Material defects flattening

The determination of Eg, values by OCP can also be complicated by materials that have a high density of defect sites which can serve as recombination centers. If the sample has a high carrier recombination rate (again due to material defects), then this effect prevents the creation of a compensating electric field, and hence higher light intensities are required to achieve flat-band conditions. However, if the lamp is not sufiiciently intense, it may not be possible to completely flatten the... 

There are a number of sources of shape problems in flat-rolled products. There are also a variety of means for correcting them. Each type of leveling or flattening equipment has its own capabilities and limits relative to specific defects in the incoming material. In this section, we will discuss shape defects dimensional problems in material which is supposed to be flat and is not, and the equipment options for correcting the problems. 

Dynamic fatigue is more widely recognized as a cause of fracture, and most handbooks provide fatigue data in the form of S-N curves, as illustrated in Fig. 8.20. These curves usually flatten out beyond 10 cycles, in which case it is possible to define a fatigue endurance limit, i.e. the minimum st ress required to cause failure within 10 cycles. Both the static and the dynamic tests reflect the response of the material to the small defects that are present in the unnotched specimens, and in a sense are measuring the distribution of intrinsic flaw sizes as much as the fracture resistance of the polymer. Consequently, when the component is to be used in a critical application, there is a good case for mounting a full-scale fracture mechanics study. 

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