Standard method ASTM D6004 describes the test to measure the shear strength of adhesives used to bond resilient flooring and carpets to specific substrates (e.g carpet underlayments). It provides a quantitative basis for measuring and recording the shear strength of various adhesive and underlayment combinations. Shear loading is the most common cause of failure of such joints, hence the importance of measuring shear strength. In flooring applications, the applied load will vary depending on the traffic. Heavy traffic areas (such as in airports) will impose maximum flooring loads, while moderate traffic and loads may exist in office areas. Residential or hotel rooms are typical light traffic areas.
In ASTM D6004, three wooden underlayment pieces are prepared as specified and the adhesive is applied by using a trowel as per the manufacturer’s instructions. A section of each piece is kept free, as it needs to be gripped in the shearing fixture. Duck cloth (natural, untreated, #10, 14.73 oz.) representing the carpet material is stuck over the area of adhesive application on each wooden piece such that a small portion of cloth juts-out, to enable gripping by the shearing fixture. A 10 lb deadweight is placed on each specimen to ensure bond formation. The three adhesively bonded lap shear specimens, are then kept in a convection oven for the specified duration (upto two weeks) at 122 °F ± 2 °F. The samples are then subjected to 180° shear testing, which involves shearing the joint by pulling the underlayment and the duck cloth in opposite directions. The testing can be done on any universal testing machine, but a special shear fixture is needed for ASTM D6004, since the shear must be uniformly applied across the area of contact. The applied force should be ≥30 psi for specimens meant for heavy traffic, ≥ 20 psi for moderate traffic, and ≥ 12 psi for light traffic. The stress value at joint failure is recorded.
Video 01: Composite shear testing
For ASTM D6004, each underlayment sample will be 2 inches × 3 inches. The duck cloth can be of the same size, but with a portion jutting-out for gripping and pulling.
The ASTM D6004 adhesive shear strength is reported in pounds per square inch (psi).
Standard method ASTM D6004 describes the test to measure the shear strength of adhesives used to bond resilient flooring and carpets to specific substrates (e.g carpet underlayments).