In this study, the influence of the clamped-free beam specimen length on the measured fundamental vibration frequencies of flat sandwich beams is investigated. First, sandwich beams having flat galvanized steel faces, and a rigid foam core are produced, and clamped beam vibration tests are conducted on specimens having three different lengths. The experimental results obtained are compared with the numerical results obtained using a 1D finite element model. The results obtained show that the clamped beam vibration test yields satisfactory results, and the longer specimens yield more accurate results. Figure A. The experimental setupPurpose: The main purpose is to determine the influence of specimen length on the vibration test results.Theory and Methods: The experimental results obtained using a MEMS type accelerometer are compared with the numerical results obtained using a shear deformable beam finite element model. Results:The results obtained show that the numerical and experimental results are in good agreement, especially for longer specimens. Conclusion: (i)The numerical and experimental results obained are in better agreement for longer beam specimens. (ii) It is observed that the frequency ratio decreases with increasing specimen length. (iii) The material properties used in the numerical model are verified by the experimental results obtained in this study. (iv) It is shown that MEMS type accelerometers can be used to conduct simple vibration tests. (v) The results obtained show that the the not-perfect clamped end conditions cause deviations between the numerical and the experimentally obtained results.

In this study, a modified three rail shear test (or double shear test) procedure is described for the determination of the shear moduli and the shear strength values of rigid foamed materials and test results are presented for light extruded polystyrene, which is a typical core material used in sandwich construction. The main idea is to obtain a nearly uniform shear stress distribution in the shear test specimens by strengthening them against bending. First, using a finite element model, it is numerically shown that a nearly pure shear stress state may be obtained in the strengthened three rail shear test specimens. Then, it is shown that the finite element numerical results obtained for the strengthened specimens are in excellent agreement with the analytical results. Next, three rail shear tests are performed on bare and strengthened specimens and the experimental results obtained are presented in comparison with the analytical results. Also, clamped beam vibration and three-point bending tests are conducted to validate the shear modulus values obtained. The results obtained show that, the strengthened three rail shear test specimens yield more accurate results for both shear modulus, and strength comparing with the bare specimens.

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