ASTM D7249Sandwich Flexural Stiffness

Scope:

Sandwich flexural test by ASTM D7249 measures the strength (tensile and compressive), stiffness, and shear modulus of a variety of materials. The core materials include multiple surfaces for different applications like continuous (foam) and non-continuous (honeycomb) materials.

Flexural tests are generally used to determine the flexural strength or modulus of the material. It is analogous to the tensile strength, however much more affordable with slightly different results. A sandwich flexural test comprises four-point flexure of flat sandwich constructions. The main aim is to produce the curvature of the sandwich plane.

Test Procedure:

ASTM D7249 test specimens are fitted with bonded strain gauges (if applicable). The specimens are then placed in the Universal Test Machine with a 4-point test fixture. The specimen is perpendicularly aligned to the loading bars, and the loading bars are perpendicular to the plane of the specimen facing. A compressive force is started and it keeps going until it collapses. The basic loading configuration is four points.

Specimen size:

Five specimens are measured for their thicknesses. Standard specimens are rectangular, with a width of 75 mm (3.0 inches) and a length of 600 mm (24.0 inches).

Data:

The following measurements can be made using 4-point flexure results

Force vs Displacement
Ultimate stress limit
Facing stress limit
Effective tensile chord and compressive modulus
Sandwich flexural stiffness
Failure type

Conclusion:

Hence, ASTM D7249 is a standard test method that faces properties of sandwich constructions by long beam flexure, so called four point flexure.