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ISO 7798-2017 pdf free download
ISO 7798-2017 pdf free download.Cross-country skis — Determination of fatigue indexes — Cyclic loading test
Skis defond — Determination des indices defatigue — Essni en flexion aiternee.
fatigue Index Kh
percentage change of bottom camber height of the ski after cyclical loading and recovery time
The ski is subjected to cyclic loading and recovery. The fatigue indexes are determined by calculation of the percentage permanent change in bottom camber height.
5.1 Cyclic bending machine.
The cyclic bending machine shall be constructed essentially as shown in Figure t The machine has two supports which are vertically and horizontally adjustable. The support rolls shall have a diameter of approximately 5 cm. The supports shall have spring loaded clamping rolls In order to prevent lifting of the ski.
The driving mechanism consists of a disk fly wheel with adjustable crank pin, a connecting rod and a push rod with clamping fixture. The disk fly wheel shall have sufficient mass and driving power to effect a smooth sinusoidal flexing. The distance between crank pin and rotation axis shall be adjustable in order to be able to adjust the proper stroke length with respect to the spring constant of the deflected part of the ski (see Figure 3).
The frequency of the stroke shall be between 2 lIz and 3 Hz. The clamping fixture shall have a pitting joint and jaws with elastic rubber layers, as shown in Figure 2. in order to avoid stress concentration at the clamp.
Dimensions of the rubber layer shall be as follows.
— Thickness: (4 ± 1) mm
— Width: 40 mm
— Hardness: (95 ± 5) Shore A
In addition, a counter shall be fixed to the push rod in order to record the number of cycles.
5.2 Measuring device for bottom camber height.
For measuring the weighted bottom camber, a flat surface plate and a dial indicator with indicator holder shall be used.
6 Test specimens
The test shall be carried out on five skis of the same model-size.
7 Temperatures for conditioning and testing
The fatigue properties of the ski described in this document can be affected by the test temperature to a greater or lesser extent depending on the particular material configuration of the ski. Therefore, two versions of test procedure with different test temperatures are specified:
— version A. standard laboratory test: (+20 ± 2) °C;
— version B, cold chamber test: (—20 ± 2) °C.
All measurements shall be carried out on a ski conditioned at the test temperature for at least 2 h.
8 Test procedure
8.1 Measurement of original weighted bottom camber, hB
Measure the height of the original bottom camber, h8, after conditioning and prior to the bending by cyclic loading. Mark the measurement point on the top surface of the ski. Press the ski against the flat surface plate. Place the dial indicator at the measurement point on the top surface of the ski and set to zero. Remove the flattening load, and read the bottom camber height from the dial indicator to an accuracy of ±0,03 mm.ISO 7798-2017 pdf free download.
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