.2514/6.1989-1368

Cited by 5 publications

(2 citation statements)

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“…Recently, the equation has been modified to predict the lifetime strength of a single constituent material due to "n" diverse effects or variables (Boyce and Chamis, 1989;Boyce et al, 1991;Boyce and Bast, 1992). These effects could include variables such as high temperature, creep, mechanical fatigue, thermal fatigue, corrosion or even radiation attack.…”

Section: Nomenclaturementioning

confidence: 99%

A Thermal Fatigue Model for Probabilistic Lifetime Strength of Propulsion System Components

Boyce

Bast

1993

Volume 3A: General

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This paper describes the development of methodology for a probabilistic material strength degradation model, that provides for quantification of uncertainty in the lifetime material strength of structural components of aerospace propulsion systems subjected to a number of diverse random effects. The model has most recently been extended to include thermal fatigue. The discussion of thermal fatigue, in the context of probabilistic material strength degradation, is the central feature of this paper. The methodology, for all effects, is embodied in two computer programs, PROMISS and PROMISC. These programs form a “material resistance” model that may be used in the aerospace structural reliability program, NESSUS or in other applications. A probabilistic material strength degradation model for thermal fatigue and other relevant effects, in the form of a postulated randomized multifactor interaction equation, is used to quantify lifetime material strength. Each multiplicative term in the model has the property that if the current value of an effect equals the ultimate value, then the lifetime strength will be zero. Also, if the current value of an effect equals the reference value, the term equals one and lifetime strength is not affected by that particular effect. Presently, the model includes up to four effects that typically reduce lifetime strength: high temperature, mechanical fatigue, creep and thermal fatigue. Statistical analysis of experimental data for Inconel 718 obtained from the open literature and laboratory reports is also included in the paper. The statistical analysis provided regression parameters for use as the model’s empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high temperature, mechanical fatigue, creep and thermal fatigue. Finally, using the PROMISS computer program, a sensitivity study was performed with the calibrated random model to illustrate the effects of mechanical fatigue, creep and thermal fatigue, at about 1000 °F, upon random lifetime strength.

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Section: Nomenclaturementioning

confidence: 99%

A Thermal Fatigue Model for Probabilistic Lifetime Strength of Propulsion System Components

Boyce

Bast

1993

Volume 3A: General

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“…5) is used to evaluate the scatter in material properties for structures subjected to high temperatures and high cyclic loading. The fundamental assumption for this model is that the material behavior can be simulated by primitive (random) variables.…”

Section: Probabilistic Materials Properties Modelmentioning

confidence: 99%

A methodology for evaluating the reliability and risk of structures under complex service environments

Shiao

Chamis

1990

31st Structures, Structural Dynamics and Materials Conference

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SUMMARYAerospace components are often subjected to complex service environments such as random excitations and random temperature conditions. In addition, small variations in the material properties or geometry may significantly affect the structural performance and durability of aerospace components. Therefore, a methodology was developed to determine structural reliability and to assess the associated risk due to various uncertainties in the design variables. The methodology consists of a probabilistic structural analysis by a special computer code NESSUS (Numerical Evaluation of Stochastic Structures Under Stress), a generic probabilistic material property model (multifactor, interaction equation), and a probabilistic fatigue analysis. The methodology is versatile and is equally applicable to structures operating at hightemperature and/or cryogenic environments. The relationship between the probability of crack initiation and fatigue cycles is developed. The probabilistic crack propagation at a given risk level is studied. The most probable fracture path at a given cycle is determined. Those results serve as a guideline for component certification and for setting inspection criteria. The methodology is demonstrated to be capable of formally evaluating structural reliability and risk -including uncertainties in material properties, structural parameters, and loading conditions. It is described in detail with an application to the space shuttle main engine (SSME) blade.

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Probabilistic Material Degradation under High Temperature, Fatigue, and Creep

Boyce

1993

J. Aerosp. Eng.

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Probabilistic constitutive relationships for material strength degradation models

Cited by 5 publications

References 1 publication

A Thermal Fatigue Model for Probabilistic Lifetime Strength of Propulsion System Components

A Thermal Fatigue Model for Probabilistic Lifetime Strength of Propulsion System Components

A methodology for evaluating the reliability and risk of structures under complex service environments

Probabilistic Material Degradation under High Temperature, Fatigue, and Creep

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