Methodology for exciting dynamic shear and moment failure in composite sandwich beams

The increasing use of composites in high performance structural applications subjected to dynamic loading drives the need for understanding basic material failure properties and structural response as a function of loading rate. Balsa core sandwich beams having woven carbon/vinylester composite facesheets were investigated in both shear and bending failure at quasi-static and dynamic loading speeds producing strain rates ranging from 10(-5) to 10(0) s(-1). Short sandwich beam tests show weak rate dependency, with a slight decreasing trend in the balsa core shear failure strain for increased strain rate. Wide scatter in core shear failure strain was observed due to the highly variable nature of the balsa material, as well as its heterogeneous tiled construction within the sandwich panel. Excitation of facesheet compressive failure in sandwich beams with weak core of 50.8 mm thickness required the use of 2.43 m long sandwich beams subject to high speed loading (10 m/s) in order to achieve 10(0) s(-1) strain rate. Facesheet compressive failure strain in the long beam specimens under dynamic loading was measured to be 10% higher than for quasi-static loading. Comparison of long sandwich beam bending results to shorter solid laminate bending strength measurements show a different trend in rate dependency, and thus it is recommended that full-depth sandwich beams (and panels) be used to characterize the failure of these types of sandwich structures.