This article discusses how to perform a polyurethane foam tear strength test on a universal testing machine (polyolefin foams are tested similarly). Complete instructions for a foam tear strength test can be found in ASTM D3574 Test F which applies to slab, bonded, and molded flexible cellular urethane foams. There are many tests in this specification including tests for density, ball rebound, airflow, etc. However, the most common tests in the specification are the mechanical tests that can be performed on a universal testing machine such as indentation force deflection, compression force deflection and tensile strength. This article discusses Test F, the foam tear resistance test.
The purpose of performing the tear test on polyurethane foam is to measure the peak force during a foam tear. This provides a measure of the material’s resistance to tearing. The specification does not call for this, but it is common to measure the average load across an extension range. The average calculation is built into our testing systems, all you need to do is specify two displacement points that you want to average between. For example, if you tear your sample four inches, you may want to average the load from 1″ to 3″ to eliminate the starting or ending forces that may not be consistent with the normal tear strength.
The foam tear strength test is similar to testing other polymers, but due to the thickness, gripping the foam is sometimes a challenge. The specimen is usually 1″ wide by 1″ thick with 1/2″ of the split sample being held by each grip. Foams do not typically have high tear strengths, so low force (1kN) capacity grips are fine. Therefore the most commonly used grips are wide opening (at least 20mm) 1kN capacity vise or pneumatic grips.
With the right equipment and test procedure, the test is actually quite easy. A video of a foam tear strength test is shown here: