Large scale bridging in brittle matrix composites

Zok, Frank W.; Hom, Craig L.

doi:10.1016/0956-7151(90)90301-v

Cited by 121 publications

(49 citation statements)

References 11 publications

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“…This means that more external load is required to maintain the propagation of the crack. The similar crack resistance curves can also be seen in metal and ceramic matrix composites with bridging effect (Zok and Hom, 1990). This is because the R-curve of a finite beam represents the apparent fracture resistance that always approaches infinity when the crack length approaches the depth of beam.…”

Section: Numerical Resultsmentioning

confidence: 86%

Fracture Resistance of a Cracked Concrete Beam Post-strengthened with FRP Sheets

Bailey

2005

Int J Fract

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Fibre-reinforced plastic (FRP) composites have been increasingly used in rehabilitation and strengthening of concrete structures. Significant increases in stiffness and strength have been achieved by applying this technique. However, there is concern about the ductility or toughness performance of FRP/concrete hybrid structures, which is critical in the application of this technology. This paper presents a new theoretical method to predict the fracture resistance behaviour of FRP poststrengthened concrete flexural beams. No slip between the FRP and plain concrete matrix is assumed and Mode I fracture propagation is considered. The model is valid for a wide range of span-to-depth ratios and any crack length. The influence of the bridging stresses provided by the fracture process zone (FPZ) at the tip of a fictitious fracture is examined. The effect of various material and geometric parameters on the resistance curve and toughness of the hybrid structure is discussed, based on the numerical results from the developed theoretical formulae. The results provide a useful insight into the strengthening/toughening and the design of FRP sheet/concrete beam structures.

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Section: Numerical Resultsmentioning

confidence: 86%

Fracture Resistance of a Cracked Concrete Beam Post-strengthened with FRP Sheets

Bailey

2005

Int J Fract

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“…The layered architecture of the Ti layers is accounted for by the volume fraction ( f ) in the equation [6] The assumption of a constant () in the previous model has had some success before. [15,90] Zok and Hom [90] have pointed out that once the ductile bridging ligaments furthest from the crack tip fail, a steady-state value is attained by both the bridging length and the R-curve behavior. Furthermore, they suggested that such R-curve saturation is observed during SSB, where the bridging lengths are small compared to the crack length and the uncracked ligament dimensions: [7] The weight function for a single edge-cracked finite-width specimen (m(␣,)) in Eq.…”

Section: Models For Toughening In Laminatesmentioning

confidence: 98%

“…The simplest approximation is obtained through a rectilinear bridgingtraction law, [53] given by [4] and [5] where e (u) is the stress-displacement curve measured experimentally. Constrained stress-displacement curves have been determined for a number of systems; [22,25,64,66,67] however, a simplified approach is to assume a constant () value, [15,17,90] equal to the constrained flow stress of the ductile reinforcement over the entire bridging length. In Ti-Al 3 Ti MIL composites, constrained tensile tests have indicated constrained-flow stress ratios less than 1.1.…”

Section: Models For Toughening In Laminatesmentioning

confidence: 99%

Fracture of Ti-Al3Ti metal-intermetallic laminate composites: Effects of lamination on resistance-curve behavior

Adharapurapu

Vecchio

Jiang

et al. 2005

Metall Mater Trans A

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The fracture toughness and resistance-curve (R-curve) behavior of Ti-Al 3 Ti metal-intermetallic laminate (MIL) composites have been studied in the crack-divider orientation, by examining the effect of ductile-laminate-layer thickness and volume fraction. The MIL composites were fabricated in open air by a novel one-step process, and the final structure consists of alternating layers of ductile Ti and brittle Al 3 Ti. Such a laminate architecture in conjunction with a relatively low volume fraction of tougher Ti (18 to 40 pct) was seen to augment the fracture toughness of the inherently brittle intermetallic by over an order of magnitude. Additionally, as a result of their low density, MIL composites exhibit a specific fracture toughness (K/) on par with tougher but relatively denser ductile metals such as high-strength steel. Such vast improvements may be rationalized through the toughening provided by the ductile Ti layers. Specifically, toughening was obtained through plastically stretching the intact ductile Ti layers that formed bridging zones in the crack wake, thus reducing the crack driving force. Such toughening resulted in R-curve behavior, and the toughness values increased with an increase in the volume percentage of Ti. Weight-function methods were used to model the bridging behavior, and they indicated that large bridging zones (ϳ2 to 3 mm) were responsible for the observed increase in toughness. The role of large-scale bridging (LSB) conditions on the resistance curves is explored, and steady-state toughness (K SS ) values are estimated using small-scale bridging (SSB) approximations. A new approach to gage the potential of laminate composites in terms of their true fracture-toughness values as determined from a cyclic crack-growth fatigue test is proposed, wherein small-scale specimens can be utilized to obtain fracture-toughness values.

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“…However, apparent fracture toughness by CTOD may overestimate the real material properties by large damage zone present ahead of the initial notch. 26 The contribution to the toughness due to metal layer can be quantitatively analyzed by K Rcurve behavior. Recent work done on K R -curve toughening in other micro-laminated composites shows that LSB more appropriate than the SSB model for application to particle-reinforced composites.…”

Section: Ctod and K R -Curve Behaviormentioning

confidence: 99%

Tensile and fracture properties of NiAl/Ni micro-laminated composites prepared by reaction synthesis

et al. 2006

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The mechanical properties of NiAl/Ni micro-laminated composites with highly gradient microstructure have been investigated. Two types of composites with different gradient microstructures were prepared by reaction synthesis. Intermetallics of type I and type II composites mainly consisted of Al-rich Ni 0.45 Al 0.55 with variable thickness and Ni-rich Ni 0.58 Al 0.42 with similar thickness, respectively. As intermetallic volume fraction increased, yield strength of type II followed the rule-of-mixture well, while that of type I deviated due to the composition variation of intermetallic phases. Fracture toughness of type II was higher than that of type I, and all showed K R curves with upward curvature by large-scale bridging. Even though the relative strength of constituent phases in intermetallic/metal laminates was not constant due to the gradient microstructure, the fracture mode transition showed similar behavior to that of metal/ceramic laminates.

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Large scale bridging in brittle matrix composites

Cited by 121 publications

References 11 publications

Fracture Resistance of a Cracked Concrete Beam Post-strengthened with FRP Sheets

Fracture Resistance of a Cracked Concrete Beam Post-strengthened with FRP Sheets

Fracture of Ti-Al3Ti metal-intermetallic laminate composites: Effects of lamination on resistance-curve behavior

Tensile and fracture properties of NiAl/Ni micro-laminated composites prepared by reaction synthesis

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