Voids, micro

Fig. 9. The effect of voids due to poor wetting on adhesive strength, (a) The zippering effect of voids aligned in the plane of shear, (b) Macro-voids in the resin formed during the manufacture of a carbon fiber reinforced prepregs. (c) Micro-voids caused by axial crenulations along carbon fiber surfaces.

Detection Capability Can detect HTHA only after cracks have formed. Cannot detect microscopic damage. Can detect and distinguish microfissuring and micro voids due to HTHA from other indications very reliably. Can detect HTHA only after macro size cracks have formed. Cannot detect microscopic damage. Blisters are readily apparent when present. However, HTHA may frequently occur without the formation of surface blisters. Reported to be capable of detecting cracks. Currently not known whether microscopic damage can be detected. 

Figure 5. SEM micrographs showing the ductility observed at low hydrogen fiigacities (region 1 of Figure 4(b)) in the parent metal of the (a) HY-100 and (b) HSLA-100 alloys and the micro-void coalescence (MVC) fracture morphology in (c) HY-100 and (d) HSAL-100.

FIG. 13.78 Schematic view of brittle stresses as functions of time, an extension of Fig. 13.76. (a) brittle curve (b) ductile curve (A) brittle fracture region (B) ductile fracture region (C) brittle fracture region (evolution of micro-voids). According to Van der Vegt (2005). 

The factors (298 Tg) and (Tg 298) are the "thermal distances" of Tg from room temperature for rubbers and glasses respectively. The influence of these "thermal distances" is probably connected with the fractional free volume of the polymer in rubbery amorphous polymers this f.f.v. increases with decreasing Tg, in glassy amorphous polymers the f.f.v. increases with increasing Tg (increasing formation of micro-voids), hence lowering of the activation energy. 

This equation has become known as the "dual sorption model", because obviously two separate sorption mechanisms are operative for gases in glassy polymers. One mode (first term on the right in Eq. (18.36)) follows the Henry s law the other mode (second term) follows a Langmuir form. This additional mode is attributed to sorption into micro-voids that apparently pre-exist in the glassy state of the polymer (and only there ) it disappears above Tg (see Fig. 18.9b). 

Technologies, such as coextrusion and coinjection, allow PET and other plastics to package foods and other products.225 226> 227 Care must be taken to control the process so that the melt when blown will not have micro-voids in the container walls or will delaminate. Coextrusion and coinjection (or multilayer processes) are essential technique in the production of high performance BM products (Chapters 4 and 5). The parison or preform is coextruded with a number of different layers, each of which contributes an important property to the finished product. Increasingly, a mid layer may consist of recycled material which is encapsulated between inner and outer layers of virgin plastics. 

Further examples of positron study of defects in HTSC are studies carried out to understand the nature of flux-pinning defects that lead to an increase in critical-current density on neutron-irradiated Y 1 2 3. Experiments [59] on positron lifetime and critical-current density measurements on various neutron-irradiated samples of Y 1 2 3 indicate that the critical current density is correlated with the micro-void density, as obtained from the analysis of positron lifetime measurements. Investigation of defects in other HTSC superconductors, such as La-Sr-Ca-Cu-0 [60], Bi-Sr-Ca-Cu-0 [49], and Nd-Ce-Cu-O [52], have also been carried out. 

The following basic alloy microstructures and impurities on the reacting surfaces art considered, i.e. (a) bulk (point defect-zero degree defect including impurities), (b) grain-boundaries (2-D defect), (c) dislocations (1-D defect), and (d) open micro voids during fabrication of the alloy... 

III. The third step of direct longitudinal transmission of strain onto connected crystalline blocks leads to a perfect stretching of these fibrils. Because of the alignment of the molecules the fibers in this condition should possess a strength about 1 to 2 orders of magnitude higher than the yield stress of randomly distributed folded polycrystals. As the fibrils are able to stabilize the enhanced micro-void volume between them, a lateral coalescence of these voids finally provides a local deformation zone in the shape of a craze as known from amorphous polymers. 

Type-IV sorption isotherm is a combination of type-11 sorption at low concentration and type-111 sorption at high concentration. Type-V isotherm as dehned here (Figure 5.1) is exhibited by glassy polymers/polymers containing adsorptive fillers. This type of sorption is dehned as dual mode sorption, which is a combination of Henry s type and Langmuir type. The former applies to the bulk polymer and the latter to the hller/micro-voids in the polymer. Netke et al. [35] have studied the permeation of acetic acid-water mixmres in silicalite hlled PDMS. Equations governing type-V isotherm are... 

Once inside the metal electrode, diffusing hydrogen atoms can recombine around defects such as micro-voids, inclusions, interfaces and grain boundaries, forming molecular hydrogen. High-... 

The Random-pore Model This model was originally developed for pellets containing a bidisperse pore system, such as the alumina described in Chap. 8 (Table 8-5 and Fig. 8-10). It is supposed that the pellet consists of an assembly of small particles. When the particles themselves contain pores (micropores), there exists both a macro and a micro void-volume distribu-... 

During the period of the current decay, there are two competitive processes, densification to form the barrier layer and dissolution of barrier layer to form the porous layer. Under the high electrical field strength (constant voltage mode), the densification of the aluminium oxide films is favoured for process durations shorter than 3700 s. When the constant voltage was kept for a long anodisation time (beyond 10900 s), the dissolution of the aluminium oxide film becomes more dominant. Thus, the film could be contaminated by inward migration of the electrolyte into the film or by formation of micro-voids. 

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