Page 309 - Mechanics Analysis Composite Materials

294 Mechanics and analysis of' coniposite niaterials

should compare numerous laminate structures and can hardly test all of them, this
approach can be successfully used for structures that are under stable and mass
production. For example, the segments of two structures of composite drive shafts -
one made of fabric and the other of unidirectional composite, are shown in Fig.
6.20. Testing these segments in tension. compression, and torsion we can plot the
strength envelope on the plane (M, T), where A4 is the bending moment and Tis the
torque, and evaluate the shaft strength for different combinations of A4 and T with
high accuracy and reliability.

6.3. Examples

As the first example, consider a problem of torsion of a thin-walled cylindrical
drive shaft (see Fig. 6.21) made by winding of a glass%poxy fabric tape at angles
*45". Material properties are El = 23.5 GPa, E2 = 18.5 GPa, GI? = 7.2 GPa, 1'12 =
0.16, = 0.2, 0: = 510 MPa, a, = 460 MPa, 0; = 280 MPa, 0; = 260 MPa,
212 = 85 MPa. Shear strain induced by torque Tis (Vasiliev, 1993) -

Here T is the torque, R = 0.05 m is the shaft radius, and B44 is the shear stiffness
of the wall. According to Eqs. (5.39), B44 = A44h, where h = 5 mm is the wall
thickness, while A44 is specified by Eqs. (4.72) and can be presented as (4 = 45")

Fig. 6.20. Segments of composite drive shafts with test fixtures. Courtesy of CRISM.