Microstructure fractured surfaces

Thus far, seif-mated pin-on-disk siiding wear tests have been carried out with RBSN, HSN, and SSC materials. The tests were performed at a velocity of 0.1 m/s with a 1 kg static load in air at room temperature and a total sliding distance of 1000 meters. Tabie 4 summarizes the friction results obtained. The breakaway friction coefficients were measured prior to wear testing on surfaces polished to a 1 )xm finish. The values reported for the kinetic friction coefficients are the steady state values obtained after 500 meters of sliding. The microstructure, fracture surface, and reactions at the wear interface are currently being studied to provide more insight into the wear behavior of these ceramics. 

Lapique, F. Meakin, P. Feder, J. Jossang, T. (2000). Relationships between microstructure, fracture-surface morphology, and mechanical properties in ethylene and propylene polymers and copolymers. Journal of Applied Polymer Science, Vol.77, No.ll, (September 2000), pp. 2370-2382, ISSN 1097-4628... 

More recently, the work of Beetle and Steward (Ref 49), using SEM, has shown it well-suited for studies of steel fracture surfaces produced by expl action. Several Si-Mn steels with selected, known microstructures were formed into cylinders and explosively fragmented using Comp... 

Microstructures in cast irons are also dramatically influenced by cooling rates. If cooling is rapid, no graphite precipitates. Rather, the alloy solidifies in the metastable Fe-Fe3C state. In that state, the carbon is combined with iron as iron carbides. The fractured surface of carbidic cast iron is white. Such irons are hard and are not readily machined. Carbidic iron castings are used for some special applications, when abrasion resistance is important. 

The relationships between the K1C and fracture surface energy are similar to each other, and generally decrease with increasing spinel content, apart from the in situ formed composites which show different microstructures and fracture paths. It is therefore clear that the development of thermal shock resistance in the magnesia-spinel composites cannot be linked to any increased fracture toughness. 

A transverse cross-section through the fracture initiation site was examined by metallography. The fracture surface profile was found to be relatively flat and there was no crack branching. The microstructure showed dark-etching-tempered martensite. Further no plastic deformation was observed at the fracture initiation site. 

Unless a wet cell or cryo stage is used, the fine microstructure is much altered by dehydration in the instrument (J10,S41). However, localized drying occurs in any paste even before it is placed in a high vacuum, as soon as the RH falls below saturation. The water is lost initially from the wider pores, which are probably represented disproportionately on fracture surfaces. The state of the cement paste in a practical concrete may thus vary on both a macro and a micro scale between dry and saturated. 

The mechanical properties of rapidly polymerizing acrylic dispersions, in simulated bioconditions, were directly related to microstructural characteristics. The volume fraction of matrix, the crosslinker volume in the matrix, the particle size distribution of the dispersed phase, and polymeric additives in the matrix or dispersed phase were important microstructural factors. The mechanical properties were most sensitive to volume fraction of crosslinker. Ten percent (vol) of ethylene dimethacrylate produced a significant improvement in flexural strength and impact resistance. Qualitative dynamic impact studies provided some insight into the fracture mechanics of the system. A time scale for the elastic, plastic, and failure phenomena in Izod impact specimens was qualitatively established. The time scale and rate sensitivity of the phenomena were correlated with the fracture surface topography and fracture geometry in impact and flexural samples. 

The morphology or microstructure of powders and well-polished pellets was observed with TEM (H-800) and SEM (Hitachi X-650). Au coating was applied on the surfaces or fracture surfaces to prevent charging before observation and photo-taken. 

SEM photographs of the surfaces of the sintered samples are shown in Fig. 4 (A). The surface microstructure reveals uniform and fine grain growth about 2-3 pm. No pores were observed on the surface of the sample, but there were some pores from the fracture surface of the sample, as shown in Fig. 4 (C). The sintered density is 6.6 g/cm, which is over 95% of the theoretical value. The residual pores may be partly attributed to the agglomerates in the source powders that lowered the sinterability of the green bodies. It can also be seen that there are no great changes between the pellets sintered in air before and after heat treatment at 750°C for 5h in H2. This result is in aecordance with that of XRD. It confirms that the samples are chemically stable in H2 atmosphere at least below 750°C. 

In comparing the shear fracture surfaces of amorphous and semi-crystalline polymers, it appears that the features in both cases are quite similar (Fig. 39a -c ). This indicates that, under comparable conditions, the local stress field rather than details of the crystalline-amorphous microstructure of the polymers tested determines the operating deformation mechanism. Only secondary effects arise from the morphology of the cry stalline material. 

To examine craze microstructure, and to study the effect of molecular variables on craze morphology, the method described by Kramer was followed. Samples of polymers were cast in the form of thin films, strained in tension while bonded to carbon-coated grids, and examined in the transmission electron microscope either before or after staining. The TEM observations were made with an Hitachi HU-11 A unit or with a JEOL JEM-IOOCX unit, operating usually at 75-80 kV. Fracture surfaces of many bulk samples were coated with a thin layer of gold-palladium and examined by an Etec scanning electron microscope. 

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