Low-Temperature Fatigue Crack Propagation in a ?-Titanium Alloy PDF Download
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Author: CJ. Beevers
Publisher:
ISBN:
Category : Crack closure
Languages : en
Pages : 18
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Book Description
Fatigue crack growth rates and crack closure have been examined for a body-centered-cubic (bcc) titanium alloy (Ti-30Mo) at five test temperatures ranging from 123 to 340 K. In the same temperature range the influence of internal hydrogen (as provided by gas phase charging) has been studied. Detailed fractographic analyses have been made to quantify the amount of cleavage fracture as a function of test temperature, hydrogen concentration, and stress intensity factor range. The extent of cleavage, both cyclic and static, increased with decreasing temperature. For the lowhydrogen content specimens the fatigue crack growth resistance increased with increasing cleavage over the temperature range from 340 to 190 K. The fatigue crack growth resistance for the high hydrogen alloy remained relatively insensitive to the increasing amounts of cleavage over the same temperature range. An examination of the fatigue crack growth rate data shows that the power exponent in the following expression is in the range of 2 to 2.5 for temperatures of 123 to 340 K: dadn=B(?Ki-?Kthi)n where ?K = ?Ki = ?Kc and ?Ki is the intrinsic component and ?Kc is the closure component. These observations indicate that the factor dominating the fatigue crack growth rate and the resulting cyclic cleavage process is the reverse plasticity in the crack tip region. The increased resistance to fatigue crack growth in the temperature range from 340 to 190 K for the low hydrogen contents is attributed to the higher yield stresses in this region. The role of hydrogen in determining fatigue crack growth rates and fatigue thresholds (?Kth) is discussed in terms of its influence on both ?Ki and ?Kc.
Author: CJ. Beevers
Publisher:
ISBN:
Category : Crack closure
Languages : en
Pages : 18
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Book Description
Fatigue crack growth rates and crack closure have been examined for a body-centered-cubic (bcc) titanium alloy (Ti-30Mo) at five test temperatures ranging from 123 to 340 K. In the same temperature range the influence of internal hydrogen (as provided by gas phase charging) has been studied. Detailed fractographic analyses have been made to quantify the amount of cleavage fracture as a function of test temperature, hydrogen concentration, and stress intensity factor range. The extent of cleavage, both cyclic and static, increased with decreasing temperature. For the lowhydrogen content specimens the fatigue crack growth resistance increased with increasing cleavage over the temperature range from 340 to 190 K. The fatigue crack growth resistance for the high hydrogen alloy remained relatively insensitive to the increasing amounts of cleavage over the same temperature range. An examination of the fatigue crack growth rate data shows that the power exponent in the following expression is in the range of 2 to 2.5 for temperatures of 123 to 340 K: dadn=B(?Ki-?Kthi)n where ?K = ?Ki = ?Kc and ?Ki is the intrinsic component and ?Kc is the closure component. These observations indicate that the factor dominating the fatigue crack growth rate and the resulting cyclic cleavage process is the reverse plasticity in the crack tip region. The increased resistance to fatigue crack growth in the temperature range from 340 to 190 K for the low hydrogen contents is attributed to the higher yield stresses in this region. The role of hydrogen in determining fatigue crack growth rates and fatigue thresholds (?Kth) is discussed in terms of its influence on both ?Ki and ?Kc.
Author: C. M. Hudson
Publisher:
ISBN:
Category : Materials at high temperatures
Languages : en
Pages : 40
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Book Description
Author: S. Lesterlin
Publisher:
ISBN:
Category : Environment
Languages : en
Pages : 23
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Book Description
The fatigue crack propagation behavior of a Ti-6Al-4V alloy has been investigated at room temperature and at 300°C. Tests were run in air, high vacuum, and some other environments with controlled partial pressure of water vapor and oxygen. The enhancement of the fatigue crack growth rates observed in air in comparison to high vacuum, considered as an inert environment, is clearly attributed to the presence of water vapor. Tests in a controlled environment demonstrate that very low partial pressure can accelerate crack propagation. On the basis of previous studies on Al alloys and steels, two controlling mechanisms are considered and discussed, namely, a propagation-assisted water vapor adsorption and a hydrogen-assisted propagation.
Author: A. Carpinteri
Publisher: Newnes
ISBN: 0444600329
Category : Technology & Engineering
Languages : en
Pages : 834
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Book Description
The purpose of this Handbook is to provide a review of the knowledge and experiences in the field of fatigue fracture mechanics. It is well-known that engineering structures can fail due to cyclic loading. For instance, a cyclically time-varying loading reduces the structure strength and can provoke a fatigue failure consisting of three stages: (a) crack initiation (b) crack propagation and (c) catastrophic failure. Since last century many scientists have tried to understand the reasons for the above-mentioned failures and how to prevent them. This Handbook contains valuable contributions from leading experts within the international scientific community and covers many of the important problems associated with the fatigue phenomena in civil, mechanical and nuclear engineering.
Author: R.J.H. Wanhill
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Ralph Ivan Stephens
Publisher: ASTM International
ISBN: 9780803104112
Category : Technology & Engineering
Languages : en
Pages : 329
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Book Description
Author: Y. Pardhi
Publisher:
ISBN:
Category : Fatigue crack propagation
Languages : en
Pages : 19
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Book Description
The inertia friction welding process is being extensively investigated for the joining of high strength titanium alloys for aerospace applications. Although it offers solid state joining, the thermal cycle and deformation involved results in microstructural inhomogeneity across the weld interface. In this paper, the fatigue crack propagation behavior in an inertia welded microstructure in a high strength, high temperature ?/? titanium alloy is considered. The fatigue crack propagation behavior in corner notched weld specimens at varying stress ratios is studied at room and elevated temperatures and compared with that of the parent material. Fatigue crack growth rates at lower stress intensity ranges are comparable with those in the parent material. However, in weld specimens tested at room temperature, unstable crack growth occurs at lower stress intensity range values compared to that at high temperature. Fracture surface observations show that this difference is related to a change in fracture mode from transgranular to intergranular/mixed mode during room temperature tests. This change in fatigue crack growth mechanism is deduced to be due to low ductility intergranular failure of grain boundary ? in the refined transformed beta microstructure across the weld interface.
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781720523284
Category :
Languages : en
Pages : 74
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Book Description
Fatigue crack growth rates of Ti 6-2-2-2-2 as a function of stress ratio, temperature (24 or 177 C), tensile orientation and environment (laboratory air or ultrahigh vacuum) are presented. Fatigue crack growth rates of Ti 6-2-2-2-2 are also compared with two more widely used titanium alloys (Timetal 21S and Ti 6Al-4V). The fatigue crack growth rate (da/dN) of Ti 6-2-2-2-2 in laboratory air is dependent upon stress ratio (R), particularly in the near-threshold and lower-Paris regimes. For low R (less than approximately 0.5), da/dN is influenced by crack closure behavior. At higher R (> 0.5), a maximum stress-intensity factor (K(sub max)) dependence is observed. Fatigue crack growth behavior is affected by test temperature between 24 and 177 C. For moderate to high applied cyclic-stress-intensity factors (delta-K), the slope of the log da/dN versus log delta-K curve is lower in 177 C laboratory air than 24 C laboratory air. The difference in slope results in lower values of da/dN for exposure to 177 C laboratory air compared to room temperature laboratory air. The onset of this temperature effect is dependent upon the applied R. This temperature effect has not been observed in ultrahigh vacuum. Specimen orientation has been shown to affect the slope of the log da/dN versus log delta-K curve in the Paris regime.Smith, Stephen W. and Piascik, Robert S.Langley Research CenterCRACK PROPAGATION; FATIGUE (MATERIALS); TITANIUM ALLOYS; CORROSION; STRESS RATIO; TEMPERATURE EFFECTS; CRACK CLOSURE; STRESS INTENSITY FACTORS
Author:
Publisher:
ISBN:
Category : Titanium
Languages : en
Pages : 70
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Book Description
Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
ISBN: 9781723767173
Category : Science
Languages : en
Pages : 34
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Book Description
To study the effects of atmospheric species on the fatigue crack growth behavior of an a+B titanium alloy (Ti 6-2-2-2-2) at room temperature and 177 C, fatigue tests were performed in laboratory air, ultrahigh vacuum, and high purity water vapor, oxygen, nitrogen and helium at various partial pressures. Accelerated fatigue crack growth rates in laboratory air compared to ultrahigh vacuum are linked to the damaging effects of both water vapor and oxygen. Observations of the fatigue crack growth behavior in ultrahigh purity environments, along with surface film analysis using X-ray photoelectron spectroscopy (XPS), suggest that multiple crack-tip processes govern the damaging effects of air. Three possible mechanisms are proposed: 1) at low pressure (less than 10(exp -1) Pa), accelerated da/dN is likely due to monolayer adsorption on crack-tip surfaces presumably resulting in decreased bond strengths at the fatigue crack tip, 2) for pressures greater than 10(exp -1) Pa, accelerated da/dN in oxygen may result from oxidation at the crack tip limiting reversible slip, and 3) in water vapor, absorption of atomic hydrogen at the reactive crack tip resulting in process zone embrittlement.Smith, Stephen W. and Piascik, Robert S.Langley Research CenterFATIGUE TESTS; FATIGUE (MATERIALS); CRACK PROPAGATION; TITANIUM ALLOYS; EMBRITTLEMENT; ATMOSPHERIC COMPOSITION; X RAY SPECTROSCOPY; WATER VAPOR; ULTRAHIGH VACUUM; PHOTOELECTRON SPECTROSCOPY
