FRACTURE MORPHOLOGY Subject

Analysis of fracture surfaces revealed no explicit difference in the fracture morphology of the pure mode I, mixed-mode, or pure mode II specimens. However, it should be mentioned that unlike dense ceramics the coating material has provided a challenging subject on fractography because of its unique open and microcracked platelet... 

Goldberg A, Lesuer DR, Part J (1989) Fracture morphologies of carbon-blackloaded SBR subjected to low-cycle, high-stress fatigue. Rubber Chem Technol 62 272-287... 

The mode of creep failure in thermoplastic materials is not unique. As an example the creep fracture morphologies of PVC tubes subjected to different stress levels have been reproduced in Chapter 1. At higher stresses (oy = 50 MN/m ) PVC tubes fail in a brittle manner after little creep deformation, and one speaks of delayed brittle frac-ture (Fig. 1.1). At medium stresses (42 MN/m ) and after prolonged times the tubes show large scale plastic deformation, i.e. delayed yielding (Fig. 1.2). At lower stresses Oy < 20 MN/m ) failure does either not occur at all within experimental time scales or by a competing mechanism, the formation of a creep crack (Fig. 1.3). 

The fracture surface of the sample subjected to an impact speed of 650 m/s revealed two distinct zones one, as observed previously, showed a morphology similar to that induced by natural crystal growth, while the other was smooth (Fig. 16.5a). The cracks were more extensive and represented the contours of crystalline aggregates. A clear shift in some areas relative to others was observed. The smooth sections show heterogeneity, and the crystalline zone features relief structures that show smaller differences in height but look similar to the projections. 

The reasons for flow instabilities, such as those causing melt fracture, are the subject of scientific research and theories. In a recent study, optical velocimetry was used to measure flow kinetics. Morphological changes on the surface (sharkskin formation) were monitored by high speed video microscopy. It was confirmed in this study that the velocity of the material stream, after it has just left the exit, determines melt fiacture. Increase in throughput rate increases velocity... 

The surface energy of a material is of fundamental interest, for example in the prediction of crystal morphologies and in understanding fracture. Accurate experimental measurements of the surface energy are difficult to perform. In fact, such measurements are mostly constrained to the determination of surface energies at high temperatures and are subject to numerous errors due to surface-active contaminants. For... 

Extensive morphological studies of polypropylene fracture surfaces have been carried out by Menges et al. [121, 136] and quite recently by Friedrich [183]. Using polypropylenes of different molecular weight and tacticity subjected to different thermal treatment Friedrich [183] obtained samples of different microstructure ... 

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