Simulation debonding

To simulate debonding phenomena that can occur during the scratch test described in Section 2, at first contact calculation must be carried out. At a normal load Ff) = 1 N, the measured coefficient of friction between the diamond indentor and the CF/PEEK specimen for N-fiber orientation was /x = 0.1. 

Now that the top-down internal state variable theory was established, the bottom-up simulations and experiments were required. At the atomic scale (nanometers), simulations were performed using Modified Embedded Atom Method, (MEAM) Baskes [176], potentials based upon interfacial atomistics of Baskes et al. [177] to determine the conditions when silicon fracture would occur versus silicon-interface debonding [156]. Atomistic simulations showed that a material with a pristine interface would incur interface debonding before silicon fracture. However, if a sufficient number of defects were present within the silicon, it would fracture before the interface would debond. Microstructural analysis of larger scale interrupted strain tests under tension revealed that both silicon fracture and debonding of the silicon-aluminum interface in the eutectic region would occur [290, 291]. 

Another important result from the atomistic simulations was that the stress-strain response of a region of material around an interface that debonded could be represented by an elastic fracture analysis at the next higher size scale if the interface was assumed to be larger than 40 A. Hence, an elastic fracture criterion was used in the microscale finite element analysis, which focused on void-crack... 

K.A. Gall et al Atomistic simulations on the tensile debonding of an Aluminum-Silicon interface. J. Mech. Phys. Solids 48, 2183-2212 (2000)... 

Small Debond Energy. For SDE, when cr< crs, the unloading modulus E depends on r0, but is independent of T, and Cl. However, the permanent strain e0 depends on T, and Cl, as well as r0. These differing dependencies of E and e0 on constituent properties have the following two implications. (1) To simulate the stress-strain curve, both e0 and E are required. Consequently, r0, T, and Cl must be known. (2) The use of unloading and reloading to evaluate the constituent properties has the convenience that the hysteresis is dependent only on tq. Consequently, precise determination of r0 is possible. Moreover, with t0 known from the hysteresis, both T,- and Cl can be evaluated from the permanent strain. The principal SDE results are as follows. 

This equation shows that debonding stress increases with adhesion and filler fraction and decreases with particle size. Figure 7.27 shows the effect of particle size on prediction of yield stress based on the debonding simulated by an equation derived from Eq 7.27. Decreasing particle size increases the stress required for debonding. 

Xu, X.P. and Needleman, A. (1993) Void nucleation by inclusion debonding in a crystal matrix. Modeling and Simulation in Materials Science and Engineering, 1, 111-132. 

Based on the micrograph observation in Fig. 7.10, AE wave due to debonding of stainless steel from base metal is simulated. As illustrated in the figure, a penny-shaped tensile crack of 10 pm diameter and 1 pm crack opening is assumed from the observation. Results of detected AE wave... 

Finally a numerieal method able to reproduce three-dimensionally the fatigue debonding and/or delamination evolution in bonded structures has been proposed in order to improve their performances. The eohesive zone model previously developed by the authors to simulate fatigue erack growth at interfaces in 2D geometries is extended to 3D cracks imder mixed-mode I/II loading... 

In addition to indentation simulations, researchers have investigated the use of FEA to simulate the adhesion and debonding of thin films and coatings. Sauer and Mergel... 

Finite Eiement Simulation of the Fiber/Matrix Debonding... 

The debonding models use a linear elastic-plastic material law for the matrix material that allows to study the plastic deformation in the matrix material. Due to this fact, the smaller diamond indentor (R = 100 jam) with a normal load Fn= 1N was used in the debonding simulation. The friction coefficient, obtained experimentally for N-fiber orientation, was = 0.1. The results presented here are only for N-fiber orientation, although additional investigations were carried out also for P- and AP-fiber orientation. ... 

K. Friedrich, T. Goda, K. Viradi, B. Wetzel (2004) Finite element simulation of the fiber/matrix debonding in polymer composites produced by a sliding indentor Part 1 - Normally oriented fibers, J. Compos, Mater., 38,1583. 

---