The standard “PSA D41 1536 Cardboard - Bending of pressed wood”, developed by the French automobile company Renault, describes the bending properties of samples cut from cardboard and wood panels (fibers, pressed and plywood particles) and composite materials based on cardboard or wood with a thickness of one to five millimeters. This method complies with the standard “ISO 178 Plastics - Determination of bending properties”.
This test method consists in principle of placing a parallelepiped barrel on two supports and distorting it by applying a punch moving at a constant speed at equal distances from the supports. This method allows one or more of the following properties to be measured:
The equipment used in these tests includes:
The distance between the supports should be equal to 50 mm.
Test samples should be representative of the size to be characterized. To ensure this representation, it is necessary to find the basic characteristics of the population under study. Selection criteria for test samples should be stated in the test report in accordance with the PSA A10 0156 standard. In case of doubt about sampling, PSA should be contacted for the rules to be followed.
When preparing test specimens, at least four specimens are required for the tests. Two rectangular specimens with the following dimensions are collected using a cutting tool: length 80 mm plus/minus 1 mm, width 20 mm plus/minus 1 mm. In the case of materials anisotropic in the thickness direction (e.g. composite materials), the test specimens are tested such that the bending force to which they are subjected is in the same direction as that which would practically be applied to the part from which the specimens are collected. In the case of anisotropic materials in plan, the specimens shall be collected according to the principal directions of anisotropy.
The samples are conditioned in the room for at least 24 hours. In very hygroscopic materials or materials that establish equilibrium with the ambient humidity slowly (such as vegetable fibers, cardboards), the conditioning period may extend up to a week.
The tests are carried out in a conditioned room. Using a slide caliper, a width of 0,1 mm is measured at the centre of the specimen. The specimen is placed on supports according to the figure in the annex of the standard. The specimen is loaded halfway between supports without applying restraint. The load-deflection curve is recorded and the following values are observed: the breaking load if the specimen breaks, the maximum load reached if it does not break and the load corresponding to a deflection of 1 mm from the beginning of the curve.
For each sample, the load corresponding to a full 20 mm width is calculated according to the formula given in the standard. In addition, the arithmetic mean of the maximum loads in bending is calculated. For each sample, the load is determined. The arithmetic mean of the loads corresponding to a one millimeter deviation is calculated.
The format and minimum contents of the test report are defined in the PSA A10 0156 standard. The test report must include:
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