Overload Effects on Sustained Load Crack Growth at Elevated Temperature PDF Download

Author: Kevin E. Harms (CAPT, USAF.)
Publisher:
ISBN:
Category : Nickel
Languages : en
Pages : 334

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Author: K. E. Harms
Publisher:
ISBN:
Category :
Languages : en
Pages : 178

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This theses investigates the crack growth behavior of Inconel 718 effected by over-loads at elevated temperature. A cumulative damage model was developed to predict the total time-to-failure. Predictions were noted to improve at higher values of stress intensities. All tests were conducted under sustained loading with isothermal conditions of 650 C. Precracked compact tension specimens were used to establish a data base for baseline and overload conditions. The delay time associated with crack growth retardation was determined by comparing the baseline behavior with the results of the overload specimens. The effects of 20-and 50-percent overloads of 1 minute or 1 hour duration were investigated. The shape of the crack tip plastic zone and, hence, the retardation effect was found to be independent of overload duration. The retardation delay time was found to be dependent upon the overload magnitude and the value of K at which the overload was removed. It was also found that a sudden crack advancement occurred when the overload was applied. The above factors were accounted for in the model development. The model was generally capable of predicting the time-to-failure within about 10 percent of the actual material behavior. Originator supplied keywords: Sustained-load crack growth; Crack growth retardation; Elevated temperature; Nickel-based superalloy; Crack growth model; Overloads; Data reduction; Graphs.

Author: Robert L Hastie (Jr)
Publisher:
ISBN:
Category :
Languages : en
Pages : 140

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This thesis investigates methods of modeling the effects of overloads on high-temperature sustained-load crack growth. In addition to a model previously developed for this specific problem, a computer program developed for low-temperature, high-frequency cyclic load applications was evaluated. Sustained-load hold times were converted to equivalent fatigue cycles to analyze a load spectrum, consisting of sustained-load with periodic overloads. The CRACKS crack growth program was used with the Wheeler and Willenborg models used to account for crack growth retardation due to overloads. Predictions were compared with experimental test data generated on specimens of Inconel 718 at 650 C with periodic overloads of either 20 or 50 percent. Crack measurements were made using a electric potential system. The application of the electric potential system to crack growth measurement following overloads was extensively evaluated. It was concluded that the system had to be recalibrated after each overload due to a sudden advancement in crack length.

Author: D. F. Bryan
Publisher: ASTM International
ISBN: 9780803107205
Category : Technology & Engineering
Languages : en
Pages : 256

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Author: T. Nicholas
Publisher:
ISBN:
Category : Crack growth
Languages : en
Pages : 11

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Crack-growth-rate experiments were conducted on compact tension (CT) specimens of Inconel 718 in air at 649°C. The loading spectrum consisted of a single 1 Hz cycle at R = 0.1, where R is the ratio of minimum to maximum stress-intensity factors, and a hold time which was applied at various levels of the fatigue cycle. The ratio of the hold-time amplitude to the maximum amplitude of the fatigue cycle, Rin, was kept at 1.0, 0.9, 0.8, or 0.5. Hold times were varied from 0 to 200 s. Tests were performed under computer-controlled constant-K conditions using values of the maximum of the fatigue cycle of 40 and 50 MPa m1/2. Data show that for Rin = 1.0, a linear summation model works well, while at Rin = 0.9 there is a measurable retardation effect on the crack growth during the hold time. For values of Rin less than or equal to 0.8, the sustained-load crack growth is almost completely retarded. A simple retardation model is proposed which can fit the experimental data and is based on the concept of an overload plastic zone being produced by the fatigue cycles. It is concluded that hold times do not contribute to crack growth in this material unless their amplitude is at or near the maximum amplitude of the adjacent fatigue cycles.

Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 562

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Author: D. T. Read
Publisher: ASTM International
ISBN: 0803109490
Category : Fractura de sólidos
Languages : en
Pages : 1108

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Author: K. Salama
Publisher: Elsevier
ISBN: 1483294064
Category : Technology & Engineering
Languages : en
Pages : 3063

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Held every four years, the International Congress on Fracture is the premier international forum for the exchange of ideas between scientists and engineers involved in producing and using materials resistant to fracture and fatigue. This major six-volume work which forms the proceedings of the Seventh International Congress on Fracture therefore provides the most comprehensive account available of the current status of research into fracture and fatigue, and the application of this knowledge to the design, fabrication and operation of materials and structures. As such, it will be an essential reference for materials scientists and mechanical, structural, aeronautical and design engineers with an interest in fracture and its prevention.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 306

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Author: Lewis
Publisher: ASTM International
ISBN: 9780803107304
Category : Technology & Engineering
Languages : en
Pages : 666

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