This practice provides instructions for modifying the long beam flexure test method, ASTM D7249/D7249M, to determine open-hole facesheet properties of sandwich constructions subjected to flexural loading. The proposed standard practice consists of subjecting a long beam of sandwich construction with a centrally located through-hole to flexural loading using a 4-point loading fixture. The resulting bending moment produces facesheet failure through the hole and the ultimate facesheet strength is calculated based on the gross cross-sectional area. While the hole causes a stress concentration and reduced net section, it is common aerospace practice to develop notched design allowable strengths based on gross section stress to account for various stress concentrations (fastener holes, free edges, flaws, damage, and so forth) not explicitly modeled in stress analyses.
composite materials; sandwich composites; sandwich construction; open-hole flexural strength; flexural testing; notch sensitivity
The proposed test method will be used to determine the open-hole (notched) strength of a composite sandwich panel under flexural loading. The notched strength properties of a sandwich construction will be used in material selection, product development, research and development activities, and establishing design allowables.
The title and scope are in draft form and are under development within this