Particle debonding

The stress distribution analysis shows that maximum stress concentration develops in the radial direction at the pole of the particle, and shear yielding is initiated at around 45° on the surface of rigid particles. Debonding occurs at the pole of the particle, and extends to a critical angle [27]. In case of total adhesion, debonding does not occur and there is cavitation in the matrix, at some distance from the particle pole (not at the interface). 

Major results Figure 14.16 shows the effect of mean particle size of spherical silica (flame-fused synthetic silica) on acoustic emission. The emission increases with the particle size of filler increasing. The source of this increase in acoustic emission is thought to be related to the fracture of particles, debonding of particles from... 

LLDPE with 10% and 37.5% PS, respectively. The decrease in ay suggested that PS particles debonded from the LLDPE matrix and lost their load-bearing capacity before the yield point was reached. Debonding probably initiated near the onset of nonlinearity in the stress-strain curve. 

Figure 3. Schematic representation of particle debonding and void growth during deformation of Type I blends.

It is often observed in filled ductile polymers that if adhesion is poor and deformation is accompanied by particle debonding followed by void formation... 

Debonding between well-bonded APTFS-Al O nanoparticles and epoxy matrix depends on the crack propagation speed. It is observed only in the mirror zone. However, in the nanocomposites having poorly bonded NT- AljOj particles, particle debonding is noticed everywhere. 

In conclusion, it can be stated that the effect of fillers on modulus is relatively well understood and may be predicted. The other properties are less easy to predict as they are measured under conditions where the composite is deformed to a greater extent. This means that other factors such as particle debonding, particle re-orientation and polymer orientation, must be considered. 

Figure 4.11 Fracture surfaces of PMMA/TPU blends with PMMA particles debonding at the interfaces particle diameter and void size increase with increasing PMMA content ...

The volume concentration of debonded particles or the fraction of the debonded filler, ( )o = ( )xAj)f can be determined by measuring the Young s modulus of a filled elastomer before and after preloading that breaks adhesion contacts. When studying the filler separation in the model samples, it was noted that not all particles debond simultaneously, and that the number of debonded particles depends not only on the magnitude of the disturbing stress, but also on the time... 

The second mechanism by which dispersants improve impact resistance is by reducing bonding between filler and polymer. When impact occurs, the filler debonds from the polymer to create multiple microvoids as each filler particle debonds. These voids or crazes help to adsorb energy. It is well known that crazing is a mechanism to improve... 

Such films are made by compounding calcium carbonate into polypropylene. The calcium carbonate is surface treated with stearic acid to decrease adhesion between the filler and the polymer. A film of the material is made and then stretched whereupon the filler particles debond from the polymer to leave voids that permit permeation. 

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