Sandwich Flexural Stiffness by ASTM D7249

Facing properties of sandwich constructions by long beam flexure, so called four point flexure.

Four point flexure of flat sandwich constructions to produce curvature of the sandwich facing plane. The test provides information on sandwich flexural stiffness, core shear strength, shear modulus, facing compressive strength and facing tensile strength. Core materials applicable include continuous (foams) and discontinuous bonding surfaces (honeycomb).

Test procedure: Bonded strain gages are applied to the specimens (if applicable). Specimens are conditioned (if required). The specimens are installed into the 4-point test fixture of the Universal Test Machine. The fixture and specimen are aligned – specimen perpendicular to the loading bars with the bars perpendicular to the plane of the specimen facing. Initiate a compressive force until failure. The four-point loading configuration is standard.

Specimen size: Five specimens tested at thickness. Standard specimens are rectangular 75 mm [3.0 inch] width x 600 mm [24.0 inch] long.

Data: From 4-point flexure results the following calculations can be made:

1. Force-Displacement Behavior
2. Facing Ultimate Stress
3. Ultimate Facing Stress
4. Effective Compressive and Tensile Chord Modulus
5. Effective Sandwich Flexural Stiffness
6. Failure type/mode

**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. Standards may be obtained from appropriate standard authorities.