tailieunhanh - ADVANCED MECHANICS OF COMPOSITE MATERIALS Episode 8

Tham khảo tài liệu 'advanced mechanics of composite materials episode 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 232 Advanced mechanics of composite materials This condition allows us to determine the axial strain as ơ TZ- Ex where Ex E f 1 - 1 tanh Ằ n 1 1 is the apparent modulus of an angle-ply specimen. Consider two limiting cases. First suppose that Gxz 0 . that the plies are not bonded. Then À 0 and because lim tanh À 1 Ằ À 0 Ex E . Second assume that Gxz x . that the interlaminar shear stiffness is infinitely high. Then À rc and Eq. yields e Ex r 1 n This result coincides with Eq. which specifies the modulus of an angle-ply layer. For finite values of Gxz the parameter À in Eqs. is rather large because it includes the ratio of the specimen width a to the ply thickness Ỗ which is usually a large number. Taking into account that tanh À 1 we can neglect the last term in Eq. in comparison with unity. Thus this equation reduces to Eq. . This means that tension of angle-ply specimens allows us to measure material stiffness with good accuracy despite the fact that the fibers are cut on the longitudinal edges of the specimens. However this is not true for the strength. The distribution of stresses over the halfwidth of the carbon-epoxy specimen with the properties given above and a 8 20 Ộ 45 is shown in Fig. . The stresses ơx Txy and Txz were calculated with the aid of Eqs. whereas stresses ơ1 ơ2 and T12 in the principal material directions of the plies were found using Eqs. for the corresponding strains and Hooke s law for the plies. As can be seen in Fig. there exists a significant concentration of stress ơ2 that causes cracks in the matrix. Moreover the interlaminar shear stress Txz that appears in the vicinity of the specimen edge can induce delamination of the specimen. The maximum value of stress ơ2 is ơ2max ơ2 y 1 E2 1 V21 v sin2 Ộ V21 Vyx cos2 ệ 1 V21 n y x sin ệ cos ệ Using the modified strength condition . ơ2 ax ơ to evaluate the strength of 60 specimen we arrive at the result shown with a .