Posted by Andrew DeWolfe on Fri, Apr 23, 2010 @ 07:37 AM
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:
We have a lot of information on polyurethane foam testing according to ASTM D3574. Click the links below to learn more:
1. General Equipment requirements for ASTM D3574
2. Indentation Force Deflection Test (IFD)
3. Tensile Strength
Click here if you would like to ask an engineer a question, or click here if you would like a quote on a system.
ASTM D3574 tear strength test report from ADMET's MTESTQuattro software
ASTM D3574 tear strength test setup on an ADMET eXpert 7601
ASTM D3574 tear strength sample
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Posted by Andrew DeWolfe on Thu, Apr 22, 2010 @ 09:40 AM
This article discusses foam tensile strength testing. A foam tensile strength test can be found in ASTM D3574 Test E 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 tear resistance. This article discusses Test E, the foam tension test.
The purpose of performing the tension test on polyurethane foam is to measure the tensile strength and elongation. The tensile strength is obtained by simply dividing the peak load observed during the test by the cross-sectional area of the sample.
The foam tensile strength test is similar to testing other polymers, but gripping and measuring extension require a bit more care. The minimum foam thickness during testing is 12.5mm and it is common to measure thicker samples. Foams do not typically have high tensile strengths, so low force (1kN) capacity grips are fine. Therefore the best grips to use are wide opening (at least 20mm) 1kN capacity vise or pneumatic grips.
Measuring extension is tricky. Because the sample is "dogbone" shaped, using grip separation to measure elongation is less than ideal due to the error caused by the non-uniform specimen width. Despite this, it is still common to measure elongation using grip separation. The reason for this is because contact extensometers clip on the foam and this distorts the sample thickness and causes premature sample breakage. Non contact optical extensometers work well but the high cost (often times more expensive than the rest of the testing machine) makes them unpractical.
With the right equipment, the test is actually quite easy. A video of a foam tensile strength test is shown here:
We have a lot of information on polyurethane foam testing according to ASTM D3574. Click the links below to learn more:
1. General Equipment requirements for ASTM D3574
2. Indentation Force Deflection Test (IFD)
3. Tear Strength
Click here if you would like to ask an engineer a question, or click here if you would like a quote on a system.
Notice how the extensometer distorts the foam too much
Foam "dogbone" shape specimen
Tensile test setup
Test report from MTESTQuattro software
Click on these links for more information...
More Testing News
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ADMET 1-800-667-3220 www.ADMET.com