Softening strip

Net-tension failures can be avoided or delayed by increased joint flexibility to spread the load transfer over several lines of bolts. Composite materials are generally more brittle than conventional metals, so loads are not easily redistributed around a stress concentration such as a bolt hole. Simultaneously, shear-lag effects caused by discontinuous fibers lead to difficult design problems around bolt holes. A possible solution is to put a relatively ductile composite material such as S-glass-epoxy in a strip of several times the bolt diameter in line with the bolt rows. This approach is called the softening-strip concept, and was addressed in Section 6.4. 

Sun. C.T. and Luo, J. (1988). Failure loads for notched graphite/epoxy laminates with a softening strip. Composites Sci. Techno . 22, 121-133. 

Demonstrations Take a strip — 0.25 mm X 1 cm X 15 cm of cold-rolled (work-hardened) brass and bend it (on edge) on the overhead until permanent deformation takes place. Anneal brass strip at bright red head for — 0.5 min to soften it. After cooling replace on overhead and show that permanent deformation takes place at a much smaller deflection than before. This illustrates the importance of large Uy in springs. 

The effect is best illustrated by a numerical example (Table 31.4). Let us take the case of hard and alkaline deep well water such as that found to the north of London, whose main characteristics are shown in the first column of Table 31.4. The second column shows its quality after de-alkalization has removed nine-tenths of the temporary hardness and converted it into CO2 gas. This is removed from the water by stripping it with air in a packed degassing column, and the product then softened in the third stage to yield the product shown in the third column. 

NOTE Periodic cleaning of softener resin with an iron stripping formulation based on phosphonate or a terpolymer is useful. The cleaner is introduced into the resin bed, perhaps via the brine draw during resin regeneration, at a level of, say, 1 to 2 U.S. pints/cuft (16-32 ml/l) of resin. The regeneration process is temporarily halted for several hours and the resin is allowed to soak the process is then restarted and the stripped iron goes to drain. 

Aeration, Stripping Lime Softening Anion Cation Reverse Osmosis Ultrafiltration Chemical Oxidation Disinfection GAC PAG Granular Ferric Hydroxide Activated Alumina... 

The elongation of film strips of fixed dimensions subjected to a constant load of 0.17 kg./sq.mm. is measured as a function of temperature. Heating rate is standardized at 10°C. per minute. The temperature range where an appreciable rise in elongation of the films is observed is taken as the softening point (S.P.)... 

The dissolved air left in boiler feedwater (BFW) is stripped out with steam, in the deaerator shown in Fig. 8.9. The cold BFW has been taken first from the Mississippi River and then filtered to remove sand and sediment. Removal of the bulk of the calcium salts that would cause hardness deposits in the boilers is often accomplished by hot-lime softening. If excess C02 gas appears in downstream units consuming the steam, it is the fault of the lime softening, not the deaerator. 

In the manufacture of cellulose ester plastic, the appropriate ester is blended with plasticizer and other additives, such as stabilizers, ultraviolet inhibitors, dyes, and pigments, commonly in a large sigma-blade mixer. The mixture thus obtained is heated to its softening temperature and kneaded until it is homogeneous. This is done on hot milling rolls, in a compounding extruder, or in a Banbury mixer. The molten mass of plastic that results is formed into small rods or strips that are then cut into cylindrical or cubical pellets, which ordinarily have dimensions of about J inch (3 millimeters). See Fig. 2. 

---