Scope:

ASTM D3576 yields an apparent cell size because it assumes no demonstrable change in the average cell size from edge to edge or top to bottom and that the cell size is constant. Distribution is typical around the average cell size. There could be significant differences in either the cell size distribution or average cell size. Before beginning this test technique, the strategy should be made according to the material’s specifications, preparations, conditioning, or dimensioning of test specimens. The material’s specifications must be taken into consideration.

Procedure:

Procedure A: In ASTM D3576, a specimen is cut 50 by 50 mm by thickness (2 by 2 in.) from the sample. The specimen is prepared by cutting a thin slice of foam. The thin-sliced foam specimen is inserted into the cell size slide assembly. The zero on the grid line should be positioned at the top of the area to be measured. The slide assembly is inserted into the projector. The projector on the wall or screen is focused so that a sharp image shadow-graph is obtained.

Procedure B: A 25-mm section is cut across the width of the sample. The length, width, and direction of the specimen are identified. For samples with an apparent cell size of 0.3 mm or smaller, the cell size is measured using a scope with a 10-mm calibrated reference line. For samples with an apparent cell size of 1.0 mm, a handheld eyepiece with a calibrated scale of 30-mm length is used. For ASTM D3576 testing, the number of cell walls is counted, which intersects the reference line. The average cell chord length is determined and divided by the length of the reference line.

Specimen size:

In ASTM D3576, a cutting blade apparatus is employed which is capable of slicing thin specimens (0.02 mm) for cell size viewing.

Data:

d = t(1.623) 

where: d is cell size, mm, and t is average cell chord length, mm

Result:

For ASTM D3576 testing, the average cell size in millimeters for each direction is measured. For those foams having a cell size larger than 1.0 mm, the reported value is nearest to 0.1 mm. For those smaller than 1.0 mm, the reported value is nearest to 0.01 m.

Conclusion:

ASTM D3576 yields an apparent cell size because it assumes no demonstrable change in the average cell size from edge to edge or top to bottom and that the cell size is constant.