Method of fabricating a damage tolerant shaft

#This invention relates to a shaft with internal connecting ribs that is tolerant of damage to a portion of the shaft because a closed path formed by the undamaged segment of the shaft and the internal connecting ribs continue to carry the torque loading on the shaft.

#Drive shafts are used in various vehicles, such as automobiles, aircrafts and rotorcrafts. Drive shafts generally connect a rotatable member to an engine that drives the rotation. The engine power rotates the drive shaft, which, in turn, rotates the workpiece. For example, rotorcrafts, such as helicopters, have drive shafts between the rotor, gearboxes and the fuselage-mounted engine(s) to enable the engine to drive the rotation of the rotor blades. The rotation of the rotor blades in relation to the motor creates torque on the drive shaft to transmit power. To ensure safe vehicle operation, the drive shaft must be designed to carry the necessary torque. In addition, the design process must take into account the potential for damage to the drive shaft.

#The torque loading on a drive shaft creates internal shear stresses in the drive shaft. The internal shear stresses naturally flow around the outermost closed path of the drive shaft. Thus, in undamaged solid or hollow drive shafts, the internal shear stresses flow around the closed path of the outer perimeter of the drive shaft.

#Having thus described the invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

#FIG. 1 is a cross-sectional view of a damage tolerant shaft according to one embodiment of the present invention having four ribs and four lobes;

#FIG. 2 is a cross-sectional view of a damage tolerant shaft according to another embodiment of the present invention having three ribs and three lobes;

#The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

#The damage tolerant shaft 10 according to one embodiment of the present invention is depicted in FIG. 1. As shown, the shaft includes an annular body 16 that is symmetrical about an axis and ribs 14 that extend inwardly from the annular body 16. The axis generally extends lengthwise through the annular body 16 at a location coincident with the center of the annular body 16. The ribs 14 also extend lengthwise along the annular body 16 and connect within the interior of the annular body 16 at a connecting point 18. The annular body 16 and ribs 14 cooperate to define voids 12 that extend lengthwise between the annular body 16 and ribs 14. The voids 12 may be hollow or filled with a filler material, such as foams, adhesives, syntactic resin, wood, aerogel or other compatible material. If the damage tolerant shaft 10 is to be used in a weight-sensitive application, then the voids 12 are preferably hollow or filled with a material of light or negligible weight. Through analysis or testing, the weight of the filler material can be traded against the weight of the shaft body itself to achieve the best load carrying capability for the least weight.

#Although FIG. 1 shows a damage tolerant shaft 10 with four ribs 14 and four voids 12, a damage tolerant shaft may have two or more ribs to form two or more voids. For example, FIG. 2 depicts a damage tolerant shaft 20 that has an annular body 26 and three ribs 24 that extend from the annular body 26 and meet at a connecting point 28 to define three voids 22. The aspects of a damage tolerant shaft as discussed hereinabove regarding FIG. 1 also apply to any damage tolerant shaft with two or more ribs that form two or more voids, including the shaft 20 depicted in FIG. 2.