GB/T 18941-2003Flexible cellular polymeric materials -- Determination of fatigue constant-load pounding (English PDF)

1 Scope

This Standard stipulates the determination methods for the thickness reduction value and the hardness reduction value of flexible cellular materials that are used in interior decoration. This test method provides/ evaluates the means for the functional performance of the latex-type and polymeric acid-type flexible cellular materials for bearing decoration. The measured thickness reduction value and hardness reduction value are related to the possible loss in use; but they are not necessarily the same.

This Standard applies to standard-size samples that are taken from finished materials, and also to molded parts.

2 Normative references

The following standards contain provisions which, through reference in this text, constitute provisions of this Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below.

GB/T 12825, Polymeric materials, cellular flexible - Determination of hardness by indentation technique

3 Principle

Through an indenter whose area smaller than the sample, repeatedly indent into the sample; reach the maximum load in each impact cycle within the specified range.

4 Instruments

A reciprocating impact testing machine that has the following components.

4.1 A platform that can fully support the sample, and has a hole, whose diameter is about 6 mm and spacing is about 20, that is suitable for ventilation, so that air can escape under the sample.

4.2 An indenter that has a diameter of 250 mm ± 1 mm and has a rounded corner whose radius is 25 mm ± 1 mm at its lower edge. It is installed on a device that can apply a maximum force of 750 N ± 20 N in a load cycle. The indenter shall be firmly installed on its guide rod; its surface shall be smooth and shall not be polished. Through a curved roller or other suitable mechanical device, the testing machine shall be able to bear the weight of the platen (4.1) or the indenter support for advance and return movement; one impact to the other from the vertical direction at a rate of (70 ± 5) times per minute; the impact amplitude shall be adjustable.

4.3 An indenter support. When the support and the platform are close together, this indentation force can be transmitted through it except for the impact point.

At this time, all the indentation force is borne by the sample; the indenter shall be freely lifted by the support, so as prevent the test piece from being overloaded. During the entire period when a force is applied to the sample through the indenter, at any impact point, measures shall be taken to use it to control the impact time; this time is not greater than 25% of the duration of each impact cycle.

4.4 A force measuring device. It can be used to measure the load that is applied to the sample through the indenter; a suitable method is to fix the platform on the load sensor.

Note: In the case of manual calibration, through the axis that is vertical to the guide rod on the platform that bear the weight of the sample, the adjustment of the vertical position of the indenter whose indenter is fixed at the lower end of the indenter opposite to the platform can control the length of time at which any impact point is subjected to full indentation force by the sample. The recommended method for reliable automatic calibration is shown in Figure 1, so that the length of time during which the sample is subjected to the indenter can be controlled by the valve opening time.

40% ± 1% according to the provisions of 7.2 (Method A) in GB/T 12825; it shall include the pre-indentation procedure that is specified in 7.1 of the national standard; besides, the 40% ± 1% indentation shall be calculated by the initial thickness measurement d 1 .

For the two remaining samples, repeat the above steps from the initial thickness to the hardness index measurement at the beginning of this section.

7 Result expression