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Author: K-Y Hour Publisher: ISBN: Category : Crack closure Languages : en Pages : 12
Book Description
The effects of mean stress on crack growth behavior have been studied by performing various load ratio experiments at elevated temperature. It was found that at low load ratios a transgranular crack growth mode dominates whereas at high load ratios an intergranular crack growth mode was observed. The crack closure phenomenon was observed for experiments in which the transgranular crack growth mode was significant. In such cases, the crack opening stress was found to be constant for Stage II crack growth for each individual experiment at fixed load ratio, but varied with load ratio. Based on this, it was found that the crack growth rate correlated well with the effective stress intensity factor range, ?Keff. At R = 0.6 and above, crack closure effects were not observed and the linear rate line integral parameter, C*, based on elastic-plastic fracture mechanics, was found to correlate better crack growth rate because time-dependent processes were significant in those experiments. In the regime where both fatigue and creep mechanisms might interact, the linear cumulative rule, which combines the two parameters ?Keff and C*, accounting for fatigue and creep effects, respectively, was found to overestimate crack growth rates.
Author: K-Y Hour Publisher: ISBN: Category : Crack closure Languages : en Pages : 12
Book Description
The effects of mean stress on crack growth behavior have been studied by performing various load ratio experiments at elevated temperature. It was found that at low load ratios a transgranular crack growth mode dominates whereas at high load ratios an intergranular crack growth mode was observed. The crack closure phenomenon was observed for experiments in which the transgranular crack growth mode was significant. In such cases, the crack opening stress was found to be constant for Stage II crack growth for each individual experiment at fixed load ratio, but varied with load ratio. Based on this, it was found that the crack growth rate correlated well with the effective stress intensity factor range, ?Keff. At R = 0.6 and above, crack closure effects were not observed and the linear rate line integral parameter, C*, based on elastic-plastic fracture mechanics, was found to correlate better crack growth rate because time-dependent processes were significant in those experiments. In the regime where both fatigue and creep mechanisms might interact, the linear cumulative rule, which combines the two parameters ?Keff and C*, accounting for fatigue and creep effects, respectively, was found to overestimate crack growth rates.
Author: DC. Maxwell Publisher: ISBN: Category : Aluminum alloys Languages : en Pages : 14
Book Description
Effects of temperature, frequency, and cycles with superimposed hold times are evaluated in Ti-1100 in order to study the complex creep-fatigue-environment interactions in this material. Crack growth rate tests conducted at a cyclic loading frequency of 1.0 Hz show that raising the temperature from 593 to 650°C has only a slightly detrimental effect on crack growth rate, although these temperatures produce growth rates significantly higher than at room temperature. From constant ?K tests, the effects of temperature at constant frequency show a minimum crack growth rate at 250°C. From the minimum crack growth rate at 250°C, the crack growth rate increases linearly with temperature. Increases in frequency at constant temperatures of 593 and 650°C produce a continuous decrease in growth rate in going from 0.001 to 1.0 Hz, although the behavior is primarily cycle dependent in this region. Tests at 1.0 Hz with superimposed hold times from 1 to 1000 s are used to evaluate creep-fatigue-environment interactions. Hold times at maximum load are found to initially decrease and then increase the cyclic crack growth rate with increasing duration. This is attributed to crack-tip blunting during short hold times and environmental degradation at long hold times. Hold times at minimum load show no change in growth rates, indicating that there is no net environmental degradation to the bulk material beyond that experienced during the baseline 1 Hz cycling.
Author: M. A. Meyers Publisher: Elsevier ISBN: 0080537235 Category : Technology & Engineering Languages : en Pages : 317
Book Description
The importance of the nanoscale effects has been recognized in materials research for over fifty years, but it is only recently that advanced characterization and fabrication methods are enabling scientists to build structures atom-by-atom or molecule-by molecule. The understanding and control of the nanostructure has been, to a large extent, made possible by new atomistic analysis and characterization methods pioneered by transmission electron microscopy. Nano and Microstructural Design of Advanced Materials focuses on the effective use of such advanced analysis and characterization techniques in the design of materials. - Teaches effective use of advanced analysis and characterization methods at an atomistic level - Contains many supporting examples of materials in which such design concepts have been successfully applied
Author: T. Nicholas Publisher: ISBN: Category : Creep/fatigue interactions Languages : en Pages : 14
Book Description
An experimental investigation was conducted to evaluate the effects of hold times on the fatigue crack growth rate of Inconel 718 at 649°C using compact tension specimens. Tests were run under computer-controlled constant K conditions using compliance to determine crack length. Hold times ranging from 5 to 50 s were applied at maximum, minimum, and intermediate load levels. The data show that the hold times at maximum load were the most damaging in terms of crack growth rate. Hold times greater than 5 s led to purely time-dependent crack growth behavior which was predictable from sustained load data using K as a correlating parameter. Hold times at minimum or intermediate load levels had little or no effect on crack growth rate. A linear cumulative damage model based solely on fatigue and sustained load data was found to be adequate for spectrum loading so long as the hold times were at maximum load.
Author: C. Varandas Publisher: Elsevier ISBN: 0444599754 Category : Science Languages : en Pages : 1057
Book Description
The objective of these proceedings was to provide a platform for the exchange of information on the design, construction and operation of fusion experiments. The technology which is being developed for the next step devices and fusion reactors was also covered.
Author: C. Moura Branco Publisher: Springer Science & Business Media ISBN: 9780792341130 Category : Science Languages : en Pages : 758
Book Description
This volume contains the edited version of lectures and selected research contributions presented at the NATO ADVANCED STUDY INSTITUTE on MECHANICAL BEHA VI OUR OF MATERIALS AT HIGH TEMPERATURE, held in Sesimbra, Portugal, 12th-22nd September 1995, and organized by 1ST-Lisbon Institute of Technology, PortugaL The Institute was attended by 88 participants, including 15 lecturers from 17 countries including five CP countries. The lecturers were leading scientists and technologists from universities, research institutions and industry. The students were mainly young PhD students and junior academic or research staff with postgraduate qualifications (MSc or PhD). Fourteen students were from the five CP countries. The students presented research papers or posters during the Institute reporting the current progress of their research projects. A total of thirty three lectures, ten research papers and fifty posters were presented. This book does not contain the poster presentations and seven research papers were selected for publication. All the sessions were very active and quite extensive discussions on scientific aspects took place during the Institute. The Advanced Study Institute provided a forum for interaction among scientists and engineers from different areas of research, and young researchers.
Author: Roger C. Reed Publisher: Wiley-TMS ISBN: 9780873397285 Category : Technology & Engineering Languages : en Pages : 0
Book Description
This volume contains the proceedings of the 11th International Symposium on Superalloys held September 14-18, 2008, in Champion, Pennsylvania. The symposium covered all aspects of the development, production, behavior and integration of superalloys, and related high temperature materials, into gas turbines for aircraft, power generation and other applications. Symposium topics included cast, wrought and powder superalloys and associated coating systems. Behavioral studies in these areas were also discussed: solidification processing environmental properties mechanical behavior alloy development life prediction methodologies modeling and simulation performance of materials in service environments high temperature coatings joining and repair techniques Emphasis is placed on the perspective of the customer, e.g., the airlines, military, and power generation utilities. Current trends in customer requirements and the latest response of the superalloys community to customer challenges are highlighted in the volume.
Author: F. Ellyin Publisher: Springer Science & Business Media ISBN: 9400915098 Category : Technology & Engineering Languages : en Pages : 484
Book Description
Fatigue failure is a multi-stage process. It begins with the initiation of cracks, and with continued cyclic loading the cracks propagate, finally leading to the rupture of a component or specimen. The demarcation between the above stages is not well-defined. Depending upon the scale of interest, the variation may span three orders of magnitude. For example, to a material scientist an initiated crack may be of the order of a micron, whereas for an engineer it can be of the order of a millimetre. It is not surprising therefore to see that investigation of the fatigue process has followed different paths depending upon the scale of phenomenon under investigation. Interest in the study of fatigue failure increased with the advent of industrial ization. Because of the urgent need to design against fatigue failure, early investiga tors focused on prototype testing and proposed failure criteria similar to design formulae. Thus, a methodology developed whereby the fatigue theories were proposed based on experimental observations, albeit at times with limited scope. This type of phenomenological approach progressed rapidly during the past four decades as closed-loop testing machines became available.
Author: K-Y Hour
Author: K-Y Hour
Author: DC. Maxwell
Author: M. A. Meyers
Author: T. Nicholas
Author: C. Varandas
Author: C. Moura Branco
Author: Roger C. Reed
Author: Robert S. Piascik
Author: F. Ellyin
Author: John D. Landes