BS ISO 9538:2017 pdf download.Aerospace series – Hydraulic tubing joints and fittings – Planar flexure test.
This document specifies a flexure test procedure for reconnectable and permanent hydraulic tube joints. This procedure is intended for conducting flexure tests on fittings with high-strength hydraulic tubes made of corrosion-resisting steel, titanium and aluminium for use on commercial and military aircraft.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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4 Device for flexure test
The test device should be similar to that shown in Eiguzcj.. It shall consist of a vibrator, a manifold to receive at least six test specimens, and a hydraulic supply unit capable of constantly maintaining the static operating pressure during testing, including monitors inducing the shutdown of the system in the event of pressure drop.
5 Flexure test specimens
The test specimens shall consist of the tube fitting to be tested (for example straight union), the test
tube and the fitting to seal the tube.
6 Stress determination
The maximum permissible flexure fatigue stress of the test tubing is determined for the combined stress level.
The combined stress, a, is composed of the tensile stress, resulting from the internal pressure and the wall thickness of the tube, and the bending stress, b.
Strain gauges shall be used to demonstrate the bending stress, and the deflection can be checked during testing by means of angle gauges.
A typical stress cycle is illustrated in Figure 3.
The bending stress, i,, is determined by the maximum permissible flexure fatigue stress of the test tube and shall be specified for each application.
7 Procedure
7.1 Instrumentation and strain gauges
A strain gauge shall be mounted on each test specimen.
They shall be mounted as shown in Figure 4. Their location should be as follows.
a) For tube sizes to DN 16: approximately 4 mm from the attachment- point tube to ftting.
b) For tube sizes to DN 20 and above: approximately 8 mm from the attachment- point tube to ftting.
7.2 Frequency
7.2.1 Test frequency
It is recommended to perform the test at approximately 100 Hz.
7.2.2 Natural frequency of the specimens
To minimize the power input of the vibrator used, the natural frequency of the specimens should be within the frequency range 110 Hz to 120 Hz.
The test frequency shall be approximately 10 % to 20 % below the natural frequency of the specimens to prevent their resonance range from being reached.
7.2.3 Determination of tube length
Screw the fully assembled tube, fitted with strain gauges, into the header in order to determine the tube length required. Connect the strain gauges, apply the nominal pressure and vibrate the tube. The tube length shall be adjusted until the natural frequency of the specimen is between 110 Hz and 120 Hz.
7.3 Bending stress calibration of test specimen
Submit the prepared tube to a static load (F) corresponding to the specified bending stress (see ClauseA) in order to produce the required moment. After the tube bending setting is complete, introduce the specified pressure and read the stress transmitted by the strain gauge on an oscilloscope.
Start the vibrator and increase the vibration amplitude olthe vibrator until the oscillograph shows the previously determined stress value.
The angle gauge allows the deflection(s) to be read for further control. The angle gauge shall be mounted at the end cap of the test specimen. To control the deflection of the test specimen, a suitable stroboscope with variable flash frequency shall be used.
8 Requirements
The flexure test specimens shall withstand 107 cycles.
Leakages and failures are not acceptable.BS ISO 9538 pdf download.