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Advanced mechanics of materials (1993-John Willey) Episode 7

Tham khảo tài liệu 'advanced mechanics of materials (1993-john willey) episode 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 1 342 8 SHEAR CENTER 8.4 SHEAR CENTER OF COMPOSITE BEAMS FORMED FROM STRINGERS AND THIN WEBS Often particularly in the aircraft industry beams are built up by welding or riveting longitudinal stiffeners called stringers to thin webs. Such beams are often designed to carry large bending loads and small shear loads. Two examples of cross sections of such beams are shown in Fig. 8.6. A beam whose cross section consists of two T-section stringers joined to a semicircular web is shown in Fig. 8.6 and a beam whose cross section consists of a vertical web joined to two angle section stringers that in turn are joined to two horizontal webs that support two T-section stringers is shown in Fig. 8.6h. Caution In practice beams with cross sections similar to those shown in Fig. 8.6h have webs so thin that they may buckle before they fail due to yielding Chapter 12 particularly in aircraft applications. Consider for example a cantilever beam subject to end load Fig. 8.7 . Before buckling the state of stress at the neutral axis is pure shear as indicated on the volume element A in Fig. 8.7. After . buckling the state of stress is as indicated on volume element B in Fig. 8.7. A photo Langhaar 1942 of a similar beam with a buckled web is indicated in Fig. 8.8. After buckling of the web the shear in the beam is carried by diagonal tension block B Fig. 8.7 Bleich 1952 Timoshenko and Gere 1961 Kuhn 1956 . H To strengthen such beams transverse stiffeners are placed at each end and along the beam as indicated in Fig. 8.8. These stiffeners restrain relative motion between the longitudinal stiffeners so that the beam may develop resistance to the diagonal tension. In addition transverse stiffeners are located at sections where loads are applied to the beam. In this chapter we assume that the web thickness is sufficiently thick so that the shear flow does not cause web buckling. The calculation of the shear center location for beam cross sections similar to those shown in Fig. 8.6 is .