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The Contribution of Bridging Ligament Rupture to Energy Absorption During Fracture of Metal–Ceramics Laminates

Key Engineering Materials

November 1996
127:1127-1136

DOI:10.4028/www.scientific.net/KEM.127-131.1127

Authors:

Stacie-Jo Howard

Nova Southeastern University

Bill Clyne

University of Cambridge

Experiments are described in which lead sheets, sandwiched between two pairs of steel plates separated by a pre-specified gap midway along the specimen, have been loaded in tension. The nominal stress at the onset of global yielding was found experimentally to be about twice the unconstrained yield stress of the metal, over a range of values for the initial gap. The nominal stress was then found to fall in an approximately linear fashion with increasing displacement, as the load-bearing section necked down. This behaviour is quantitatively consistent with experimental data for the fracture energy of metal-ceramic laminates loaded in bending, which failed by the propagation of a single dominant crack, assuming that rupture of the bridging ligaments made the dominant contribution. An attempt is made to predict the nominal stress at the onset of global yielding, using an analytical treatment of the initial small scale yielding around the notch and a slip line field solution for fully developed global plasticity. This gave an overestimate of the stress at the onset of global yielding, relative to the experimental data, by a factor of between two and three. This is attributed to the use of a simplified notch geometry in the slip line field solution.

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Key Engineering Materials Online: 1996-11-01

ISSN: 1662-9795, Vols. 127-131, pp 1127-1136

doi:10.4028/www.scientific.net/KEM.127-131.1127

Tech Publications Ltd, www.scientific.net. (Research Gate for subscription journals-12/02/24,15:54:21)

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Feb 2005

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Aug 1999
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Jun 2006

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Dec 2014
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Processing of Intermetallic Foam by Combustion Reaction

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Oct 2002
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Mar 2006
ENG FRACT MECH

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Article

Jun 1998
MATER SCI TECH-LOND

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On the Toughning of Ceramics by Strong Reinforcements

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Dec 1986
Acta Metall

Some effects of intact particles in the crack wake on the fracture toughness of ceramics have been analyzed. The result have been applied to interpretation of the toughening of ceramics by strong well-bonded metal particles and by whiskers. Trends in toughness with microstructure have been predicted for various reinforced ceramic systems.

Toughening in Brittle Systems by Ductile Bridging Ligaments

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Jul 1992
Acta Metall Mater

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The Role of Metal Plasticity and Interfacial Strength in the Cracking of Metal-Ceramic Laminates

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Apr 1995
Acta Metall Mater

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Cracking patterns in metal-ceramic laminates: Effects of plasticity

Article

May 1996
J MECH PHYS SOLIDS

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The Deformation and Fracture of Constrained Metal Sheets

Article

Nov 1991
Acta Metall Mater

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Flow Characteristics of Highly Constrained Metal Wires

Article

Jul 1989
Acta Metall

Brittle solids can be toughened by incorporating ductile inclusions into them. The inclusions bridge the crack and are stretched as the crack opens, absorbing energy which contributes to the toughness. To calculate the contribution to the toughness it is necessary to know the force-displacement curve for an inclusion, constrained (as it is) by the stiff, brittle matrix. Measured force-displacement curves for highly constrained metal wires are described and related to the unconstrained properties of the wire. The constraint was achieved by bonding the wire into a thick-walled glass capillary, which was then cracked in a plane normal to the axis of the wire and tested in tension. Constraint factors as high as 6 were found, but a lesser constraint gives a larger contribution to the toughness. The diameter of the wires (or of the inclusions) plays an important role. Simple, approximate, models for the failure of the wires are developed. The results allow the contribution of ductile particles to the toughness of a brittle matrix composite to be calculated.

Ceramic/Metal Interfacial Crack Growth: Toughening by Controlled Microcracks and Interfacial Geometries

Article

Aug 1988
Acta Metall

Toughening of ceramic/metal interfaces through the use of controlled interfacial geometries and non-coplanar microcrack-like pores is examined with respect to both critical and subcritical crack growth. Patterned uniform arrays of inclined interfacial steps and of "microcracks/voids" (with width 22 μm and spacing 10 μm), out-of-plane to the main interfacial crack, were produced for glass/copper interfaces by photo-lithographic techniques combined with evaporation and diffusion bonding processes. Significant toughening and improved stress corrosion crack-growth resistance is achieved through the promotion of crack-tip shielding primarily from crack bridging. Specifically, plastic void growth within the copper is seen to generate bridged ligaments of metal film between the glass substrates; the resulting mechanical crack bridging leads to plastic stretching of the film and provides the dominant toughening mechanism, with a smaller contribution from crack deflection. Correspondingly, subcritical (pre-instability) crack-growth rates with the patterned arrays in "wet" and "dry" gaseous atmospheres are retarded by orders of magnitude compared to rates for plain interfaces. The toughness with the various patterned interfaces exhibits marked resistance-curve (R-curve) behavior with fracture toughness values increased by factors of 4-9 compared to intrinsic fracture toughness, G0, values of ∼2 J/m2 for these plain glass/copper interfaces. Surface roughness of the glass substrate is reasoned to be a controlling parameter for the shape and magnitude of such crack-resistance curves.

Cracking and Damage Mechanisms in Ceramic/Metal Multilayers

Article

Nov 1993
Acta Metall Mater

Investigations of cracking in multilayered ceramic/metal composites are presented. Two aspects are considered: crack renucleation across intact single metal layers and subsequent crack extension. Crack renucleation criteria are determined and compared with predictions. High-resolution strain-mapping techniques are employed to determine the surface strain fields surrounding cracks. Good agreement is found between these experimental measurements and the predictions of a small-scale yielding model. Subsequent crack progression occurs either by the extension of a dominant, nearly planar crack or by the formation of a zone of periodically spaced cracks. Both patterns are analyzed. The dominant cracking behavior is found to depend on the volume fraction and yield strength of the metal.

The Strength of Ceramics Bonded with Metals

Article

Aug 1988
Acta Metall

The strength of Al2O3 materials bonded using thin Pt layers is investigated. The measured strength levels are interpreted by conducting elastic/plastic stress analysis in conjunction with weakest link statistics. Comparisons between theory and experiment includes bond thickness effects, coupled with the role of interfacial flaws and the flow stress of the Pt.RésuméNous étudions la résistance mécanique de matériaux Al2O3 liés à l'aide de couches minces de platine. Nous interprétons les valeur expérimentales de la résistance mécanique grâce à une analyse des contraintes élastiques et plastiques menée conjointement avec une statistique des liaisons les plus faibles. La comparaison entre la théorie et l'experience tient compte des effets d'épaisseur de liant ainsi que du rôle des défauts à l'interface et de la contrainte d'écoulement du platine.ZusammenfassungDie Festigkeit von Materialien aus Al2O3, verbunden mit dünnen Pt-Schichten, wird untersucht. Die gemessenen Festigkeitswerte werden mit einer Analyse der elastisch/plastischen Spannungen in Zusammenhang mit Statistiken der schwachsten Verbindung gedeutet. Vergleich zwischen Theorie und Experiment umfaßt Einflüsse der Dicke der Verbindungen, einschließlich der Rolle von unverbundenen Bereichen an der Grenzfläche und der Fließspannung des Platins.

The Strength and Fracture of Alumina Bonded to Aluminum Alloys

Article

Jul 1989
Acta Metall

Alumina has been liquid state bonded with pure Al and Al-4 wt% Mg and the mechanical behavior of the bonds has been characterized. It has been shown that failure never occurs by interface cracking. Instead, when the bond layer is thick, the bond strength is limited either by plastic flow or by ductile fracture in the metal. Conversely, when the bond layer is thin, failure occurs in the ceramic, limited by the strength of the ceramic. The Al alloy bond has also been shown capable of arresting cracks by plastic blunting.RésuméOn a lié de l'alumine avec de l'aluminium pur et de l'aluminium à 4% en poids de magnésium, à l'état liquide, et l'on a caractérisé le comportement mécanique des liaisons. La rupture n'a jamais lieu par rupture interfaciale. Par contre, quand la couche de liaison est épaisse, la résistance de la liaison est limitée soit par l'écoulement plastique, soit par la rupture ductile dans le métal. Réciproquement, quand la couche de liaison est mince, la rupture a lieu dans la céramique, et elle est limitée par la résistance de la céramique. La liaison en aluminium allié est également capable d'arrêter les fissures par émoussage plastique.ZusammenfassungAluminiumoxid wurde mit reinem Al und mit Al-4 Gew.-%Mg im schmelzflüssigen Zustand kontaktiert; das mechanische Verhalten dieser Verbindungen wurde untersucht. Der Bruch tritt niemals an der Grenzfläche auf. Stattdessen ist die Festigkeit der Verbindung begrenzt entweder durch plastisches Flieβen oder duktilen Bruch des Metalls, wenn die Verbindungsschicht dick ist. Ist sie dagegen dünn, dann tritt Bruch in der Keramik auf, entsprechend der Festigkeit der Keramik. Auch bei der Al-Legierung wurde gezeigt, daβ sie Risse durch plastisches Abstumpfen behindern kann.