ISO 1798 investigates the
tensile strength and deformation properties of flexible cellular polymeric materials when extended at a constant rate of displacement until failure.
In principle, the test specimen is supported between two clamping jaws and fitted with an extensometer for a given gauge length. The specimen is pulled apart until the specimen fractures at a constant rate of displacement. The load and strain is recorded during the test, and is used for determine the tensile strength and elongation at break. To record the test it is important to have a high speed intelligent test data logging rate. This is the transfer rate to the PC of 100Hz or more to capture and record all the data.
For this test, we used pneumatic action grips with rubber coated jaw faces for clamping of the material fitted to a tensile testing machine. While manual action grips will work, many of our users prefer the pneumatic action grips for ease of use, productivity, and better repeatability. Pneumatic action grips allow you to set a clamping pressure, while the manually operated grips depend on the operator's strength (which may not be so repeatable). We find that gripping pressure and specimen alignment are very important in these tests. Too much gripping pressure can produce premature breaks, while not enough gripping pressure can lead to specimen slippage or breaks at or near the jaws. These grips are usually fitted to single-column or dual-column table-top design.
Two methods of strain measurement can be adopted. A contacting long travel extensometer is attached to the test specimen. This incorporate a mechanism suitable for determining the relative change in length of the appropriate part of the test specimen. Or a non-contacting video extensometer can be used as a viewing mechanism suitable for determining the relative change in length of the appropriate part of the test specimen.
We suggest using a materials testing software, such as Bluehill® 2, to input specimen details, set the desired test control, automatically calculate the desired results and statistics, and produce a test report all in accordance with the standard.
We suggest reviewing ISO 1798 to fully understand the test fixture and results requirements.