Crack resistance behavior

Crack propagation, ceramics, 5 628-630 Crack-resistance behavior... 

Grellmann, W. Seidler, S. Jung, K. Kotter, I. (2001). Crack-resistance behavior of polypropylene copolymers. Journal of Applied Polymer Science, Vol.79, No.l3, (January 2001), pp. 2317-2325, ISSN 1097-4628... 

Crack toughness behavior of MWCNT/polycarbonate nanocomposites was also reported (Xiao et al., 2004 Foster et al., 2005). When 2 wt.% MWCNTs was added into the composites, the resistance to crack propagation was markedly increased compared to pure Polycarbonate. At 4 wt.% MWCNTs, a tough-to-brittle transition has been observed. The attack of crack initiation needs shorter time for nanocomposites with 4 wt.% MWCNT compared to the composites with 2 wt.% MWCNTs, which supports that a tough-to-brittle transition exists in these nanocomposites. 

Liquid reactive rubbers were also used for UP and vinyl ester formulations (Suspene et al., 1993 Siebert et al., 1996). Increases in fracture energy and fatigue- crack resistance were reported for some systems, although no significant improvements were observed for some other systems. These different behaviors are probably related to the heterogeneous structure of the matrix (Chapter 7). Toughening mechanisms in three-phase systems are not yet well established. 

The thin inner shell of the core-shell polymers contained less than 20% rubber by weight, with 60% by weight of a plastic core in the particles. It is unusual to enhance the toughness of the normally brittle epoxy-resin system at such a low level of rubber content. We believe that the unique design, the use of a multilayer toughener with a thin, elastomeric inner layer, and the large plastic core together produced behavior like that of solid rubber particles and, hence, enhanced crack resistance. 

Zr(C, N) layers together with a variety of other layers were successfully introduced for cutting tools for turning steel. A microstructure of such a multilayer is shown in Fig. 30 where Zr(C, N) represents a thick top layer. The favorable performance of such Zr(C, N) containing layers stems for the thermal expansion behavior of Zr(C, N), which is the lowest amongst the group iv carbonitrides, and which reduces tensile stress upon thermal load. Such a behavior enhances the performance of the coatings because of increased crack resistance and adhesion. 

Figure 14.13 Mechanics of fracture of a material demonstratingcrack-growth resistance behavior. The thick solid line represents the material s crack growth resistance, R, or R-curve...

Figure 14.14 Crack growth resistance behavior as a function of grain size (4, 9, and 16nm) for alumina using a single-edge notched beam (SENB) sample. From Ref [12].

---