This paper presents the results of analysis and tests conducted on the static bending strength of carbon fiber filament-wound (F.W.) cylindrical pipes and also the results of tests on fatigue flexural strength of the same F.W. pipes. The relation between the winding angles of F.W. pipes and their fracture strengths under pure bending is investigated. The analytical method of the fracture strength of F.W. pipe is as follows; the threedimensional stress components referring to the plane including fibers are analysed, taking account of the elastic failure prior to the overall fracture and then are compared with the fundamental strengths corresponding to the four kinds of fracture mechanisms of unidirectional fiber reinforced composites. As the results of the analysis, the fracture modes under pure bending of the helical winding pipe are determined in relation to its winding angle; 1) Winding angle α=0°∼10°, Fracture caused by compression stress in the fiber direction. 2) Winding angle α=15°∼30°, Fracture caused by tensile stress normal to fibers. 3) Winding angle α=35°∼50°, Fracture caused by shear stress. 4) Winding angle α=55°∼90°, Fracture caused by tensile stress normal to fibers. The static and fatigue flexural tests are done on carbon fiber F.W. pipes in which helical winding angles are α=15°, 25°, 35°, 45°. By using a newly-devised chuck, the fatigue test of the F.W. cylindrical pipe was carried out successfully. The bending fracture test results on the fracture strength and fracture modes coincide with the analytical ones. The flexural fatigue test results which showed that the ratio of the flexural fatigue strength at 10⁷ cycles to the static bending strength are about 0.3 for the helical winding angle α=15°, 25°, and about 0.2 for α=35°, 45°.

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The investigation on the deflection of sandwich beams is of prime importance for the reasonable evaluation of the structural efficiency. The multi-layer built-up theory in which a sandwich beam is assumed as a laminated beam with three layers can be applied satisfactorily to the analysis of sandwich type beams used for house building components. Comparing the built-up theory with Hoff's theory and the conventional beam theory, the analytical results due to the multi-layer built-up theory were found to agree well with the experimental results obtained by three-point bending tests for various sandwich panels practically used for house building members. The maximum central deflection of simply supported sandwich beam can be generally predicted by two kinds of nondimensional parameters. The maximum deviation of the experimental deflections from the theoretical ones was within ±15 percent.

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