Crack Bridging Model Research Articles

Interfaces in composites: Relations between structure and properties

The toughness of ceramic composites is mainly governed by the mechanical behavior of the interfaces between the ceramic matrix and the ductile particle or the strong fiber/whisker reinforcements. The toughening can be described by a bridging zone mechanism. In the crack bridging models, debonding of the reinforcement at the interface plays an important role. The status of present understanding is reviewed. Transmission electron microscopy has been used to study the interfacial structure and behavior of ductile particles and fiber/whisker reinforced composites. Furthermore, model systems of ceramic/ceramic and metal/ceramic interfaces have been investigated. The atomic structure of such interfaces can be determined by a quantitative analysis of high resolution micrographs. Chemical reaction products and structural defects at the interface can be identified by analytical electron microscopy. The results of such studies will help to tailor the interfaces in composites.

The crack-bridging model with the consideration of residual stress in particulate-reinforced ceramics

The crack-bridging model with the consideration of residual stress in paniculate-reinforced ceramics is presented. The compressive residual stress in the matrix is obtained through microstructural analysis. In this paper, the bridging particles are treated as randomly distributed discrete springs, and the bridging stress distribution with the consideration of residual stress is derived. A rough estimation on toughening in Al 2O 3/Al composites gives reasonable results.

R-curve behaviour in a macro-defect-free cement paste

Abstract The fracture resistance of a macro-defect-free cement paste has been studied in terms of the crack growth resistance (K R) curve. It is shown that, in contrast to common belief, a single fracture parameter, such as the critical stress intensity factor (K c) or the critical potential energy release rate (G c), cannot be used to characterize the critical failure event in this material. Using double-cantilever-beams together with both optical and scanning electron microscopy, the toughening mechanisms giving rise to the K R-curve behaviour were identified and found to occur behind the advancing crack tip. The predominant mechanism was due to unbroken cement ligaments bridging across the crack faces with other less significant contributions due to frictional interlocking of adjacent grains on the fracture plane and tearing of polymer fibrils. Approximate solution for the crack resistance curve was given in accordance with the Mai-Lawn crack-bridging model originally developed for alumina ceramics.

Application of the crack-bridging model for fracture resistance (R-curve behaviour) to PMMA

The rising fracture toughness behaviour of PMMA was characterized using a crack-bridging model originally developed for coarse-grained alumina that predicts a mechanism for crack resistance from the bridging of unbroken grains behind the crack tip. Based on the published experimental observation of PMMA, the craze zone behind the crack tip was thought to be analogous to the effective grain-bridging zone in the model in which the fibrils in the craze zone were related to the restraining interfacial ligaments. Self-consistent results in terms of the model were obtained which indicates that the crack-bridging model can be used to account for the fibril-toughening mechanism in PMMA.