Renault D41 1540 Rubber or Plastic Based Cellular Materials - Residual Deformation After Compression at Constant Deformation

The standard "Renault D41 1540 Cellular materials based on rubber or plastics - Residual deformation after compression under constant deformation" developed by the French automobile company Renault describes a method used to determine the residual deformation of cellular materials based on rubber or plastics under constant deformation. This method is not applicable to flexible cellular filling materials and parts made of cellular materials with self-forming skins, to which the test method described in the Renault D45 1046 standard applies.

In principle, this method consists of subjecting the sample to constant deformation at a certain temperature and for a certain time and then measuring the remaining deformation under certain time and temperature conditions.

Equipment used in this test method includes:

• Compression device: This device consists of two flat and parallel polished plates made of chrome or stainless steel, attached to the crosspieces of the traction machine, between which the test pieces can be compressed. These plates must be sufficiently rigid not to deform during the test. The machine plates must be parallel, their surfaces must be larger than the surface of the test piece used. The speed of the moving crosshead must be adjustable to a very low value (maximum 20 mm/min). The plates must be parallel and have a hole network of 20 mm plus/minus 0,1 mm in diameter, with a distance of 6 mm plus/minus 1 mm between the axes (test method described in the Renault D45 1394 standard).
• Compaction machine: This machine must be equipped with a recording device to draw the load-sink diagram.
• Thickness wedges that allow adjustment of the desired compression ratio.
• Thermostatic oven (adjusted to test temperature).
• Conditioning room: Conditioned at 23 degrees plus/minus 2 degrees temperature and 50 percent plus/minus 5 percent relative humidity.

The test pieces consist of rectangular parallelograms cut from the plate or piece, with sides varying between 20 mm and 25 mm and a thickness of at least 6 mm. The thickness of the sample must be appropriate to the direction in which the piece is compressed in service. The test is carried out on at least three test pieces. The casting skins of the plate or piece are retained. If only plates or pieces with a thickness of less than 6 mm are available, it is possible to work by stacking test pieces of the same size until a thickness of approximately 6 mm is reached. If the width of the sample is less than 20 mm, the test is carried out on a test piece with the same width as the piece.

In rubber-based materials, the time between the end of vulcanization and the beginning of the test must be at least 24 hours. Test tubes are kept in the enclosure for 24 hours. Measurements must be made in the enclosure. The duration and temperature of the test must be selected from the values ​​specified in the standard.

When starting the test, the initial thickness of the test piece is measured using a compression machine in accordance with the Renault D45 1394 standard test method. Here, the pressure values ​​defined in the table given in the standard are used.

The appropriate wedges are selected to obtain the desired compression ratio (usually 50 percent). The test specimen is placed between the plates of the pressure apparatus. Wedges are placed on both sides of the test piece. The bolts are tightened so that the plates hold the wedges. The assembly is placed in a thermostatic oven, set to the test temperature. At the end of the set time, the assembly is removed from the oven, the test piece is released within 2 minutes and allowed to cool on a non-metallic surface inside the enclosure for 24 hours plus/minus 2 hours. The thickness of the test piece is then measured after reworking using a compression machine in accordance with the Renault D45 1394 standard test method.

The residual deformation after compression is expressed as a percentage of the applied deformation according to the formula given in the standard. The average of the three values ​​obtained is obtained so that the relative deviation between them is not more than 15 percent. In case of a larger deviation, it is recommended to repeat the test. The results obtained for the three test tubes are averaged.

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