Author: Dian ZhengPublisher:
ISBN:
Category : Metals
Languages : en
Pages : 474
Book Description
Environment-dependent Fatigue Crack Growth in Alloy 718
Mechanisms and Modelling of Environment-Dependent Fatigue Crack Growth in a Nickel Based Superalloy
Author: H. GhonemPublisher:
ISBN:
Category :
Languages : en
Pages : 252
Book Description
At loading frequencies below that of the transitional frequency level, which is typical of mission cycles of jet engines, the elevated temperature fatigue crack growth process in Alloy 718 is viewed to be fully environment-dependent. Of all the crack growth stages, this process, while is the most critical in high temperature application due to its highly accelerated crack growth rate, is the least studied or understood. The objective of this research program is to focus on the understanding or the mechanism controlling this oxidation-dependent stage in order to develop the ability to predict its associated crack growth performance under different environment conditions. For this purpose, three major studies have been carried out; the first was to provide evidence of the existence of the fully environment-dependent stage in which the crack growth rate would be equal to the oxygen penetration rate at the crack tip. The second study was to establish a crack tip oxidation mechanism on the basis of material, environmental and loading parameters interactions in the crack tip region. The last objective of this program is to establish a micromechanical based quantitative model to predict the environmentally-dominated crack growth stage.
Fatigue Crack Propagation in Metals and Alloys
Author: Ulrich KruppPublisher: John Wiley & Sons
ISBN: 3527315373
Category : Technology & Engineering
Languages : en
Pages : 312
Book Description
This comprehensive overview of the whole field of fatigue and fracture of metallic materials covers both the theoretical background and some of the latest experimental techniques. It provides a summary of the complex interactions between material microstructure and cracks, classifying them with respect to the overall damage process with a focus on microstructurally short cracks and dynamic embrittlement. It furthermore introduces new concepts for the numerical treatment of fatigue microcrack propagation and their implementation in fatigue-life prediction models.This comprehensive overview of the whole field of fatigue and fracture of metallic materials covers both the theoretical background and the latest experimental techniques. It provides a summary of the complex interactions between material microstructure and cracks, classifying them with respect to the overall damage process. It furthermore introduces new concepts for the numerical treatment of fatigue microcrack propagation and their implementation in fatigue-life prediction models.
Experimental Study of Oxygen-Assisted Crack Growth in Alloy 718 and Alloy TI-1100
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 201
Book Description
The high Temperature fatigue crack growth behavior of alloy 718 is reviewed and investigated. FCGR have then been measured under constant K and various oxygen partial pressures. A transition pressure associated with an important increase of the FCGR is found. At this transition pressure (10-2mbar) the crack propagation path changes from transgranular to intergranular. From this study it is concluded, that intergranular crack growth requires the formation of Ni based oxide during the early stage of the oxidation as well as high intergranular internal stresses promoted by an inhomogeneous distribution of the deformation. The crack growth behavior of TI-1100 is investigated for loading frequencies ranging from 30 Hz to 0.005 Hz at temperature levels extending from 23 Cto 650 C in both air and vacuum environments. Two types of time-dependent damage mechanisms have been identified; oxidation and creep effects. It is concluded that effect of oxidation on the crack growth acceleration is rapid and constant in relation to the frequencies tested and is weekly dependent on cycle time. Creep effects, on the other hand, are dominant at low frequencies in both air and vacuum and are loading-rate dependent.
Near-Threshold Fatigue Crack Growth Behavior of Fine-Grain Nickel-Based Alloys
Author: John A. NewmanPublisher:
ISBN:
Category : Fracture mechanics
Languages : en
Pages : 16
Book Description
Proceedings of the 8th International Symposium on Superalloy 718 and Derivatives
Author: The Minerals, Metals & Materials Society (TMS)Publisher: John Wiley & Sons
ISBN: 1119016886
Category : Technology & Engineering
Languages : en
Pages : 951
Book Description
Fatigue Crack Growth Rate of Inconel 718 Sheet at Cryogenic Temperatures
Author: National Aeronautics and Space Administration (NASA)Publisher: Createspace Independent Publishing Platform
ISBN: 9781721816958
Category :
Languages : en
Pages : 38
Book Description
Inconel 718 sheet material was tested to determine fatigue crack growth rate (FCGR) at cryogenic conditions representative of a liquid hydrogen (LH2) environment at -423 degree F. Tests utilized M(T) and ESE(T) specimen geometries and environments were either cold gaseous helium or submersion in LH2. The test results support a significant improvement in the fatigue crack growth threshold at -423 degree F compared to -320 degree F or 70 degree F. Wells, Douglas and Wright, Jonathan and Hastings, Keith Langley Research Center; Marshall Space Flight Center NASA/TM-2005-213948, L-19198
Effect of Microstructure on Creep-Fatigue Crack Growth in Alloy 718
Author: K. SadanandaCrack Growth in Alloy 718 Under Thermal-Mechanical Cycling
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 183
Book Description
An investigation was conducted to evaluate and model the crack growth rates in a nickel-base super-joy under load controlled thermal-mechanical cycling. Experiments were conducted on center-cracked panel specimens of Inconel 718 with temperature limits of 427 C to 649 C. closed-loop temperature control in the cracked region of the specimen was maintained by a microcomputer and four quartz heating lamps. A D.C. electric potential drop method was used to monitor crack lengths. The elastic stress intensity factor, K, was used to correlate all crack growth data. & A linear cumulative damage model was developed which sums cycle-dependent, mixed-mode, and time-dependent damage terms to predict thermal-mechanical fatigue crack growth rates. The model was developed entirely from isothermal baseline test data. The cycle-dependent term was based on low temperature (427 C) high frequency (10 Hz) crack growth data. The mixed-mode term was developed from low frequency (0.01 Hz) fatigue crack growth tests at 538 C and 649 C. The time-dependent term was developed from sustained-load crack growth tests at 538 C, 593 C, and 649 C. All thermal and mechanical cycles used during thermal-mechanical fatigue (TMF) testing were symmetric, triangular, and 96 seconds long. Crack growth rates were determined over a range of Sigma K using a stress ratio, R, of 0.1. Tests were conducted with the maximum load leading the maximum temperature by phase angles of 0, 90%, 180, 225, 270, and 315. The in-phase test (0') produced the highest crack growth rates, with the 315', 270', 225', 180', and 90' tests following in order. The 0' and 90' crack growth rates were separated by over a factor of ten at all AK values tested.% All TMF crack growth rates were bracketed by the isothermal growth rates at 427 C and 649 C.
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