ASTM D7766/D7766M-16

5.1 This practice provides supplemental instructions that allow Test Methods D6264/D6264M (for quasi-static indentation testing) and D7136/D7136M (for drop-weight impact testing) to determine damage resistance properties of 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 damage resistance properties of a sandwich panel is useful for product development and material selection.

5.2 Sandwich damage resistance testing can serve the following purposes:

5.3 The properties obtained using these practices can provide guidance in regard to the anticipated damage resistance capability of sandwich structures with similar materials, geometry, stacking sequence, and so forth. However, it must be understood that the damage resistance of a sandwich structure is highly dependent upon several factors including geometry, thickness, stiffness, mass, support conditions, and so forth.

5.4 The standard indenter and impactor geometries have blunt, hemispherical tips. Historically, these tip geometries have generated a larger amount of internal damage for a given amount of external damage, when compared with that observed for similar indentations or impacts using sharp tips. Alternative indenter and impactor geometries may be appropriate depending upon the damage resistance characteristics being examined. For example, the use of sharp tip geometries may be appropriate for certain facing penetration resistance assessments.

5.5 Some testing organizations may desire to use these practices in conjunction with a subsequent damage tolerance test method to assess the residual strength of specimens containing a specific damage state, such as a defined dent depth, damage geometry, damage location, and so forth. In this case, the testing organization should subject several specimens, or a large panel, to multiple indentations or impacts, or both, at various energy levels using these practices. A relationship between force or energy and the desired damage parameter can then be developed. Subsequent residual strength tests can then be performed using specimens damaged using an interpolated energy or force level that is expected to produce the desired damage state.

1.1 This practice provides instructions for modifying laminate quasi-static indentation and drop-weight impact test methods to determine damage resistance properties of sandwich constructions. 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, truss cores and fiber-reinforced cores).

1.2 This practice supplements Test Methods D6264/D6264M (for quasi-static indentation testing) and D7136/D7136M (for drop-weight impact testing) with provisions for testing sandwich specimens. Several important test specimen parameters (for example, facing thickness, core thickness and core density) are not mandated by this practice; however, repeatable results require that these parameters be specified and reported.

1.3 Three test procedures are provided. Procedures A and B correspond to D6264/D6264M test procedures for rigidlybacked and edge-supported test conditions, respectively. Procedure C corresponds to D7136/D7136M test procedures. All three procedures are suitable for imparting damage to a sandwich specimen in preparation for subsequent damage tolerance testing.

1.4 In general, Procedure A is considered to be the most suitable procedure for comparative damage resistance assessments, due to reduced influence of flexural stiffness and support fixture characteristics upon damage formation. However, the selection of a test procedure and associated support conditions should be done in consideration of the intended structural application, and as such Procedures B and C may be more appropriate for comparative purposes for some applications.

1.5 The 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 exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

1.6 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 and health practices and determine the applicability of regulatory limitations prior to use.