An adhesive bonded joint when subjected to shear, either in compression or tension, must resist sliding forces acting on the adhesive and adherend components. The ASTM D3931 standard method covers the procedure to test the shear strength of gap-filling adhesives in wood-to-wood joints under a compressive load, for comparative purposes, as well as for structural design and quality control. A gap-filling adhesive creates and maintains an adhesive bond between two surfaces in which a gap must be bridged. Compressive shear testing involves the splitting apart of a specimen by applying compressive forces from opposite sides in a parallel plane. In this way, the material is stressed in a sliding motion. The ASTM D3931 standard prescribes the specified thicknesses of the bondline and conditions of specimen preparation, conditioning, and loading in compression. This test method is intended as an evaluation of gap-filling adhesives such as those used to bond plywood to lumber, lumber to lumber, and other similar materials in building constructions. The test method may also be used for testing the shear properties of wood species other than those specified in this standard.
The testing machine needs to have a loading capability of about 15000 lbs in compression, to be applied at the uniform specified rate recommended in ASTM D3931. This is done by a suitable fixture attached by threaded coupling, that transfers the load onto the bonded specimen. The loading anvil has a self-alignment seat to ensure uniform lateral distribution of the load.
Video 01: ASTM D3931 Compression loading shear fixture with self-adjusting bearing
A typical specimen for ASTM D3931 comprise two pieces of wood, each 2 inch × 2 inch × 1.5 inch thick, bonded together by the test adhesive.
The ASTM D3931 adhesive shear strength is reported in pounds per square inch (psi).
The ASTM D3931 standard method covers the procedure to test the shear strength of gap-filling adhesives in wood-to-wood joints under a compressive load for comparative purposes, as well as for structural design and quality control.