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A theoretical study of the feasibility of using fiber stitching to prevent transverse matrix cracking in cross‐ply ceramic composites is reported. The prototype problem solved is a curved composite beam subject to pure bending (the C‐specimen), which develops a transverse tensile stress σ 0 acting across its circumferential midplane. Fiber stitches normal to this plane bridge a circumferential matrix crack lying along the midplane of the specimen. Results are presented for the energy release rate of this matrix crack as a function of a nondimensional parameter characterizing the fiber stitches. Sufficiently large values of this parameter ensure the applicability of the classical ACK (Aveston, Cooper and Kelly) limit for a steady‐state matrix crack subject to σ 0 . The results obtained can be used to choose the level of stitching such that transverse matrix cracking will be excluded.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPreparation of tertiary phosphine-olefin complexes of platinum(0): a convenient synthesis of ethylenebis(triethylphosphine)platinum(0)Ralph G. Nuzzo, Thomas J. McCarthy, and George M. WhitesidesCite this: Inorg. Chem. 1981, 20, 4, 1312–1314Publication Date (Print):April 1, 1981Publication History Published online1 May 2002Published inissue 1 April 1981https://pubs.acs.org/doi/10.1021/ic50218a073https://doi.org/10.1021/ic50218a073research-articleACS PublicationsRequest reuse permissionsArticle Views217Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts
Kagome truss plates have properties that suggest they should be uniquely effective as an actuation plane for sandwich plates: a Kagome truss plate has in-plane isotropy, optimal stiffness and strength, and its truss members can be actuated with minimal internal resistance. In this paper, sandwich plates are studied that are comprised of one solid face sheet and one actuated Kagome face sheet joined by a pyramidal truss core. Various aspects of the actuation behavior of these plates are investigated, including internal resistance and strains resulting from actuation and efficiency of actuation. Single and double curvature actuation modes are investigated. Contact is made with analytic results for actuation modes with long wavelength.
: Oxide coatings used for various components in the hot section of aero-turbine engines experience temperature gradients at various stages during their flight cycle. One gradient exists during steady-state, due to the combination of the combustion environment next to the free surface and internal cooling of the underlying superalloy substrate. Other gradients develop during cooling of the surface when engine power is reduced. It is argued that deep delaminations, when observed within the oxide layer, can only be explained by the presence of a significant stress gradient in the coating, governed by these thermal circumstances. Two extreme cool-down scenarios are addressed. In one, the surface is cooled suddenly to a lower temperature, followed by slow uniform cooling. In the other, the entire system reduces its temperature uniformly before the temperature gradient in the TBC is eliminated. Criteria for guarding against delaminations within the oxide layer and along the interface with the substrate are provided and the outcome visualized in the form of delamination maps. A comparison with engine experience has provided a preliminary assessment of the relevant thermal scenarios.
Foreign object damage (FOD) occurs when hard, millimeter-sized objects such as gravel or sand are ingested into aircraft jet engines. Particles impacting turbine blades at velocities up to about 300 m/s produce small indentation craters which can become sites for fatigue crack initiation, severely limiting the lifetime of the blade. A framework for analyzing FOD and its effect on fatigue cracking is established in this paper. Finite element analysis is used to determine the residual stresses and geometric stress concentration resulting from FOD. The roles of material rate sensitivity and inertia are delineated. The most important non-dimensional parameters governing impact indents are identified, significantly reducing the set of independent parameters. The second step in the analysis focuses on the potency of cracks emerging from critical locations at the indents. The results have been used to address the question: When and to what extent do the residual stresses and stress concentration caused by FOD reduce the critical crack size associated with threshold fatigue crack growth? For deep indents, it is found that elastic stress concentration is the dominant factor in reducing critical crack threshold when the applied cyclic load ratio, R, is large, otherwise the residual stresses are also important. Comparisons with a set of experiments conducted in parallel with the theory show that the numerical approach can account for various phenomena observed in practice.
Results are presented for the cracking to be expected when a sudden temperature increase is applied over a localized region on a surface of a brittle solid. A localized temperature increase is applied to the surface of a body whose interior is initially at uniform temperature. A three‐part analysis is conducted: (i) for the evolving temperature distribution, (ii) for the evolving thermal stresses induced by the nonuniform temperature field, and (iii) for stress intensity factors of cracks oriented either parallel to or perpendicular to the surface and initiated at times when the stresses are critical. Plane‐strain and axisymmetric versions of the problems are considered. For the plane‐strain problem, the complete trajectory of the crack is determined under the assumption that its tip advances maintaining a pure mode I field at all times. Conditions for excluding cracking due to localized hot shock are given.
Major studies have been started on (1) The conditions governing the localization of plastic flow at the onset of rupture. Specific calculations of critical conditions for a number of material models have been made possible through a theoretical framework by which localization is formulated as a constitutive instability, in the form of a bifurcation into a localized mode from a state of previously homogeneous deformation, and (2) The strength of interfaces with and without the presence of dissolved segregants. Criteria for brittle vs. ductile response of an interface were developed on the basis of dislocation mechanisms and thermodynamic relations, and applied to hydrogen embrittlement. Further progress has been achieved in the analysis of stress and deformation at a crack tip by the application of the large-strain elastic-plastic finite element program developed over the last two years. Work has continued on particle and sub-boundary strengthening in steels and an experimental study of fracture initiation at particles was begun.
