Alternate load paths

Another consideration in developing connection details for blast resistant structures is the provision for redundant load path. Because these elements may be stressed near their ultimate capacity the possibility of single failures must be considered. Where possible, it is desirable to provide an alternate load path should a failure occur. Consideration should be given to the number of components in the load path and the consequences of single failures. The key concept in the development of these details is to trace the load or reaction through the connection. This is much more critical in blast design than in conventionally loaded structures. 

Using a composite structural member, either to replace the deficient component or to provide an alternative load path. In the latter case, the repair patch, typically made from fibre reinforced plastics, would be directly attached to the structure, either mechanically or via an adhesive bond. These topics will be discussed further, below. 

Other potential aerospace apphcations of titanium alloys include drive mechanism components and launch locks (mechanisms used to distribute the load induced by an aerospace vehicle laimch through an alternate load path). Replacement of steel gears with titanium alloy gears would reduce subsystem wei t and result in reduced laimch costs. The effects of various surface treatments on the wear life and efficiency of annealed Ti-6A1-4V gears have been studied by vacuum testing (Ref 17). As shown in Fig. 8, boronized (5 pm layer of metalhc borides), Tifi an (5 im layer of complex oxides), and ion-plated aluminum coatings exhibited the best wear resistance and the lowest power losses. 

They offer limited redundancy and few alternative load paths. 

Crack propagation containment or through the use of alternative load paths... 

If one loads a plastic with 5 percent by volume of 6-mil size in a random distribution (Figure 5.13a), there will be, on the average, a 6-mil gap to the nearest sphere. Heat or electrons flowing through such a matrix would thus cross alternate paths of about equal lengths in the two media. The picture, however... 

Another approach to improve durability involves overdesigning the bond so that the actual stresses experienced are a small fraction of the stresses that the joint is capable of withstanding. Stresses are thereby reduced to below any critical level and the load can be carried even if moisture ereates a disbond over a portion of the joint. Of course, this approach may not be feasible from a cost or weight standpoint. Alternatively, the bond can be designed so that moisture has a long diffusion path to reaeh a eritical area—the same general principle by whieh sealants work. 

With the stray field type, the load, usually in the form of a thin web, passes over the electrodes of alternating polarity. Since the load represents the path of least electrical resistance, the dielectric field passes through it, causing heating. The staggered type is usually used for sheet materials and thick webs. The distance between the electrodes is kept to a minimum in order to achieve heating without arcing. 

---