High-resolution electron microscopy of high-modulus carbon fibres*

High-resolution electron-microscope images of high-modulus carbon-fibre fragments have been recorded under conditions which allow resolution of the individual 0.34 nm graphite layer planes. Extinction bands previously observed at low resolution are now seen to originate from several different structural features. Single bands are caused by lattice distortion due to non-basal edge dislocations and low-angle boundaries of tilt or twist character; periodic bands are the result of Moiré effects from overlapping or interlinked crystallites. Accurately controlled tilting experiments give further insight into the complex interlinked nature of the crystallites and the results are summarized in terms of a model which is also capable of explaining the partial recrystallization observed with boron doping.     

Interpretation of surface and bulk effects using the pulsed MIS capacitor

The interpretation of lifetimes and surface generation velocities determined from pulsed MIS-C measurements is examined. The effect of surface generation on the C-t response and ‘Zerbst’ plot is demonstrated and values for s₀ are correlated with the density of fast surface states. Different kinds of surface dominated responses are analyzed and we discuss how the bulk characteristics can be retrieved. It is also shown that pulsing from inversion significantly lowers s₀, but for high densities of surface states this technique does not suffice to eliminate surface effects. Finally, an approximate analysis of the C-t data is shown to agree quite well with the more exact analysis and it is then applied to lifetime maps of Si wafers.     

An optical-interference method for experimental stress analysis of cracked structures

An optical interference technique can be used to measure the crack opening in a cracked transparent model of a structure under load. The measured crack opening as a function of distance from the crack tip can be used in conjunction with the opening mode crack tip stress field equations to determine the opening mode stress intensity factor. Application of this method to double cantilever beam specimens comprised of two glass arms bonded together with an epoxy adhesive gave results which were in close agreement with K-calibrations based on compliance measurements. The measuring techniques and the scheme of analyzing the data could be used to obtain K-calibrations of more complex structures.