BENDING BUCKLING TESTS OF SANDWICH CYLINDERS

Abstract

Abstract : Buckling tests were conducted on thin- and thick-walled sandwich cylinders under bending loads. Cylinders were constructed with cores weak in shear (cellular cellulose acetate, CCA) and cores strong in shear (end-grain balsa, EGB) to check the validity of theoretical procedures for predicting over-all buckling and wrinkling. The 1/8-in.-thick sandwich was considered to have the minimum thickness feasible. To study the wrinkling behavior of cylinders under bending loads, a 1/2-in.-thick sandwich was used. The cylinders had a 6-in. nominal radius and a 36-in. length. The cylinder-face material was 0.010-in. 24S-T3 aluminum alloy. To facilitate installation of the test specimens, 2-in.-wide hardwood blocks were bonded to both the inside and outside faces at each end of the cylinder. Data are given for the shear modulus, elastic-compressive modulus, and failing loads. The experimental failing load under bending averaged 32% higher than the theoretical value of Wang and Sullivan (TIP U20334) for the 1/8-in. CCA cylinders. The experimental failing load under axial compression averaged approximately 2% higher than the theoretical value of Teichmann, Wang, and Gerard (J. of the Aeronaut. Sci. 18, no. 6:338-406, 1951) for the 1/8-in. CCA cylinders, indicating excellent agreement. In bending, the 32% higher experimental value was in agreement with the fact that the thin-walled EGB cylinders were not even as strong as the CCA cylinders was difficult to reconcile with the core properties. The experimental values of maximum failing stress were considerably below the predicted values for the thick-walled cylinders. The predicted wavelengths were somewhat less than the observed values.