Abstract
Since the establishment of the bending theory of sandwich beams by N.J. Hoff or E. Reissner in 1940's, various investigations on sandwich constructions have been reported. A simple “mechanics of materials” approaches on sandwich constructions is often based on the assumption that the bending rigidity of the both faces is negligible and also the shear rigidity of the core material is infinite. This type of theory is called “Compositebeam theory” (“I-beam theory”). But, the various types of sandwich panels are now being applied in the building industry, and some of the panels are composed of relatively thick faces and such soft core materials as foamed plastics. It is necessary to consider therefore that the bending rigidity of faces are large and shear rigidity of core is very low. Consequently it seems to be necessary to introduce the “multi-layer built-up theory” -taking into consideration of displacement among the layers in the total section of beam corresponding to the shear moduli of core materials as being adopted in the field of wooden building construction. In this context, this paper deals with the defference of stress distribution between two types of sandwich beam of photoelastic materials-ratio of elastic moduli between face and core : k=Ef/Ec is 6.6 and 530-under three point bending, and then the applicability of multi-layer built-up theory is investigated. It is clear that the strength and rigidity of a sandwich beam depend upon the coupling moment caused by the inverse axial force in the two facings. The effect of the coupling moment is defined as the ratio of the coupling moment (Ms) to the total sectional moment (Mt) : α=Ms/Mt. If the “k” value and the proportional of a sandwich composite are given, the “α” can be defined as an index of the sandwich efficiency.
