Dynamic modeling of crack propagation in ceramic laminate toughened composites with weak interfaces by using discrete element method

  • Dynamische Modellierung der Rissausbreitung in gehärteten Keramik-Laminat-Verbundstoffen mit schwachen Schnittstellen mithilfe der Diskrete-Elemente-Methode

Zhang, Wen; Telle, Rainer (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2013, 2014)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2013

Abstract

Tough ceramics can be made by introducing weak interfaces which deflect a growing crack. The presence of weak interfaces in a brittle material can cause a consequent increase in the resistance of crack growth. The failure patterns of the toughened ceramics demonstrate the so-called "graceful failure" feature. In order to numerically reproduce the dynamic process of the crack propagation in such toughened ceramic laminates, discrete element method (DEM) is employed to study the crack growth in the SiC-C laminate with the graphite as weak interfaces. The two-dimensional Bonded-Particle-Model (BPM) is employed to model and calibrate the SiC and graphite. Regarding the thickness of the thin interlayer, two different BPMs are testified, and a simple and explicit model is proposed to model the SiC-C laminate. The feasibility of applying BPM to model fracture behaviors of laminate has been verified. By modeling the three-point-bending test of the laminate, fracture behaviors like de-lamination and crack deflection are observed dynamically. The loading curve shows the "graceful failure" feature and significant R-curve behaviors are found in the modeled laminates. It is found out that, for the toughening effect to occur, the strength of the weak interface has to be in a certain range. In order to increase the strength of the toughened laminate, a minimum presence of the weak interface is required. Crack deflection as toughening mechanism has direct analogues in some biological structures like bone, wood and nacre. With very complex hierarchical designs in their highly sophisticated structure, these materials are generally difficult to mimic and synthesize. From the DEM modeling, effective design optimizations and production suggestions can be gained for the bio-mimic laminate, as like the suitable strength of the weak interface and the optimum number of weak interfaces in respect to certain laminate geometry. With further development of this discrete element model to three-dimensional, other applications would be possible, for instance the dynamic modeling of the crack propagation in fiber reinforced composites and the reproducing and understanding of the complex "crumple-zone" which are observed in MAX-phases.

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