A tubular shaft similar to that shown in Fig- ure 16.11 is to be designed that has an out- side diameter of 100 mm (4 in.) and a length of 1.25 m (4.1 ft). The mechanical charac- teristic of prime importance is bending stiff- ness in terms of the longitudinal modulus of elasticity. Stiffness is to be specified as maximum allowable deflection in bending; when subjected to three-point bending as in Figure 12.32, a load of 1700 N (380 lbf) is to produce an elastic deflection of no more than 0.20 mm (0.008 in.) at the midpoint position.

Continuous fibers that are oriented parallel to the tube axis will be used; possible fiber materials are glass, and carbon in standard-, intermediate-, and high-modulus grades. The matrix material is to be an epoxy resin, and fiber volume fraction is 0.40.

(a) Decide which of the four fiber materi- als are possible candidates for this application, and for each candidate determine the required inside diameter consistent with the above criteria.

(b) For each candidate, determine the re- quired cost, and on this basis, specify the fiber that would be the least expensive to use. Elastic modulus, density, and cost data for the fiber and matrix materials are con- tained in Table 16.6.