【国外标准】 Standard Practice for Open-Hole Flexural Strength of Sandwich Constructions

5.1 This practice provides supplemental instructions that allow the use of Test Method D7249/D7249M to determine the open-hole (notched) strength of the sandwich panel facesheets for structural design allowables, material specifications, and research and development. Due to the curvature of the flexural test specimen when loaded, the open-hole sandwich facesheet strength from this test may not be equivalent to the open-hole sandwich facesheet strength of sandwich structures subjected to pure edgewise (in-plane) tension or compression.5.2 Factors that influence the notched facesheet strength and shall therefore be reported include the following: facesheet material, core material, adhesive material, methods of material fabrication, facesheet stacking sequence and overall thickness, core geometry (cell size), core density, adhesive thickness, specimen geometry (including hole diameter, diameter-to-thickness ratio, and width-to-diameter ratio), specimen preparation (especially of the hole), specimen conditioning, environment of testing, specimen alignment, loading procedure, speed of testing, facesheet void content, adhesive void content, and facesheet volume percent reinforcement. Further, notched facesheet strength may be different between precured/bonded and co-cured facesheets of the same material.1.1 This practice provides instructions for modifying the long beam flexure test method to determine open-hole facesheet properties of flat sandwich constructions subjected to flexure in such a manner that the applied moments produce curvature of the sandwich facesheet planes and result in compressive and tensile forces in the facesheets. Permissible core material forms include those with continuous bonding surfaces (such as balsa wood and foams) as well as those with discontinuous bonding surfaces (such as honeycomb). This practice supplements Test Method D7249/D7249M with provisions for testing specimens that contain a centrally located through-hole.1.2 Units—The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, to enforce conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.1.2.1 Within the text, the inch-pound units are shown in brackets.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.