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R. D. Carter

Bio: R. D. Carter is an academic researcher from United States Army Corps of Engineers. The author has contributed to research in topics: Grain size & Slip (materials science). The author has an hindex of 1, co-authored 1 publications receiving 131 citations.

Papers
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TL;DR: In this paper, the effects of slip character and grain size on the intrinsic material and extrinsic closure contributions to fatigue crack growth resistance have been studied for a 7475 aluminum alloy.
Abstract: The effects of slip character and grain size on the intrinsic material and extrinsic closure contributions to fatigue crack growth resistance have been studied for a 7475 aluminum alloy. The alloy was tested in the underaged and overaged conditions with grain sizes of 18 μm and 80 μm. The fracture surface exhibited increased irregularity and planar facet formation with increased grain size, underaging, and tests in vacuum. These changes were accompanied by an increased resistance to fatigue crack growth. In air the 18 μm grain size overaged material exhibited relatively poor resistance to fatigue crack growth compared with other microstructural variants, and this was associated with a lower stress intensity for closure. All materials exhibited a marked improvement in fatigue crack growth resistance when tested in vacuum, with the most significant difference being ˜1000× at a ΔK of 10 MPa m1/2 for the 80 μm grain size underaged alloy. This improvement could not be accounted for by either an increase in closure or increased crack deflection and is most likely due to increased slip reversibility in the vacuum environment. The intrinsic resistance of the alloy to fatigue crack growth was microstructurally dependent in vacuum, with large grains and planar slip providing the better fatigue performance.

136 citations


Cited by
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TL;DR: Aluminum alloys have been the primary material of choice for structural components of aircraft since about 1930 as discussed by the authors and have been used extensively in high-performance military aircraft and are being specified for some applications in modern commercial aircraft, including the fuselage, wing, and supporting structure of commercial airliners and military cargo and transport.

1,077 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined the effect of crack tip shielding on fatigue crack propagation behavior in metals, composites and ceramics, and showed that, whereas crack-tip shielding can provide a potent means of enhancing resistance to crack growth, such extrinsic toughening mechanisms can result in the apparently anomalous behavior of small cracks and to the susceptibility of brittle materials to fatigue failure.
Abstract: Crack tip shielding phenomena, whereby the “effective crack-driving force” actually experienced at the crack tip is locally reduced, are examined with reference to fatigue crack propagation behavior in metals, composites and ceramics. Sources of shielding are briefly described in terms of mechanisms relying on the production of elastically constrained zones which envelop the crack (zone shielding), on the generation of wedging, bridging or sliding forces between the crack surfaces (contact shielding) and on crack path deflection and meandering. Examples are taken from the fatigue behavior of high strength lithium-containing aluminum alloys, aluminum alloy-aramid fiber-epoxy laminate composites, and zirconia ceramics. It is shown that, whereas crack tip shielding can provide a potent means of enhancing “resistance” to crack growth, such extrinsic toughening mechanisms can result in the apparently anomalous behavior of “small cracks” and to the susceptibility of brittle materials to fatigue failure.

731 citations

Journal ArticleDOI
Subra Suresh1
TL;DR: In this paper, a simple linear elastic analysis of tilted cracks is proposed to estimate the variation of cyclic crack propagation rates under the combined influence of crack kinking and fracture surface contact.
Abstract: The variation of cyclic crack propagation rates, under thecombined influence of crack kinking (deflection) and fracture surface contact (closure), is estimated from simple linear elastic analyses of tilted cracks. The predictions of the models are consistent with the experimental results of linear and kinked crack advance in high strength aluminum alloys testedin vacuo. Examples of crack deflection in various engineering alloy systems and some generalizations ofaverage deflection parameters based on microstructural and mechanical factors are discussed. The individual contributions to overall growth rates from deflection and closure processes are evaluated for different mechanical and metallurgical conditions. The significance, implications, and limitations of the models are outlined.

246 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the stress-life fatigue behavior and fatigue crack growth characteristics of pure Ni as a function of grain size spanning a range of tens of nanometer to tens of micrometer and found that grain refinement to the nanocrystalline regime generally leads to an increase in total life under stress-controlled fatigue whereas a deleterious effect was seen on the resistance to fatigue cracks growth at low and high tensile load ratio levels.

246 citations

Journal ArticleDOI
TL;DR: The design of an aluminum alloy having good strength while maintaining a high resistance to fracture is discussed in this article, where the desired microstructure consists of a small volume fraction of an ultra-fine dispersion of hard particles.
Abstract: The design of an aluminum alloy having good strength while maintaining a high resistance to fracture is discussed. Theory suggests that the desired microstructure consists of a small volume fraction of an ultra-fine dispersion of hard particles. In addition to conventional heat treatments, dispersion hardened aluminum alloys have been recently produced by rapid solidification or mechanically alloying and powder metallurgy consolidation. Alloys which can serve as models for mechanistic studies of nucleation of non-coherent phases as well as the basis for a new class of engineering aluminum alloys are identified.

184 citations