Sandwich Flexural Stiffness ASTM D7249

Four Point Flexure Test for Flat Sandwich Constructions

Flat sandwich constructions, consisting of two facing materials bonded to a core material, are widely used in a range of industries, including aerospace, automotive, and construction. The mechanical properties of sandwich constructions, including sandwich flexural stiffness, core shear strength, shear modulus, facing compressive strength, and facing tensile strength, can be determined through a four-point flexure test.

Test Procedure

Before testing, bonded strain gauges may be applied to the specimens, and the specimens may be conditioned if necessary. The specimens are then installed into the four-point test fixture of the Universal Test Machine, and the fixture and specimen are aligned. The specimen should be perpendicular to the loading bars, with the bars perpendicular to the plane of the specimen facing. A compressive force is initiated until the specimen fails, and the four-point loading configuration is standard.

Specimen Size

Five specimens are tested at thickness, with standard specimens being rectangular, 75 mm (3.0 inches) in width and 600 mm (24.0 inches) in length.

Data

From the four-point flexure test results, various calculations can be made, including force-displacement behavior, facing ultimate stress, ultimate facing stress, effective compressive and tensile chord modulus, effective sandwich flexural stiffness, and failure type/mode.

Core materials applicable to this test include continuous materials, such as foams, and discontinuous bonding surfaces, such as honeycomb. The test is widely used across industries to determine the mechanical properties of sandwich constructions and ensure they meet specific performance standards.