Indentation Hardness
This is one of the most current characteristics to be tested on finished foam parts such as seats and mattresses. Formed parts are normally tested on an adapted counterpart with holes. The standard DIN 53459-1 is generally used as a reference for testing of finished parts.
The Zwick C-Frame machine is specially designed for testing of larger foam parts. It includes a large support surface, so that mattresses can easily be moved into the test position. If small parts are to be tested, the support tables can be folded down.
The modern control electronic testControl provides adaptive travel and load control functions which are needed especially for hysteresis tests and for the determination of the “comfort value” as prescribed in Volkswagen PV 3410.
Testing of block foams is specified in ISO 2439 and ASTM D 3574. The specimen size of 380x380 mm allows the usage of standard Zwick testing machines. These machines come with a frame-stiffness-compensation function, able to ensure the accuracy of the indentation depth measurement.
The software testXpert® includes a complete standard program library covering all relevant ISO, ASTM and DIN standards as well as all current test methods deployed by the Volkswagen Group, DaimlerChrysler, BMW, GM, the PSA-Group, Ford and other key manufacturers.
Compression Characteristics
This test describes the compression over the whole surface of the specimen. The specimens are square sized with an edge length of 50 or 100 mm.
The test normally consists of 3 pre-cycles, followed by one measurement cycle in which the results are to be determined. Variants of this method are detailed in the individual company specifications.
With a balance connected to the PC of the testing machine, the task of measuring the apparent density can be integrated in this workflow.
Tensile Characteristics, Tear Strength
The specimens are normally cut from the finished part. For this, the Zwick cutting presses and dies with integrated ejector are particularly well adapted.
Grips in mechanical or pneumatic versions are available for these tests.
For the measurement of elongation at break, Zwick supplies long stroke extensometers in both a mechanical and optical version.
Constant Load Pounding Test
This test, specified in ISO 3385 as well as in several In-house-Standards, serves to determine the long-term stability against mechanical fatigue of a foam. The test simulates for example the charges a seat is submitted to during its use.
In the first Step, the indentation hardness and the parts thickness of a new part are to be measured. Then, in the second step, the foam is submitted to several ten-thousand load pounding cycles. The last step is to measure again the indentation hardness and thickness. The results are hardness loss and thickness.loss after cycling.
Zwick supplies a specific electro mechanic testing machine, designed to work at the high speeds needed for this type of test. This testing machine can be used for both, the indentation hardness test, as well as the cyclic load pounding.
The test is used to determine the hardness and thickness loss after submitting a foam to several ten-thousand load application cycles. Static Zwick testing machines measure hardness and thickness before and after cycling. For the cycling itself, a specific machine type is available.
Rebound Resilience
ISO 8307 sets out the guidelines for this test. Zwick supplies an adapted apparatus, consisting of a transparent vertical tube, a steel ball with a release mechanism, and a light barrier to measure the rebound speed.
