Semi-coherent particle

Fig. 1.11. Coherent and semi-coherent particles. The symbol L in subfigure (b) denotes inserted half-planes of the lattice. The edge where such a half-plane ends is called an edge dislocation. This will be discussed in section 6.2...

Depending in the crystal structure of the two phases, the interface between them may adopt different structures If the crystal structures and the crystal orientation of both phases are identical and the lattice constants do not differ too much, the particles of the second phase will be coherent i. e., the lattice planes of the matrix continue within the particle (see figure 1.11(a)). If the lattice structure and orientation are identical, but the lattice constants differ strongly, the particles will be semi-coherent because some lattice planes of the matrix continue inside the particle but others do not (figure 1.11(b)). Generally, the crystal lattice is distorted near to the coherent or semi-coherent particle. If the lattice structure of both phases or the lattice orientation differ, the particles are incoherent the lattice planes of particle and matrix have no relation at all (figure 1.12). 

Indeed, as obvious from both exemples given in Fig. 2, the transition could thus be determined accurately within 0.1-0.2 decades of test speeds with few samples in a relative short time frame. Moreover, as the apparent values (Kimax) are always lower than the effective parameters (Keff), none of the material descriptor would be overestimated. In addition, since Kjmax-values have been shown to provide a semi-quantitative evaluation (in terms of test speed or temperature) of fracture resistance parameters, a coherent material comparison would be possible over the whole investigated range. This remark remains true as long as the grades have similar rp. For iPP grades, it should be checked (and considered with more caution) when materials exhibit different particle and matrix melt flow rates, or different crystalline structures. It should also be investigated in detail when different polymer families (ABS versus HIPS or rubber modified iPP) are compared. 

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