ASTM D8388/D8388M-22

5.1This practice provides supplemental instructions that allow the use of Test Method D7249/D7249M to determine residual compressive or tensile strength properties of damaged sandwich constructions. Susceptibility to damage from concentrated out-of-plane forces is one of the major design concerns of many structures made using sandwich constructions. Knowledge of the residual strength properties of a sandwich panel is useful for product development, establishing design allowables, and material selection.

5.2The residual compressive or tensile strength data obtained using this test practice is most commonly used in material selection, research and development activities, and establishing design allowables.

5.3The properties obtained using this test practice can provide guidance in regard to the anticipated compressive or tensile residual strength capability of sandwich constructions of similar facesheet and core material, adhesive, facesheet and core thickness, facesheet stacking sequence, and so forth. However, it must be understood that the residual strength of sandwich constructions is highly dependent upon several factors including geometry, thickness, stiffness, support conditions, and so forth. Significant differences in the relationships between the damage state and the residual compressive or tensile strength can result due to differences in these parameters.

5.4The compression strength from this test may not be equivalent to the compression strength of sandwich structures subjected to pure edgewise (in-plane) compression.

5.5The reporting section requires items that tend to influence residual strength to be reported; these include the following: facesheet and core materials, core density, cell size and wall thickness if applicable, film adhesive, methods of material fabrication, accuracy of lay-up orientation, facesheet stacking sequence and thickness, core thickness, overall specimen thickness, specimen geometry, specimen preparation, specimen conditioning, environment of testing, type, size and location of damage (including method of non-destructive inspection), specimen/fixture alignment, time at temperature, and speed of testing.

1.1This practice provides instructions for modifying the long beam flexure test method to determine the tensile or compressive residual strength properties of sandwich constructions that have been subjected to quasi-static indentation or drop-weight impact per Practice D7766/D7766M. The tensile or compressive strength result is determined by which facesheet contains the damage, either the loaded-span or support-span facesheet, based on how the specimen is positioned in the fixture.

1.2This practice supplements Test Method D7249/D7249M with provisions for testing damaged sandwich specimens. Several important test specimen parameters (for example, facesheet thickness, core thickness and core density) are not mandated by this practice; however, repeatable results require that these parameters be specified and reported.

1.3UnitsThe values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used independently of the other, and values from the two systems shall not be combined.

1.4This 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.

1.5This 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.