Lapped Block Shear Strength of Adhesive Bonds (ASTM D905)

Model No. WTF-BA (Stainless Steel)

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Fig. 1: Assembled fixture without specimen installed

This ASTM D905 Lapped Block Shear Test Method (Reference 1) was developed primarily for determining the adhesive bond strength of wood and similar materials. However, it can be used to determine the adhesive bond shear strength between other adherends as well.

Although the test fixture configuration is quite different, the basic testing principle is similar to that of the ASTM D4501 Block-Shear Test Method (Reference 2) described in Section I-4. A compressive rather than a tensile loading is applied to generate the shear stress, and two rectangular blocks of equal size, staggered ¼ in., are bonded together, rather than one small square block being bonded in the center of a large square block. But a guillotine-type loading is applied in both cases to shear off one block from the other. The ASTM D905 test fixture is shown in the following photograph.

The standard specimen consists of two blocks, each 1.75 in. high and 2 in. wide, bonded together with a ¼ in. vertical stagger (a ¼ in. step between blocks in the vertical direction).

The upper block of the bonded specimen is placed on the base of the fixture and the guillotine assembly (shown removed in the photograph below) is lowered onto the top of the lower block. The large pin shown at the top of the guillotine assembly is a handle, for ease in raising and lowering the assembly. The loading surface of the guillotine assembly is free to rotate relative to the remainder of the assembly, to accommodate any non-parallelism of the top and bottom surfaces of the bonded specimen. The small pin in the cutout arc holds the two parts of the assembly together.

The shear strength of the adhesive is simply calculated as the force required to shear the two blocks apart divided by the bond area between the blocks.

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Fig. 2: Test fixture with assembled guillotine blade (left) removed

Source of Additional Information:

1) ASTM Standard D905-03 (2003), “Standard Test Method for Strength Properties of Adhesive Bonds in Shear by Compression Loading,” American Society for Testing and Materials, West Conshohocken, Pennsylvania (first published in 1947).

 

2) ASTM Standard D4501-01 (2001), “Standard Test Method for Shear Strength of Adhesive Bonds Between Rigid Substrates by the Block-Shear Method,” American Society for Testing and Materials, West Conshohocken, Pennsylvania (first published in 1985).